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Q  P34  .  K63  1 893     Hand-book  of  physiol 


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Digitized  by  the  Internet  Archive 

in  2010  with  funding  from 

Open  Knowledge  Commons  (for  the  Medical  Heritage  Library  project) 


http://www.archive.org/details/handbookofphysio1893kirk 


HAND-BOOK 


OF 


PHYSIOLOGY. 


BLDDD-5PECTRA  COMPARED  WITH  SPECTRUM  DP  ARGAND- LAMP 


1  Spectrum  oT  Ardand-lamp  with  FrauntiDfErs  lines  in  position. 

2  Spectrum  oP  Dxyhsmoplohln  m  diluted  blood. 
.'3  Spectrum  nP  Reduced  nEmoQlnbin. 

4  Spectrum  oP  Carbanic  oxide  MffirnoQlobin. 

5  Spectrum  oP  AcidHsmatin  m  etherial  solution. 

6  Spectrum  oP  Alkaline  HEmatm. 

7  Spectrum  Dp  ChlDroForm  extract  oF  aciriulated  Dx-Bile. 

8  Spectrum  oP  MEthsmo^labin. 

9  Bpectrom  oP  PiffimachrnrnD^En. 
10  Spectrum  oP  HEmatoporphyrin. 

Mosfofthp  ubov'p  Spec  fret  httiT  bpen  ifnnm  Frnnt  observations  hy  MTWlepmik  ECS. 


KIEKES'    HAND-BOOK  OF   PHYSIOLOGY 


HAND-BOOK 


OF 

PHYSIOLOGY 


BY 


W.  MOKRANT  BAKER,  F.KC.S. 

LATE    SURGEON   TO    AND    LECTURER    ON    PHYSIOLOGY    AT    ST.   BARTHOLOMEW'S    HOSPITAL,   ETC. 

AXD 

VINCENT  DORMER  HARRIS,  M.D.  Lond.,  F.R.C.R 

EXAMINER  IN    PHYSIOLOGY    AT    THE    CONJOINT    BOARD    OF    THE    ROYAL    COLLEGES    OP    PHYSICIANS    AND 

SURGEONS,  AND  IN  THE  UNIVERSITY  OF   DURHAM;    DEMONSTRATOR  OF  PHYSIOLOGY  AT 

ST.    BAKTHOLOMEW"s    HOSPITAL;    PHYSICIAN    TO    THE    VICTORIA 

PARK  HOSPITAL  FOR  DISEASES  OF  THE  CHEST 


THIRTEENTH    EDITION 


WITH  UPWARDS  OF  FIVE  HUNDRED  ILLUSTRATIONS 


INCLUDING  MANY  IN  COLORS 


NEW  Y^ORK 

WILLIAM    WOOD    &    COMPANY 

1893 


PEEFACE  TO  THE  THIRTEENTH  EDITIOISr. 


In  the  preparation  of  a  new  edition  of  this  Handbook  the  Authors 
have  endeavored  to  furnish  the  student  with  an  account  of  Physiology 
brought  up  as  far  as  possible  to  the  present  time.  The  account  does 
not  profess  to  be  exhaustive,  but  it  is  one  upon  which,  they  venture  to 
think,  a  knowledge  of  Physiology  may  be  safely  based. 

The  whole  book  has  undergone  a  very  thorough  revision,  and  the 
scope  of  the  work  has  been  to  some  extent  enlarged.  The  Authors  have, 
however,  kept  constantly  in  view  the  fact  that  the  medical  student, 
for  whom  the  book  is  specially  intended,  studies  Physiology  only  as  an 
introduction  to  Medicine,  and  does  not  require  such  minute  detail  as 
would  be  necessary  for  one  whose  sole  object  of  study  is  Physiology. 

It  would  be  out  of  place  to  mention  the  names  of  all  the  important 
works  dealing  with  the  subject  of  Physiology  in  its  various  branches, 
of  which  free  use  has  been  made  in  preparing  the  present  edition,  but 
the  Authors  would  specially  desire  to  record  their  obligation  to  those 
(text-books  and  monographs)  of  Professors  M.  Foster,  Schiifer,  Halli- 
burton, Stohr,  Cadiat,  McKendrick,  Sherrington,  Mott,  and  Waller. 
They  would  also  tender  their  thanks  to  their  colleagues  Dr.  Gow  and 
Mr.  Paterson,  for  revising  respectively  the  chapters  on  Generation  and 
on  the  Teeth;  to  Dr.  Cautley,  for  kindly  reading  through  the  chief 
portion  of  the  proof  sheets,  and  to  Professor  Lowne  for  several  sugges- 
tions and  corrections. 

Mr.  Danielsson  has  undertaken  and  carried  out  with  much  skill  the 

whole  of  the  new  illustrations. 

W.  MORRANT  BAKER. 

VINCENT  D.  HARRIS. 

WiMPOLE  Street,  W., 
Augtist,  1892. 

V 

374600 


CONTENTS. 


CHAPTER  I. 

PAGE 

The  Phenomena  of  Life, 1 

Properties  of  Protoplasm, 3 

Structure  of  Protoplasmic  Cells, 9 

The  Cell  Nucleus, 11 

Cell  Division, 13 

Plants  compared  with  Animals, 15 

CHAPTER   II. 

The  Functions  op  Organized  Cells, 20 

CHAPTER  III. 

The  Structure  of  the  Elementary  Tissues, 24 

Epithelial  Tissues, 26 

Connective  Tissue, 38 

The  Teeth, 67 

Development  of  Teeth, 74 

Muscular  Tissue, . 79 

Nervous  Tissue, 89 

CHAPTER  IV. 

The  Chemical  Composition  op  the  Body, 102 

Organic  Substances, 103 

Inorganic  Substances, 114 

CHAPTER  V. 

The  Blood, 117 

Coagulation, 119 

The  Corpuscles, 129 

Chemical  Composition, 137 

Development  of  Corpuscles, 154 

CHAPTER  VI. 

The  Circulation  of  the  Blood, 158 

The  Heart 159 

The  Arteries, 167 

The  Capillaries, 170 

vii 


Vlll  CONTENTS. 

PAGE 

The  Circulation  of  the  Blood  {Continued). 

The  Veins, 173 

The  Action  of  the  Heart, 176 

Blood  Pressure, 191 

The  Arterial  Flow, 199 

The  Venous  Flow, 212 

Local  Peculiarities, 216 

The  Regulation  of  the  Flow, 219 

Proofs  of  the  Circulation  of  the  Blood, 237 

CHAPTER  VII. 

Respiration, 239 

The  Respiratory  Apparatus, 240 

The  Respiratory  Mechanism, 249 

Respiratory  Changes, 259 

Special  Respiratory  Acts, 266 

Nervous  Mechanism, 269 

Effect  on  the  Circulation, 275 

Asphyxia, 280 

CHAPTER   VIII. 

Food  and  Digestion, 285 

Organic  Nitrogenous  Foods, 285 

Organic  Non-Nitrogenous  Foods, 288 

Mineral  Foods, 288 

Liquid  Food, .         .        .289 

The  Mouth  and  Mastication, 290 

The  Salivary  Glands, 292 

The  Tongue, .  803 

Deglutition, 309 

The  Stomach, 310 

The  Intestines, 326 

The  Pancreas, 334 

The  Liver, 340 

Digestion  in  Small  Intestine, 353 

Digestion  in  Large  Intestine, 355 

Micro-Organisms  in  Intestines, 356 

Movements  of  the  Intestines, 357 

Action  of  Nervous  System, 358 

Fseces, 359 


CHAPTER   IX. 

Absorption, 363 

Methods, 363 

The  Lymphatic  System 367 

The  Lymph  and  Chyle, 376 

Channels  of  Absorption, 377 

Where  Absorption  may  take  place, 379 


CONTEXTS.  IX 


CHAPTER  X. 

PAGE 

Excretion, 381 

The  Kidneys, 381 

The  Urine, 390 

Method  of  Excretion  of  Urine, 403 

Passage  of  Urine  into  Bladder, 409 

The  Skin, 410 

Functions  of  the  Skin, 417 

CHAPTER  XL 

The  Metabolism  of  the  Tissues, 421 

Muscular  Metabolism, 421 

Muscle  at  Rest, 423 

Muscle  in  Activity, 426 

Muscle  in  Rigor  Mortis, 440 

Action  of  the  Voluntary  Muscles, 441 

Action  of  the  Involuntary  Muscles, 446 

Electrical  Currents  in  Nerves, 446 

CHAPTER  XII. 

The  Metabolism  of  the  Tissues, 453 

Glandular  Metabolism,     - 453 

Secreting  Glands 458 

The  Mammary  Glands, 462 

Milk 465 

Metabolism  in  the  Liver, 467 

Formation  of  Bile, 467 

Glycogenesis, 468 

Formation  of  Urea, 471 

Metabolism  in  Vascular  Glands, 476 

CHAPTER  XIII. 

AiS'iMAL  Heat, 488 

Production  of  Heat, 490 

Regulation  of  the  Temperature, 493 

CHAPTER  XIV. 

Nutrition  and  Diet, 499 

Requisites  of  a  Normal  Diet, 506 

Variations  in  Diet  Tables, 509 

Income  and  Output  of  Energj', 509 

CHAPTER  XV. 

The  Production  of  the  Voice, 514 

Laryngoscope, 519 

Movements  of  the  Vocal  Cords, 522 

The  Voice  in  Singing  and  Speaking, 523 


CONTENTS. 


CHAPTER  XVI. 

PAGE 

The  Nervous  System, 530 

Functions  of  Nerve-Fibres, 530 

The  Spinal  Cord  and  its  Nerves, 537 

Functions  of  Spinal  Nerve-roots, 546 

Functions  of  the  Spinal  Cord, 547 

The  Relations  of  the  Different  Parts  of  the  Brain,        ....  556 

The  Bulb, 563 

Functions  of  the  Bulb, 568 

The  Cranial  Nerves, 571 

The  Pons  Varolii, 587 

The  Crura  Cerebri 588. 

Corpora  Striata, 590 

Optic  Thalanii, 591 

Corpora  Quadrigemina, 591 

Corpora  Geniculata, 591 

Corpora  Dentata, 591 

The  Cerebrum, 591 

Motor  Areas  of  the  Cerebral  Cortex, 599 

Functions  of  the  Cerebrum 606 

Sensory  Centres, 612 

The  Cerebellum,         ....                615 

The  Sympathetic  System, 621 

CHAPTER  XVII. 

The  Senses 638 

Sense  of  Touch, 631 

Sense  of  Taste, 638 

Sense  of  Smell, 641 

Sense  of  Hearing, 646 

Sense  of  Sight, 663 

CHAPTER  XVIII. 

The  Reproductive  Organs,       .        .        . 712 

Of  the  Female, 712 

Of  the  Male, 718 

CHAPTER   XIX. 

Development, 734 

The  Changes  in  the  Ovum, 734 

Development  of  Organs, 756 

APPENDIX 793 

INDEX, 805 


FAHEENHEIT 

and 

CENTIGRADE 

SCALES. 


F. 

500° 
401 
39e 
38:3 
374 
350 
:M7 
338 
3-29 
320 
311 
303 
2*y 
275 
286 
248 
239 
230 
212 
203 
194 
176 
167 
140 
122 
113 
105 
104 
100 


C. 
260° 
205 
200 
195 
190 
ISO 
175 
170 
165 
160 
155 
150 
140 
135 
130 
120 
115 
110 
100 

95 


75 

60 

50 

45 

40.54 

40 

37.8 


98.5 
95 


-  4 

-  13 


36.0 

35 

30 

25 

20 

10 

5 

0 

-  5 

-  10 

-  15 
-20 
-25 

-  30 

-  40 

-  60 


1    deg.  F. 
1.8       '• 
3.6       " 
4.5       " 

5.4 


.54°C. 
1°C. 
2°U. 
2  .5°C. 
3°C. 


To  convert  de- 
grees F.  into  de- 
grees C,  subtract 
32.  and  multiply 


To  convert  de- 
grees C.  into  de- 
grees F.,  multiply 
b}'  I.  and  add  32°. 


MEASUREMENTS. 

FRENCH  INTO  ENGLISH. 


LENGTH. 

1  m^tre  "i 

10  decimetres    I    =  39..37  English 
100  centimetres  f  inches. 

1,000  millimetres  j  (or  1  yd.  and  3}^  in.) 


1  decimetre      ) 

10  centimetres  >•  =  3.037  inches 
100  millimetres  j  (or  nearly  4  inches.) 


1  centimetre    (    —  .3937  or  about 
10  millimetres   ("       (nearly  g  inch.) 
1  millimetre         =  nearly  ^^  inch. 

Or, 

One  Metre  =  39.37079  inches. 
(It  is  the  ten-millionth  part  of  a  quarter 

of  the  meridian  of  the  earth.) 

1  Decimetre    =  4  in. 

1  Centimetre  =  f^  in. 

1  Millimetre    =V5in. 

Decametre      =  b2.80  feet. 

Hectometre    ;=  109..36  yds. 

Kilometftj       =  0.62  miles. 
One  inch  =  2.539  Centimetres. 
One  foot  —  3.047  Decimetres. 
One  yard  =  0.91  of  a  Metre. 
One  mile  =  1.60  Kilometre. 
The  cubic  centimetre  (1.5.432  grains — 1 
gramme)  is  a  standard  at  4°  C,  the 
grain  at  16°.66  C. 


WEIGHT. 

(One  gramme  is  the  weight  of  a  cubic 
centimetre  of  water  at  4°  C.  at  Paris). 
1  gramme  1 

10  decigrammes    i  =  15.4.32349  grs. 
100  centigrammes  f      (or  nearly  1.5}.^). 
1,000  milligrammes  J 


1  decigramme      j 
10  centigrammes  ^  =  rather  more 
100  milligrammes  )      than  IJ^  grain. 


1  centigramme 
10  decigrammes 


=  rather  more 
than  5^5  grain. 


1  milhgramme 


=  rather  more 
than  2^  grain. 


Or 


1  Decigramme  =;  2  dr.  34  gr. 

1  Hectogrm.      =  3!^  oz.  (Avoir.) 

1  Kilogrm.  =.  21b.  3oz.  2 dr.  (Avoir.) 


A  grain  equals  about  1.16  gram., 

a  Troj'  oz.  about  31  gram., 

a  lb.  Avoirdupois  about  ^  Kilogrm.. 

and  1  cwt.  about  50  Kilogrms. 


CAPACITY. 

1.000  cubic  decimetres  '.  =  1  cubic 
1.000.000  cubic  centmietres  )       metre. 


1  cubic  decimetre 
or 
1,000  cubic  centimetres 


Or 


^=1 


litre. 


One  Litre  =  1  pt.  15  oz.  1  dr.  40. 
(For  simplicity.  Litre  is  used  to  signify 
1  cubic  decimetre,  a  little  less  than  1 
Englisli  quart.) 


Decilitre  (100  c.c.) 
Centilitre  (10  c.c.) 
Millilitre(l  c.c.) 
lieealitre 
Hectolitre 


=  S]4  oz. 
=  24  dr. 
=  17  m. 
=  2J  gal. 
=  22  gals. 


Kilolitre  (cubic  mStre)  =  271^^  bushels. 
A  cubic  inch  =  16.38  c.c.  :  a  cubic  foot 
=  2S.315  cubic  dec,  and  a  gallon  — 
4.54  litres. 


CONVERSION  SCALE. 

To  convert  Grammes  to  Ounces  avoir- 
dupois, multiply  by  20  and  divide  by  567. 

To  convert  Kilogrammes  to  Pounds. 
multiply  by  1,000  and  divide  by  454. 

To  convert  Litres  to  Gallons,  mul- 
tiply by  22  and  divide  by  100. 

To  convert  Litres  to  Pints,  multiply 
by  88  and  divide  by  50. 

To  convert  Millimetres  to  Inches. 
multiply  by  10  and  divide  by  254. 

To  convert  Metres  to  Yards,  multi- 
ply by  70  and  divide  by  64. 


SURFACE    MEASURE. 

1  square  metre  —  about  1.550  sq.  inches. 
Or  10.000  sq.  centimetres,  or  10.75  .sq.  ft. 
1  sq.  inch  =  about  6  4  sq.  centimetres. 
1  sq.  foot  =       ••     930      ■' 


ENERGY  MEASURE. 

1  kilogrammetre=about7.24  ft.  pounds. 
1  foot  pound        =     ••      .1381  kgm. 
1  foot  ton  =     ••      310  kgm. 


HEAT  EQUIVALENT. 

1  kilocalorie  =  424  kiiogrammetres. 


ENGLISH    MEASURES. 

Apothecaries  Weight.  '  Avoirdupois  VTeight. 

7000  grains  =  1  lb. 

Or 
437.5  grains  =  1  oz. 


16  drams      =  1  oz. 
16  oz.  =  1  lb. 

28  lbs.  =;  1  quarter. 

4  quarters  =  1  ewt. 
20  cwt.  =  1  ton. 


Measure  of  1  d^cini^tre,  or  10  centimetres,  or  100  millimetres. 

III!!      I      I      !      I      I      I      I      1      I  III 


Cranium 

-  7  Cervical  Vertebrae 

Clavicle. 
Scapula. 

12  Dorsal  Vertebrae. 
Humerus. 

5  Lumbar  Vertebrae. 


—  Ilium. 

Ulna. 

Radius. 

Pelvis. 


Bones  of  the  Carpus. 
Bones   of    the     Meta^ 

carpus. 
Phalanges  of  Fingers. 


Femur. 


~    Patella. 


Tibia. 
Fibula. 


Bones  of  the  Tarsus. 
Bones   of    the    Meta- 
tarsus. 
Phalanges  of  Toes. 


THE    SKELETON  (after  Holden). 


Highest        , 
point  of 
Crest  of  the 
nium. 


Symphysis  Puhis. 


DIAGRAM    OF    THORACIC    AND    ABDOMINAl,    REGIONS. 


A.  Aortic  Valve. 
M.  Mitrai  Valve. 


P.  Pulmonary  Valve. 
r.  Tricuspid  Valve. 


Handbook  of  Physiology. 


CHAPTER  I. 

THE  PHEIS^OMENA  OF  LIFE. 

HuMAX  Physiology  is  the  science  which  treats  of  the  various  pro- 
cesses or  changes  which  take  place  during  life  in  the  organs  and  tissues 
of  the  body  of  man.  These  processes,  however,  must  not  be  considered 
as  by  any  means  peculiar  to  the  hiiman  organism  since,  putting  aside 
the  properties  which  serve  to  distinguish  man  from  other  animals,  us 
well  as  those  which  mark  out  one  animal  from  another,  the  changes 
which  go  on  in  the  tissues  of  man  go  on  much  in  the  same  way  in  the 
tissues  of  all  other  animals  as  long  as  the}"  live.  Furthermore  it  is 
found  that  similar  changes  proceed  in  all  living  vegetable  tissues;  they 
indeed  constitute  what  are  called  vital  j^fienomena,  a,Tid  are  those  proper- 
ties which  mark  out  living  from  non-living  material. 

The  lowest  types  of  life,  whether  animal  or  vegetable,  are  found  to 
consist  of  minute  masses  of  a  jelly-like  substance,  which  is  now  gener- 
ally known  under  the  name  of  2)rotoj)Ia><in.  Eacli  such  minute  mass  is 
called  a  cell,  so  that  these  minute  elementary  organisms  are  designated 
unicelhilar.  Not  only  is  it  true  that  the  lowest  types  of  life  are  made 
up  of  protoplasm,  but  it  has  also  been  shown  that  the  tissues  of  which 
the  most  complex  organisms  are  composed  consist  of  protoplasmic  cells. 

Thus,  for  example,  the  human  body  can  be  shown  by  dissection  to 
be  constructed  of  various  dissimilar  parts,  bones,  muscles,  brain,  heart, 
lungs,  intestines,  etc.,  and  these  on  more  minute  examination  with  the 
aid  of  the  microscope,  are  found  to  be  composed  of  different  tissues, 
such  as  epithelial,  connective,  nervous,  muscular,  and  the  like.  Each  of 
these  tissues  is  made  up  of  ceils  or  of  their  altered  equivalents.  Again, 
wc  are  taught  by  Embryology,  the  science  which  treats  of  the  growth 
and  structure  of  organisms  from  their  first  coming  into  being,  that  the 
human  body,  made  up  of  all  these  dissimilar  structures,  commenced  its 
life  as  a  minute  cell  or  ovum  (fig.  2)  about  Yjijth  of  an  inch  in  diame- 
ter, consisting  of  a  spherical  mass  of  protoplasm  in  the  midst  of  which 
was  contained  a  smaller  spherical  body,  the  nucleus  or  germinal  vesicle. 

1 


2 


HANDBOOK    OF    I'll YSrOLOGY. 


'J  lie  phenomena  of  life  then  are  exhibited  in  cells,  whether  existing 
alone  or  developed  into  the  organs  and  tissues  of  animals  and  plants. 
It  must  be  at  once  evident  that  a  correct  knowledge  of  the  nature  and 
activities  of  the  cell  forms  the  very  foundation  of  physiology;  cells 
being,  in  fact,  physiological  no  less  than  morphological  units. 

The  prime  importance  of  the  cell  as  an  element  of  structure  was  first 
established  by  the  researches  of  the  botanist  Schleiden,  and  his  conclu- 
sions, drawn  from  the  study  of  vegetable  histology,  were  at  once  ex- 
tended by  Theodor  Schwann  to  the  animal 
kingdom.  The  earlier  observers  defined  a  cell 
as  a  more  or  less  spherical  body  limited  by  a 
membrane,   and    containing    a    smaller    body 


Space  con- 
taining 
"    liquid. 


Protoplasm. 

Nucleus. 


—  Cell-wall. 


Nucleus  or  germinal 
.    vesicle. 

Nucleolus  or  germi- 
nal SJJOt. 

Space  left  by  retrac- 
tion of  yelk. 

.Yelk  or  vitellus. 


—Vitelline  membrane. 


Vegetable  cells. 


Fig.  3. — Semidiagramiiiatic  representation  of  a  human 
ovum,  showing  the  parts  of  an  animal  cell.    (Cadiat.) 


termed  a  nucleus,  which  in  its  turn  incloses  one  or  more  still  smaller 
bodies  or  nucleoli.  Such  a  definition  applied  admirably  to  most  vege- 
table cells,  but  the  more  extended  investigation  of  animal  tissues  soon 
showed  that  in  many  cases  no  limiting  membrane  or  cell-wall  could  be 
demonstrated. 

The  presence  or  absence  of  a  cell-wall,  therefore,  was  now  regarded 
as  quite  a  secondary  matter,  while  at  the  same  time  the  cell-substance 
came  gradually  to  be  recognized  as  of  primary  importance.  Many  of 
the  lower  forms  of  animal  life,  e.g.,  the  Rhizopoda,  were  found  to  con- 
sist almost  entirely  of  matter  very  similar  in  appearance  and  chemical 
composition  to  the  cell-substance  of  higher  forms;  and  this  from  its 
chemical  resemblance  to  flesh  was  termed  Sarcoile  by  Dujardin.  When 
recognized  in  vegetable  cells  it  was  called  Protoplasm  by  Mulder,  while 
Remak  applied  the  same  name  to  the  substance  of  animal  cells.  As  the 
presumed  formative  matter  in  animal  tissues  it  was  termed  Blastema, 
and  in  the  belief  that,  wherever  found,  it  alone  of  all  substances  has  to 
do  with  generation  and  nutrition,  Beale  has  named  it  Germinal  matter 
or  Bioplasm.  Of  these  terms  the  one  most  in  vogue  at  the  present  day, 
as  we  have  already  said,  is  Protoplasm,  and  inasmuch  as  all  life,  both  in 
the  animal  and  vegetable  kingdoms,  is  associated  with  protoplasm,  we 


THE    PHEISTOMENA    OF   LIFE.  3 

are  justified  in  describing  it,  with  Huxley,  us  the  "physical  basis  of 
life,"  or  simply  "'  living  matter." 

A  cell  may  now  be  defined  as  a  nucleated  mass  of  protoplasm,  of 
microscopic  size,  varying  in  the  human  body  from  the  red  blood- cell 
which  is  about  30V0"  ^^^  ^^^  inch  in  diameter  to  the  ganglion  cell,  3-^  of 
an  inch,  which  possesses  sufficient  individuality  to  have  a  life-history  of 
its  own.  Each  cell  goes  through  the  same  cycle  of  changes  as  the  whole 
organism,  though  doubtless  in  a  much  shorter  time.  Beginning  with 
its  origin  from  some  pre-existing  cell,  it  grows,  produces  other  cells,  and 
finally  dies.  It  is  true  that  several  lower  forms  of  life  consist  of  non- 
nucleated  protoplasm,  but  the  above  definition  holds  good  for  all  the 
higher  plants  and  animals. 

Properties  of  Protoplasm. 

Protoplasm  is  a  semi-fluid  substance,  which  swells  up  but  does  not 
mix  with  water.  It  is  transparent  and  generally  colorless,  with  refrac- 
tive index  higher  than  that  of  water  but  lower  than  that  of  oil.  It  is 
neutral  or  weakly  alkaline  in  reaction,  but  may  under  special  circum- 
stances be  acid,  as,  for  example,  after  activity.  It  undergoes  stiffening 
or  coagulation  at  a  temperature  of  about  54.5°  C.  (130°  F.),  and  hence 
no  organism  can  live  when  its  own  temperature  is  raised  above  that 
point ;  it  is  also  coagulated  and  therefore  killed  by  alcohol,  by  solutions 
of  many  of  the  metallic  salts,  by  strong  acids  and  alkalies,  and  by  many 
other  substances. 

Under  the  microscope  it  is  seen  almost  universally  to  be  granular, 
the  granules  consisting  of  different  substances,  either  albuminous,  or 
fatty  matters,  or  more  rarely  of  inorganic  salts.  The  granules  are  not 
equally  distributed  throughout  the  whole  cell-mass,  as  they  are  some- 
times absent  from  the  outer  part  or  layer,  and  very  numerous  in  the 
interior.  The  granules  may  exhibit  an  irregular  shaking,  dancing  move- 
ment, which  is  not  vital  and  is  known  as  the  Broivnian  movement.  In 
addition  to  granules,  protoplasm  generally  exhibits  spaces  or  vacuoles, 
generally  globular  in  shape,  excejjting  during  movement  when  they  may 
be  irregular,  filled  with  a  watery  fiuid.  These  vacuoles  are  more  numer- 
ous and  pronounced  in  vegetable  than  in  animal  cells.  Gas  bubbles  also 
sometimes  exist  in  cells. 

It  is  impossible  tc  make  any  definite  statement  as  to  the  exact  chem- 
ical composition  of  living  protoplasm,  since  the  methods  of  chemical 
analysis  necessarily  imply  the  death  of  the  cell;  it  is,  however,  stated 
that  protoplasm  contains  SO  to  85  per  cent  of  water,  and  of  the  15  to  20 
per  cent  of  solids,  the  most  important  part  belongs  to  the  class  of  sub- 
stances called  proteids  or  albumins.  These  are  bodies  which  contain 
the  chemical  elements,  carbon,  hydrogen,  nitrogen,  oxygen,  and  sulphur. 


4  HANDBOOK    OF    PHYSIOLOGY. 

in  certain  slightly  varying  but  arbitrary  proportions  in  the  molecule, 
and  which  react  to  certain  chemical  tests  which  will  be  enumerated 
later  on.  A  certain  amount  of  proteid  at  any  rate  is  essential  to  the 
composition  of  protoplasm.  Associated  with  the  proteid  substances 
other  bodies  are  frequently  present,  such  as  glycogen,  starch,  and  cellu- 
lose, each  of  which  contains  the  elements  carbon,  hydrogen,  and  oxygen, 
the  last  two  in  the  proportion  to  form  water,  and  hence  are  termed 
carbohydrates,  the  carbon  in  the  molecule  being  either  six  or  a  multiple 
of  six;  chlorophyll,  the  coloring  matter  of  plants;  fatty  bodies  contain- 
ing carbon,  hydrogen,  and  oxygen,  but  not  combined  in  the  same  pro- 
portion as  in  carbohydrates;  lecithin,  a  complicated  fatty  body  contain- 
ing phosj^horus;  CQrin.m  fermeiits  and  other  substances. 

The  vital  or  physiological  characteristics  of  protoplasm  may  be 
well  studied  in  the  microscopic  animal  called  the  amoeba,  a  unicellular 
organism  found  chiefly  in  fresh  water,  but  also  in  the  sea  and  in  damp 


Fig.  3.— Amcebge. 

earth.  These  properties  may  be  conveniently  studied  under  the  follow- 
ing heads: — 

1.  Tlie  Power  of  Spontaneous  Movement. — When  an  amceba  is  ob- 
served with  a  high  power  of  the  microscope,  it  is  found  to  consist  of  an 
irregular  mass  of  protoplasm  probably  containing  one  or  more  nuclei, 
the  protoplasm  itself  being  more  or  less  granular  and  vacuolated.  If 
watched  for  a  minute  or  two,  an  irregular  projection  is  seen  to  be  grad- 
ually thrust  out  from  the  main  body  and  retracted;  a  second  mass  is 
then  protruded  in  another  direction,  and  gradually  the  whole  proto- 
plasmic substance  is,  as  it  were,  drawn  into  it.  Tlie  amoeba  thus  comes 
to  occupy  a  new  position,  and  when  this  is  repeated  several  times  we 
have  locomotion  in  a  definite  direction,  together  with  a  continual  change 
of  form.  These  movements,  when  observed  in  other  cells,  such  as  the 
colorless  blood-corpuscles  of  higher  animals  (fig.  2),  in  the  branched 
cornea  cells  of  the  frog  and  elsewhere,  are  hence  termed  amoeboid. 

The  remarkable  movement  of  pigment  granules  observed  in  the 
branched  pigment  cells  of  the  frog's  skin  by  Lister  are  also  probably 
due  to  amoeboid  movement.  These  granules  are  seen  at  one  time  distrib- 
uted uniformly  through  the  body  and  branched  processes  of  the  cell, 
while  at  another  time  they  collect  in  the  central  mass  leaving  the 
branches  quite  colorless. 


THE    PHEXOMENA    OF    LIFE.  0 

This  movement  within  the  pigment  cells  might  also  be  considered 
an  example  of  the  so-culled  streaming  movement  not  infrequent!}-  seen 
in  certain  of  the  protozoa,  in  which  the  mass  of  protoplasm  extends 
long  and  fine  processes,  themselves  very  little  movable,  but  upon  the 
surface  of  which  freely  moving  or  streaming  granules  are  seen.  A  glid- 
ing movement  has  also  been  noticed  in  certain  animal  cells;  the  motile 


Fig.  4. — Human  colorless  blood-corpuscle,  showing  its  successive  changes  of  outline  within  ten 
minutes  when  kept  moist  on  a  wann  stage.     (Schofleld.) 

part  of  the  cell  being  composed  of  protoplasm  bounding  a  central  and 
more  compact  mass.  By  means  of  the  free  movement  of  this  layer, 
the  cell  may  be  observed  to  move  along. 

In  vegetable  cells  the  protoplasmic  movement  can  be  well  seen  in 
the  hairs  of  the  stinging-nettle  and  Tradescantia  and  the  cells  of  Vallis- 
neria  and  Chara;  it  is  marked  by  the  movement  of  the  granules  nearly 
always  imbedded  in  it.  For  example,  if  j)art  of  a  hair  of  Tradescantia 
(fig.  5)  be  viewed  under  a  high  magnifying  j)ower,  streams  of  proto- 
plasm containing  crowds  of  granules  hurrying  along,  like  the  foot- 
passengers  in  a  busy  street,  are  seen  flowing  steadily  in  definite  direc- 
tions, some  coursing  round  the  film  which  lines  the  interior  of  the  cell- 
Avall,  and  others  flowing  toward  or  away  from  the  irregular  mass  in  the 
centre  of  the  cell-cavity.     Many  of  these  streams  of  protoplasm  run 


Fig.  5.— Cell  of  Tradescantia  drawn  at  successive  intervals  of  two  minutes. — The  cell-contents 
consist  of  a  central  mass  connected  by  many  irregular  processes  to  a  peripheral  film,  the  whole 
forming  a  vacuolated  mass  of  protoplasm,  which  is  continually  changing  its  shape.    (Schofield.) 


together  into  larger  ones  and  are  lost  in  the  central  mass,  and  thus 
ceaseless  variations  of  form  are  produced.  The  movement  of  the  pro- 
toplasmic granules  to  or  from  the  periphery  is  sometimes  called  vegeta- 
ble circuhition,  whereas  the  movement  of  the  protoplasm  round  the  in- 
terior of  the  cell  is  called  rotation. 

The  first  account  of  the  movement  of  protoplasm  was  given  by 
Rosel  in  1755,  as  occurring  in  a  small  Proteus,  probably  a  large  fresh- 
water amoeba.     His   description  was   followed   twenty   years  later   by 


6  HANDBOOK    OF    PHYSIOLOGY. 

Corti's  demonstration  of  the  rotation  of  the  cell  sap  in  cliaraceae,  and  in 
the  earlier  part  of  the  century  by  Meyer  in  Vallisneria,  1827;  Eobert 
Brown,  1831,  in  "  Staminal  Hairs  of  Tradescantia.''  Then  came  Dujar- 
din's  description  of  the  granular  streaming  in  the  ]3seudopodia  of  Ehizo- 
pods  and  movement  in  other  cells  of  animal  protoplasm  (Planarian  eggs, 
V.  Siebold,  1841;  colorless  blood-corpuscles,  Wharton  Jones,  184G). 

2.  The  Power  of  Resijonse  to  Stinndl,  or  Irritability. — Although  the 
movements  of  the  amoeba  have  been  described  above  as  spontaneous,  yet 
they  may  be  increased  under  the  action  of  external  agencies  which 
excite  them  and  are  therefore  called  stimuli,  and  if  the  movement  has 
ceased  for  the  time,  as  is  the  case  if  the  temperature  is  lowered  beyond 
a  certain  point,  movement  may  be  set  up  by  raising  the  temperature. 
Again,  contact  with  foreign  bodies,  gentle  joressure,  certain  salts,  and 
electricity,  produce  or  increase  the  movement  in  the  amoeba.  The  pro- 
toplasm is,  therefore,  sensitive  or  irritable  to  stimuli,  and  shows  its  irri- 
tability by  movement  or  contraction  of  its  mass. 

The  effects  of  some  of  these  stimuli  may  be  thus  further  detailed: — 

a.  Changes  of  Temperature. — Moderate  heat  acts  as  a  stimulant;  the 
movement  stops  below  0°  C.  (32°  F.),  and  above  40°  C.  (104°  F.);  be- 
tween these  two  points  the  movements  increase  in  activity;  the  oj)timum 
temperature  is  about  07°  to  38°  C.  Exposure  to  a  temperature  even 
below  0°  C.  stops  the  movement  of  protoplasm,  but  does  not  prevent  its 
reappearance  if  the  temperature  is  raised;  on  the  other  hand,  prolonged 
exposure  to  a  temperature  of  over  40°  C.  altogether  kills  the  protoplasm 
and  causes  it  to  enter  into  a  condition  of  coagulation  or  lieat  rigor. 

h.  Mechanical  Stimuli. — When  gently  squeezed  between  a  cover  and 
object-glass  under  proper  conditions,  a  colorless  blood-corpuscle  is  stim- 
ulated to  active  amoeboid  movement. 

c.  Nerve  Infiuence. — By  stimulation  of  the  nerves  of  the  frog's  cornea, 
contraction  of  certain  of  its  branched  cells  has  been  produced. 

cl.  Cliemical  Stimuli. — Water  generally  stops  amoeboid  movement, 
and  by  imbibition  causes  great  swelling  and  finally  bursting  of  the  cells. 
In  some  cases,  however  (myxomycetes),  protoplasm  can  be  almost  en- 
tirely dried  up,  but  remains  capable  of  renewing  its  movements  when 
again  moistened.  Dilute  salt-solution  and  many  dilute  acids  and  alka- 
lies stimulate  the  movements  temporarily.  Strong  acids  or  alkalies 
permanently  stop  the  movements;  ether,  chloroform,  veratria,  and  qui- 
nine also  stop  it  for  a  time. 

Movement  is  suspended  in  an  atmosphere  of  hydrogen  or  carbonic 
acid  and  resumed  on  the  admission  of  air  or  oxygen,  but  complete  with- 
drawal of  oxygen  will  after  a  time  kill  the  protoj)lasm. 

e.  Electrical. — Weak  currents  stimulate  the  movement,  while  strong 
currents  cause  the  cells  to  assume  a  spherical  form  and  to  become 
motionless. 


THE    PHEXOMEJfA   OF   LIFE, 


3.  The  Poiver  of  Digestion,  Respiration,  ami  Nutrition. — This  con- 
sists in  the  power  which  is  possessed  by  the  amoeba  and  similar  animal 
ceils  of  taking  in  food,  modifying  it,  building  up  tissue  by  assimilating 
it,  and  rejecting  what  is  not  assimilated.  These  various  processes  are 
effected  by  the  protoplasm  simply  flowing  round  and  inclosing  within 
itself  minute  organisms  such  as  diatoms  and  the  like,  from  which  it 
extracts  what  it  requires,  and  then  rejects  or  excretes  the  remainder, 
which  has  never  formed  part  of  the  body.  This  latter  proceeding  is 
done  by  the  cell  withdrawing  itself  from  the  material  to  be  excreted. 
The  assimilation  constantly  taking  place  in  the  body  of  the  amoeba,  is 
for  the  pur2:>ose  of  replacing  waste  of  its  tissue  consequent  ujion  mani- 
festation of  energy.    The  respiratory  process 

of  absorbing  oxygen  goes  on  at  the  same  time. 

The  processes  which  take  place  in  cells, 
both  animal  and  vegetable,  are  summed  up 
under  the  term  metabolism  (from  iJ-zTafiuk-fj, 
change).  The  changes  which  go  on  are  of 
two  kinds,  viz.,  assimilation,  or  building  up, 
and  disassimilation,  or  breaking  down ;  they 
may  be  also  called  composition  or  decom- 
position, or,  using  the  nomenclature  of  Gas- 
kell,  anabolism  or  constructive  metabolism, 
and  kataholisni  or  destructive  metabolism. 
In  the  direction  of  anabolism  two  processes 
occur,  viz.,  the  building  up  of  materials  which 
it  takes  in,  and  secondly,  the  building  up  of 
its  own  substance  by  those  or  other  mate- 
rials. As  we  shall  see  in  a  subsequent  para- 
graph, the  process  of  anabolism  differs  to 
some  extent  in  vegetable  and  animal  cells. 
The  katabolism  of  the  cell  consists  in  chem- 
ical changes  which  occur  in  the  cell-substance  itself,  or  in  substances 
in  contact  with  it. 

The  destructive  metabolism  of  a  cell  is  increased  by  its  activity,  but 
goes  on  also  during  quiescence.  It  is  jorobably  of  the  nature  of  oxida- 
tion, and  results  in  the  evolution  of  carbonic  anhydride  and  water  on 
the  one  hand,  and  in  the  formation  of  various  substances  on  the  other, 
some  of  which  may  be  stored  up  in  the  cell  for  future  use,  and  are 
called  secretions,  and  others,  like  the  carbonic  anhydride  and  certain 
bodies  containing  nitrogen,  are  eliminated  as  excretioois. 

4.  The  Poicer  of  Growth.— In  protoplasm  then,  it  is  seen  that  the 
two  processes  of  waste  and  repair  go  on  side  by  side,  and  as  long  as  they 
are  equal  the  size  of  the  animal  remains  stationary.  If,  however,  the 
building  up  exceed  the  waste,  then  the  animal  grows  ;  if  the  waste  ex- 


Fig.  6.— Cells  from  the  staminal 
hairs  of  Tradescantia.  A,  Fresh  in 
water;  B,  tlie  same  cell  after  sliglit 
electrical  stimulation;  o,  b,  region 
stimulation ;  c,  ri,  clumps  and  knobs 
of  contracted  protoplasm.   (Kiihne.) 


S  HANDBOOK    OF    PHYSIOLOCJY. 

ceed  the  repair,  the  animal  decays;  and  if  decay  go  on  beyond  a  certain 
point,  life  becomes  impossible,  and  the  animal  dies. 

Growth,  or  the  inherent  power  of  increasing  in  size,  although  essen- 
tial to  our  idea  of  life,  is  not,  it  must  be  recollected,  confined  to  living 
beings.  A  crystal  of  common  salt,  for  example,  if  placed  under  appro- 
priate conditions  for  obtaining  fresh  material,  will  grow  in  a  fashion  as 
definitely  characteristic  and  as  easily  to  be  foretold  as  that  of  a  living 
creature;  but  the  growth  of  a  crystal  takes  place  merely  by  additions 
to  its  outside;  the  new  matter  is  laid  on  particle  by  particle,  and  layer 
by  layer,  and,  when  once  laid  on,  it  remains  unchanged.  In  a  living 
structure,  where  growth  occurs,  it  is  by  addition  of  new  matter,  not  to 
the  surface  only,  but  throughout  every  part  of  the  mass. 

Again,  all  living  structures  are  subject  to  constant  decay.  Thus,  a 
man's  body  is  not  composed  of  exactly  the  same  particles  day  after  day, 
although  to  all  intents  he  remains  the  same  individual.  Almost  every 
part  is  changed  by  degrees;  but  the  change  is  so  gradual,  and  the  re- 
newal of  that  which  is  lost  so  exact,  that  no  difference  may  be  noticed, 
except  at  long  intervals  of  time.  A  lifeless  structure,  as  a  crystal,  is 
subject  to  no  such  laws;  neither  decay  nor  repair  is  a  necessary  condi- 
tion of  its  existence.  That  which  is  true  of  structures  which  never  had 
to  do  with  life  is  true  also  with  respect  to  those  which,  although  they 
are  formed  by  living  parts,  are  not  themselves  alive.  Thus,  an  oyster- 
shell  is  formed  by  the  living  animal  which  it  incloses,  but  it  is  as  lifeless 
as  any  other  mass  of  inorganic  matter;  and  in  accordance  with  this 
circumstance  its  growth  takes  place  layer  by  layer,  and  it  is  not  subject 
to  constant  decay  and  reconstruction.  The  hair  and  nails  are  examjiles 
of  the  same  fact. 

In  connection,  too,  with  the  growth  of  lifeless  ma-sses  there  is  uo 
alteration  in  the  chemical  composition  of  the  material  which  is  taken 
up  and  added  to  the  previously  existing  mass.  For  example,  when  a 
crystal  of  common  salt  grows  on  being  placed  in  a  fluid  which  contains 
the  same  material,  the  properties  of  the  salt  are  not  changed  by  being 
taken  out  of  the  liquid  by  the  crystal  and  added  to  its  surface  in  a  solid 
form.  But  the  case  is  essentially  different  in  living  beings,  both  animal 
and  vegetable,  as  the  materials  which  serve  ultimately  to  build  them 
up  are  much  altered  before  they  are  finally  assimilated  by  the  structures 
they  are  destined  to  nourish. 

The  growth  of  all  living  things  has  a  definite  limit,  and  the  law 
which  governs  this  limitation  of  increase  in  size  is  so  invariable  that  we 
should  be  as  much  astonished  to  find  an  individual  plant  or  animal 
without  limit  as  to  growth  as  w'ithout  limit  to  life. 

5.  The  Poioer  of  Reprodxidion. — The  amoeba,  to  return  to  our  former 
illustration,  when  the  growth  of  its  protoplasm  has  reached  a  certain 
point,  manifests  the  power  of  reproduction,  by  splitting  up  into  (or  in 


THE    PHENOMENA    OF    LIFE. 


9 


some  other  way  produoing)  two  or  more  parts,  each  of  which  is  capable 
of  independent  existence.  The  new  amoebae  manifest  the  same  projaer- 
ties  as  their  parent,  perform  the  same  functions,  grow  and  reproduce  in 
their  turn.     This  cycle  of  life  is  being  continually  passed  through. 

In  more  complicated  structures  than  the  amoeba,  the  life  of  indi- 
vidual protoplasmic  cells  is  probably  very  short  in  comparison  wkh  that 
of  the  organism  they  compose;  and  their  constant  decay  and  death 
necessitate  constant  reproduction. 

The  mode  in  which  this  takes  place  has  long  been  the  subject  of 
great  controversy. 

It  is  now  very  generally  believed  that  every  cell  is  descended  from 
some  pre-existing  (mother-)  cell.     This  derivation  of  cells  from  cells 


Fig.  r.— Diagram  of  an  ovum  (a)  undergoing  segmentation— In  (h)  it  has  divided  into  two,  in 
(c)  into  four;  and  in  (d)  tbie  process  has  ended  in  the  production  of  tlie  so  called  "mulberrj'  mass." 
(Frey.) 

takes  place  by  (1)  gemmation,  which  essentially  consists  in  the  budding 
off  and  separation  of  a  portion  of  the  parent  cell;  or  (3)  fission  or  divi- 
sion. 

The  exact  manner  of  the  division  of  cells  is  a  matter  of  some  diffi- 
culty, and  will  not  be  described  until  the  subject  of  the  structure  of 
protoplasmic  cells  has  been  considered. 


Structure  of  Protoplasmic  Cells. 

It  was  formerly  the  custom  to  consider  protoplasm  to  be  homogene- 
ous; it  was  so  described  by  Engelmann;  it  api3ears,  however,  that  this 
idea  requires  modification,  and  that  in  the  majority  of  cells,  if  not  in 
every  cell,  two  parts  can  be  made  out  in  the  protoplasm,  viz.,  a  fine 
network  or  spongework  of  fibrils  of  a  firmer  consistence  than  the  more 
fluid  part  which  is  contained  within  its  interstices.  The  amount  of  the 
two  j^arts  in  each  cell  varies;  in  young  cells  the  more  fluid  part  is  more 
developed,  and  as  time  goes  on  the  fibrillary  meshwork  increases.  The 
intra-cellular  meshwork  has  been  called  by  different  names,  protoplasma, 
reticulum,  or  siJongiojjlasm,  while  the  more  fluid  substance  has  received 
the  names  jJaraplasma,  enchyUma,  or  liiialoplasm.  The  reticulum  is  more 
refractile  than  its  contents,  is  elastic  and  extensile,  has  an  affinity  for 
staining  reagents.     The  hyaloplasm  has  no  such  affinity. 

The  arrangement  of  the  reticulum  varies  considerably  in  different 
cells,  and  even  in  different  parts  of  the  same  cell.  Sometimes,  for  ex- 
ample (fig.  8),  the  meshwork  has  an  elongated  radial  arrangement  from 


10 


HANDBOOK    OF    PHYSIOLOGY. 


the  nucleus;  iit  others,  the  meshwork  is  more  evenly  disposed,  as  in 
fig.  9.  At  tlie  junctions  of  the  fibrils  there  are  usually  slight  enlarge- 
ments or  nodes. 

In  some  cells,  particularly  in  plants,  but  also  in  some  fixed  animal 
cells,  such  as  compose  epithelial  membranes,  there  is  a  tendency  toward 


,  Membrane  of  nucleus. 


,>l'\^j^l       Achromatic  substance  of 
pXv^TJ^iSji"  nucleus. 

:;--V-rr_i?:l Chromatic  substance  of 

nucleus. 


Fig.  8.— Cell  with  its  reticulum  disposed  radially ;  from  the  intestinal  epithelium  of  a  worm. 

(Carney.) 

a  formation  of  a  firmer  external  envelope,  constituting  in  vegetable  cells 
a  membrane  distinct  from  the  more  central  and  more  fiuid  part  of  the 
protoplasm.  In  such  cases  the  reticulum  at  the  periphery  of  the  cell  is 
made  up  of  very  fine  meshes.  The  membrane  when  formed  is  usually 
pierced  with  pores  by  which  fluid  may  pass  in,  or  through  which  pro- 
trusion of  the  protoplasmic  filaments  forming  the  cell's  connection  with 
other  cells  surrounding  it  may  take  jDlace. 

It  is  an  exceedingly  interesting  question  whether  in  cells  the  one 


Fig.  9. — (a.)  The  colorless  blood-corpuscle  showing  the  intra-cellular  network,  and  two  nuclei 
with  intra-nuclear  network,  (b.;  Colored  blood-corpuscle  of  newt  shuwing  the  intra-cellular  net- 
work of  fibrils.  Also  oval  nucleus  composed  of  limiting  membrane  and  fine  intra-nuclear  network 
of  fibrils.     X  800.     (Klein  and  Noble  Smith.) 


part  of  the  protoplasm  can  exist  without  the  other.  Schiifer  summar- 
izes the  matter  thus:— "There  are  cells,  and  unicellular  organisms  both 
animal  and  vegetable,  in  which  no  reticular  structure  can  be  made  out, 
and  these  mat/  be  formed  of  hyaloplasm  alone.  In  that  case,  this  must 
be  looked  upon  as  the  essential  part  of  protoplasm.  So  far  as  amoeboid 
phenomena  are  concerned  it  is  certainly  so;  but  whether  the  chemical 


THE    PHEXOMEXA    OF   LIFE.  11 

changes  which  occur  in  many  cells  are  effected  by  this  or  by  spongio- 
plasm  is  another  matter." 

Another  question  about  which  there  is  some  difference  of  opinion  is, 
which  part  of  the  protoplasm  is  chiefly  contractile.  It  is  usually  con- 
cluded that  this  property  rests  in  the  meshwork,  but  there  seems  a 
considerable  amount  of  evidence  in  favor  of  the  view  that  part  if  not 
all  of  the  contractility  resides  in  the  hyaloplasm;  for  example,  in  ama3- 
boid  cells  the  pseudopodial  protoplasm  are  certainly  made  of  this  and 
not  of  spongioplasm,  and  when  the  corpuscle  is  stimulated  the  hyalo- 
plasm flows  back  into  the  reticular  network.  If  the  view  that  the  hyalo- 
plasm is  chiefly  contractile  be  a  correct  one,  the  sijecial  condition  of  an 
amoeboid  cell  must  be  considered  to  be  condition  of  contraction,  and 
the  flowing  out  of  the  process  to  be  relaxation. 

The  Cell  Nucleus. 

Nearly  all  cells  at  some  period  of  their  existence  possess  nuclei.  As 
has  been  incidentally  suggested  the  origin  of  a  nucleus  in  a  cell  is  the 
first  trace  of  the  differentiation  of  protoplasm.  The  existence  of  nuclei 
was  first  pointed  out  in  the  year  1833  by  Robert  Brown,  who  observed 
them  in  vegetable  cells.  They  are  either  small  transparent  vesicular 
bodies  containing  one  or  more  smaller  particles  (nucleoli),  or  they  are 
semi-solid  masses  of  protojjlasm  always  in  the  resting  condition  bounded 
by  a  well-defined  envelope.  In  their  relation  to  the  life  of  the  cell  they 
are  certainly  hardly  second  in  importance  to  the  protoj^lasm  itself,  and 
thus  Beale  is  fully  justified  in  comprising  both  under  the  term  "ger- 
minal matter."  They  exhibit  their  vitality  by  initiating,  in  the  major- 
ity of  cases,  the  process  of  division  of  the  cell  into  two  or  more  cells 
(fission)  by  first  themselves  dividing.  Distinct  observations  have  been 
made  showing  that  spontaneous  changes  of  form  may  occur  in  nuclei 
as  also  in  nucleoli. 

Histologists  have  long  recognized  nuclei  by  two  important  char- 
acters : — 

(1.)  Their  power  of  resisting  the  action  of  various  acids  and  alkalies, 
particularly  acetic  acid,  by  which  their  outline  is  more  clearly  defined, 
and  they  are  rendered  more  easily  visible.  This  indicates  some  chemi- 
cal difference  between  the  protoplasm  of  the  cells  and  nuclei,  as  the 
former  is  destroyed  by  these  reagents. 

(2.)  Their  quality  of  staining  in  solutions  of  carmine,  hematoxylin, 
etc.  Nuclei  are  most  commonly  oval  or  round,  and  do  not  generally 
conform  to  the  diverse  shapes  of  the  cells;  they  are  altogether  less  vari- 
able elements  than  cells,  even  in  regard  to  size,  of  which  fact  one  may 
see  a  good  example  in  the  uniformity  of  the  nuclei  in  cells  so  multiform 
as   those  of  epithelium.     But  sometimes  nuclei  appear  to  occupy  the 


13 


HANDBOOK    OF    PHYSIOLOGY. 


whole  of  the  cell,  as  is  the  case  in  the  lymjjh  corpuscles  of  lymphatic 
glands,  and  in  some  small  nerve  cells. 

Their  position  in  the  cell  is  very  variable.     In  many  cells,  especially 
where  active  growth  is  jDrogressing,  two  or  more  nuclei  are  present. 


Structure  of  Nuclei. 

The  nucleus  when  in  a  condition  of  rest  is  bounded  by  a  distinct 
membrane,  possibly  derived  from  the  spongioplasm  of  the  cell.     Besides 


Node  of  meshwork 


Node  of  meshwork 


.^»-Nuclear  membrane. 

Nucleolus. 

Nuclear  matrix. 

Nuclear  meshwork. 


Fig.  10.— The  resting  nucleus— diagrammatic.     (Waldeyer.) 


the  membrane  the  nucleus  consists  of  two  parts,  viz.,  (1)  of  a  reticular 
network,  consisting  of  anastomosing  fibrils  made  up  according  to  Eabl 
(fig.  10)  of  primary  and  thicker  fibres  and  thinner  connecting  branches. 
This  network  has  a  marked  affinity  for  staining  of  reagents  and  hence 
is  called  clii'omoplasm.  The  fibres  are  not  without  structure,  since  in 
certain  cases  they  have  been  shown  to  consist  of  minute  highly-refract- 
ing particles  which  stain  deeply  imbedded  in  a  regular  series  in  a  struc- 


..--'*' 


p.cj 


Fig.  11. — Diagram  of  nucleus  showing  the  arrangement  of  chief  chromatic  filaments,  a.  Viewed 
from  the  side,  tlie  polar  end  being  uppermost,  p.c.f..  Primary  chromatic  filaments;  «,.,  nucleolus; 
n.o.vi.,  node  of  meshwork.  «.  Viewed  at  the  polar  end.  l.c.f.,  Looped  chromatic  filament;  «./.,  ir- 
regular filament.    (Rabl.) 

tureless  matrix  forming  the  filament,  the  former  being  called  chromatin 
and  the  latter  «c/iro?>/f/if«  from  their  respective  reaction  to  stains.  Ac- 
cording to  some  histologists,  nucleoli  are  the  mere  thickenings  of  the 
reticulum  at  the  nodes  or  junctions  of  the  fibrils,  but  others  consider 
them  to  be  distinct  rounded  bodies  free  from  the  meshwork. 

(2)  The  second  part  of  the  nuclear  contents  is  of  a  homogeneous 
material  rich  in  proteids  but  not  necessarily  fluid,  which  fills  up  the 


THE    PHENOMENA    OF    LIFE. 


13 


mesh  work.     This  material  has  but  slight  affinity  for  stains,  and  hence 
is  called  achromatic  substance  or  nuclear  matrix. 


Cell  Division. 

The  division  of  a  cell  is  preceded  by  division  of  its  nucleus.  Nuclear 
division  may  be  either  (1)  simple  or  direct,  which  consists  in  the  simple 
exact  division  of  the  nucleus  into  two  equal  parts  by  constriction  in  the 
centre,  which  may  have  been  preceded  by  division  of  the  nucleoli;  or 
(2)  indirect,  which  consists  in  a  series  of  changes  which  goes  on  in  the 
arrangement  of  the  nuclear  reticulum,  resulting  in  the  exact  division  of 
the  chromatic  fibres  into  two  parts  which  form  the  chromoplasm  of  the 
daughter  nuclei. 

Indirect  division  is  called  karyokinesis  (xdpuov,  a  kernel),  or  mitotic 
{jiiro^,  a  thread),  and  direct  division  is  called  amitotic  or  akinetic  {xi.'riffi'} 


Fig:.  12 Karyokinesis.    a,  Ordinary  nucleus  of  a  columnar  epithelial  cell;  b,  c,  the  same  nucleus 

in  the  stage  of  convolution;  d,  the  wreath  or  rosette  form;  e,  the  aster,  or  single  star;  f,  a  nuclear 
spindle  from  the  Deseemet's  endothehum  of  the  frog's  cornea;  G,  h,  i,  diaster;  k,  two  daughter 
nuclei.     (Klein.) 

movement).  It  is  now  believed  that  the  mitotic  nuclear  division  is  all 
but,  if  not  quite,  universal.  Somewhat  different  accounts  of  the  stnges  of 
the  nuclear  division  have  been  given  by  different  authorities,  according 
to  the  kind  of  cell  in  which  the  nuclear  changes  have  been  studied.  The 
following  will  summarize  the  stages  of  karyokinesis  as  observed  by  Klein : 
The  nucleus  in  a  resting  condition,  i.e.,  before  any  changes  preceding 
division  occur,  consists  of  a  very  close  meshwork  of  fibrils,  which  stain 
deeply  in  carmine,  embedded  in  protoplasm,  which  does  not  possess  this 
property,  the  whole  nucleus  being  contained  in  an  envelope.  The  first 
change  consists  of  a  slight  enlargement,  the  disappearance  of  the  envel- 
ope and  the  increased  definition  and  thickness  of  the  nuclear  fibrils, 
which  are  also  more  separated  than  they  were  and  stain  better.  This  is 
the  stage  of  convolution  (fig.  11,  B,  c).     The  next  step  in  the  process  is. 


14 


HANDBOOK    OF    PHYSIOLOGY. 


the  arrangement  of  the  fibrils  into  some  definite  figure  by  an  alternate 
looping  in  and  out  around  a  central  space,  by  which  means  the  rosette  or 
ivreath  stage  (fig.  12,  d)  is  reached.  The  loops  of  the  rosette  next  be- 
come divided  at  the  periphery  and  their  central  points  become  more 
angular,  so  that  the  fibrils  divided  into  portions  of  about  equal  length 
are,  as  it  were,  doubled  at  an  acute  angle,  and  radiate  V-shaped  from 
the  centre,  forming  a  star  (aster)  or  wheel  (fig.  12,  e),  or  perhaps  from 
two  centres,  in  which  case  a  double  star  (diaster)  results  (fig.  12,  g,  h. 


Achromatic  spiral 


Figr.  13.— Early  stages  of  Ivaryokinesis.  a.  The  thicker  primary  fibres  remain  and  the  achro- 
matic spindle  appears,  b.  The  thick  fibres  split  into  two  and  the  achromatic  spindle  becomes  longi- 
tudinal.    (Waldeyer.) 

and  I).  After  remaining  almost  unchanged  for  some  time,  the  V-shaped 
fibres  being  first  re-arranged  in  the  centre,  side  by  side  (angle  outward), 
tend  to  separate  into  two  bundles  which  gradually  assume  position  at 
either  pole.  From  these  groups  of  fibrils  the  two  nuclei  of  the  new  cells 
are  formed  (daughter  nuclei)  (fig.  12,  k),  and  the  changes  they  pass 
through  before  reaching  the  resting  condition  are  exactly  those  through 
which  the  original  nucleus  (mother  nucleus)  has  gone,  but  in  a  reverse 

^^^^^r>K, --.    Pole  of  spindle. 

Outer  granular  zone. 

VA 

j^\^A SpUt  fibres. 

liL Inner  clear  zone. 

'J 

'  'iJijn, Polar  corpuscle. 

Fig.  14. — Monaster  stage  of  karyokinesls.    (Waldeyer.) 

order,  viz.,  the  star,  the  rosette,  and  the  convolution.  During  or  shortly 
after  the  formation  of  the  daughter  nuclei  the  cell  itself  becomes  con- 
stricted and  then  divides  in  a  line  about  midway  between  them. 

According  to  Waldeyer  the  stages  are  somewhat  different,  the  first 
(ihange  {spirem  stage)  which  occurs  is  that  the  fine  fibrils  of  the  reticu- 
lum of  the  resting  nucleus  disappear,  leaving  the  thicker  more  or  less 
V-shaped  skeins  remaining  (fig.  13,  a).  These  thick  loops  then  split 
longitudinally  into  two  finer  threads,  and  at  the  same  time  the  achromatic 


THE    PHENOMEXA    OF    LIFE. 


15 


spindle  appears.  The  spindle  then  assumes  a  more  central  direction  at 
right  angles  to  the  skeins  (fig.  13,  b),  which  it  did  not  occupy  before, 
so  that  the  nucleus  has  two  poles,  the  terminations  of  the  spindle,  at 
each  of  which  is  developed  a  corpuscle  {polar  corpuscle) — the  inclosing 
membrane  is  lost,  and  the  matrix  of  the  nucleus  becomes  continuous 
with  that  of  the  cell;  the  hyaloplasm  separates  into  two  zones,  a  granu- 


\  _F'"^  uniting 
■""    fllaments. 


Fig.  15.— Metakinesis— chromatic  figure,  spindle,    a.  Early  stage,    b.  Later  stage,    c.  Latest  stage 
—formation  of  diaster.     (Waldeyer.) 

lar  zone  at  the  periphery  and  a  clear  zone  in  the  centre;  this  is  the 
monaster  stage.  The  chromatic  fibres,  at  first  with  their  angles  toward 
the  centre,  then  arrange  themselves  {metakinesis)  with  their  looj^s  toward 
the  poles,  and  move  along  the  spindle  further  and  further  from  each 
other,  being  connected  by  the  fine  fibres  of  the  spindle  only.  In  this 
way.  around  each  pole,  loops  of  fibres  are  grouped,  which  soon  take  the 
arrangement  and  appearance  of  the  primary  chromatic  fibres  {diaster). 
Next  the  new  nuclear  membrane  begins  to  form,  and  the  jDolar  corpuscle 


Remains  of  spindle. 


Line  of  separation 
of  the  two  cells. 

Antipole  of  daugh- 
ter nucleus. 


Lighter    substance 
of  the  nucleus. 


Cell  protoplasm. 
HUus. 


Fig.  16.— Final  stages  of  karyokinesis.    In  the  lower  figure  the  changes  are  still  more  advanced  than 

in  the  upper.     (Waldeyer.) 

disappears.  Thus  are  two  daughter  nuclei  formed  {dispirem  stage). 
The  cell  itself  divides,  and  the  nuclear  fibres  of  the  daughter  nuclei  as- 
sume the  arrangement  of  the  resting  nucleus. 


Differences  between  Animals  and  Plants. 

Having  considered  at  some  length  the  vital  proj)erties  of  protoplasm, 
as  shown  in  cells  of  vegetable  as  well  as  of  animal  organisms,  we  are  now 
in  a  position  to  discuss  the  question  of  the  differences  betwee^i  jJlants  and 


16 


HANDBOOK    OF    PHYSIOLOGY. 


animals.  It  might  at  the  outset  of  our  inquiry  have  seemed  an  unnec- 
essary thing  to  recount  the  distinctions  which  exist  between  an  animal 
and  a  vegetable  as  they  are  in  many  cases  so  obvious,  but,  however  great 
the  differences  may  be  between  the  higher  animals  '-ind  plants,  in  the 
lowest  of  them  the  distinctions  are  much  less  plain. 

In  the  first  place,  it  is  important  to  lay  stress  upon  the  differences 
between  vegetable  and  animal  cells,  first  as  regards  their  structure  and 
next  as  regards  their  functions. 

(].)  It  has  been  already  mentioned  that  in  animal  cells  an  envelope 
or  cell-wall  is  by  no  means  always  present.     In  adult  vegetable  cells,  on 
the  other  hand,  a  well-defined  cellulose  wall  is  highly  characteristic; 
this,   it   should    be  remembered,   is   non-nitrogenous,  and  thus   differs' 
chemically  as  well  as  structurally  from  the  contained  protoplasmic  mass. 

Moreover,  in  vegetable  cells  (fig.  17,  b),  the  protoplasmic  contents 
of  the  cell  fall  into  two  subdivisions:  (1)  a  continuous  film  which  lines 
the  interior  of  the  cellulose  wall;  and  (2)  a  reticulate  mass  containing 


Fig.  17. — (a.)  Young  vegetable  cells,  showing  cell-cavity  entirely  filled  with  granular  protoplasm 
inclosing  a  large  oval  nucleus,  with  one  or  more  nucleoli,  (b.)  Older  cells  from  same  plant,  show- 
ing distinct  cellulose-wall  and  vacuolation  of  protoplasm. 

the  nucleus  and  occupying  the  cell  cavity;  its  interstices  are  filled  with 
fluid.  In  young  vegetable  cells  such  a  distinction  does  not  exist;  a 
finely  granular  protoplasm  occupies  the  whole  cell-cavity  (fig.  17,  a). 

Another  striking  difference  is  the  frequent  presence  of  a  large  quan- 
tity of  intercellular  substance  in  animal  tissues,  while  in  vegetables  it  is 
comparatively  rare,  the  requisite  consistency  being  given  to  their  tissues 
by  the  tough  cellulose  walls,  often  thickened  by  deposits  of  lignin. 
As  an  example  of  the  manner  in  which  this  end  is  attained  in  animal 
tissues,  may  be  mentioned  the  deposition  of  lime  salts  in  a  matrix  of 
intercellular  substance  which  occurs  in  the  formation  of  bone. 

As  regards  the  respective  functions  of  animal  and  vegetable  cells, 
one  of  the  most  important  differences  consists  in  the  power  which  vege- 
table cells  possess  of  being  able  to  build  up  new  complicated  nitrogenous 
and  non -nitrogenous  bodies  out  of  very  simple  chemical  substances  ob- 
tained from  the  air  and  from  the  soil.  They  obtain  from  the  air,  oxy- 
gen, carbonic  anhydride,  and  water,  as  well  as  traces  of  ammonia  gas; 
and  from  the  soil  they  obtain  water,  ammonium  salts,  nitrates,  sulphates, 


THE    PHENOMENA    OF   LIFE,  17 

and  phosphates,  and  sucli  bases  as  potassium,  calcium,  magnesium,  so- 
dium, iron,  and  others.  The  majority  of  plants  are  able  to  work  up 
these  elementary  compounds  into  other  and  more  complicated  bodies. 
This  they  are  able  to  do  in  consequence  of  their  containing  a  certain 
coloring  matter  called  clilorophyll,  the  presence  of  which  is  the  cause  of 
the  green  hue  of  plants.  In  all  plants  which  contain  chlorophyll  two 
processes  are  constantly  going  on  when  they  are  exposed  to  light :  one, 
which  is  called  trtie  respiration  and  is  a  process  common  to  animal  and 
vegetable  cells  alike,  consists  in  the  taking  of  the  oxygen  from  the  at- 
mosphere and  the  giving  out  of  carbon  dioxide;  the  other,  which  is 
peculiar  apparently  to  bodies  containing  chlorophyll,  consists  in  ihe 
taking  in  of  carbon  dioxide  and  the  giving  out  of  oxygen.  It  seems  that 
the  chlorophyll  is  capable  of  decomposing  the  carbon  dioxide  gas  and 
of  fixing  the  carbon  in  the  structures  in  the  form  of  some  new  com- 
pound, one  of  the  most  rapidly  formed  of  which  is  darcli.  The  first 
step  in  the  formation  of  starch  is  the  union  of  carbon  dioxide  and  water 
to  form  formic  aldehyde,  C02+Il20  =  CH204-02,  oxygen  being  evolved; 
then  by  polymerization  the  formation  of  sugar  thus,  6  CIl20  =  C6Hi206; 
and  by  dehydration,  C6H12O6 — Ii20  =  C6Hio05,  the  production  of  starch. 
In  this  way  is  starch  synthesized  or  built  up.  Vegetable  protoplasm  by 
the  aid  of  its  chlorophyll  is  able  to  build  up  a  large  number  of  bodies 
besides  starch,  the  most  interesting  and  important  being  proteid  or 
albumin.  It  appears  to  be  a  fact  that  the  power  which  bodies  possess 
of  being  able  to  synthesize  is  to  a  large  extent  dependent  upon  the  chlo- 
rophyll they  contain.  Thus  the  power  is  only  present  to  any  marked 
extent  in  the  plants  in  v/hicli  chlorophyll  is  found  and  is  absent  in  those 
Avhich  do  not  possess  it;  while  on  the  other  hand  it  is  present  in  the 
extremely  few  animals  which  contain  it  and  is  absent  except  in  certain 
rare  instances  as  one  of  the  properties  of  animal  protoplasm. 

It  must  be  recollected,  however,  that  chlorophyll  without  the  aid  of 
the  light  of  tlie  sun  can  do  nothing  in  the  way  of  building  up  substances, 
and  a  plant  containing  chlorophyll  when  placed  in  the  dark,  as  long  as 
it  liyes,  and  that  is  not  as  a  rule  long,  acts  as  though  it  did  not  contain 
any  of  that  substance.  It  is  an  interesting  fact  that  certain  of  the  bac- 
teria have  the  chlorophyll  replaced  by  a  similar  pigment  which  is  able 
to  decompose  carbon  dioxide  gas. 

Animal  cells,  except  in  the  very  rare  cases  above  alluded  to,  do  not 
possess  the  power  of  building  up  from  simple  materials ;  their  activity 
is  chiefly  exercised  in  the  opj)Osite  direction,  viz,,  they  have  brought  to 
them  as  food  the  complicated  compounds  produced  by  the  vegetable 
kingdom,  and  with  them  they  are  able  to  perform  their  functions,  set- 
ting free  energy  in  the  direction  of  heat,  motion,  and  electricity,  and  at 
the  same  time  eliminating  such  bodies  as  carbon  dioxide  and  water,  and 
producing  other  bodies,  many  of  which  contain  nitrogen,  but  which  are 
2 


18  HANDBOOK    OF    PHYSIOLOGY. 

derived  from  decomposition,  and  only  in  very  rare  cases  from  building 
up. 

It  must  be  distinctly  understood,  however,  that  there  are  instances 
of  animal  cells  performinci^  synthetic  functions  and  of  combining  two 
simpler  compounds  to  produce  one  more  comjilex,  and  it  is  quite  possi- 
ble that  many  of  the  processes  performed  by  the  cells  of  certain  organs 
are  instances  of  synthesis,  and  not  as  they  have  been  described  of  break- 
ing down ;  and  the  reverse  is  undoubtedly  the  case  with  vegetable  cells, 
so  that  it  is  impossible  to  generalize  to  a  greater  extent  than  to  say  that 
the  tendency  of  the  activity  of  the  vegetable  cell  is  chiefly  toward  syn- 
thesis, and  of  the  animal  cell  toward  analysis. 

With  reference  to  the  substance  chlorophyll  it  is  necessary  to  say  a 
few  words.  It  has  been  noted  that  the  synthetical  operations  of  vege- 
table cells  are  peculiarly  associated  with  the  possession  of  chlorophyll 
and  that  these  operations  are  deiDendent  upon  the  light  of  the  sun.  It 
has  been  further  shown  that  a  solution  of  chlorophyll  has  a  definite 
absorption  spectrum  when  examined  with  the  spectroscope,  and  that  it 
is  particularly  those  parts  of  the  solar  spectrum  corresponding  to  these 
absorption  bands  which  are  chiefly  active  in  the  decomposition  of  car- 
bonic anhydride,  and  that,  moreover,  the  position  of  the  maximum  absorp- 
tion corresponds  with  the  maximum  of  energy  of  light.  In  the  synthet- 
ical processes  of  the  plant  then,  by  aid  of  its  chlorophyll,  the  radiant 
energy  of  the  sun's  rays  becomes  stored  up  or  rendered  potential  in  the 
products  formed.  The  potential  energy  is  set  free,  or  is  again  made 
kinetic,  when  these  products  simply  by  combustion  produce  heat,  or 
when  they  are  taken  into  the  animal  organism  and  used  as  food  and  to 
produce  heat  and  motion. 

The  influence  of  light  is  not  an  absolute  essential  to  animal  life;  in- 
deed, it  is  said  not  to  increase  the  metabolism  of  animal  tissue  to  any 
extent,  and  the  animal  cell  does  not  receive  its  energy  directly  from  the 
sun's  light,  nor  yet  to  any  extent  from  the  sun's  heat,  but  from  the 
products  formed  by  vegetable  metabolism  supplied  as  food,  either  di- 
rectly, as  in  the  case  of  herbivora,  or  indirectly  in  the  case  of  carnivora. 
The  potential  energy  of  these  food  stuffs  is  set  free  in  the  destructive 
metabolism  of  the  animal  cell  already  alluded  to.  But  it  must  be  always 
recollected  that  anabolism  is  not  peculiar  to  vegetable,  or  katabolism  to 
animal  cells;  both  processes  go  on  in  each,  but  the  cJiief  function,  as 
far  as  we  know  at  present  of  the  former,  is  to  transform  kinetic  into  po- 
tential energy,  and  of  the  latter  to  render  potential  energy  kinetic,  as 
in  heat,  motion,  and  electricity. 

With  reference  to  the  food  of  plants,  it  should  not  be  forgotten  that 
some  of  the  lowest  forms  of  vegetable  life,  e.g.,  the  bacteria,  will  live 
only  in  a  highly  albuminous  medium,  and  in  fact  seem  to  require  for 
their  growth  elements  of  food  stuffs  which  we  shall  see  later  on  are  es- 


THE    PHEXOME>rA    OF    LIFE.  19 

seutial  to  animal  life.  In  their  metabolism,  too,  they  very  closely  ap- 
proximate to  animal  cells,  not  only  requiring  an  atmosphere  of  oxygen, 
but  giving  out  carbonic  anhydride  freely,  and  secreting  and  excreting 
many  very  complicated  nitrogenous  bodies,  as  well  as  forming  proteid, 
carbohydrates,  and  fat,  requiring  heat  but  not  light  for  the  due  perform- 
ance of  their  functions. 

(2.)  There  is,  commonly,  a  difference  in  general  chemical  composition 
between  vegetables  and  animals,  even  in  their  lowest  forms ;  for  associated 
with  the  protoplasm  of  the  former  is  a  considerable  amount  of  cellulose, 
a  substance  closely  allied  to  starch  and  containing  carbon,  hydrogen,  and 
oxygen  only.  The  presence  of  cellulose  in  animals  is  much  more  rare 
than  in  vegetables,  but  there  are  many  animals  in  which  traces  of  it  may 
be  discovered,  and  some,  the  Ascidians,  in  which  it  is  found  in  consider- 
able quantity.  The  presence  of  starch  in  vegetable  cells  is  very  charac- 
teristic, though,  as  we  have  seen  above,  it  is  not  distinctive,  and  a  sub- 
stance, glycogen,  similar  in  composition  to  starch,  is  very  common  in  the 
organs  and  tissues  of  animals. 

(3.)  Inherent  power  of  movement  is  a  quality  which  we  so  commonly 
consider  an  essential  indication  of  animal  nature,  that  it  is  difficult  at 
first  to  conceive  it  existing  in  any  other.  The  capability  of  simple  mo- 
tion is  now  known,  howe.ver,  to  exist  in  so  many  vegetable  forms,  that 
it  can  no  longer  be  held  as  an  essential  distinction  between  them  and 
animals,  and  ceases  to  be  a  mark  by  which  the  one  can  be  distinguished 
from  the  other.  Thus  the  zoospores  of  many  of  the  Cryptogamia  ex- 
hibit ciliary  or  amoeboid  movements  of  a  like  kind  to  those  seen  in 
amoebge;  and  even  among  the  higher  orders  of  plants,  many,  e.^.,  i)w/ifea 
Muscijmla  (Venus's  fly-trajD),  and  Mimosa  sensitiva  (Sensitive  plant),  ex- 
hibit such  m.otion,  either  at  regular  times,  or  on  the  application  of 
external  irritation,  as  might  lead  one,  were  this  fact  taken  by  itself,  to 
regard  them  as  sentient  beings.  Inherent  joower  of  movement,  then, 
although  especially  characteristic  of  animal  nature,  is,  when  taken  by 
itself,  no  proof  of  it. 

(4.)  The  presence  of  a  digestive  canal  is  a  very  general  mark  by  which 
an  animal  can  be  distinguished  from  a  vegetable.  But  the  lowest  ani- 
mals are  surrounded  by  material  that  they  can  take  as  food,  as  a  plant  is 
surrounded  by  an  atmosphere  that  it  can  use  in  like  manner.  And  every 
part  of  their  body  being  adapted  to  absorb  and  digest,  they  have  no  need 
of  a  special  receptacle  for  nutrient  matter,  and  accordingly  have  no  di- 
gestive canal.     This  distinction  then  is  not  a  cardinal  one. 


CHAPTER   II. 

THE  FUNCTIONS  OF  ORGANIZED   CELLS. 

As  we  proceed  upward  in  the  scale  of  life  from  unicellular  organisms, 
we  find  that  another  phenomenon  is  exhibited  in  the  life  history  of  the 
higher  forms,  namely,  that  of  Development.  An  amceba  comes  into  be- 
ing derived  from  a  previous  amoeba;  it  manifests  the  properties  and 
performs  the  functions  of  its  life  which  have  been  already  enumerated; 
it  grows,  it  reproduces  itself,  whereby  several  amoebas  result  in  place  of 
one,  and  it  dies.  It  cannot  be  said  to  develop,  however,  unless  the  for- 
mation of  a  nucleus  can  be  considered  as  an  indication  of  such  a  process. 
In  the  higher  organisms  it  is  different;  they,  indeed,  begin  as  a  single 
cell,  but  this  cell  on  division  and  subdivision  does  not  form  so  many 


*aSi*''*-^SiI3=»  < 


Fig.  18.— Transverse  section  througrh  embryo  chick  (26  hours).  «,  Epiblast;  ft,  mesoblast:  c, 
hypoblast;  d,  central  portion  of  mesoblast,  which  is  liere  fused  with  epiblast;  e,  primitive  groove; 
/,  dorsal  ridge.    (Klein.) 

independent  organisms,  but  produces  the  material  from  which,  by  devel- 
opment, the  complete  and  perfect  whole  is  to  be  derived.  Thus,  from 
the  spherical  ovum,  or  germ,  which  forms  the  starting-point  of  animal 
life  and  which  consists  of  a  protoplasmic  cell  with  a  nucleus  and  nucle- 
olus, in  a  comparatively  short  time,  by  the  process  of  segmentation  which 
has  been  already  mentioned,  a  complete  membrane  of  cells,  polyhedral 
in  shape  from  mutual  pressure,  called  the  Blastoderm,  is  formed,  and 
this  speedily  divides  into  two  and  then  into  three  layers,  chiefly  from 
the  rapid  proliferation  of  the  cells  of  the  first  single  layer.  These  layers 
are  called  the  Epiblast,  the  Mesoblast,  and  the  Hypoblast  (fig.  18). 
It  is  found  in  the  further  development  of  the  animal  that  from  each 
of  these  layers  is  produced  a  very  definite  part  of  its  completed  body. 
For  example,  from  the  cells  of  the  epiblast  are  derived,  among  other 

20 


THE    FUXCTIONS    OF    ORGAXIZED    CELLS.  21 

■structures,  the  skin  and  the  central  nervous  system ;  from  the  mesobkst 
is  derived  the  flesh  or  muscles  of  the  body,  and  from  the  hypoblast  the 
epithelium  of  the  alimentary  canal  and  some  of  the  chief  glands,  and  so  on. 

It  is  obvious  that  the  tissues  and  organs  so  derived  exhibit  in  a  vary- 
ing degree  the  primary  properties  of  jDrotoplasm.  The  muscles,  for 
example,  derived  from  certain  cells  of  the  mesoblast  are  particularly  con- 
tractile and  respond  to  stimuli  readily,  while  the  cells  of  the  liver, 
although  possibly  contractile  to  a  certain  extent,  have  to  do  chiefly  with 
the  processes  of  nutrition. 

Thus,  in  development,  we  see  that  as  the  cells  of  the  embryo  in- 
crease in  number  it  speedily  becomes  necessary  for  the  organism  to 
depute  to  different  groups  of  cells,  or  to  their  equivalents  {i.e.,  to  the 
tissues  or  organs  to  which  they  give  rise),  special  functions,  so  that  the 
Tarious  functions  which  the  original  cell  may  be  supposed  to  discharge, 
and  the  various  properties  it  maybe  supposed  to  possess,  become  divided 
up  among  various  groups  of  resulting  cells.  The  work  of  each  group 
is  specialized.  As  a  result  of  this  division  of  labor,  as  it  may  be  called, 
these  functions  and  properties  are,  as  might  be  expected,  develoj^ed  and 
made  more  perfect,  while  the  tissues  and  organs  arising  from  each 
group  of  cells  are  developed  also,  with  a  view  to  the  more  convenient 
and  effective  exercise  of  their  functions  and  employment  of  their  pro^v 
erties. 

In  studying  the  functions  of  the  human  body  it  is  necessary  first  of 
all  to  know  of  what  it  is  composed,  of  what  tissues  and  organs  it  is  made 
up;  this  can  of  course  only  be  ascertained  by  the  dissection  of  the  dead 
body,  and  thus  it  comes  that  Anatomy  (avar/.avw,  to  cut  up)  the  science 
which  treats  of  the  structure  of  organized  bodies,  is  closely  associated 
with  physiology;  so  closely,  indeed,  that  Histology  (iVr.)?,  a  web),  which 
is  especially  concerned  with  the  minute  or  microscopic  structure  of  the 
tissues  and  organs  of  the  body,  and  which  is  strictly  s2Deaking  a  depart- 
ment of  anatomy,  is  usually  included  in  works  on  physiology.  There  is 
much  to  be  said  in  favor  of  such  an  arrangement,  since  it  is  impossible 
to  consider  the  changes  which  take  jflace  in  any  tissue  during  life, 
apart  from  the  knowledge  of  the  structure  of  the  tissues  themselves. 
To  understand  the  structure  of  the  human  body  in  an  intelligent  wa}', 
much  help  is  obtained  from  the  study  of  the  structure  of  other  animals, 
from  the  lowest  to  the  highest,  which  is  the  province  of  Comparative 
Anatomy ;  while  Embryology,  which  is  concerned  Avith  the  mode  of 
origin  of  the  various  tissues  in  the  embryo  of  each  animal,  and  which  is 
usually  studied  at  the  end  of  physiology,  should  from  some  i^oints  of 
view  be  considered  as  an  introduction  to  the  subject. 

A  second  important  essential  to  the  right  comprehension  of  the 
changes  which  take  place  in  the  living  organism  is  a  knowledge  of  the 
chemical  composition  of  the  body.     Here,  however,  we  can  only  deal 


22  HANDl'.OOK    OF    PHYSIOLOGY. 

with  the  chemieal  composition  of  tlie  dead,  body,  and  it  is  as  well  at 
once  to  admit  that  there  may  be  many  chemical  differences  between 
living  and  not  living  tissues;  but  as  it  is  imjicjssible  to  ascertain  the 
exact  chemical  composition  of  the  living  tissues,  the  next  best  thing 
which  can  be  done  is  to  find  out  as  much  as  2)ossible  about  the  com- 
position of  the  same  tissues  after  they  are  dead.  This  is  the  assistance 
which  the  science  of  Chemistry  can  afford  to  the  physiologist,  and  the 
same  science  is  concerned  with  the  composition  of  the  ingesta  and  egesta, 
as  well  as  with  that  of  the  fluids  of  the  body. 

Having  mastered  the  structure  and  composition  of  the  body,  we  are 
brought  face  to  face  with  physiology  proj^er,  and  have  to  investigate  the 
vital  changes  which  go  on  in  the  tissues,  the  various  actions  taking  jihice 
as  long  as  the  organism  is  at  work.  The  subject  includes  not  only  the 
observation  of  the  manifest  processes  which  are  continually  taking 
place  in  the  healthy  body,  but  the  conditions  under  which  these  are 
brought  about,  the  laws  which  govern  them  and  their  effects. 

We  know  from  our  study  of  biology  that  the  cells  of  which  the  tis- 
sues are  composed  cannot  live  without  food,  both  solid  and  liquid.  In 
a  complicated  organism  like  the  body  of  man,  the  tissues  cannot  sujijDly 
themselves  with  food  directly  like  the  amoeba,  and  so  it  comes  that  the 
various  tissues  are  furnished  with  what  they  require  by  means  of  a 
fluid,  the  blood,  which  is  carried  to  them  in  tubes  or  canals,  the  blood- 
vessels, which  are  distributed  to  every  region  of  the  body.  In  order  that 
the  blood  shall  reach  all  parts,  the  system  of  vessels  in  which  it  is  con- 
tained is  supplied  with  a  central  pumping  organ,  the  heart.  Then  we 
find  that  as  the  oxygen,  which  is  one  of  the  requisites  of  the  life  of  the 
tissues,  and  which  is  carried  to  the  tissues  by  the  blood,  is  used  up,  a 
special  means  is  provided  by  respiration,  or  breathing,  by  means  of 
which  the  blood  is  exposed  to  a  new  supply  of  oxygen  of  the  air,  which 
is  taken  into  special  organs,  the  lungs,  for  the  purpose,  and  which  at 
the  same  time  allows  of  the  elimination  of  the  carbonic  anhydride  the 
blood  conveys  from  the  tissues.  Then  again,  as  the  solid  food  for  the 
tissues  cannot  be  conveyed  in  the  blood  in  the  exact  form  in  which  it  is 
introduced  into  the  body,  a  special  and  complicated  apparatus  is  pro- 
vided, that  of  digestion,  by  means  of  which  the  necessary  changes  are 
brought  about  in  the  food.  The  digested  food  is  then  absorbed  and 
carried  to  the  blood,  either  directly  with  little  further  change  by  means 
of  another  system  of  vessels  in  connection  with  the  blood-vessels,  the 
lymplialic  vessels,  or  after  jDassing  through  a  special  organ  or  gland,  the 
liver,  by  means  of  which  some  further  changes  take  place.  In  the 
digestive  apparatus  we  have  the  organs,  the  stomach  and  intestines,  into 
which  the  food  is  received  for  the  ^iurpose  of  being  acted  upon  by  cer- 
tain chemical  agents,  of  which  ferments,  bodies  which  are  capable  of 
setting  up  profound  changes  in  other  bodies  without  themselves  under- 


THE    FUNCTIONS    OF    ORGANIZED    CELLS.  ^        23 

going  change,  are  the  most  important;  there  is  added  the  apparatus  by 
means  of  which  the  altered  food  stuffs  are  absorbed  or  reach  the  two 
systems  of  blood-vessels  already  mentioned,  and  a  muscular  apparatus 
contained  in  the  walls  of  the  intestinal  tube  by  means  of  which  that 
part  of  the  food  which  is  not  fit  for  absorption  is  removed  from  the 
body.  In  addition  to  this  excretory  apparatus  we  have  another,  the 
kidneys,  which  are  concerned  with  the  removal  of  certain  substances 
from  the  blood  which  have  served  their  purpose  in  the  economy. 

Then  we  have  the  muscular  system,  which  by  its  special  power  of 
contraction  is  capable  of  bringing  about  all  the  movements  of  the  body 
— those  of  the  frame,  the  head,  arms,  legs,  etc.,  as  well  as  those  of  the 
heart,  the  vessels,  the  alimentary  canal,  and  the  like.  The  nervous  sys- 
tem, by  the  aid  of  which  the  processes  of  the  living  body  may  be  regu- 
lated and  controlled.  Lastly,  we  have  a  special  system — that  of  the 
generative  system,  by  means  of  which  the  reproduction  of  the  species 
may  take  place. 

To  these  subjects,  the  merest  outline  of  which  has  been  here 
sketched,  our  attention  has  to  be  given  in  the  succeeding  chapters,  but 
it  may  be  well  to  mention  as  a  preliminary  that  the  information  about 
them  which  we  have  at  our  disposal  has  been  derived  from  many  sources, 
the  chief  of  which  are  as  follows : — 

(1.)  From  actual  observation  of  the  various  phenomena  occurring  in 
the  human  body  from  day  to  day,  and  from  hour  to  hour,  as,  for  exam- 
ple, the  estimation  of  the  amount  and  composition  of  the  ingesta  and 
egesta,  the  respiration,  the  beat  of  the  lieart,  and  the  like; 

(3.)  From  observations  upon  other  animals,  the  bodies  of  which  we 
are  taught  by  comparative  anatomy  approximate  to  the  human  body 
in  structure; 

(3.)  From  observations  of  the  changes  produced  by  experiment  upon 
the  various  processes  in  such  animals; 

(4.)  From  observations  of  the  changes  in  the  working  of  the  human 
body  produced  by  disease; 

(5.)  From  observations  upon  the  gradual  changes  which  take  place 
in  the  functions  of  organs  when  watched  in  the  embryo  from  their 
earliest  beginnings  to  their  completed  development. 

In  accordance  with  the  plan  sketched  out'  above,  the  next  chapter 
will  be  devoted  to  a  consideration  of  the  minute  structure  of  the  ele- 
mentary tissues,  and  the  one  after  that  to  a  jDreliminary  account  of  the 
chemical  composition  of  the  body.  These  two  chapters  will  serve  as  an 
introduction  to  the  study  of  the  problems  of  physiology  proper,  which 
will  be  commenced  in  Chapter  V. 


CHAPTER   III. 

THE  STRUCTURE   OF  THE  ELEMENTARY  TISSUES. 

The  careful  examination  of  the  minute  anatomy  of  the  body  has 
shown  that  there  are  certain  elementary  structures,  of  which,  alone  or 
when  combined  in  varying  proportions,  the  whole  of  the  organs  and 
tissues  of  the  body  are  made  up.  These  Elementary  Tissues  are  four 
in  number,  called:  (1.)  The  Epitlielial ;  (2.)  The  Cofinective  ;  (3.)  The 
Mnsctdar,  and  (4.)  7'he  Nervous.  To  these  four,  some  would  add  a  fifth, 
looking  upon  the  Blood  and  Lympli,  containing,  as  they  do,  formed 
elements  in  a  fluid  menstruum,  as  a  distinct  tissue. 

All  of  these  elementary  tissues  consist  of  cells  and  of  their  altered 
equivalents.  It  will  be  as  well  therefore  to  indicate  some  of  the  differ- 
ences between  the  cells  of  the  body.  They  are  named  in  various  ways, 
according  to  their  shape,  situation,  contents,  origin,  awd  functions. 

(a.)  From  their  shape,  cells  are  called  spherical  or  spheroidal,  which 
is  the  typical  shape  of  the  free  cell;  this  maybe  altered  to  polyhedral 
when  the  pressure  on  the  cells  in  all  directions  is  nearly  the  same;  of 
this  the  primitive  segmentation  cells  afford  an  example.  The  discoid 
form  is  seen  in  blood-corpuscles,  and  the  scale-like  form  in  superficial 
epithelial  cells.  Some  cells  have  a  jagged  outline  and  are  then  called 
prickle  cells.  Cells  of  cylindrical,  conical,  or  prismcitic  form  occur  in 
various  places  in  the  body.  Such  cells  may  taper  off  at  one  or  both 
ends  into  fine  processes,  in  the  former  case  being  caudate,  in  the  latter 
fusiform.  They  may  be  greatly  elongated  so  as  to  become  fibres.  Cells 
"with  hair-like  processes,  or  cilia,  projecting  from  their  free  surfaces,  are 
a  special  variety.  The  cilia  vary  greatly  in  size,  and  may  even  exceed 
in  length  the  cell  itself.  Finally,  cells  may  be  hranched  or  stellate  with 
long  outstanding  processes. 

(J.)  From  their  situation  cells  may  be  called /re(?,  as  in  the  blood, 
or  comhined,  when  connected  together  or  with  other  elements  to  form 
organs  and  tissues. 

(c.)  From  their  contents  cells  are  called,  when  containing  fat  for 
example, /a«f  cells  ;  when  containing  Y^gra^wi,  pigment  cells,  etc. 

(fZ.)  From  their  function  cells  are  called  secreting,  protective,  sensi- 
tive, contractile,  and  the  like. 

(e.)  From  their  origin  cells  are  called  epiblastic  and  mesoblastic  and 
Tiypoblastic. 

24 


THE    STRUCTURE    OF   THE    ELEMENTARY   TISSUES.  '^5 

Modes  of  Connection. — Cells  are  conuected  together  to  form 
tissues  in  various  ways. 

(1.)  By  mean  of  a  cementing  intercellular  substance.  This  is  prob- 
ably always  present  as  a  transparent,  colorless,  viscid,  albuminous  sub- 
stance, even  between  the  closely  apposed  cells  of  epithelium,  while  in 
the  case  of  cartilage  it  forms  the  main  bulk  of  the  tissue,  and  the  cells 
only  appear  as  imbedded  in,  not  as  cemented  together  by,  the  intercel- 
lular substance.  This  intercellular  substance  may  be  either  homogene- 
ous or  fibrillated.  In  many  cases  {e.g.,  the  cornea)  it  can  be  shown  to 
•contain  a  number  of  irregular  branched  cavities,  which  communicate 
witli  each  other,  and  in  which  branched  cells  lie:  through  these  branch- 
ing spaces  nutritive  fluids  can  find  their  way  into  the  very  remotest 
parts  of  a  non-vascular  tissue. 

As  a  special  variety  of  intercellular  substance  must  be  mentioned  the 
basement  membrane  {memhrana  projyria)  which  is  found  at  the  base  of 
the  epithelial  cells  in  most  mucous  membranes,  and  especially  as  an 
Investing  tunic  of  gland  follicles  which  determines  their  shape,  and 
which  may  persist  as  :).  hyaline  saccule  after  the  gland  cells  have  all 
been  discharged. 

(2.)  By  anastomosis  of  their  processes.  This  is  the  usual  way  in 
which  stellate  cells,  e.g.  of  the  cornea,  are  united :  the  individuality  of 
■each  cell  is  thus  to  a  great  extent  lost  by  its  connection  with  its  neigh- 
bors to  form  a  reticulum:  as  an  example  of  a  network  so  produced  we 
may  cite  the  stroma  of  lymphatic  glands. 

Sometimes  the  branched  processes  breaking  up  into  a  maze  of 
minute  fibrils,  adjoining  cells  are  connected  by  an  intermediate  reticu- 
lum :  this  is  tlie  case  in  the  nerve  cells  of  the  spinal  cord. 

Derived  Tissue-elements.— Besides  the  Cell,  which  may  be  termed 
the  primary  tissue-element,  there  are  materials  which  may  be  termed 
secondary  or  derived  tissue-elements.  Such  are  Intercellular  substance. 
Fibres,  and  Tubules. 

a.  Intercellular  substance  is  probably  in  all  cases  directly  derived 
from  the  cells  themselves.  In  some  cases  {e.g.  cartilage),  by  the  use  of 
re:igents  the  cementing  intercellular  substance  is,  as  it  were,  analyzed 
into  various  masses,  each  arranged  in  concentric  layers  around  a  cell  or 
group  of  cells,  from  which  it  was  probably  derived. 

/?.  Filrres.  In  the  case  of  the  crystalline  lens,  and  of  muscle  both 
striated  and  non-striated,  each  fibre  is  simply  a  metamorphosed  cell:  in 
the  case  of  a  striped  fibre,  the  elongation  being  accompanied  by  a  mul- 
tiplication of  the  nuclei.  The  various  fibres  and  fibrillaj  of  connective 
tissue  result  from  a  gradual  transformation  of  an  originally  homogene- 
ous intercellular  substance.  Fibres  thus  formed  may  undergo  great 
<.'hemical  as  well  as  physical  transformation :  this  is  notably  the  case 
with  yellow  elastic  tissue,  in  which  the  sharply  defined  elastic  fibres, 


26  HAXDBOOK    OF    PHYSIOLOGY. 

possessing  great  jDower  of  resistance  to  reagents,  contrast  strikingly 
witli  the  honiogeueous  matter  from  which  they  are  derived. 

y.  Tubules,  such  as  the  capillary  blood-vessels,  which  were  originally 
supposed  to  consist  of  a  structureless  membrane,  have  now  been  proved 
to  be  composed  of  flat,  thin  cells,  cohering  along  their  edges. 

Decay  and  Death  of  Cells.— There  are  two  chief  ways  in  which  the 
comparatively  brief  existence  of  cells  is  brought  to  an  end.  (1)  Mechan- 
ical abrasion,  (2)  Chemical  transformation. 

1.  The  various  epithelia  furnish  abundant  examples  of  mechanical 
abrasion.  As  it  approaches  the  free  surface,  the  cell  becomes  more  and 
more  flattened  and  scaly  in  form  and  more  horny  in  consistency,  till  at 
length  it  is  simply  rubbed  off  as  in  the  epidermis.  Hence  we  find  epi- 
thelial cells  in  the  mucus  of  the  mouth,  intestine,  and  genito-urinary 
tract. 

2.  In  the  case  of  chemical  transformation  the  cell-contents  undergo- 
a  degeneration  Avliich,  though  it  may  be  pathological,  is  very  often  a 
normal  process. 

Thus  we  have  (a)  fatt//  metamorphosis  producing  oil-globules  in  the 
secretion  of  milk,  fatty  degeneration  of  the  muscular  fibres  of  the  uterus- 
after  the  birth  of  the  fo3tus,  and  of  the  cells  of  the  Graafian  follicle 
giving  rise  to  the  "corpus  luteum."  (b)  Pirjmetdary  degeneration  from, 
deposit  of  pigment,  e.g.  in  the  epithelium  of  the  air  vesicles  of  the  lungs, 
(c)  Calcareous  degeneration,  which  is  common  in  the  cells  of  many 
cartilages. 

I.  The  Epithelial  Tissues. 

The  term  epithelium  is  applied  to  the  cells  covering  the  skin,  the 
mucous  and  serous  membranes,  and  to  those  forming  a  lining  to  other 
parts  of  the  body  as  well  as  entering  into  the  formation  of  glands.  For 
example: — 

Epithelium  clothes  (1)  the  whole  exterior  surface  of  the  body,  form- 
ing the  epidermis  with  its  appendages — nails  and  hairs;  becoming  con- 
tinuous at  the  chief  orifices  of  the  body — nose,  mouth,  anus,  and  urethra 
— with  the  (2)  ej)ithelium  which  lines  the  whole  length  of  the  (3)  respi- 
ratory, alimentary,  and  genito-urinary  tracts,  together  with  the  ducts  of 
their  various  glands.  Epithelium  also  lines  the  cavities  of  (4)  the  brain 
and  the  central  canal  of  the  spinal  cord,  (5)  the  serous  and  synovial 
membranes,  and  (6)  the  interior  of  all  blood-vessels  and  lymphatics. 

Epithelial  cells  possess  an  intracellular  and  an  intranuclear  network 
(p.  9  and  10).  When  combi^ied  together  to  form  a  tissue,  they  are  held 
together  by  a  clear,  albuminous,  cement-substance,  scanty  in  amount. 
The  viscid  semi-fluid  consistency  both  of  cells  and  intercellular  sub- 
stance permits  such  changes  of  shape  and  arrangement  in  the  individual 


THE    STRUCTURE    OF   THE    ELEMEXTARY    TISSUES.  27 

cells  as  are  necessary  if  the  epithelium  is  to  maintain  its  integrity  in 
organs  the  area  of  whose  free  snrface  is  so  constantly  changing,  as  the 
stomach,  lungs,  etc.  Thus,  if  there  be  but  a  single  layer  of  cells,  as  in 
the  epithelium  lining  the  air  vesicles  of  the  lungs,  the  stretching  of  this 
membrane  causes  such  a  thinning  out  of  the  cells  that  they  change 
their  shape  from  spheroidal  or  short  columnar,  to  squamous,  and  vice 
versa,  when  the  membrane  shrinks. 

Epithelial  tissues  are  non-vascular,  that  is  to  say,  do  not  contain 
blood-vessels,  but  in  some  varieties  minute  channels  exist  between  the 
cells  of  certain  layers  through  w^hich  they  may  be  supplied  with  nour- 
ishment from  the  subjacent  blood-vessels.  Xerve  fibres  are  suj^jjlied  to 
the  cells  of  many  epithelia. 

Epithelial  tissue  is  classified  according  as  tiie  cells  composing  it  are 
arranged  in  a  single  layer  when  it  is  ni/njjle,  or  in  several  layers  when  it 
is  called  stratified  or  laminated,  or  in  two  or  three  layers  occupying  a 
position  between  the  other  two  forms,  when  it  is  termed  transitional. 
Of  each  form,  when  there  are  several  varieties,  they  are  named  accord- 
ing to  the  shaj)e  of  the  cells  composing  it. 

Classification  of  Epithelium. 

(a)  Simple. — (1.)  Squamous,  scaly,  pavement,  or  tessellated;  (3.) 
Spheroidal  or  glandular;  (3.)  Columnar,  cylindrical,  conical  or  goblet- 
shaped;  (4.)   Ciliated. 

(b)  Transitional. 

(c)  Stratified. 

(a)  Simple  Epithelium. 

Squamous  Epitlielium. — This  form  of  epithelium  is  found  arranged 
as  a  single  layer  of  flattened  cells,  as  («)  the  pigmentary  layer  of  the 
retina,  and  forms  the  lining  of  {h)  the  interior  of  the  serous  and  syno- 
vial sacs,  (c)  the  alveoli  of  the  lungs,  and  {d)  of  the  heart,  blood-  and 
lymph-vessels.  It  consists  of  cells,  which  are  flattened  and  scaly,  with 
a  more  or  less  irregular  outline. 

In  the  pigment  cells  of  the  retina  there  is  a  deposit  of  pigment  in 
the  cell-substance.  This  pigment  consists  of  minute  molecules  of  a 
colored  substance,  melanin,  imbedded  in  the  cell-substance  and  almost 
concealing  the  nucleus,  which  is  itself  transparent. 

In  white  rabbits  and  other  albino  animals,  in  which  the  pigment  of 
the  eye  is  absent,  this  layer  is  found  to  consist  of  colorless  pavement 
epithelial  cells. 

The  squamous  epithelium  which  is  found  as  a  single  layer  lining  the 
serous  membranes,  and  the  interior  of  blood-  and  lymphatic-vessels,  is 
generally  called  by  a  distinct  name — Endothelium. 


•28 


HANDBOOK    OF    PHYSIOLOGY. 


The  presence  of  endothelium  in  any  locality  may  be  demonstrated  by 
staining  the  part  lined  by  it  with  silver  nitrate,  which  brings  into  view 
±he  intercelluar  cement  substance. 

It  is  found  that  when  a  small  portion  of  a  perfectly  fresh  serous 


Fig.  19.— Piginent-cells  from  the  retina.  A,  Cells  still  culieiiug,  seen  on  their  surface;  o,  nucleus 
"indistinctly  seen.  In  the  other  cells  the  nucleus  is  concealed  by  the  pigment  granules,  b.  Two  cells 
rseen  in  profile;  a,  the  outer  or  posierior  part  containing  scarcely  any  pigment.     X  310.    (Heule.) 

membrane  for  example  (fig.  20),  is  immersed  for  a  few  minutes  in  a 
solution  of  silver  nitrate,  and  exposed  to  the  action  of  light,  the  silver 
is  precipitated  in  some  form  in  the  intercellular  cement  substance,  and 
the  endothelial  cells  are  thus  mapped  out  by  fine,  dark,  and  generally 
sinuous  lines  of  extreme  delicacy.  The  cells  vary  in  size  and  shape,  and 
.areas  a  rule  irregular  in  outline;  those  lining  the  interior  of  blood - 


Fig.  20.— A  piece  of  the  omentum  of  a  cat,  stained  in  silver  nitrate.  X  100.  The  tissue  forms  a 
''fenestrated  niernbrnne,''' that  is  to  say,  one  which  is  studded  with  lioles  or  windows.  In  the 
figure  these  are  of  various  shapes  and  sizes,  leaving  trabeeula?,  the  basis  of  which  is  fibrous  tissue. 
The  trabecute  are  of  various  sizes  and  are  covered  witli  endothelial  cells,  the  nuclei  of  which  have 
been  made  evident  by  staining  with  hfeiiiatoxylin  after  the  silver  nitrate  has  outlined  the  cells  by 
staining  the  intercellular  substance.    ( Y.  D.  Harris. ) 

vessels  and  lymphatics  being  spindle-shaped  Avith  a  very  wavy  outline. 
They  inclose  a  clear,  oval  nucleus,  which,  when  the  cell  is  viewed  in 
profile,  is  seen  to  project  from  its  surface.  The  nuclei  are  not  however 
evident  unless  the  tissue  which  has  been  already  stained  in  silver  nitrate. 


THE    STRUCTURE    OF   THE    ELEMENTARY    TISSUES. 


29- 


is  placed  in  another  dye,  sucii  as  h^ematoxylin,  which  has  the  property 
of  selecting  and  staining  its  nuclei. 

Endothelial  cells  in  certain  situations  may  be  ciliated,  e.g.,  those  of 
the  mesentery  of  the  frog,  especially  during  the  breeding  season. 


Fig.  81. — Abdominal  surface  of  central  tendon  of  the  diaphragm  of  rabbit,  showing  the  general- 
polygonal  shape  of  the  endothelial  cells:  each  cell  is  nucleated.     (Klein.)     x  300. 

Besides  the  ordinary  endothelial  cells  above  described,  there  are 
found  on  the  omentum  and  parts  of  the  pleura  of  many  animals,  little- 
bud-like  processes  or  nodules,  consisting  of  small  polyhedral  granular- 
cells,  rounded  on  their  free  surface,  which  have  multiplied  very  rapidly 
by  division  (figs.  22  and  23).  These  constitute  what  is  known  as  ge7'- 
minating  endothelium.  The  process  of  germination  doubtless  goes  on 
in  health,  and  the  small  cells  which  are  thrown  off  in  succession  are- 


Fig.  22.— Peritoneal  surface  of  a  portion  of  the  septum  of  the  great  lymph-sacs  of  frog.  The- 
stomata,  some  of  which  are  open,  some  collapsed,  are  surrounded  by  endothelial  cells.  (Klein.) 
X  160. 

carried  into  the  lymphatics  and  contribute  to  the  number  of  the  lymph 
corpuscles.  The  buds  may  be  enormously  increased  both  in  number 
and  size  in  certain  diseased  conditions. 

On  those  portions  of  the  peritoneum  and  other  serous  membranes  in 
whicli  lymphatics  abound  apertures  (fig.  22)  are  found  surrounded  by 
small,  more  or  less  cubical,  cells.  These  apertures  are  called  siomafa. 
They  are  particularly  well  seen  in  the  anterior  wall  of  the  great  lymph 


30 


HAXDIiOOK    OF    PHYSIOLOGy. 


sac  of  the  frog  (fig.  22),  and  in  the  omentum  of  the  rabbit.     These  are 
really  the  open  mouths  of  lymphatic  vessels  or  spaces,  and  through 


Fig  '^3.— A  portion  of  the  great  omentum  of  dog,  which  shows,  among  the  flat  endothelium  of 
the  surface,  small  and  large  groups  of  germinating  endothelium  between  which  are  many  stomata. 
(Klem.j     X  300. 

them  lymph-corpuscles  and  the  serous  fluid  from  the  serous  cavity  pass 
into  the  lymphatic  system.  They  should  be  distinguished  from  smaller 
and  more  numerous  apertures  between  the  cells  which  are  not  lined  by 


Fig.  24. 


Fig.  25. 


Fig.  24.— A  small  piece  of  the  liver  of  the  horse.     (Cadiat.) 

Fig.  25.— Glandular  epitlielium.    Small  lobule  of  a  mucous  gland  of  the  tongue,  showing  nu- 
cleated glandular  cells.     X  200.     (V.  D.  Harris.) 

small  cells,  although  the  surrounding  cells  seem  to  radiate  from  them, 
filled  up  by  intercellular  substance  or  by  processes  of  the  cells  under- 
neath.    These  are  called  pseudo-stomata  (fig.  23). 


THE    STRUCTURE    OF   THE    ELEMENTARY    TISSUES. 


31 


In  the  neighborhood  of  the  stomata  the  cells  often  manifest  indica- 
tions of  germinating.  They  mu}^  be  either  large  with  two  or  more 
nuclei,  or  about  half  the  size  of  the  generality  of  cells.  Germinating 
cells  of  this  kind  or  of  the  kind  above  described,  are  generally  very 
granular. 

Spheroidal  or  glandular  epifhelium  forms  the  active  secreting  agent 
in  the  glands,  the  cells  are  however  not  always  of  the  same  shape  but 
may  be  besides  the  typical  spheroidal,  polyhedral  from  mutual  pressure, 
or  even  columnar. 

Examples  of  glandular  epithelium  are  to  be  found  in  the  liver  (fig. 
24),  in  the  secreting  tubes  of  the  kidney,  and  in  the  salivary  (fig.  25) 
and  gastric  glands. 

Columnar  epithelium  (fig.  28,  a  and  b)  as  a  single  layer  lines  (a.)  the 
mucous  membrane  of  the  stomach  and   intestines,  from  the    cardiac 


Fig.  26. 


Fig.  27. 


Fig.  26.— Columuar  epithelial  cells  from  the  intestinal  mucous  membrane  of  a  cat.    a  and  6, 
Small  cells  of  the  lowest  layer:  c,  superficial  layer;  d,  goblet  cells     (Cadiat.) 
Fig.  27.— Goblet  cells.     (Klein.) 

orifice  of  the  stomach  to  the  anus,  and  (b.)  wholly  or  in  jjart  the  ducts 
of  the  glands  opening  on  its  free  surface;  also  (c.)  many  gland-ducts  in 
other  regions  of  the  body,  e.g.,  mammar}^  salivary,  etc. 

Columnar  epithelium  consists  of  cells  which  are  cylindrical  or  pris- 
matic in  form  containing  a  large  oval  nucleus.  They  vary  in  size  and 
also  to  a  certain  extent  in  shape;  the  outline  is  often  jagged  and  irreg- 
ular from  pressure  of  neighboring  cells,  but  one  end  of  the  cell  is  always 
narrower  than  the  other,  and  by  this  narrower  end  the  cell  is  as  a  rule 
attached  to  the  membrane  beneath.  The  intracellular  and  intranuclear 
networks  are  well  developed,  and  in  some  cases  the  spongioplasm  is 
arranged  in  rods  or  longitudinal  striae  at  one  part  of  the  cell,- generally 
the  attached  border,  as  in  some  of  the  cells  of  the  ducts  of  salivary 
glands. 

This  may  also  be  the  case  with  the  columnar  epithelial  cells  of  the 
alimentary  canal  which  possess  an  apparently  structureless  layer  on 
their  free  surface :  such  a  layer,  appearing  striated  when  viewed  in  sec- 
tion, is  termed  the  "striated  basilar  border"  (fig.  28,  a). 

The  protoplasm  of  columnar  cells  may  be  vacuolated  and  may  also 


32  HANDBOOK    OF    PHYSIOLOGY. 

contain  fat  or  other  substances,  of  which  the  most  h"kely  is  mucin  or 
its  antecedent  mucigen,  to  be  seen  in  the  form  of  granules.  It  is  to  the 
presence  of  mucin  that  a  curious  transformation  which  columnar  cells 
may  undergo  is  due,  and  from  which  the  alteration  in  their  shape 
whereby  "goblet-cells"  are  produced  (fig.  27)  arises.  These  altered  cells, 
are  hardly  ever  evident  in  a  perfectly  fresh  specimen;  but  if  such  a 
specimen  be  watched  for  some  time,  little  knobs  are  seen  gradually  to 
appear  on  the  free  surface  of  the  epithelium  and  are  finally  detached; 
these  consist  of  the  cell-contents  which  are  discharged  by  the  open 
mouth  of  the  goblet,  leaving  the  nucleus  surrounded  by  the  remains  of 
the  protoplasm  in  its  narrow  stem. 

This  transformation  is  a  normal  process  which  is  continually  going- 
on  during  life,  the  discharged  cell-contents  contributing  to  form  mticus. 


,!  ig;.  38. — Vertical  section  of  an  intestinal  villus  of  a  eat.  o.  The  striated  basilar  border  of  the 
epithelium;  b,  columnar  epitheliimi;  c,  goblet  cells;  d.  central  lymph-vessel;  e,  unstriped  muscular 
fibres;  /,  adenoid  stroma  of  the  villus  in  which  are  contained  lymph  corpuscles.    cKlein.) 

the  cells  themselves  being  supposed  in  many  cases  after  discharge  to 
recover  their  original  shape. 

Ciliated  ejjitheliuni  consists  of  cells  which  are  generally  cylindrical 
in  form  (figs.  29,  30),  but  may  be  spheroidal  or  even  almost  squamous. 

This  form  of  epithelium  lines — (a.)  the  mucous  membrane  of  the 
respiratory  tract  beginning  just  beyond  the  nasal  aperture  and  com- 
pletely covering  the  nasal  passages,  except  the  uj^per  part  to  which  the 
olfactory  nerve  is  distributed,  and  also  the  sinuses  and  ducts  in  connec- 
tion with-it  and  the  lachrymal  sac;  the  upper  surface  of  the  soft  palate 
and  the  naso-pharynx,  the  Eustachian  tube  and  tympanum,  the  larynx, 
except  over  the  vocal  cords,  to  the  finest  subdivisions  of  the  bronchi. 
In  part  of  this  tract,  however,  the  epithelium  is  in  several  layers,  of 
which  only  the  most  superficial  is  ciliated,  so  that  it  should  more  accu- 
rately be  termed  transitional  (p.  35)  or  stratified,  (b.)  Some  portions 
of  the  generative  apparatus  in  the  male,  viz.,  lining  the  "  vasa  eflerentia  '* 
of  the  testicle,  and  their  prolongations  as  far  as  the  lower  end  of  the 


THE    STRUCTUKE    OF   THE    ELEMENTARY    TISSUES. 


33 


epididymis;  in  the  female  (c.)  commencing  about  the  middle  of  the 
neck  of  the  uterus,  and  extending  throughout  the  uterus  and  Fallopian 
tubes  to  their  fimbriated  extremities,  and  even  for  a  short  distance  on 
the  peritoneal  surface  of  the  latter,  (d.)  The  ventricles  of  the  brain 
and  the  central  canal  of  the  spinal  cord  are  clothed  with 'ciliated  epithe- 
lium in  the  child,  but  in  the  adult  this  epithelium  is  limited  to  the 
central  canal  of  the  cord.  In  the  embrj^o  the  jjharynx,  oesophagus,  and 
part  of  the  stomach  may  also  be  lined  with  ciliated  cells,  (e.)  The  ex- 
cretory ducts  of  certain  small  glands  in  different  localities,  (f.)  In 
certain  animals,  especially  the  lower  vertebrates,  ciliated  cells  line  the 
beginning  of  the  tubes  of  tlie  kidneys. 

The  Cilia  are  fine  hair-like  processes  Avhich  give  the  name  to  this 
variety  of  epithelium j  they  vary  a  good  deal  in  size  in  different  classes 


Fig.  39. 


Fig.  .30. 


Fig.  29.— Spheroidal  ciliated  cells  from  the  mouth  of  th«  frog,     x  300  diameters.    (Sharpey.) 
Fig.  30. — Ciliated  epithelium  fi-oin  the  human  trachea.    Large,  fully  formed  cell.    6,  Shorter 
cell;  c,  developing  cells  with  more  than  one  nucleus.    (Cadiat.) 


of  animals,  being  very  much  smaller  in  the  higher  than  among  the 
lower  orders,  in  which  they  sometimes  exceed  in  length  the  cell  itself. 

The  number  of  cilia  on  any  one  cell  ranges  from  ten  to  thirty,  and 
those  attached  to  the  same  cell  are  often  of  different  lengths,  in  the 
huinan  trachea  measuring  j q-Ju  to  -o^Vo  of  ^^^  inch,  but  nearly  ten  times 
the  length  in  the  cells  of  the  epididymis. 

The  cilia  themselves  are  fine  rounded  or  flattened  processes,  appar- 
ently homogeneous,  pointed  toward  their  free  extremities.  According 
to  some  observers  these  processes  are  connected  through  intervening 
knob-like  Junctions  with  longitudinal  fibres  which  pass  to  the  other 
end  of  the  cell,  but  which  are  not  connected  with  the  nucleus. 

When  living  ciliated  epithelium,  e.g.,  from  the  gill  of  a  mussel,  or 
oyster,  or  from  the  mouth  of  the  frog,  or  from  a  scniping  from  a  polypus 
from  the  human  nose,  is  examined  under  the  microscope  in  a  drop  of 
O.G  per  cent  solution  of  common  salt  {normal  saline  solutioii),  the  cilia 
are  seen  to  be  in  constant  rapid  motion,  each  cilium  being  fixed  at  one 
end,  and  swinging  or  lashing  to  and  fro.  The  general  impression  given 
3 


34  HANDBOOK    OF    I'll  Y.SIOLOG  Y. 

to  the  eye  of  the  observer  is  very  similar  to  tliat  produced  by  waves  in  a 
field  of  corn,  or  swiftly  running  and  ri^ipling  water,  and  the  result  of 
their  movement  is  to  produce  a  continuous  current  in  a  definite  direc- 
tion, and  this  direction  is  invariably  the  same  on  the  same  surface, 
being  always,  in  the  case  of  a  cavity,  toward  its  external  orifice. 

Ciliary  Motion. — Ciliary,  which  is  closely  allied  to  amoeboid  and 
muscular  motion,  is  alike  independent  of  the  will,  of  the  direct 
influence  of  the  nervous  system,  and  of  muscular  contraction.  It  may 
continue  for  several  hours  after  death  or  removal  from  the  body,  pro- 
vided the  portion  of  tissue  under  examination  be  kept  moist.  Its  inde- 
pendence of  the  nervous  system  is  shown  also  in  its  occurrence  in 
the  lowest  invertebrate  animals  apparently  unprovided  with  anything 
analogous  to  a  nervous  system,  in  its  persistence  in  animals  killed  by 
prnssic  acid,  by  narcotic  or  other  poisons,  and  after  the  direct  ajiplica- 
tion  of  narcotics,  such  as  morphia,  ojoium,  and  belladonna,  to  the 
ciliary  surface,  or  of  electricity  through  it.  The  vapor  of  chloroform 
arrests  the  motion;  but  it  is  renewed  on  the  discontinuance  of  the 
application.  The  movement  ceases  when  the  cilia  are  deprived  of 
oxygen,  although  it  may  continue  for  a  time  in  the  absence  of  free 
oxygen,  but  is  revived  on  the  admission  of  this  gas.  Carbonic  acid 
stops  the  movement.  The  contact  of  various  substances,  e.g.,  bile,  strong 
acids,  and  alkalies,  will  stop  the  motion  altogether;  but  this  seems  to 
depend  chiefly  on  destruction  of  the  delicate  substance  of  which  the 
cilia  are  composed.  Temj^eratures  above  45°  C.  and  below  0°  C.  stop 
the  movement,  whereas  moderate  heat  and  dilute  alkalies  are  favorable 
to  the  action  and  revive  the  movement  after  temporary  cessation.  The 
exact  explanation  of  ciliary  movement  is  not  known;  whatever  may  be 
the  exact  cause,  however,  at  any  rate  the  movement  must  depend  ujoon 
some  changes  going  on  in  the  cell  to  which  the  cilia  are  attached,  as 
when  the  latter  are  cut  otf  from  the  cell  the  movement  ceases,  and  when 
severed  so  that  a  portion  of  the  cilia  are  left  attached  to  the  cell,  the 
attached  and  not  the  severed  j)ortions  continue  the  movement.  The 
most  probable  cause  of  the  movement  is  that  it  is  part  of  the  inherent 
power  which  protoplasm  possesses  and  that  the  cilia  are  but  prolonga- 
tions of  the  spongioplasm  of  the  cell.  It  has  been  suggested  by  Engel- 
mann  that  if  this  be  the  case,  the  contractile  part  of  the  protoplasm  is 
only  on  the  concave  side  of  a  curved  cilium,  and  that  when  this  con- 
tracts that  the  cilium  is  brought  downward;  where  relaxation  occurs, 
the  cilium  rebounds  as  if  by  the  elastic  recoil  of  the  remainder  or  convex 
border. 

As  a  special  subdivision  of  ciliary  action  may  be  mentioned  the 
motion  of  spermatozoa,  which  may  be  regarded  as  cells  with  a  single 
cilium. 


THE    STRUCTURE    OF   THE    ELEMENTARY   TISSUES. 


55 


(b)  Transitional  Epithelium. 

This  term  has  been  applied  to  cells,  which  are  neither  arranged  in  a 
single  layer,  as  is  the  case  with  simple  epithelium,  nor  yet  in  many 
superimposed  strata  as  in  laminated;  in  other  words,  it  is  emjDloyed 
when  epithelial  cells  are  found  in  two,  three,  or"  four  superimposed 
layers. 

The  upper  layer  may  be  either  single  columnar,  columnar  ciliated, 
or  squamous.  When  the  uj^per  layer  is  columnar  or  ciliated  the  second 
layer  consists  of  smaller  cells  fitted  into  the  inequalities  of  the  cells 
above  them,  as  in  the  trachea  (fig.  30). 

The  epithelium  which  is  met  with  lining  the  urinary  bladder  and 
ureters  is,  however,  the  transitional  j^wr  excellence.     In  this  variety  there 


Fig.  31. 


Fig.: 


Fig.  31.— Epithelium  of  the  bladder,  a.  One  of  the  cells  of  the  first  row;  b,  a  cell  of  the  second 
row;  c,  cells  in  situ,  of  first,  second,  and  deepest  layers.    (Obersteiner.) 

Fig.  32. — Transitional  epithelial  cells  from  a  scraping  of  the  mucous  membrane  of  the  bladder  of 
the  rabbit.    CV.  D.  Harris.) 

are  two  or  three  layers  of  cells,  the  upper  being  more  or  less  flattened 
according  to  the  full  or  collapsed  condition  of  the  organ,  their  under 
surface  being  marked  with  one  or  more  depressions,  into  which  the 
heads  of  the  next  layer  of  club-shaped  cells  fit.  Between  the  lower  and 
narrower  parts  of  the  second  row  of  cells  are  fixed  the  irregular  cells 
which  constitute  the  third  row,  and  in  like  manner  sometimes  a  fourth 
row  (fig.  31).  It  can  be  easily  understood,  therefoi-e,  that  if  a  scraping 
of  the  mucous  membrane  of  the  bladder  be  teased,  and  examined  under 
the  microscope,  cells  of  a  great  variety  of  forms  may  be  made  out  (fig. 
32).  Each  cell  contains  a  large  nucleus  and  the  larger  and  superficial 
cells  often  possess  two. 

(c)  Stratified  Epithelium. 

The  term  stratified  epithelium  is  employed  when  the  cells  forming 
the  epithelium  are  arranged  in  a  considerable  number  of  superimposed 
layers.  The  shape  and  size  of  the  cells  of  the  different  layers,  as  well 
as  the  number  of  the  layers,  vary  in  different  situations.     Thus  the 


36 


HANDBOOK    OF    PHYSIOLOGY. 


superficial  cells  are  as  a  rule  of  the  squamous,  or  scaly  variety,  and  the 
deepest  of  the  columnar  form. 

The  cells  of  the  intermediate  layers  are  of  different  shapes,  but  those 
of  the  middle  layers  are  more  or  less  rounded.  The  superficial  cells  are 
broad  and  overlap  by  their  edges  (figs.  33  and  34).     Their  chemical  corn- 


Fig.  33.--Sqiiamous  epithelium  scales  from  the  inside  of  the  mouth.     X  260.    (Henle.) 

position  is  different  from  that  of  the  underlying  cells,  as  they  contain 
keratin,  and  are  therefore  horny  in  character. 

The  nucleus  is  often  not  apparent.  The  really  cellular  nature  of 
even  the  dry  and  shrivelled  scales  cast  off  from  the  surface  of  the  ej)i- 
derniis  can  be  proved  by  the  application  of  caustic  potash,  which  causes 
them,  rapidly  to  swell  and  assume  their  original  form. 

The  squamous  cells  exist  in  the  greatest  number  of  layers  in  the  epi- 
dermis or  superficial  part  of  the  skin;  the  most  superficial  of  these  are 
being  continually  removed  by  friction,  and  new  cells  from  below  supply 
the  place  of  those  cast  off. 

The  intermediate  cells  approach  more  to  the  flat  variety  the  nearer 
they  are  to  the  surface,  and  to  the  columnar  as  they  approach  the  lowest 


Fig.  34.— Vertical  section  of  the  stratified  epithelium  of  the  rabbit's  cornea,  a.  Anterior  epithe- 
lium, showing  the  different  shapes  of  tlie  cells  at  various  deptlis  from  the  free  surface;  b,  a  portion 
of  the  substance  of  cornea.     (Klein.) 

layer.  There  may  be  considerable  intercellular  intervals;  and  in  many 
of  the  deeper  layers  of  epithelium  in  the  mouth  and  skin,  the  outline  of 
the  cells  is  very  irregular,  in  consequence  of  processes  passing  from  cell 
to  cell  across  these  intervals. 

Such  cells  (fig.  35)  are  termed  "  ridge  and  furrow/'  "  cogged  "  or 
"  prickle  "  cells.  These  "  prickles  "  are  prolongations  of  the  intracellular 
network  which  run  across  from  cell  to  cell,  thus  joining  them  together, 


THE    STRUCTURE    OF    THE    ELEMENTARY    TISSUES.  37 

the  interstices  being  filled  by  the  transparent  intercellular  cement-sub- 
stance. When  this  increases  in  quantity  in  inflammation  the  cells  are 
pushed  further  apart,  and  the  connecting  fibrils  or  "  prickles  "  elongated 
and  therefore  more  clearly  visible. 

The  columnar  cells  of  the  deepest  layer  are  distinctly  nucleated;  they 
multiply  rapidly  by  division;  and  as  new  cells  are  formed  beneath,  they 
press  the  older  cells  forward  to  be  in  turn  pressed  forward  themselves 
toward  the  surface,  gradually  altering  in  shape  and  chemical  composition 
until  they  are  cast  off  from  the  surface. 

Stratified  epithelium  is  found  in  the  following  situations:  (1.)  Form- 
ing the  epidermis,  covering  the  whole  of  the  external  surface  of  the  body; 
(2.)  Covering  the  mucous  membrane  of  the  nose,  tongue,  mouth,  pharynx, 
and  oesophagus;  (3.)  As  the  conjunctival  epithelium,  covering  the  cor- 
nea; (4.)  Lining  the  vagina  and  the  vaginal  j^art  of  the  cervix  uteri. 


Fig.  35.— Jagged  cells  from  the  middle  layers  of  pavement  epithelium,  from  a  vertical  section  of  the 
gum  of  a  new-born  infant.     (Klein.) 

Functions  of  Epithelium. — According  to  function,  epithelial  cells 
may  be  classified  as:  (1.)  Protective,  e.g.,  in  the  skin,  mouth,  blood- 
vessels, etc.  (2.)  Protective  and  moving — ciliated  epithelium.  (3.) 
Secreting — glandular  epithelium;  or.  Secreting  formed  elements — epi- 
thelium of  testicle  secreting  spermatozoa.  (4.)  Protective  and  secreti)tg, 
e.g.,  epithelium  of  intestine.  (5)  Sensoi'ial,  e.g.,  olfactory  cells,  rods  and 
cones  of  retina,  organ  of  Corti. 

Epithelium  forms  a  continuous  smooth  investment  over  the  whole 
body,  being  thickened  into  a  hard,  horny  tissue  at  the  points  most  ex- 
posed to  pressure,  and  developing  various  appendages,  such  as  hairs  and 
nails,  whose  structure  and  functions  will  be  considered  in  a  future  chapter. 
Epithelium  lines  also  ihe  sensorial  surfaces  of  the  eye,  ear,  nose,  and 
mouth,  and  thus  serves  as  the  medium  through  which  all  impressions 
from  the  external  world — touch,  smell,  taste,  sight,  hearing — reach  the 
delicate  nerve  endings,  whence  they  are  conveyed  to  the  brain. 

The  ciliated  epithelium  which  lines  the  air-passages  serves  not  only 
as  a  jjrotective  investment,  but  also  by  the  movements  of  its  cilia  pro- 
motes currents  of  the  air  in  the  bronchi  and  bronchia,  and  is  enabled  to 
propel  fluids  and  minute  particles  of  solid  matter  so  as  to  aid  their  ex- 


38  HANDBOOK    OF    PHYSIOLOGY. 

pulsion  from  the  body.  In  the  case  of  the  Fallopian  tube,  this  agency 
assists  tl)e  progress  of  the  ovum  toward  the  cavity  of  the  uterus.  Of  the 
purposes  served  by  cilia  in  the  ventricles  of  the  brain  nothing  is  known. 

The  epithelium  of  the  various  glands,  and  of  the  whole  intestinal 
tract,  has  the  power  of  secretion,  i.e.,  of  chemically  transforming  certain 
materials  of  the  blood ;  in  the  case  of  mucus  and  saliva  this  has  been 
proved  to  involve  the  transformation  of  the  epithelial  cells  themselves; 
the  cell-substance  of  the  epithelial  cells  of  the  intestine  being  discharged 
by  the  rupture  of  their  enveloj^es,  as  mucus. 

Epithelium  is  likewise  concerned  in  the  processes  of  transudation, 
diffusion,  and  absorption. 

It  is  constantly  being  shed  at  the  free  surface  and  reproduced  in  the 
deeper  layers.  The  various  stages  of  its  growth  and  development  can 
be  well  seen  in  a  section  of  any  laminated  epithelium  such  as  the  epidermis. 

II.  The  Connective  Tissues. 

This  group  of  tissues  forms  the  Skeleton  with  its  various  connections 
— bones,  cartilages,  and  ligaments  -  and  also  affords  a  supporting  frame- 
work and  investment  to  the  various  organs  composed  of  nervous,  mus- 
cular, and  glandular  tissue.  Its  chief  function  is  the  mechanical  one  of 
support,  and  for  this  purpose  it  is  so  intimately  interwoven  with  nearly 
all  the  textures  of  the  body  that  if  all  other  tissues  could  be  removed, 
and  the  connective  tissues  left,  we  should  have  a  wonderfully  exact  model 
of  almost  every  organ  and  tissue  in  the  body,  correct  even  to  the  small- 
est minutiffi  of  structure. 

Structure  of  Connective  Tissues  in  General. 

Connective  tissue  is  made  up  of  two  chief  elements,  namely,  cells 
and  intercellular  suhstance. 

(A.)  Cells. — The  cells  are  of  two  kinds: 

(«.)  Fixed  Cells. — These  are  of  a  flattened  shape,  with  branched  pro- 
cesses, which  are  often  united  together  to  form  a  network:  they  can  be 
most  readily  observed  in  the  cornea,  in  which  they  are  arranged,  layer 
above  layer,  parallel  to  the  free  surface.  They  lie  in  spaces  in  the  inter- 
cellular or  ground  substance,  which  are  of  the  same  shape  as  the  cells 
they  contain,  but  rather  larger,  and  which  form  by  anastomosis  a  s)'stem 
of  branching  canals  freely  communicating  (fig.  36). 

To  this  class  of  cells  belong  the  flattened  tendon  corpuscles  which 
are  arranged  in  long  lines  or  rows  parallel  to  the  fibres  (fig.  42). 

These  branched  cells,  in  certain  situations,  contain  a  number  of  pig- 
ment granules,  giving  them  a  dark  appearance;  they  form  one  variety 
of  pigment  cell.  Branched  pigment  cells  of  this  kind  are  found  in  the 
outer  layers  of  the  choroid  (fig.  37).     In  many  of  the  lower  animals. 


THE   STRUCTUKE    OF   THE    ELEMENTARY    TISSUES, 


39 


such  a,s  the  frog,  they  are  found  widely  distributed,  not  only  in  the 
skin,  but  also  in  internal  parts,  e.g.,  the  mesentery  and  sheaths  of  blood- 
vessels. In  the  web  of  the  frog's  foot  such  cells  may  be  seen  with  pig- 
ment granules  evenly  distributed  throughout  the  body  of  the  cell  and 
its  processes;  but  under  the  action  of  light,  electricity,  and  other  stim- 
uli, the  pigment  granules  become  massed  in  the  body  of  the  cell,  leaving 
the  processes  quite  hyaline;  if  the  stimulus  be  removed,  they  will  grad- 
ually be  distributed  again  throughout  the  processes.  Thus  the  skin  in 
the  frog  is  sometimes  uniformly  dusky,  and  sometimes  quite  light-colored, 
with  isolated  dark  spots.  In  the  choroid  and  retina  the  pigment  cells 
absorb  light. 

(/>.)  Amwhoid  Cells,  of  an  approximately  spherical  shape;  they  have 
a  great  general  resemblance  to  colorless  blood-corpuscles,  with  which 


Fig.  30.— Hoi-izontal  preparation  of  the  cornea  of  frog:,  stained  in  gold  chloride;  showing  the 
network  of  branched  cornea  corpuscles.  The  ground  substance  is  completely  colorless.  X  400. 
(Klein.) 


some  of  them  are  probably  identical.  They  consist  of  finely  granular 
nucleated  protoplasm,  and  have  the  property,  not  only  of  changing  their 
form  but  also  of  moving  about,  hence  they  are  termed  mir/ratori/.  They 
are  readily  distinguished  from  the  branched  connective-tissue  corpuscles 
by  their  free  condition,  and  the  absence  of  processes.  Some  are  much' 
larger  than  others,  and  are  found  especially  in  the  sublingual  gland  of 
the  dog  and  guinea-pig,  and  in  the  mucous  membrane  of  the  intestine. 
A  second  variety  of  these  cells  called  plasma  cells  are  larger  than  the 
amoeboid  cells,  apparently  granular,  less  active  in  their  movements.  They 
are  chiefly  to  be  found  in  the  inter-muscular  septa,  in  the  mucous  and 
snb-mucous  coats  of  the  intestine,  in  lymphatic  glands,  and  in  the  omen- 
tum. 

(B.)  Intercellular  Substance. — This  may  be  fihrillar,  as  in  the 
fibrous  tissues,  and  in  certain  varieties  of  cartilage;  or  homogeneous,  as 
in  hyaline  cartilage. 


40 


HANDBOOK    OF    PHYSIOLOGY. 


The  fibres  composing  the  former  are  of  two  kinds — (a.)  White  fibres. 
(b.)  Yellow  elastic  fibres. 

(a.)  White  Fibres. — These  are  arranged  parallel  to  each  other  in  wavy 
bundles  of  various  sizes;  such  bundles  may  either  have  a  ijarallel  ar- 


^-^ 


Fig.  3:. 


Fig.  38. 


Fig.  39. 

X  350. 


a,  CeU 


Fig.  37.— Ramified  pigment  cells  from  the  tissue  of  the  choroid  coat  of  the  eye. 
with  pigment;  6,  colorless  fusiform  cells.     •'Kolliker.') 

Fig.  38.— Flat,  pigmented,  branched  connective-tissue  cells  from  the  sheath  of  a  large  blood- 
vessel of  the  frog's  mesentery:  the  pigment  is  not  distributed  uniformly  throughout  the  substance 
of  the  larger  cell,  consequently  some  parts  of  it  look  blacker  than  others  (uncontracted  state).  In 
the  two  smaller  cells  most  of  the  pigment  is  withdrawn  into  the  cell-body,  so  that  they  appear 
smaller,  blacker,  and  less  branched,     x  3.50.    (Klein  and  Noble  Smith.) 

Fig.  39. — Fibrous  tissue  of  cornea,  showing  bundles  of  fibres  with  a  few  scattered  fusiform  cells 
(a)  lying  in  the  inter-fascicular  spaces.     X  400.    (Klein  and  Noble  Smith.) 

rangement  (fig.  39),  or  may  produce  quite  a  felted  texture  by  their  inter- 
lacement. The  individual  fibres  composing  these  fasciculi  are  exceedingly 
fine,  varying  from  -^J^nr  to  ¥?innT  inch,  i.e.,  g-oVo  to  -nrVo-  mm-./  or  0.5  to 


IP;  homogeneous,  unbranched,  and  of  the 
same  diameter  throughout.  They  can  readily 
be  isolated  by  macerating  a  portion  of  white 
fibrous  tissue  {e.g.,  a  small  piece  of  tendon) 
for  a  short  time  in  lime,  or  baryta-water,  or 
in  a  solution  of  common  salt,  or  of  potassium 
permanganate:  these  reagents  possess  the 
power  of  dissolving  the  cementing  inter- 
fibrillar  substance  and  of  thus  separating  the 
fibres  from  each  other.  By  prolonged  boil- 
ing the  fibres  yield  gelatin. 

(b.)  Yellow  Mastic  Fibres  (fig.  40)  are  of 
all  sizes,  from  excessively  fine  fibrils,  sihro 
inch,  up  to  fibres  of  considerable  thickness, 
•j-jJy-fj-  inch  (i.e.,  from  about  Ip.  to  6//) :  they 
are  distinguished  from  white  fibres  by  the 
following  characters:  (1.)  Their  great  power 
of  resistance  even  to  the  prolonged  action  of  chemical  reagents,  e.g., 
caustic   soda,  acetic   acid,  etc.     (2.)  Their  well-defined    outlines.     (3.) 

*  ToVo  millimetre  =  1  micron,  which  is  represented  by  the  Greek  fi. 


Fig.  40. — Elastic  fibres  from 
the  ligamenta  subflava.  x  200. 
(Sharpey.) 


THE    STRUCTURE    OF   THE    ELEMENTARY    TISSUES.  41 

Their  great  tendency  to  branch  aud  to  form  networks  by  anastomosis. 
(4.)  Their  twisted  corkscrew-like  appearance,  and  that  their  free  ends 
usually  curl  up.  (5.)  Their  yellowish  tint  and  considerable  elasticity. 
(6.)  'Their  resistance  to  hematoxylin  and  similar  reagents,  and  their 
affinity  for  magenta  and  other  aniline  staining  colors. 

These  fibres  yield  on  boiling  not  gelatin,  but  a  gelatinous  substance 
called  elastin. 

The  chief  varieties  of  connective  tissues  may  be  thus  classified : 

I.  The  Fibro2(s  Connective  Tissues. 

A. — Chief  Forms, 

a.  White  fibrous. 
h.  Elastic. 
c.  Areolar. 

B. — S'pecial  Varieties. 

a.  Gelatinous. 

b.  Adenoid  or  Eetiform. 

c.  Adipose. 

II.  Cartilage. 
IIL  Bone. 

I.  Fibrous  Con'nective  Tissues. 

A. — Chief  Forms. — (a.)  White  Fibrous  Tissue. 

Distribution. — It  is  found  typically  in  tendon;  also  in  ligaments,  in 
the  periosteum  and  perichondrium,  the  dura  mater,  the  pericardium, 
the  sclerotic  coat  of  the  eye,  the  fibrous  sheath  of  the  testicle;  in  the 
fascife  and  aponeuroses  of  muscles,  aud  in  the  sheaths  of  lymphatic 
glands. 

Structure. — To  the  naked  eye  tendons  and  many  of  the  fibrous 
membranes,  when  in  a  fresh  state,  present  an  appearance  as  of  watered 
silk.  This  is  due  to  the  arrangement  of  the  fibres  in  wavy  parallel  bun- 
dles. Under  the  microscope  the  tissue  appears  to  consist  of  long,  often 
parallel,  bundles  of  fibres  (if  different  sizes.  The  fibres  of  the  same  bun- 
dle now  and  then  intersect  each  other.  The  cells  in  tendons  (fig.  42) 
are  arranged  in  long  chains  in  the  ground  substance  separating  the  bun- 
dles of  fibres,  and  are  more  or  less  regularly  quadrilateral  with  large 
round  nuclei  containing  nucleoli,  which  are  generally  placed  so  as  to  be 
contiguous  in  two  cells.  Each  of  these  cells  consist  of  a  thick  body, 
from  which  processes  pass  in  various  directions  into,  and  partially  fill 
up  the  spaces  between,  the  bundles  of  fibres.  The  rows  of  cells  are 
separated  from  one  another  by  lines  of  cement  substance.  The  cell 
spaces  can  be  brought  into  view  by  silver  nitrate.     The  cells  are  gener- 


42 


HANDBOOK    OF    PHYSIOLOGY. 


ally  marked  by  one  or  more  lines  or  stripes  when  viewed  longitudinally. 
This  appearance  is  really  iiroduced  by  the  wing-like  processes  of  the 
cell  which  project  away  from  the  chief  part  of  the  cell  in  different  di- 
rections. These  processes  not  being  in  the  same  plane  as  the  body  of 
the  cell  are  out  of  focus  and  give  rise  to  these  bright  stripes  are  looked 
at  from  above  and  are  in  focus. 

The  branched  character  of  the  cells  is  seen  in  transverse  section  in 
fig.  43. 

(b)  Yellow  Elastic  Tissue. 

Distribution. — In  the  ligamentum  nuch^e  of  the  ox,  horse,  and  many 
other  animals;  in  the  ligamenta  subflava  of  man;  in  the  arteries,  con- 
stituting the  fenestrated  coat  of  Henle;  in  veins;  in  the  lungs  and  tra- 


.,,«\\\  '\\  \l\^]    \\\\\ 


Fig.  42. 

Fig.  41.— Mature  white  fibrous  tissue  of  tendon,  consisting  mainly  of  fibres  with  a  few  scattered 
fusiform  cells.    (Strieker.) 

Fig.  4-3.— Caudal  tendon  of  young  rat,  showing  the  arrangement,  f onn,  and  structure  of  the 
tendon  cells.     X  300.    (Klein.) 


chea;  in  the  stylo-hyoid,  thyro-hyoid,  and  crico-thyroid  ligaments;  in 
the  true  vocal  chords;  and  in  areolar  tissue. 

Structure. — Elastic  tissue  occurs  in  various  forms,  from  a  structure- 
less, elastic  membrane  to  a  tissue  whose  chief  constituents  are  bundles 
of  fibres  crossing  each  other  at  different  angles;  when  seen  in  bundles 
elastic  fibres  are  yellowish  in  color,  but  individual  fibres  are  not  so  dis- 
tinctly colored.     The  varieties  of  the  tissue  may  be  classified  as  follows: 

(«.)  Fine  elastic  fibrils,  which  branch  and  anastomose  to  form  a  net- 
work: this  variety  of  elastic  tissue  occurs  chiefly  in  the  skin  and  mucous 
membranes,  in  subcutaneous  and  submucous  tissue,  in  the  lungs  and 
true  vocal  cords. 

(b.)  Thick  fibres,  sometimes  cylindrical,  sometimes  flattened  like 
tape,  which  branch,  anastomose  and  form  a  network:  these  are  seen 
most  typically  in  the  ligamenta  subflava  and  also  in  the  ligamentum 


THE    STRUCTURE    OF    THE    ELEMENTARY    TISSUES.  43 

nucha?  of  such  animals  as  the  ox  and  horse,  in  which  that  ligament  is 
largely  developed  (fig.  40). 

(c.)  Elastic  membranes  with  perforations,  e.g.,  Henle's  fenestrated 
membrane:  this  variety  is  found  chiefly  in  the  arteries  and  veins. 

{(l.)  Continuous,  homogenous  elastic  membranes,  e.g.,  Bowman's  an- 
terior elastic  lamina  and  Descemet's  posterior  elastic  lamina,  both  in  the 
cornea. 

A  certain  number  of  flattened  connective-tissue  cells  are  found  in 
the  ground  substance  between  the  elastic  fibres  which  make  up  this 
A'ariety  of  connective  tissue. 

(c.)  Areolar  Tissue. 

Distribution. — This  variety  of  fibrous  tissue  has  a  very  wide  distribu- 


Fig.  43.  Fig.  44. 

Fig.  4-3.— Transverse  section  of  tendon  from  a  cross  section  of  the  tail  of  a  rabbit,  showing 
sheath,  fibrous  septa,  and  branched  connective-tissue  corpuscles.  The  .spaces  left  white  in  the 
dra,wing  represent  the  tendinous  fibres  iu  transverse  section.     X  ^50.    (Klein.) 

Fig.  44.— Transverse  section  of  a  portion  of  lig.  nuchae.  showing  the  outline  of  the  fibres.  (After 
Stohr.) 

tion  and  constitutes  the  subcutaneous,  subserous,  and  submucous  tissue. 
It  is  found  in  the  mucous  membranes,  in  the  true  skin,  and  in  the  outer 
sheaths  of  the  blood-vessels.  It  forms  sheaths  for  muscles,  nerves,  glands, 
and  the  internal  organs,  and  penetrating  into  their  interior,  supports 
and  connects  the  finest  parts. 

Structure. — To  the  naked  eye  it  apx^ears,  when  stretched  out,  as  a 
fleecy,  white,  and  soft  meshwork  of  fine  fibrils,  with  here  and  there  wider 
films  Joining  in  it,  the  whole  tissue  being  evidently  elastic.  The  open- 
ness of  the  meshwork  varies  with  the  locality  from  Avhich  the  specimen 
is  taken.  Under  the  microscope  it  is  found  to  be  made  up  of  fine  white 
fibres,  which  interlace  in  a  most  irregular  manner,  together  with  a  vari- 
able number  of  elastic  fibres.  On  the  addition  of  acetic  acid,  the  Avliite 
fibres  swell  w^,  and  become  gelatinous  in  appearance;  but  as  the  elastic 
fibres  resist  the  action  of  the  acid,  they  may  still  be  seen  arranged  in 


44 


HAlS'^DBOOK    OF    PHYSIOLOGY. 


various  directions,  sometimes  tijipearing  to  pass  in  a  more  or  less  circu- 
lar or  spiral  manner  round  a  small  gelatinous  mass  of  changed  white 
fihres.  The  cells  of  the  tissue  are  not  arranged  in  a  very  regular  man- 
ner, as  they  are  contained  in  the  spaces  (areola?)  between  the  fibres. 
They  communicate,  liovvever,  with  one  another  by  branched  processes, 
and  also  with  the  cells  forming  the  walls  of  the  capillary  blood-vessels 
in  their  neighborhood.  The  fibres  are  connected  together  with  a  certain 
amount  of  albuminous  cement  substance. 

B. — Special  Forms  {a.)  Gelatinous  Tissue. 

Bistribuiion. — Gelatinous  connective  tissue  forms  the  chief  part  of 
the  bodies  of  jelly-fish;  it  is  found  in  many  parts  of  the  human  embryo, 


Fig.  45. 


Fig.  46. 


Fig.  4.5.— Tissue  of  the  jelly  of  Wharton  from  umbilical  cord,  o.  Connective-tissue  corpuscles; 
6,  fasciculi  of  connective  tissue;  c,  spherical  formative  cells.     (Frey.) 

Fig.  46.— Part  of  a  section  of  a  lymphatic  gland,  from  which  the  corpuscles  have  been  for  the 
most  part  removed,  showing  the  adenoid  reticulum.     ^Klein  and  Noble  Smith.) 

but  remains  in  the  adult  only  in  tlie  vitreous  humor  of  the  eye.  It  may 
be  best  seen  in  the  last-named  situation,  in  the  ''  Whartonian  jelly"  of 
the  umbilical  cord,  and  in  the  enamel  organ  of  developing  teeth. 

Structure'. — It  consists  of  cells,  which  in  the  vitreous  humor  are 
rounded,  and  in  the  jelly  of  the  enamel  organ  are  stellate,  imbedded  in 
a  soft  jelly-like  inter-cellular  substance  which  forms  the  bulk  of  the 
tissue,  and  which  contains  a  considerable  quantity  of  mucin.  In  the 
umbilical  cord,  that  part  of  the  jelly  immediately  surrounding  the  stel- 
late cells  shows  marks  of  obscure  fibrillation  (fig.  45). 

(i.)  Adenoid,  this  is  also  called  retiform,  lym.plioid  or  Jiimphatic  tissue. 

Distributio)!.- — -This  variety  of  tissue  makes  up  the  stroma  of  the  spleen 
and  lymphatic  glands,  and  is  found  also  in  the  thymus,  in  the  tonsils, 
in  the  follicular  glands  of  the  tongue,  in  Peyer's  patches,  and  in  the  sol- 
itary glands  of  the  intestines,  and  in  the  mucous  membranes  generally. 


THE    STKUCTURE    OF   THE    ELEMEXTARY    TISSUES.  45 

Strtictnre. — Adenoid  or  retiform  tissue  consists  of  a  very  delicate 
network  of  minute  fibrils,  formed  originally  by  the  union  of  processes 
of  branched  connective-tissue  corpuscles,  the  nuclei  of  which,  however, 
are  visible  only  during  the  early  periods  of  develojjment  of  the  tissue 
(fig.  46). 

The  nuclei  found  on  the  fibrillar  meshwork  do  not  form  an  essential 
part  of  it.  The  fibrils  are  neither  white  fibres  nor  elastic  tissue,  as  they 
are  insoluble  in  boiling  water,  although  readily  soluble  in  hot  alkaline 
solutions.  The  lymphoid  corpuscles  found  in  the  interstices  of  the  tis- 
sue are  small  round  cells,  the  protoplasm  of  which  is  practically  occupied 
by  their  spherical  nuclei. 

Development  of  Fibrous  Tissues. — In  the  embryo  the  place  of 
the  fibrous  tissues  is  at  first  occujaied  by  a  mass  of  roundish  cells,  de- 
rived from  the  "  mesoblast." 


Fig.  47. — Portion  of  subinucous  tissue  of  gravid  uterus  of  sow.    a,  Branciied  cells,  more  or  less 
spindle-sliaped;  6,  bundles  of  connective  tissue.    (Klein.) 

These  develop  either  into  a  network  of  branched  cells  or  into  groups 
of  fusiform  cells  (fig.  47). 

The  cells  are  imbedded  in  a  semi-fluid  albuminous  substance  derived 
either  from  the  cells  themselves  or  from  the  neighboring  blood-vessels; 
this  afterward  forms  the  cement  substance.  In  it  fibres  are  developed, 
either  by  some  of  the  cells  becoming  fibrils,  the  others  remaining  as  con- 
nective-tissue corpuscles,  or  by  the  fibrils  being  developed  from  the  out- 
side layers  of  the  protoplasm  of  the  cells,  which  grow  up  again  to  their 
original  size  and  remain  imbedded  among  the  fibres.  The  process  gives 
rise  to  fibres  arranged  in  the  one  case  in  interlacing  networks  (areolar 
tissue),  in  the  other  in  parallel  bundles  (white  fibrous  tissue).  In  the 
mature  forms  of  purely  fibrous  tissue  not  only  the  remnants  of  the  cell- 
substance,  but  even  the  nuclei,  may  disappear.  The  embryonic  tissue, 
from  which  elastic  fibres  are  developed,  is  composed  of  fusiform  cells, 
and  a  structureless  intercellular  substance  by  the  gradual  fibrillation  of 
which  elastic  fibres  are  formed.  The  fusiform  cells  dwindle  in  size  and 
eventually  disappear  so  completely  that  in  mature  elastic  tissue  hardly 
a  trace  of  them  is  to  be  found :  meanwhile  the  elastic  fibres  steadily  in- 
crease in  size. 


40  HANDBOOK    OF    PHYSIOLOGY. 

Another  theory  of  the  development  of  the  connective-tissue  fibrils 
supposes  that  the_y  arise  from  deposits  in  the  intercellular  substance  and 
not  from  the  cells  themselves;  these  deposits,  in  the  case  of  elastic  fibres, 
appearing  first  of  all  in  the  form  of  rows  of  granules,  which,  joining  to- 
gether, form  long  fibrils.  It  seems  probable  that  even  if  this  view  be 
correct,  the  cells  themselves  have  a  considerable  infiuence  in  the  pro- 
duction of  the  deposits  outside  them. 

Functions  of  Areolar  and  Fibrous  Tissue.— The  main  function 
of  connective  tissue  is  mechanical  rather  than  vital:  it  fulfils  the  subsid- 
iary but  important  use  of  supporting  and  connecting  the  various  tissues 
and  organs  of  the  body. 

In  glands  the  trabeculae  of  connective  tissue  form  an  interstitial 
framework  in  which  the  parenchyma  or  secreting  gland-tissue  is  lodged : 
in  muscles  and  nerves  the  septa  of  connective  tissue  support  the  bundles 
jof  fibres  which  form  the  essential  part  of  the  structure. 

Elastic  tissue,  by  virtue  of  its  elasticity,  has  other  important  uses: 


Fig.  48.— Ordinarj'  fat  cells  of  a  fat  tract  in  the  omentum  of  a  rat.    (Klein.) 

these,  again,  are  mechanical  rather  than  vital.  Thus  the  ligamentum 
nuchas  of  the  horse  or  ox  acts  very  much  as  an  India-rubber  band  in  the 
same  position  would;  being  stretched  when  the  head  is  lowered  for 
feeding  or  other  purposes  and  aiding  the  muscles  materially  afterward 
by  its  contraction,  in  raising  the  head  to  its  normal  position  and  keejaing 
it  there. 

(c.)  Adipose  Tissue. 

Didribiition. — In  almost  all  regions  of  the  human  body  a  larger  or 
smaller  quantity  of  adipose  or  fatty  tissue  is  present;  the  chief  excej)- 
tions  being  the  subcutaneous  tissue  of  the  eyelids,  penis,  and  scrotum, 
the  nymphse,  and  the  cavity  of  the  cranium.  Adipose  tissue  is  also  absent 
from  the  substance  of  many  organs,  as  the  lungs,  liver,  and  others. 

Fatty  matter,  but  not  in  the  form  of  a  distinct  tissue,  is  also  widely 
present  in  the  body,  e.g.,  in  the  liver  and  brain,  and  in  the  blood  and 
chyle. 

Adipose  tissue  is  almost  always  found  seated  in  areolar  tissue,  and 
forms  in  its  meshes  little  masses  of  unequal  size  and  irregular  shape,  to 
which  the  terra  lohules  is  commonly  applied. 


THE    STEUCTURE    OF    THE    ELEMEXTARY    TISSUES. 


47 


Structure. — Under  the  microscope  adipose  tissue  is  found  to  consist 
essentially  of  little  vesicles  or  cells  which  present  dark,  sharply-defined 
edges  when  viewed  with  transmitted  light :  they  are  about  -^^  or  -^ J-^-  of 
an  inch  in  diameter,  each  consisting  of  a  structureless  and  colorless 
membrane  or  bag  formed  of  the  remains  of  the  original  protoplasm  of 
the  cell,  filled  with  fatty  matter,  which  is  liquid  during  life,  but  in  part 
solidified  after  death  (fig.  48).  A  nucleus  is  always  present  in  some  part 
or  other  of  the  cell-protoplasm,  but  in  the  ordinary  condition  of  the  cell 
it  is  not  easily  or  always  visible  (fig.  49). 

This  membrane  and  the  niicleus  can  generally  be  brought  into  view 
by  staining  the  tissue:  it  can  be  still  more  satisfactorily  demonstrated 
by  extracting  the  contents  of  the  fat-cells  with  ether,  when  the  shrunken, 
shrivelled    membranes    remain    behind.     By  mutual  pressure,  fat-cells 


C  "■'     0 

Fig.  49. — Group  of  fat  cells  (f  c)  with  capillarj'  vessels  (c).     ('Noble  Smith.) 

come  to  assume  a  polyhedral  figure  (fig.  49).  When  stained  witli  osmic 
acid  fat-cells  appear  black. 

The  ultimate  cells  are  held  together  by  capillary  blood-vessels  (fig. 
50);  while  the  little  clusters  thus  formed  are  grouped  into  small  masses, 
and  held  so,  in  most  cases,  by  areolar  tissue. 

The  oily  matter  contained  in  the  cells  is  composed  chiefly  of  the 
compounds  of  fatty  acids  with  glycerin,  which  are  named  olein,  siearin, 
and  jml'Dii  tin. 

Development  of  Adipose  Tissue. — Fat  cells  are  developed  from 
connective-tissue  corpuscles:  in  the  infra-orbital  connective-tissue  cells 
may  be  found  exhibiting  every  intermediate  gradation  between  an  ordi- 
nary branched  connective-tissue  corpuscle  and  mature  fat-cell.  The 
process  of  development  is  as  follows:  a  few  small  drops  of  oil  make  their 
appearance  in  the  protoplasm  and  by  their  confluence  a  larger  drop  is 
produced  (fig.  .51) :  this  gradually  increases  in  size  at  the  expense  of  the 
original  protoplasm  of  the  cell,  which  becomes  correspondingly  dimin- 
ished in  quantity  till  in  the  mature  cell  it  only  forms  a  thin  crescentic 


48 


HANDBOOK    OF    PHYSIOLOGY. 


film,  closely  pressed  against  the  cell-wall,  and  with  a  nucleus  imbetfded 
in  its  substance  (figs.  48  and  4'J). 


Fig.  50. — Blood-vessels  of  adipose  tissue.  A.  Minute  flattened  fat>lobule,  in  which  the  vessels 
only  are  represented,  a.  The  terminal  artery;  v,  the  primitive  vein;  b,  the  fat- vesicles  of  one  border 
of  the  lobule  separately  represented,  x  100.  b.  Plan  of  the  arrangement  of  the  capillaries  (c)  on 
the  exterior  of  the  vesicles;  more  highly  magnified.    (Todd  and  Bowman.; 

Under  certain  circumstances  this  process  may  be  reversed  and  fat- 
cells  may  be  changed  back  into  connective-tissue  corpuscles. 


/If  "aX^^?'  ''® 
fj^  ®\9  c--^    '  -. 


to 

Fig.  51. 


\l 


Fig.  52. 


Fig.  51.— A  lobule  of  developing  adipose  tissue  from  an  eight  months'  foetus,  a,  Spherical  or, 
from  pressure,  polyhedral  cells  with  lai-ge  central  nucleus,  surrounded  by  a  finely  reticulated  sub- 
stance staining  uniformly  with  hsemato.xyliu.  6,  Similar  cells  with  spaces  from  which  the  fat  has 
been  removed  by  oil  of  cloves,  c.  Similar  cells  showing  how  the  nucleus  with  inclosing  jirotoplasm 
is  being  pressed  toward  periphery,  d,  Nucleus  of  endothehum  of  investing  capillaries.  (McCarthy.) 
Drawn  by  Treves. 

Fig.  52.— Branched  connective- tissue  corpuscles,  developing  into  fai.-cells.    (Klein.) 

Vessels  and  Nerves. — A  large  number  of  blood-vessels  are  found 
in  adipose  tissue,  which  subdivide  until  each  lobule  of  fat  contains  a 
fine  mesh  work  of  capillaries  ensheathing  each  individual  fat-globule  (fig. 


THE    STKUCTURE    OF   THE    ELEMENTARY   TISSUES.  49 

oOj.     Although  nerve  fibres  pass  through  the  tissue,  no  nerves  have  been 
demonstrated  to  terminate  in  it. 

The  Uses  of  Adipose  Tissue. — Among  the  uses  of  adipose  tissue 
these  are  the  chief : — 

a.  It  serves  as  a  store  of  combustible  matter  which  maybe  reabsorbed 
into  the  blood  when  occasion  requires,  and,  being  used  up  in  the  meta- 
bolism of  the  tissues,  may  help  to  preserve  the  heat  of  the  body. 

b.  That  part  of  the  fat  which  is  situate  beneath  the  skin  must,  by 
its  want  of  conducting  power,  assist  in  preventing  undue  waste  of  the 
heat  of  the  body  by  escape  from  the  surface. 

c.  As  a  packing  material,  fat  serves  very  admirably  to  fill  up  spaces, 
to  form  a  soft  and  yielding  yet  elastic  material  wherewith  to  wrap  ten- 
der and  delicate  structures,  or  form  a  bed  with  like  qualities  on  which 
such  structures  may  lie,  not  endangered  by  pressure.  As  examples  of 
situations  in  which  fat  serves  such  purposes  may  be  mentioned  the  palms 
of  the  hands  and  soles  of  the  feet  and  the  orbits. 

d.  In  the  long  bones  fatty  tissue,  in  the  form  known  as  yellow  mar- 
row, fills  the  medullary  canal,  and  supports  the  small  blood-vessels  which 
are  distributed  from  it  to  the  inner  part  of  the  substance  of  the  bone. 

.  II.  Cartilage. 

General  Structure  of  Curtilage. — All  kinds  of  cartilage  are  composed 
of  cells  imbedded  in  a  substance  called  the  matrix:  the  apparent  differ- 
ences of  structure  met  with  in  the  various  kinds  of  cartilage  are  more 
due  to  differences  in  the  character  of  the  matrix  than  of  the  cells. 
Among  the  latter,  however,  there  is  also  considerable  diversity  of  form 
and  size. 

With  the  exception  of  the  articular  variety,  cartilage  is  invested  by  a 
thin  but  tough  firm  fibrous  membrane  called  the  pericliondrium.  On 
the  surface  of  the  articular  cartilage  of  the  foetus,  the  perichondrium  is 
represented  by  a  film  of  epithelium;  but  this  is  gradually  worn  away 
up  to  the  margin  of  the  articular  surfaces  when  by  use  the  parts  begin 
to  suffer  friction. 

Nerves  are  probably  not  supplied  to  any  variety  of  cartilage. 

Cartilage  exists  in  three  different  forms  in  the  human  body,  viz.,  1, 
Hyaline  cartilage,  3,  Yelloio  elastic-cartilage,  and  3,  White  fibro-cartilage. 

1.  Hyaline  Cartilage. 

Distribution. — This  variety  of  cartilage  is  met  with  largely  in  the 
human  body — investing  the  articular  ends  of  bones,  and  forming 
the  costal  cartilages,  the  nasal  cartilages,  and  those  of  the  larynx  with  the 
exception  of  the  epiglottis  and  cornicula  laryngis,  as  well  as  those  of 
the  trachea  and  bronchi. 

Structure. — Like  other  cartilages  it  is  composed  of  cells  imbedded  in 
4 


50  HANDBOOK    OF    PHYSIOLOGY. 

a  matrix.  The  cells,  which  contain  a  nucleus  with  nucleoli,  are  irregular 
in  shape,  and  generally  grouj)ed  together  in  imtches  (fig.  53).  The 
patches  are  of  various  shapes  and  sizes  and  placed  at  unequal  distances 
apart.  They  generally  appear  flattened  near  the  free  surface  of  the 
mass  of  cartilage  in  which  they  are  placed  and  more  or  less  perpendicular 
to  the  surface  in  the  more-deei3ly  seated  portions. 

The  matrix  of  hyaline  cartilage  has  a  dimly  granular  appearance  like 
that  of  ground  glass,  and  in  man  and  the  higher  animals  has  no  appar- 
ent structure.  In  some  cartilages  of  the  frog,  however,  even  when  ex- 
amined in  the  fresh  state,  it  is  seen  to  be  mapped  out  into  polygonal 
blocks  or  cell-territories,  each  containing  a  cell  in  the  centre,  and  repre- 


Fig.  53.  Fig.  54. 

Fig.  5.3.— Ordinary  hyaline  cartUage  from  trachea  of  a  child.    The  cartilage  cells  are  inclosed 
singly  or  in  pairs  in  a  capsule  of  hyaline  substance.     X  150  diams.    (Klein  and  Noble  Smith.) 
Fig.  54. — Fresh  cartilage  from  the  Triton.     (A.  Rollett.) 

senting  what  is  generally  called  the  capsule  of  the  cartilage  cells  (tig. 
54).  Hyaline  cartilage  in  man  has  really  the  same  structure,  which  can 
be  demonstrated  by  the  use  of  certain  reagents.  If  a  piece  of  human 
hyaline  cartilage  be  macerated  for  a  long  time  in  diluted  acid  or  in  hot 
water  35°-45°  C.  (95°-113°  F.),  the  matrix,  which  previously  appeared 
quite  homogeneous,  is  found  to  be  resolved  into  a  number  of  concentric 
lamellae,  like  the  coats  of  an  onion,  arranged  round  each  cell  or  group 
of  cells.  It  is  thus  shown  to  consist  of  nothing  but  a  number  of  large 
systems  of  capsules  which  have  become  fused  with  one  another. 

The  cavities  in  the  matrix  in  which  the  cells  lie  are  connected  to- 
gether by  a  series  of  branching  canals,  very  much  resembling  those  in 
the  cornea:  through  these  canals  fluids  may  make  their  way  into  the 
depths  of  the  tissue. 

In  the  hyaline  cartilage  of  the  ribs  the  cells  are  mostly  larger  than 
in  the  articular  variety  and  there  is  a  tendency  to  the  development  of 
fibres  in  the  matrix  (fig.  55).     The  costal  cartilages  also  frequently  be- 


THE    STRUCTURE    OF   THE    ELEMENTARY    TISSUES.  51 

come  calcified  in  old  age,  as  also  do  some  of  those  of  the  larynx.  Fat- 
globules  may  also  be  seen  in  many  cartilages  (fig.  55). 

In  articular  cartilage  the  cells  are  smaller  and  arranged  vertically  in 
narrow  lines  like  strings  of  beads. 

In  the  foetus  cartilage  is  the  material  of  which  the  bones  are  first 
constructed;  the  "model"  of  each  bone  being  laid  down,  so  to  speak, 
in  this  substance.  In  such  cases  the  cartilage  is  termed  temporary.  It 
closely  resembles  the  ordinary  hyaline  kind;  the  cells,  however,  are  not 
grouped  together  after  the  fashion  just  described,  but  are  more  uniformly 
distributed  throughout  the  matrix. 

A  variety  of  temporary  hyaline  cartilage  which  has  scarcely  any  ma- 


Fig.  55.  Fig.  56. 

Fig.  55.— Costal  cartilage  from  an  adult  dog,  showing  the  fat  globules  in  the  cartilage  cells. 
(Cadiat.) 

Fig.  50.— Yellow  elastic  cartilage,    (Cadiat.) 

trix  is  found  in  the  human  subject  and  in  the  higher  animals  generally, 
in  early  foetal  life,  when  it  constitutes  the  cliorda  dorsalis. 

Nutrition. — Hyaline  cartilage  is  reckoned  among  the  so-called  non- 
vascular structures,  no  blood-vessels  being  supplied  directly  to  its  own 
substance;  it  is  nourished  by  those  of  the  bone  beneath.  When  hyaline 
cartilage  is  in  thicker  masses,  as  in  the  case  of  the  cartilages  of  the  ribs, 
a  few  blood-vessels  traverse  its  substance.  The  distinction,  however, 
between  all  so-called  vascular  and  non-vascular  parts  is  at  the  best  a 
very  artificial  one. 

3.  Yellow  Elastic  Cartilage. 

Distribution. — Tn  the  external  ear,  in  the  epiglottis  and  cornicula 
laryngis,  and  in  the  Eustachian  tube. 

Structure. — The  cells  in  this  variety  of  cartilage  are  rounded  or  oval, 
with  well-marked  nuclei  and  nucleoli  (fig.  56).  The  matrix  in  which 
they  are  seated  is  composed  almost  entirely  of  fine  elastic  fibres,  which 


52  HANDBOOK    OF    PHYSIOLOGY. 

form  an  intricate  interlacement  about  the  cells,  and  in  their  general 
characters  are  allied  to  the  yellow  variety  of  fibrous  tissue:  a  small  and 
variable  quantity  of  hyaline  intercellular  substance  is  also  usually  present. 

A  variety  of  elastic  cartilage,  sometimes  called  cellular',  is  found  to 
form  the  framework  of  the  external  ears  of  rats,  mice,  or  other  small 
mammals.  It  is  composed,  as  its  name  implies,  almost  entirely  of  cells 
which  are  packed  very  closely  with  little  or  no  matrix.  When  present 
the  matrix  consists  of  very  fine  fibres  which  twine  about  the  cells  in 
various  directions  and  inclose  them  in  a  kind  of  network.  Elastic  car- 
tilage seldom  or  never  ossifies. 

3.  White  Fibro-Cartilage. 

Distribution. — White  fibro-cartilage  is  found  to  occur: — 

1.  As  inter-articular  fibro-cartilage,  e.g.,  the  semilunar  cartilages  of 
the  knee-joint. 

2.  As  circumferential  or  marginal  cartilage,  as  on  the  edges  of  the 
acetabulum  and  glenoid  cavity. 

3.  As  connecting  cartilage,  e.g.,  the  inter-vertebral  fibro-cartilages. 

4.  In  the  sheaths  of  tendons  and  some- 
times in  their  substance.  In  the  latter  situ- 
ation the  nodule  of  fibro-cartilage  is  called  a 
sesamoid  fibro-cartilage,  of  which  a  specimen 


Fig.  57.  Fig.  58. 

Fig.  57.— White  flbro-cartilage.    (Cadiat.) 

Fig.  58. — White  flbro-cartilage  from  an  iater-vertebral  ligament.    (Klein  and  Noble  Smith.) 

may  be  found  in  the  tendon  of  the  tibialis  posticus  in  the  sole  of  the  foot, 
and  usually  in  the  neighboring  tendon  of  the  peroneus  longus. 

Structure. — White  fibro-cartilage  (fig.  58),  which  is  much  more  widely 
distributed  throughout  the  body  than  the  foregoing  kind,  is  composed, 
like  it,  of  cells  and  a  matrix;  the  latter,  however,  being  made  uj)  almost 
entirely  of  fibres  closely  resembling  those  of  white  fibrous  tissue. 

In  this  kind  of  fibro-cartilage  it  is  not  unusual  to  find  a  great  part 
of  its  mass  composed  almost  exclusively  of  fibres,  and  deriving  the  name 


THE    STRUCTURE    OF    THE    ELEMEXTARY    TISSUES.  d3 

of  cartilage  only  from  the  fact  that  in  another  portion,  continuous  with 
it,  cartilage  cells  may  be  pretty  freely  distributed. 

By  prolonged  boiling,  cartilage  yields  a  substance  called  cJiondriti — 
which  gelatinizes  on  cooling.  The  cells  of  white  fibro-cartilage  are  as  a 
rule  rounded  or  somewhat  flattened  but  in  some  places  are  distinctly 
branched. 

Functions  of  Cartilage. — Cartilage  not  only  represents  in  the 
fcetus  the  bones  which  are  to  be  formed  {temporary  cartilage)  but  also 
offers  a  firm,  yet  more  or  less  yielding,  framework  for  certain  parts  in 
the  developed  body,  possessing  at  the  same  time  strength  and  elasticity. 
It  maintains  the  shape  of  tubes  as  in  the  larynx  and  trachea.  It  affords 
attachment  to  muscles  and  ligaments;  it  binds  bones  together,  yet  allows 
a  certain  degree  of  movement,  as  between  the  vertebra?;  it  forms  a  firm 
framework  and  protection,  yet  without  undae  stiffness  or  weight,  as  in 
the  pinna,  larynx,  and  chest  walls;  it  deepens  joint  cavities,  as  in  the 
acetabulum,  without  unduly  restricting  the  movements  of  the  bones. 

Development  of  Cartilage. — Cartilage  is  developed  out  of  an  em- 
bryonal tissue,  consisting  of  cells  with  a  very  small  quantity  of  intercel- 
lular substance:  the  cells  multij^ly  by  fission  within  the  cell- capsules, 
while  the  capsule  of  the  parent  cell  becomes  gradually  fused  with  the 
surrounding  intercellularsubstance.  A  repetition  of  this  process  in  the 
young  cells  causes  a  rapid  growth  of  the  cartilage  by  the  multiplication 
of  its  cellular  elements  and  corresponding  increase  in  its  matrix.  Thus 
we  see  that  the  matrix  of  cartilage  is  chiefly  derived  from  the  cartilage 
cells. 

III.  Bone. 

Chemical  Composifioji. — Bone  is  composed  of  earthy  and  animal  mat- 
ter in  the  proportion  of  about  67  per  cent  of  the  former  to  33  per  cent 
of  the  latter.  The  earthy  matter  is  composed  chiefly  of  calcium  phos- 
phate, but  besides  there  is  a  small  quantity  (about  11  of  the  67  per  cent) 
of  calcium  carbonate  and  calcium  fluoride,  and  magnesium  phosphate. 

The  animal  matter  called  collagen  is  resolved  into  gelatin  by  boiling. 

The  earthy  and  animal  constituents  of  bone  are  so  intimately  blended 
and  incorporated  the  one  with  the  other  that  it  is  only  by  chemical 
action,  as  for  instance  by  heat  in  one  case  and  by  the  action  of  acids  in 
another,  that  they  can  be  separated.  Their  close  union  too  is  further 
shown  by  the  fact  that  when  by  acids  the  earthy  matter  is  dissolved  out, 
or  on  the  other  hand  when  the  animal  part  is  burnt  out,  the  shape  of 
the  bone  is  alike  preserved. 

The  proportion  between  these  two  constituents  of  bone  varies  in 
different  bones  in  the  same  individual  and  in  the  same  bone  at  different 
ages. 

Structure. — To  the  naked  eye  there  appear  two  kinds  of  structure 


54 


HANDBOOK    OF    PHYSIOLOGY, 


in  different  bones,  and  in  different  parts  of  the  same  bone,  namely,  the 
dense  or  compact,  and  the  spong//  or  cancellous  tissue. 

Thus,  in  making  a  longitudinal  section  of  a  long  bone,  as  the 
humerus  or  femur,  the  articular  extremities  are  found  capped  on  their 
surface  by  a  thin  shell  of  compact  bone,  while  their  interior  is  made  up 
of  the  spongy  or  cancellous  tissue.  The  shaft,  on  the  other  hand,  is 
formed  almost  entirely  of  a  thick  layer  of  the  compact  hone,  and  this 
surrounds  a  central  canal,  the  medullary  cavity — so  called  from  its  con- 
taining the  medulla  or  marrow. 

In  the  flat  bones,  as  the  parietal  bone  or  the  scapula,  one  layer  of  the 
cancellous  structure  lies  between  two  layers  of  the  compact  tissue,  and 
in  the  short  and  irregular  bones,  as  those  of  the  carpus  and  tarsus,  the 
cancellous  tissue  alone  fills  the  interior,  while  a  thin  shell  of  compact 
bone  forms  the  outside. 

Marrow. — There  are  two  distinct  varieties  of  marrow — the  red  and 
yellotv. 


Fig.  59. — Cells  of  the  red  marrow  of  the  guinea-pig,  hiKhly  tnagnifiecl.  a.  A  large  cell,  the  nu- 
cleus of  which  appears  to  be  partly  divided  into  three  by  constrictio.is;  6,  a  cell,  the  nucleus  of  which 
shows  an  appearance  of  being  constricted  into  a  number  of  smaller  nuclei ;  c,  a  .so-called  giant  cell, 
or  niyeloplaxe,  with  many  nuclei;  d,  a  smaller  myelo-plaxe,  with  three  nuclei;  e-i,  proper  cells  of 
the  marrow.    (E.  A.  Schafer.) 


Red  marrow  is  that  variety  which  occupies  the  spaces  in  the  cancel- 
lous tissue;  it  is  highly  vascular,  and  thus  maintains  the  nutrition  of 
the  spongy  bone,  the  interstices  of  which  it  fills.  It  contains  a  few 
fat-cells  and  a  large  number  of  marrow-cells,  many  of  which  are  undis- 
tinguishable  from  lymphoid  corpuscles,  and  has  for  a  basis  a  small 
amount  of  fibrous  tissue.  Among  the  cells  are  some  nucleated  cells  of 
very  much  the  same  tint  as  colored  blood-corpuscles.  There  are  also 
a  few  large  cells  with  many  nuclei,  termed  giant-cells  or  myeloplaxes, 
which  are  derived  from  over-growth  of  the  ordinary  marrow-cells 
(fig.  59). 

Yellow  marrow  fills  the  medullary  cavity  of  long  bones,  and  consists 
chiefly  of  fat-cells  with  numerous  blood-vessels;  many  of  its  cells  also 
are  in  every  respect  similar  to  lymphoid  corpuscles. 


THE    STEUCTURE    OF   THE    ELEMENTARY   TISSUES, 


55 


From  these  marrow-cells,  especially  those  of  the  red  marrow,  are  de- 
rived, as  we  shall  presently  show,  large  quantities  of  red  blood-corpuscles. 

Periosteum  and  Nutrient  Blood-vessels. — The  surfaces  of  bones, 
except  the  part  covered  with  articular  cartilage,  are  clothed  by  a  tough, 
fibrous  membrane,  the  jjeriosfeuin;  and  it  is  from  the  blood-vessels 
which  are  distributed  in  this  membrane,  that  the  bones,  especially  their 
more  compact  tissue,  are  in  great  part  supplied  with  nourishment, — 
minute  branches  from  the  periosteal  vessels  entering  the  little  foramina 
on  the  surface  of  the  bone,  and  finding  their  way  to  the  Haversian 
canals  to  be  immediately  described.  The  long  bones  are  supplied  also 
by  a  proper  nutrient  artery  which,  entering  at  some  part  of  the  shaft  so 


Fig.  60.— Transverse  section  of  compact  bony  tissue  (of  humerus).  Three  of  the  Haversian 
canals  are  seen,  witli  their  concentric  rings:  also  the  lacunar,  with  the  canaliculi  extending  from 
them  across  the  direction  of  the  lamellae.  The  Haversian  apertures  were  filled  with  debris  in  grind- 
ing down  the  section,  and  therefore  appear  black  in  the  figure,  which  represents  the  object.as  viewed 
with  transmitted  light.  The  Haversian  systems  are  so  closely  packed  in  this  section,  that  scarcely 
any  interstitial  lamellaB  are  visible.     X  150.    CSharpey.) 


as  to  reach  the  medullary  canal,  breaks  up  into  branches  for  the  supply 
of  the  marrow,  from  which  again  small  vessels  are  distributed  to  the 
interior  of  the  bone.  Other  small  blood-vessels  pierce  the  articular 
extremities  for  the  supply  of  the  cancellous  tissue. 

Microscopic  Struct icre  of  Bone. — "Notwithstanding  the  differences  of 
arrangement  just  mentioned,  the  structure  of  all  bone  is  found  under 
the  microscope  to  be  es3entially  the  same. 

Examined  with  a  rather  high  power  its  substance  is  found  to  contain 
a  multitude  of  small  irregular  spaces,  approximately  fusiform  in  shape, 
called  lacunae,  with  very  minute  canals  or  canaliculi,  as  they  are  termed, 
leading  from  them,  and  anastomosing  with  similar  little  prolongations 
from  other  lacunae  (fig.  60).  In  very  thin  layers  of  bone,  no  other 
canals  than  these  may  be  visible;  but  on  making  a  transverse  section  of 


56  HANDBOOK    OF    PHYSIOLOGY. 

the  compact  tissue  as  of  a  long  bone,  e.g.,  the  humerus  or  ulna,  the 
arrangement  shown  in  fig.  60  can  be  seen. 

The  bone  seems  mapped  out  into  small  circular  districts,  at  or  about 
the  centre  of  each  of  which  is  a  hole,  around  which  is  an  appearance  as 
of  concentric  layers — the  lacunm  and  canalicuU  follojving  the  same  con- 
centric plan  of  distribution  around  the  small  hole  in  the  centre,  with 
which  indeed  they  communicate. 

On  making  a  longitudinal  section,  the  central  holes  are  found  to  be 
simply  the  cut  extremities  of  small  canals  which  run  lengthwise  through 
the  bone,  anastomosing  with  each  other  by  lateral  branches  (fig.  61), 


Fig.  61.— Longitudinal  section  from  the  human  ulna,  showing  Haversian  canal,  lacunse,  and 

canaliculi.     (Kollett.) 

and  are  called  Haversian  canals,  after  the  name  of  the  physician,  Clopton 
Havers,  who  first  accurately  described  them. 

The  Haversian  canals,  the  average  diameter  of  which  is  -^^  of  an 
inch,  contain  blood-vessels,  and  by  means  of  them  blood  is  conveyed  to 
all,  even  the  densest  parts  of  the  bone;  the  minute  canaliculi  and  lacunae 
absorbing  nutrient  matter  from  the  Haversian  blood-vessels  and  con- 
veying it  still  more  intimately  to  the  very  substance  of  the  bone  which 
they  traverse. 

The  blood-vessels  enter  the  Haversian  canals  both  from  without,  by 
traversing  the  small  holes  which  exist  on  the  surface  of  all  bones  be- 
neath the  periosteum,  and  from  within  by  means  of  small  channels 
which  extend  from  the  medullary  cavity,  or  from  the  cancellous  tissue. 
The  arteries  and  veins  usually  occupy  separate  canals,  and  the  veins, 
which  are  the  larger,  often  present,  at  irregular  intervals,  small  pouch- 
like dilatations. 


THE    STRUCTURE    OF   THE    ELEMENTARY   TISSUES.  57 

The  lacunae  are  occupied  by  branched  cells,  Avhich  are  called  hojie- 
cells,  or  hone-corjnisdes  (fig.  62),  which  very  closely  resemble  the  ordi- 
nary branched  connective-tissue  corpuscles;  each  of  these  little  masses 
of  protoplasm  ministering  to  the  nutrition  of  the  bone  immediately  sur- 
rounding it,  and  one  lacunar  corpuscle  communicating  with  another, 
and  with  its  surrounding  district,  and  with  the  blood-vessels  of  the 
Haversian  canals,  by  means  of  the  minute  streams  of  fluent  nutrient 
matter  which  occupy  the  canaliculi. 

It  will  be  seen  from  the  above  description  that  bone  is  essentially 
connective-tissue  impregnated  with  lime  salts:  it  bears  a  very  close  re- 
semblance to  what  may  be  termed 
typical    connective-tissue   such   as 
the  substance  of  the  cornea.      The 
^vT""*      bone-corpuscles    with    their    pro- 


Fig.  62.  Fig.  63. 

Fig.  62. — Bone-corpuscles  with  their  processes  as  seen  in  a  thin  section  of  human  bone.   (RoUett.) 
Fig.  63. — Thin  layer  peeled  off  from  a  softened  bone.    This  figure,  which  is  intended  to  represent 

the  reticular  structure  of  a  lamella,  gives  a  better  idea  of  the  object  when  held  rather  farther  off 

than  usual  from  the  eye.     X  400.     (Sharpey.) 

cesses  occupying  the  lacunas  and  canaliculi  correspond  exactly  to  the 
cornea-corpuscles  lying  in  branched  spaces. 

Lamellae  of  Compact  Bone. — In  the  shaft  of  a  long  bone  three 
distinct  sets  of  lamellae  can  be  clearly  recognized. 

(1.)  General  or  fundamental  lamellse  ;  which  are  most  easily  tracea- 
ble just  beneath  the  periosteum,  and  around  the  medullary  cavity,  form- 
ing around  the  latter  a  series  of  concentric  rings.  At  a  little  distance 
from  the  medullary  and  periosteal  surfaces  (in  the  deeper  portions  of 
the  bone)  they  are  more  or  less  interrupted  by 

(3.)  Special  or  Haversian  lamellae,  which  are  concentrically  arranged 
around  the  Haversian  canals  to  the  number  of  six  to  eighteen  around 
each. 

(3.)  Interstitial  lamellae,  which  connect  the  system  of  Haversian 
lamellse,  filling  the  spaces  between  them,  and  consequently  attaining 


58  HANDBOOK    OF   PHYSIOLOGY. 

their  greatest  development  where  the  Haversian  systems  are  few,  and 
vice  versa. 

The  ultimate  structure  of  the  lamellae  appears  to  be  reticular.  If  a 
thin  film  be  peeled  off  the  surface  of  a  bone,  from  which  the  earthy 
matter  has  been  removed  by  acid,  and  examined  with  a  high  power  of 
the  microscope,  it  will  be  found  composed  of  a  finely  reticular  struc- 
ture, formed  apparently  of  very  slender  fibres  decussating  obliquel}^,  but 
coalescing  at  the  points  of  intersection,  as  if  here  the  fibres  were  fused 
rather  than  woven  together  (fig.  63). 

In  many  places  these  reticular  lamellae  are  perforated  by  tapering 
fibres  called  the  Claviculi  of  Gagliardi,  or  the  perforating  fibres  of, 
Sharpey,  resembling  in  character  the  ordinary  white  or  rarely  the  elastic 


Fig.  64. — Lamellae  torn  off  from  a  decalcified  human  parietal  bone  at  some  depth  from  the  sur- 
face, a,  a,  Lamellas,  showing  reticular  fibres;  b,  b,  darker  part,  where  several  lamellae  are  super- 
posed; c,  perforating  fibres.  Apertures  through  which  perforating  fibres  had  passed,  are  seen  es- 
pecially in  the  lower  part,  a,  a,  of  the  figure.    (Allen  Thomson.) 

fibrous  tissue,  which  bolt  the  neighboring  lamellae  together,  and  may  be 
drawn  out  when  the  latter  are  torn  asunder  (fig.  64).  These  perforating 
fibres  originate  from  ingrowing  processes  of  the  periosteum,  and  in  the 
adult  still  retain  their  connection  with  it. 

Development  of  Bone. — From  the  point  of  view  of  their  develop- 
ment, all  bones  may  be  subdivided  into  two  classes. 

(a.)  Those  which  are  ossified  directly  or  from  the  first  in  membrane 
or  fibrous  tissue,  e.g.,  the  bones  forming  the  vault  of  the  skull,  parietal, 
frontal,  and  a  certain  portion  of  the  occipital  bones. 

{h.)  Those  whose  form,  previous  to  ossification,  is  laid  down  in  hya- 
line cartilage,  e.g.,  humerus,  femur. 

The  process  of  development,  pure  and  simple,  may  be  best  studied  in 
bones  which  are  not  preceded  by  cartilage,  i.e.,  membrane- formed  {e.g., 


THE    STRUCTURE    OF   THE    ELEMENTARY    TISSUES.  59 

parietal)  ;  and  without  a  knowledge  of  this  process  (ossification  in  mem- 
brane), it  is  impossible  to  understand  the  much  more  complex  series  of 
changes  through  which  such  a  structure  as  the  cartilaginous  femur  of 
the  foetus  pusses  in  its  transformation  into  the  bony  femur  of  the  adult 
(ossification  in  cartilage). 

Ossification  in  Membrane. — The  membrane,  afterward  forming 
the  periosteum,  from  which  such  a  bone  as  the  parietal  is  developed, 
consists  of  two  layers — an  QxlemoX  fihroiis,  and  an  internal  cellular  or 
osteo-genetic. 

The  external  layer  is  made  up  of  ordinary  connective-tissue,  being 
composed  of  layers  of  fibrous  tissue  with  branched  connective-tissue 
corpuscles  here  and  there  between  the  bundles  of  fibres.  The  internal 
layer  consists  of  a  network  of  fine  fibrils  with  a  large  number  of  nucle- 
ated cells  with  a  certain  addition  of  albuminous  ground  or  cement  sub- 
stance between  the  fibrous  bundles,  some  of  which  are  oval,  others 
drawn  out  into  long  branched  processes:  it  is  more  richly  supplied 
with  capillaries  than  the  outer  layer.  The  relatively  large  number  of 
its  cellular  elements,  which  vary  in  size  and  shape,  together  with  the 
abundance  of  its  blood-vessels,  clearly  mark  it  out  as  the  portion  of  the 
periosteum  which  is  immediately  concerned  in  the  formation  of  bone. 

In  such  a  bone  as  the  parietal,  which  is  represented  then  when  ossi- 
fication commences  by  the  species  of  fibrous  connective  tissue  with  many 
cells  above  indicated,  the  deposition  of  bony  matter,  which  is  preceded 
by  increased  vascularity,  takes  place  in  radiating  spicule,  starting  from 
a  centre  of  ossification,  and  shooting  out  in  all  directions  toward  the 
periphery.  These  primary  bony  spicule  consist  of  the  fibres  of  the  tis- 
sue which  are  termed  osteogenetic  fibres,  comjiosed  of  a  soft  transparent 
substance  called  osteogen,  in  which  calcareous  granules  are  deposited. 
The  fibres  are  said  to  exhibit  in  their  precalcified  state  indications  of  a 
fibrillar  structure,  and  are  likened  to  bundles  of  white  fibrous  tissue,  to 
which  they  are  similar  in  chemical  composition,  but  from  Avhicli  they 
differ  in  being  stiffer  and  less  wavy.  The  deposited  granules  after  a 
time  become  so  numerous  as  to  fill  up  the  substance  of  the  fibres  and 
bon^  Dpiculse  result.  Calcareous  granules  are  deposited  also  in  the  in- 
terfibrillar  matrix.  By  the  junction  of  the  osteogenetic  fibres  and  their 
resulting  bony  spiculee  a  meshwork  of  bone  is  formed.  The  osteo- 
genetic fibres,  which  become  indistinct  as  calcification  proceeds,  are 
believed  to  persist  in  the  lamellae  of  adult  bone.  The  osteoblasts,  being 
in  part  retained  within  the  bone  trabecule  thus  produced,  form  bone 
corpuscles.  On  the  bony  trabeculse  first  formed,  layers  of  osteoblastic 
cells  from  the  osteo-genetic  layer  of  the  periosteum  are  developed  side  by 
side,  lining  the  irregular  spaces  like  an  epithelium  (fig.  65,  b).  Lime- 
salts  are  deposited  in  the  circumferential  part  of  each  osteoblast,  and 
thus  a  ring  of  osteoblasts  gives  rise  to  a  ring  of  bone  with  the  remaining 


60  HANDBOOK    OF    PHYSIOLOGY. 

uncalcified  portions  of  the  osteoblasts  imbedded  in  it  as  bone  corpuscles, 
us  in  the  first  formation;  then  the  central  portion  of  the  bony  plate 
becomes  harder  and  less  cancellous.  At  the  same  time,  the  plate  in- 
creases at  the  periphery  not  only  by  the  extension  of  the  bony  spiculie, 
but  also  by  deposits  taking  place  from  the  osteogenetic  layer  of  the 
periosteum. 

The  primitive  spongy  bone  is  formed,  and  its  irregular  branching 
spaces  are  occupied  by  processes  from  the  osteogenetic  layer  of  the  peri- 
osteum consisting  of  numerous  blood-vessels  and  osteoblasts.  Portions 
of  this  primitive  spongy  bone  are  re-absorbed.  The  osteoblasts  are 
arranged  in  concentric  successive  layers  and  give  rise  to  concentric- 
Haversian  lamellae  of  bone,  while  the  irregular  space  in  the  centre  is 
reduced  to  a  well-formed  Haversian  canal,  containing  the  usual  blood- 
vessels, the  portions  of  the  primitive  spongy  bone  between  the  Haversian 


Fig.  65.— Osteoblasts  from  the  parietal  bone  of  a  human  embiyo,  thirteen  weeks  old.  a,  Bony 
septa  with  the  cells  of  the  lacunae;  b,  layers  of  osteoblasts;  c,  the  "latter  in  transition  to  bone  cor- 
puscles.   Highly  maguifled.     (Gegenbaur.) 

systems  remaining  as  interstitial  or  ground-lamellsB  (p.  57).  The  bulk 
of  the  primitive  spongy  bone  is  thus  gradually  converted  into  compact 
bony-tissue  of  Haversian  systems.  Those  portions  of  the  ingrowths 
from  the  deej)er  layer  of  the  periosteum  which  are  not  converted  into 
bone  remain  in  the  spaces  of  the  cancellous  tissue  as  the  red  marrow. 

Ossification  in  Cartilage, — Under  this  heading,  taking  the  femur 
as  a  typical  example,  we  may  consider  the  process  by  which  the  solid 
cartilaginous  rod  which  represents  the  bone  in  the  foetus  is  converted 
into  the  hollow  cylinder  of  compact  bone  with  expanded  ends  formed 
of  cancellous  tissue  of  which  the  adult  femur  is  made  up.  We  must 
bear  in  mind  the  fact  that  this  foetal  cartilaginous  femur  is  many  times 
smaller  than  the  medullary  cavity  even  of  the  shaft  of  the  mature  bone, 
and,  therefore,  that  not  a  trace  of  the  original  cartilage  can  be  present 
in  the  femur  of  the  adult.  Its  purpose  is  indeed  purely  temporary;  and, 
after  its  calcification,  it  is  gradually  and  entirely  absorbed  as  will  be 
presently  explained. 


THE    STRUCTUKE    OF   THE    ELEMENTARY    TISSUES, 


61 


The  cartilaginous  rod  which  forms  the  foetal  femur  is  sheathed  in  a 
membrane  termed  the  pericJiondrium,  which  so  far  resembles  the  peri- 
osteum described  above,  as  to  consist  of  two  layers,  in  the  deeper  one  of 
which  spheroidal  cells  i^redominate  and  blood-vessels  abound,  while  the 
outer  layer  consists  mainly  of  fusiform  cells  which  are  in  the  mature 
tissue  gradually  transformed  into  fibres.  Thus,  the  differences  between 
the  foetal  perichondrium  and  the  periosteum  of  the  adult  are  such  as 
r'-:  : ,  -;^  usually  exist   between  the  embry- 

U'     r .--  onic  and  mature  forms  of  connec- 

;  ?:-•  ;"\  ^/  ■    .-  tive  tissue. 

'^*     ,~        ;'  Between  the   hyaline   cartilage 

'{^    0    ^  of  which  the  foetal  femur  consists 

'r  and  the  bony  tissue   forming  the 

adult  femur,  there    are    two    chief 
intermediate    stages  —  viz.    (1)    of 


Fig.  66.  Fig.  67. 

Fig.  66. — Ossifying  cartilage  showing  loops  of  blood-vessels. 

Fig.  67.— Longitudinal  section  of  ossifying  cartilage  from  the  humerus  of  a  foetal  sheep.  Cal- 
cified trabeculae  are  seen  extending  between  the  columns  of  cartilage  cells,  c,  Cartilage  cells. 
X  140.    (Sharpey.) 

calcified  cartilage,  and  (2)  of  embryonic  spongy  bone.     These  ma- 
terials, which  successively  occupy  the  place  of  the  foetal  cartilage,  are 
in  succession  entirely  absorbed,  and  their  place  is  taken  by  true  bone. 
The  process  by    which   the  cartilaginous  is  transformed    into    the 


62  HANDBOOK    OF    PHYSIOLOGY. 

bony  femur  may  however  be  divided  for  the  sake  of  clearness  into  the 
following  six  stages : — 

Stage  1. — Vascularization  of  the  Cartilage. — Processes  from  the 
osteogenetic  or  cellular  layer  of  the  perichondrium  containing  blood- 
vessels grow  into  the  substance  of  the  cartilage  much  as  ivy  insinuates 
itself  into  the  cracks  and  crevices  of  a  wall.  This  begins  at  the  "cen- 
tres of  ossification,"  from  which  the  blood-vessels  spread  chiefly  up  and 
down  the  shaft,  etc.     Thus  the  substance  of  the  cartilage,  which  previ- 


I 


Fig.  68.— Transverse  section  of  a  portion  of  a  metacarpal  bone  of  a  fcetus,  showing — 1,  fibrous 
layer  of  periosteum  :  2,  osteogenetic  layer  of  ditto  ;  3,  periosteal  bone  ;  4,  cartilage,  with  matrix 
gradually  becoming  calcified,  as  at  5,  with  cells  in  primary  areolae ;  beyond  5  the  calcified  matrix  is 
being  entirely  replaced  by  spongy  bc>ne.     X  200.     (V.  D.  Harris.) 

ously  contained  no  vessels,  is  traversed  by  a  number  of  branched  anas- 
tomosing channels  formed  by  the  enlargement  and  coalescence  of  the 
spaces  in  which  the  cartilage-cells  lie,  and  containing  loops  of  blood- 
vessels (fig.  66)  and  spheroidal  cells  which  will  become  osteoblasts. 

Stage  2. — Calcification  of  Cartilaginous  Matrix. — Lime  salts  are 
next  deposited  in  the  form  of  fine  granules  in  the  hyaline  matrix  of  the 
cartilage,  not  yet  vascularized,  and  this  gradually  becomes  transformed 
into  a  number  of  calcified  trabecule  (fig.  68,5),  inclosing  alveolar  spaces, 
which  are  the  primary  areolm,  and  which  contain  cartilage  cells.     By 


THE    STRUCTURE    OF    THE    ELEMENTARY   TISSUES.  63 

the  absorption  of  some  of  the  trabeculte  larger  spaces  are  developed, 
which  contain  cartilage-cells  for  a  very  short  time  only,  their  places  being 
taken  by  the  so-called  osteogenetic  layer  of  the  perichondrium  (before 
referred  to  in  Stage  1)  which  constitutes  the  primary  marrow.  The 
cartilage-cells,  gradually  enlarging,  become  more  transparent  and  finally 
undergo  disintegration. 

Stage  3.— Substitution  of  Embryonic  Spongy  Bone  for  Carti- 
lage.— The  cells  of  the  primary  marrow  arrange  themselves  as  a  contin- 
uous layer  like  epithelium  on  the  calcified  trabecula3  and  deposit  a  layer 
of  bone,  and  ensheath  them :  the  calcified  trabeculae,  encased  in  the 
sheaths  of  young  bone,  become  gradually  absorbed,  so  that  finally  we 
have  trabeculae  composed  entirely  of  spongy  bone,  all  trace  of  the  orig- 


Fig.  69.— A  small  isolated  mass  of  bone  next  the  periosteum  of  the  lower  jaw  of  human 
foetus,  o,  Osteogenetic  layer  of  periosteum,  g,  multinuclear  giant  cells,  the  one  on  the  left  acting 
here  probably  like  an  osteoclast.  Above  c,  the  osteoblasts  are  seen  to  become  surrounded  by  an 
osseous  matrix.    (Klein  and  Noble  Smith.) 

inal  calcified  cartilage  having  disappeared.  It  is  probable  that  the  large 
multinucleated  giant-cells  termed  osieoclasts  by  Kolliker,  which  are  de- 
rived from  the  osteoblasts  by  the  multiplication  of  their  nuclei,  are  the 
agents  by  which  the  absorption  of  calcified  cartilage,  and  subsequently 
of  embryonic  spongy  bone,  is  carried  on  (fig.  69,  g).  At  any  rate,  they 
are  almost  always  found  wherever  absorption  is  in  progress. 

Stages  2  and  3  are  precisely  similar  to  what  goes  on  in  the  growing 
shaft  of  a  bone  which  is  increasing  in  length  by  the  advance  of  the 
process  of  ossification  into  the  intermediary  cartilage  between  the  dia- 
physis  and  epiphysis.  In  this  case  the  cartilage-cells  become  fiattened 
and,  multiplying  by  division,  are  grouped  into  regular  columns  at  right 
angles  to  the  plane  of  calcification,  while  the  process  of  calcification 
extends  into  the  hyaline  matrix  between  them  (figs.  67  and  68). 


64  HANDBOOK    OF    PHYSIOLOGY. 

Stage  4. — Substitution  of  Periosteal  Bone  for  the  Primary 
Embryonic  Spongy  Bone. — The  embryouic  spongy  bone,  formed  as 
above  described,  is  simply  a  temporary  tissue  occupying  the  place  of  the 
fcetal  rod  of  cartilage,  once  representing  the  femur;  and  the  stages  1, 
2,  and  3  show  the  successive  changes  which  occur  at  the  centre  of  the 
shaft.     Periosteal  bone  is  at  the  same  time  deposited  in  successive  layers 


-c. 


Fig.  70. — Transverse  section  through  the  tibia  of  a  fcetal  kitten,  semi-diagrammatic.  X  60. 
P,  Periosteum.  O,  Osteogenetic  layer  of  the  periosteum  showing  tlie  osteoblasts  arranged  side  by 
side,  repi'esented  as  pear-shaped  black  dots  on  the  surface  of  the  newly-formed  bone.  15,  The  peri- 
osteal bone  deposited  in  successive  layers  beneath  the  periosteum  and  ensheathiug  E,  the  spongy 
endochondral  bone:  represented  as  more  deeply  shaded.  Within  the  trabeculse  of  endochondral 
spongy  bone  are  seen  the  remains  of  the  calcified  cartilage  trabeculae  represented  as  dark  wavy 
lines.  C,  The  medulla,  with  V,  V,  veins.  In  the  lower  half  of  the  figure  tlie  endocliondral  spongy 
bone  has  been  completely  absorbed.     (Klein  and  Noble  Smith.) 

beneath  the  periosteum,  i.e.,  at  the  circumference  of  the  shaft,  exactly  as 
described  in  the  section  on  ossification  in  membrane,  and  thus  a  casing 
of  periosteal  bone  is  formed  around  the  embryonic  endochondral  spongy 
bone:  this  casing  is  thickest  at  the  centre,  where  it  is  first  formed,  and 
thins  out  toward  each  end  of  the  shaft.     The  embryonic  spongy  bone  is 


THE    STRUCTURE    OF   THE    ELEMENTARY    TISSUES. 


65 


absorbed,  its  trabecala?  becoming  gradually  thinned  and  its  meshes  en- 
larging, and  finally  coalescing  into  one  great  cavity — the  medullary 
cavity  of  the  shaft. 

Stage  5. — Absorption  of  the  Inner  Layers  of  the  Periosteal 
Bone. — The  absorption  of  the  endochondral  spongy  bone  is  now  com- 
plete, and  the  medullary  cavity  is  bounded  by  periosteal  bone:  the  inner 
layers  of  this  periosteal  bone  are  next  absorbed,  and  the  medullary  cavity 
is  thereby  enlarged,  while  the  deposition  of  bone  beneath  the  periosteum 


Fig.  71. — Tranvprse  section  of  femur  of  a  human  embryo  about  eleven  weeks  old.  o,  Rudimen- 
tary Haversian  canal  in  cross-section;  b,  in  longitudinal  section;  c,  osteoblasts;  d,  newly  formed 
osseous  substance  of  a  lighter  color;  t,  that  of  greater  age;  /,  lacunae  with  their  cells;  g,  a  cell  stil? 
united  to  an  osteoblast.    (Frey.) 


continues  as  before.     The  first-formed   periosteal   bone   is   spongy   in 
character. 

Stage  6. — Formation  of  Compact  Bone. — The  transformation  of 
spongy  periosteal  bone  into  compact  bone  is  effected  in  a  manner  exactly 
similar  to  that  which  has  been  described  in  connection  with  ossification 
in  membrane  (p.  60).  The  irregularities  in  the  walls  of  the  areolse  in 
the  spongy  bone  are  absorbed,  while  the  osteoblasts  which  line  them  are 
developed  in  concentric  layers,  each  layer  in  turn  becoming  ossified  till 
the  comparatively  large  space  in  the  centre  is  reduced  to  a  well-formed 
Haversian  canal  (fig.  71).  When  once  formed,  bony  tissue  grows  to 
some  extent  interstitially,  as  is  evidenced  by  the  fact  that  the  lacunse  are 
rather  further  apart  in  full-formed  than  in  young  bone. 
5 


66  HANDBOOK    OF    PHYSIOLOGY. 

From  the  foregoing  description  of  the  development  of  bone,  it  will  be 
seen  that  the  common  terms  ossification  in  cartilage  and  ossificatioti  in 
membrane  are  aj3t  to  mislead,  since  they  seem  to  imply  two  processes 
radically  distinct.  The  process  of  ossification,  however,  is  in  all  cases 
one  and  the  same,  all  true  bony  tissue  being  formed  from  membrane 
(perichondrium  or  periosteum);  but  in  the  development  of  such  a  bone 
as  the  femur,  which  may  be  taken  as  the  type  of  so-called  ossification  in 
cartilage,  lime-salts  are  first  of  all  deposited  in  the  cartilage;  this  calci- 
fied cartilage,  however,  is  gradually  and  entirely  re-absorbed,  being  ulti- 
mately replaced  by  bone  formed  from  the  periosteum,  till  in  the  adult 
structure  nothing  but  true  bone  is  left.  Thus,  in  the  process  of  "  ossi- 
fication in  cartilage,"  calcification  of  the  cartilaginous  matrix  precedes 
the  real  formation  of  bone.  We  must,  therefore,  clearly  distinguish 
between  calcification  and  ossification.  The  former  is  simply  the  infil- 
tration of  an  animal  tissue  with  lime-salts,  and  is,  therefore,  a  change  of 
chemical  comjiosition  rather  than  of  structure;  while  ossification  is  the 
formation  of  true  bone — a  tissue  more  complex  and  more  highly  organ- 
ized than  that  from  which  it  is  derived. 

Centres  of  Ossification. — In  all  bones  ossification  commences  at 
one  or  more  points,  termed  centres  of  ossification.  The  long  bones,  e.g., 
femur,  humerus,  etc.,  have  at  least  three  such  points — one  for  the  ossifi- 
cation of  the  sltdft  or  diapliysis,  and  one  for  each  articular  extremity 
or  epiphysis.  Besides  these  three  primary  centres  which  are  always 
present  in  long  bones,  various  secondary  centres  may  be  superadded  for 
the  ossification  of  different  processes. 

Growth  of  Bone. — Bones  increase  in  lengtJi  by  the  advance  of  the 
process  of  ossification  into  the  cartilage  intermediate  between  the  dia- 
physis  and  epiphysis.  The  increase  in  length  indeed  is  due  entirely  to 
growth  at  the  two  ends  of  the  shaft.  This  is  proved  by  inserting  two 
pins  into  the  shaft  of  a  growing  bone:  after  some  time  their  distance 
apart  will  be  found  to  be  unaltered  though  the  bone  has  gradually  in- 
creased in  length,  the  growth  having  taken  place  beyond  and  not  be- 
tween them.  If  now  one  pin  be  placed  in  the  shaft,  and  the  other  in 
the  epiphysis  of  a  growing  bone,  their  distance  apart  will  increase  as  the 
bone  grows  in  length. 

Thus  it  is  that  if  the  epiphyses  with  the  intermediate  cartilage  be 
removed  from  a  young  bone,  growth  in  length  is  no  longer  possible; 
while  the  natural  termination  of  growth  of  a  bone  in  length  takes  place 
when  the  epiphyses  become  united  in  bony  continuity  with  the  shaft. 

Increase  in  tliichness  in  the  shaft  of  a  long  bone  occurs  by  the  depo- 
sition of  successive  layers  beneath  the  periosteum. 

If  a  thin  metal  plate  be  inserted  beneath  the  periosteum  of  a  grow- 
ing bone  it  will  soon  be  covered  by  osseous  deposit,  but  if  it  be  put  be- 


THE    STRUCTUKE    OF    THE    ELEMENTARY   TISSUES. 


67 


tweenthe  fibrous  and  osteogenetic  layers  it  will  never  become  enveloped 
in  bone,  for  all  the  boiae  is  formed  beneath  the  latter. 

Other  varieties  of  connective  tissue  may  become  ossified,  e.g.,  the 
tendons  in  some  birds. 

Functions  of  Bones. — Bones  form  the  framework  of  the  body;  for 
this  they  are  fitted  by  their  hardness  and  solidity  together  with  their 
comparative  lightness;  they  serve  both  to  jDrotect  internal  organs  in  the 
trunk  and  skull,  and  as  levers  worked  by  muscles  in  the  limbs;  not- 
withstanding their  hardness  they  possess  a  considerable  degree  of  elas- 
ticity, which  often  saves  them  from  fracture. 

The  material  of  which  the  chief  portion  of  the  teeth  is  made  up, 
called  Dentine,  is  frequently  classed  with  bone  and  as  one  of  the  con- 
nective tissues.  The  other  constituents  of  the  teeth  also  resemble  bone 
in  structure  to  a  considerable  degree;  it  will  be  as  well  therefore  to  give 
in  this  place  some  account  of  the  teeth. 

The  Teeth. 

During  the  course  of  his  life,  man,  in  common  with  most  other 
mammals,  is  provided  with  two  sets  of  teeth;  the  first  set,  called  the 


Pig.  72.->  Normal  well-formed  jaws,  from  which  the  alveolar  plate  has  been  in  great  part  removed, 
so  as  to  expose  the  developing  permanent  teeth  in  their  crypts  in  the  jaws.     (Tomes.) 


temporarii  or  milh  teeth,  makes  its  appearance  in  infancy,  and  is  in  the 
course  of  a  few  years  shed  and  replaced  by  the  second  or  ■permanent  set. 

The  temporary  or  milk  teeth  have  only  a  very  limited  term  of 
existence. 

They  are  ten  in  number  in  each  jaw,  namely,  on  either  side  from  the 
middle  line  two  incisors,  one  canine,  and  two  deciduous  molars,  and  are 
replaced  by  ten  permanent  teeth.     The  number  of  permanent  teeth  in 


68 


HANDBOOK    OF    PHYSIOLOOY. 


each  jaw  is,  however,  increased  to  sixteen  by  the  development  of  three 
molars  on  each  side  of  the  jaw,  which  are  called  the  permanent  or  true 
molars. 

The  following  formula  shows,  at  a  glance,  the  comparative  arrange- 
ment and  number  of  the  temporary  and  permanent  teeth : — 


MOLARS. 

9 


CANINE. 
1 


Temporary  Teeth. 

Middle  Line  of  Jaw. 

incisors.  incisors. 

2 


canine. 

1 


molars. 
2=10 


2=10 


BICUSPIDS 
TRUE  OR  PRE- 

MOLARS.     MOLARS. 

3  3 


CANINE. 
1 


Permanent  Teeth. 


Middle  Line  of  Jaw. 


INCISORS. 

2 


INCISORS. 

2 


CANINE. 
1 


BICUSPIDS 
OR  PRE-  TRUE 

MOLARS.       MOLARS. 


From  this  formula  it  will  be  seen  that  the  two  bicuspid  or  pre-molar 
teeth  in  the  adult  are  the  successors  of  the  two  deciduous  molars  in  the 
child.  They  differ  from  them,  however,  in  some  respects,  the  temporary 
molars  having  a  stronger  likeness  to  the  jjermanent  than  to  their  imme- 
diate descendants  the  so-called  bicuspids,  besides  occupying  more  space 
in  the  jaws. 

The  temporary  incisors  and  canines  differ  from  their  successors  but 
little  except  in  their  smaller  size  and  the  abrupt  manner  in  which  their 
enamel  terminates  at  the  necks  of  the  teeth,  forming  a  ridge  or  thick 
edge.     Their  color  is  more  of  a  bluish-white  than  of  a  yellowish  shade. 

The  following  tables  show  the  average  times  of  eruption  of  the 
Temporary  and  Permanent  teeth.  In  both  cases  the  eruption  of  any 
given  tooth  of  the  lower  precedes,  as  a  rule,  that  of  the  corresponding 
tooth  of  the  upper  jaw. 


Temporary  or  Milk  Teeth. 
The  figures  indicate  in  months  the  age  at  which  each  tooth  appears. 


INCISORS. 

DECIDUOUS 

PrRST 

MOLARS. 

CANINES. 

DECIDUOUS 
SKCOND 
MOLARS. 

6 

12 

18 

24     . 

THE    STKUCTUKE    OF    THE    ELEMENTARY   TISSUES. 


69 


Permanent  Teeth. 

The  age  at  which  each  tooth  is  cut  is  indicated  in  this  table  in  years. 


FIRST 
MOLARS. 


INCISORS. 


CENTRALS. 


LATERALS. 


BICUSPIDS  OR  PRE- 
MOLARS. 
FIRST.  SECOND. 


10 


11 


SECOND 
MOLAKS. 


THIRD 
MOLARS  OR 
WISDOMS. 


17  to  25 


The  times  of  eruption  given  in  the  above  tables  are  only  approxi- 
mate: the  limits  of  variation  being  tolerably  wide.  Some  children  may 
cut  their  first  teeth  before  the  age  of  six  months,  and  others  not  till 
nearly  the  twelfth  month.  In  nearly  all  cases  the  two  central  incisors 
of  the  lower  jaw  are  cut  first,  these  being  succeeded  after  a  short  inter- 
val by  the  four  incisors  of  the  upper  jaw;  next  follow  the  lateral  in- 
cisors of  the  lower  jaw,  and  so  on  as  indicated  in  the  table  till  the  com- 
pletion of  the  milk  dentition  at  about  the  age  of  two  years.  Certain 
diseases  affecting  the  bony  skeleton,  e.g.,  Rickets,  retard  the  eruptive 
period  considerably. 

The  milk-teeth  usually  come  through  in  batches,  each  period  of 
eruption  being  succeeded  by  one  of  quiescence  lasting  sometimes  several 
months.  The  milk-teeth  shonld  be  in  use  from  the  age  of  two  up  to 
within  a  few  months  of  the  time  for  tlieir  successors  to  appear.  Their 
retention  serves  the  purpose  of  preserving  the  necessary  sjiace  sufficient 
for  the  succeeding  permanent  teeth  to  occupy. 

It  is  important  to  notice  that  it  is  a  molar  which  is  the  first  tooth  to 
be  cut  in  the  permanent  dentition,  not  an  incisor  as  in  the  case  of  the 
temporary  set,  and  also  that  it  appears  behind  the  last  deciduous  molar 
on  each  side. 

The  third  molars,  often  called  Wisdoms,  are  sometimes  unerupted 
through  life  from  want  of  sufBcient  jaw  si^ace  and  the  presence  of  the 
other  teeth:  and  in  highly  civilized  races  there  are  evidences  to  show 
that  they  are  in  process  of  suppression  from  the  dental  series;  cases  of 
"whole  families  in  which  their  absence  is  a  characteristic  feature  beiug 
occasionally  met  with. 

When  the  teeth  are  fully  erupted  it  will  be  observed  that  the  upper 
incisors  and  canines  project  obliquely  over  the  lower  front  teeth  and  the 
external  cusps  of  the  upper  bicuspids  and  molars  lie  outside  those  of 
the  corresponding  teeth  in  the  lower  jaw.  This  arrangement  allows  to 
some  extent  of  a  scissor-like  action  in  dividing  and  biting  food  in  the 
case  of  incisors;  and  a  grinding  motion  in  that  of  the  bicuspids  and 
molars  when  the  side  to  side  movements  of  the  lower  jaw  bring  the  ex- 
ternal cusps  of  the  lower  teeth  into  direct  articulation  with  those  of  the 


70  HANDBOOK    OF    PHYSIOLOGY. 

upper,  and  then  cause  them  to  glide  down  the  inclined  surfaces  of  the 
external  and  up  the  internal  cusps  of  these  same  upper  teeth  during 
the  act  of  mastication. 

The  work  of  the  canine  teeth  in  man  is  similar  to  that  of  his  incisors. 
Besides  being  a  firmly  implanted  tooth  and  one  of  stronger  substance 
than  the  others,  the  canine  tooth  is  important  in  preserving  the  shape 
of  the  angle  of  the  mouth,  and  by  its  shape,  whether  pointed  or  blunt, 
long  or  short,  becomes  a  character  tooth  of  the  dentition  as  a  whole  in 
both  males  and  females. 

Another  feature  in  the  fully  developed  and  properly  articulated  set 
of  teeth  is  that  no  two  teeth  oppose  each  other  only,  but  that  each  tooth 
antagonizes  with  two,  except  the  upper  AVisdom,  usually  a  small  tooth. 
This  is  the  result  of  the  greater  width  of  the  upper  incisors,  which  so 
arranges  the  "  bite  "  of  the  other  teeth  that  the  lower  canine  closes  in 
front  of  the  upper  one. 

Should  a  tooth  be  lost,  therefor?,  it  does  not  follow  that  its  former 
opponent  remaining  in  the  mouth  is  rendered  useless  and  thereby  liable 
to  be  removed  from  the  jaw  by  a  gradual  process  of  extrusion  commonly 
seen  in  teeth  that  have  no  work  to  perform  by  reason  of  absence  of  an- 
tagonists. 

It  is  worthy  of  note  that  from  the  age  of  four  years  to  the  shedding 
of  the  first  milk-tooth  the  child  has  no  fewer  than  forty-eight  teetn, 
twenty  milk-teeth  and  twenty-eight  calcified  germs  of  permanent  teeth 
(all  in  fact  except  the  four  wisdom  teeth,  which  show  no  signs  of  devel- 
opment until  the  third  year). 

Structure  of  a  Tooth. 

A  tooth  is  generally  described  as  possessing  a  crown,  neck,  and  root 
or  root^. 

The  crown  is  the  portion  which  projects  beyond  the  level  of  the 
gum.  The  nech  is  that  constricted  portion  just  below  the  crown  which 
is  embraced  by  the  free  edges  of  the  gum,  and  the  root  includes  all  be- 
low this.  ** 

On  making  longitudinal  and  transverse  sections  through  its  centre 
(fig.  73,  A,  b),  a  tooth  is  found  to  be  principally  composed  of  a  hard 
material,  dentine  or  ivory,  which  is  hollowed  out  into  a  central  cavity 
which  resembles  in  general  shape  the  outline  of  the  tooth,  and  is  called 
the  jnclp  cavity  from  its  containing  the  very  vascular  and  sensitive  pulp. 

The  tooth  pulp  is  composed  of  fibrous  connective  tissue,  blood-vessels, 
nerves,  and  large  numbers  of  cells  of  varying  shapes,  e.g.,  fusiform,  stel- 
late, and  on  the  surface  in  close  connection  with  the  dentine  a  specialized 
layer  of  cells  called  odontoblast,^,  which  are  elongated  columnar-looking 
cells  with  a  large  nucleus  at  the  tapering  ends  or  those  farthest  from 


THE    STKUCTURE    OF   THE    ELEMENTARY    TISSUES. 


71 


the  dentine  (the  layer  is  sometimes  mentioned  as  the  memhrana  eboris, 
from  the  tenacity  with  which  it  clings  to  the  dentine),  all  are  imbedded 
in  a  mucoid  gelatinous  matrix. 

The  blood-vessels  and  nerves  enter  the  pulp  through  a  small  opening 
at  the  apical  extremity  of  each  root.  The  exact  terminations  of  the 
nerves  are  not  definitely  known.  They  have  never  been  observed  to 
enter  the  dentinal  tubes,  but  they  are  probably  connected  with  the  fibrils 
in  those  tubes  through  the  intervention  of  the  odontoblasts  and  deeper 
layer  of  cells.     No  lymphatics  have  been  traced  to  the  pulp. 

A  layer  of  very  hard  calcareous  matter,  the  enamel,  caps  that  part 
of  the  dentine  which  projects  beyond  the  level  of  the  gum;  while  sheath- 


Fig.  73. — A.  Longitudinal  section  of  a  human  molar  tooth;  c,  cement;  d.  dentine;  e,  enamel;  v, 
pulp  cavity  (Owen),    b.  Transverse  section.    The  letters  indicate  the  same  as  in  a. 

ing  the  j^ortion  of  dentine  which  is  beneath  the  level  of  the  gum,  is  a 
layer  of  true  bone,  called  the  cement  or  crasta petrosa. 

At  the  neck  of  the  tooth,  where  the  enamel  and  cement  come  into 
contact,  each  is  reduced  to  an  exceedingly  thin  layer.  The  cement 
overlapping  the  enamel  and  being  prolonged  over  it  on  the  surface  of 
the  crown  of  the  tooth  is  a  thin  membrane  called  Nasmyth's  membrane, 
or  the  ruticte  of  the  tooth.  The  covering  of  enamel  becomes  thicker 
toward  the  crown,  and  the  cement  toward  the  lower  end  or  apex  of  the 
root. 


I. — Dentine  or  Ivory. 

Chemical  Compositioti. — Dentine  closely  resembles  bone  in  chemical 
composition.  It  contains,  however,  rather  less  animal  matter;  the  pro- 
portion in  a  hundred  parts  being  about  twenty-eight  animal  to  seventy- 
two  of  earthy.  The  former,  like  the  animal  matter  of  bone,  may  be 
resolved  into  gelatin  by  boiling.  It  also  contains  a  trace  of  fat.  The 
earthy  matter  is  made  up  chiefly  of  calcium  jyhosphate,  with  a  small  por- 


72 


HANDBOOK    OF    PHYSIOLOGY. 


tion  of  the  carbonate,  and  traces  of  calcium  Jluo?nde  and  magnesivm 
^phosphate. 

Structure. — Under  the  microscope  dentine  is  seen  to  be  finely  chan- 
nelled by  a  multitude  of  delicate  tubes,  which,  by  their  inner  ends  com- 


Enamel  — 


Dentine. 


~.  Cement. 


Fig.  74. — Premolar  tooth  of  cat  in  situ. 

municate  with  the  pulp-cavity,  and  by  their  outer  extremities  come  into 
contact  with  the  under  part  of  the  enamel  and  cement,  and  sometimes 


BO  a. 

Fig  75.— Section  of  a  portion  of  the  dentine  and  cement  from  the  middle  of  the  root  of  an  incisor 
tooth,  a,  Dental  tubuli  ramifying  and  terminating,  some  of  them  in  the  interglobular  spaces  h  and 
c,  which  somewhat  resemble  bone  lacunae ;  d,  inner  layer  of  the  cement  witli  nui^ierous  closely  set 
canaUcuh;  e,  outer  layer  of  cement;  /,  lacunae;  gr,  canahculi.     X  350.    (Kolliker.J 

even  penetrate  them  for  a  greater  or  less  distance  (figs.  75,  77).  The 
matrix  in  which  these  tubes  lie  is  composed  of  "a  reticulum  of  fine 
fibres  of  connective  tissue  modified  by  calcification,  and  where  that  pro- 


THE    STKUCTURE    OF    THE    ELEMENTARY    TISSUES.  7S 

cess  is  complete,  entirely  hidden  by  the  densely  deposited  lime  salts " 
(Mummery). 

In  their  course  from  the  pulp-cavity  to  the  surface  the  minute  tubes 
form  gentle  and  nearl}^  parallel  curves  and  divide  and  subdivide  dicho- 
tomously,  but  without  much  lessening  of  their  calibre  until  they  are 
approaching  their  peripheral  termination. 

From  their  sides  proceed  other  exceedingly  minute  secondary  canals, 
Avhich  extend  into  the  dentine  between  the  tubules  and  anastomose  with 
each  other.  The  tubules  of  the  dentine,  the  average  diameter  of  which 
at  their  inner  and  larger  extremity  is  ^^Vu  o^  ^^  inch,  contain  fine  pro- 
longations from  the  tooth-pulp,  which  give  the  dentine  a  certain  faint 
sensitiveness  under  ordinary  circumstances  and,  without  doubt,  have  to 
do  also  with  its  nutrition.  These  prolongations  from  the  tooth-pulp 
are  probably  processes  of  the  dentine-cells  or  odontoblasts  which  are 
branched  cells  lining  the  pulp-cavity;  the  relation  of  these  processes  to 
the  tubules  in  which  they  lie  being  precisely  similar  to  that  of  the  pro- 
cesses of  the  bone-corpuscles  to  the  canaliculi  of  bone.  The  outer  portion 
of  the  dentine,  underlying  the  cement,  and  the  enamel  to  a  much  lesser 
degree,  forms  a  more  or  less  distinct  layer  termed  the  granular  or  in- 
tergiohidar  layer.  It  is  characterized  by  the  presence  of  a  number  of 
irregular  minute  cell-like  cavities,  much  more  closely  packed  than  the 
lacunae  in  the  cement,  and  "communicating  with  one  another  and  with  the 
ends  of  the  dentine-tubes  (fig.  75,  b,  c),  and  containing  cells  like  bone- 
corpuscles. 

II. — Enamel. 

Chemical  Composition. — The  enamel,  which  is  by  far  the  hardest  por- 
tion of  a  tooth,  is  composed,  chemically,  of  the  same  elements  that  enter 
into  the  composition  of  dentine  and  bone.  Its  animal  matter,  how- 
ever, amounts  only  to  about  2  or  3  per  cent.  It  contains  a  larger  pro- 
portion of  inorganic  matter  and  is  harder  than  any  other  tissue  in  the 
body. 

Structure. — Examined  under  the  microscope,  enamel  is  found  com- 
posed of  fine  hexagonal  fibres  (figs.  76,  77)  -s-^ot  o^  ^^  i^^h  in  diameter, 
which  are  set  on  end  on  the  surface  of  the  dentine,  and  fit  into  corre- 
sponding depressions  in  the  same. 

They  radiate  in  such  a  manner  from  the  dentine  that  at  the  top  of 
the  tooth  they  are  more  or  less  vertical,  while  toward  the  sides  they  tend 
to  the  horizontal  direction.  Like  the  dentine  tubules,  they  are  not 
straight,  but  disposed  in  wavy  and  parallel  curves.  The  fibres  are 
marked  by  transverse  lines,  and  are  mostly  solid,  but  some  of  them  may 
contain  a  very  minute  canal. 

The  enamel-prisms  are  connected  together  by  a  very  minute  quantity 
of  hyaline  cement-substance.     In  the  deeper  part  of  badly  formed  en- 


74 


HAXDBOOK    OF    PHYSIOLOGY. 


amels,  between  the  prisms,  are  small  hiaince,  or  "interglobular  spaces" 
which  have  the  processes  or  fibrils  of  the  dentine  tubes  in  connection  with 
them  (fig.  77,  c). 

A 


Fig.  76.— Enamel  fibres.  A,  Fragments  and  single  fibres  of  the  transversely-striated  enamel, 
isolated  by  the  action  of  hydrochloric  acid.  B,  Surface  of  a  small  fragment  of  enamel,  showing  the 
hexagonal  ends  of  the  fibres  with  darker  centres,  or  not  so  highly  calcified,    x  350.    (Kolliker.) 


III. — Crust  a  Petrosa. 

The  crusta  petrom,  or  cement  (fig.  75,  e,  d),  is  composed  of  true  bone, 
and  in  it  are  lacunae  (/)  and  canaliculi  {g),  which  sometimes  communi- 
cate with  the  outer  finely  branched  ends  of  the  dentine  tubules,  and 
generally  with  the  interglobular  spaces.  Its  lamingeareasit  were  bolted 
together  by  perforating  fibres  like  those  of  ordinary  bone  (Sharpey's 
fibres).  Cement  differs  from  ordinary  bone  in  possessing  no  Haversian 
canals,  or,  if  at  all,  only  in  the  thickest  part.  Such  canals  are  more 
often  met  with  in  teeth  with  the  cement  hypertrophied  than  in  the 
normal  tooth. 

Development  of  the  Teeth. 

Development  of  the  Teeth. — The  first  step  in  the  development  of  the 
teeth  consists  in  a  downward  growth  (fig.  78,  a,  1)  from  the  Kete  Mal- 
pighi  or  the  deeper  layer  of  stratified  epithelium  of  the  mucous  mem- 
brane of  the  mouth,  which  first  becomes  thickened  in  the  neighborhood 
of  the  maxillge  or  jaws  now  in  the  course  of  formation.  This  process 
passes  downward  into  a  recess  of  the  imperfectly  developed  tissue  of  the 
embryonic  jaw.  The  downward  epithelial  growth  forms  the  inimary 
enamel  organ  or  enamel  germ,  and  its  position  is  indicated  by  a  slight 
groove  in  the  mucous  membrane  of  the  jaw.  The  next  step  in  the  pro- 
cess consists  in  the  elongation  downward  of  the  enamel  groove  and  of 


THE    STRUCTUKE    OF    THE    ELEMENTARY    TISSUES. 


75 


the  enamel  germ  and  the  inclination  outward  of  the  deeper  part  (fig. 
78,  B,  /■'),  which  is  now  inclined  at  an  angle  with  the  upper  portion  or 
neck  (/),  and  has  become  bulbous.  After  this  there  is  an  increased  de- 
velopment at  certain  points  corresponding  to  the  situations  of  the  future 
milk-teeth.  The  enamel  germ,  or  common  enamel  germ,  as  it  may  be 
called,  becomes  divided  at  its  deeper  portion,  or  extended  by  further 


Fig.' 


Fig.  78 


Fig.  77. — Thin  section  of  the  enamel  and  a  part  of  the  dentine,  a,  Cuticular  pellicle  of  the 
enamel  (Nasmyth's  membrane);  b.  enamel  fibres,  or  colmnns  with  fissures  between  them  and 
cross  striee:  c,  larger  cavities  in  the  enamel,  communicating  with  the  extremities  of  same  of 
the  dentinal  tubuli  (.rf)-     X  :3oO.     (Kolliker.) 

Fig.  78. — Section  of  the_upper  jaw  of  a  foetal  sheep.  A. — 1 ,  Common  enamel  germ  dipping  down 
into  the  mucous  membrane:  2,  palatine  process  of  Jaw;  S,  rete  Malpighi.  B.— Section  similar  to  A, 
but  passing  through  one  of  the  special  enamel  germs  here  becoming  Hask-shaped;  c,  c',  epithelium 
of  mouth;  /.  neck;  /',  body  of  special  enamel  germ.  C. — A  later  stage;  r,  outline  of  epithelium  of 
gum:  /,  neck  of  enamel  germ:  /',  enamel  organ;  p,  papilla;  s,  dental  sac  forming;  f  p.  the  enamel 

ferm  of  jiermaneut  tooth ;  7n,  bone  of  jaw ;  v,  vessels  cut  across.     (Waldeyer  and  Kolliker.)    Copied 
rom  Quain's  Anatomy. 


growth,  into  a  number  of  special  enamel  germs  corresponding  to  each 
of  the  above-mentioned  milk-teeth,  and  connected  to  the  common  germ 
by  a  narrow  neck.  Each  tooth  is  thus  placed  in  its  own  special  recess  in 
the  embryonic  jaw  (lig.  78,  B,  //'). 


76 


HANDBOOK    OF    PHYSIOLOGY. 


As  these  changes  proceed,  there  grows  up  from  tlie  underlying  tissue 
into  each  enamel  germ  (fig.  78,  c,  j)),  a  distinct  vascular  ^>a/7i7Zrt  (dental 
papilla),  and  upon  it  the  enamel  germ  becomes  moulded,  and  presents 
the  appearance  of  a  cap  of  two  layers  of  epithelium  separated  by  an  in- 
terval (fig.  78,  c,/').  While  part  of  the  sub-epithelial  tissue  is  elevated 
to  form  the  dental  papillae,  the  part  which  bounds  the  embryonic  teeth 
forms  the  dental  sacs  (fig.  78,  c,  s) ;  and  the  rudiment  of  the  jaw,  at  first 
a  bony  gutter  in  v/hich  the  teeth  germs  lie,  sends  up  processes  forming 
partitions  between  the  teeth.  In  this  way  small  chambers  are  produced 
in  which  the  dental  sacs  are  contained,  and  thus  the  sockets  of  the  teeth 
are  formed.  The  papilla,  which  is  really  part  of  the  dental  sac  (if  one 
thinks  of  this  as  the  whole  of  the  sub-epithelial  tissue  surrounding  the 
enamel  organ  and  interposed  between  the  enamel  germ  and  the  develop- 
ing bony  jaw),  is  composed  of  nucleated  cells  arranged  in  a  meshwork. 


Fig  79. — Part  of  section  of  developing  tooth  of  a  young  rat,  showing  the  mode  of  deposition  of 
the  dentine.  Highly  magnified,  o,  Outer  layer  of  fully  formed  dentine;  6.  uncalcified  matrix  with 
one  or  two  nodules  of  calcareous  matter  near  the  calcified  parts;  c,  odontoblasts  sending  processes 
into  the  dentine;  d,  pulp;  e,  fusiform  or  wedge-shape  cells  found  between  odontoblasts; /.  .stellate 
cells  of  pulp  in  fibrous  connective  tissue.  The  section  is  stained  in  carmine,  which  colors  the  un- 
calcifled  matrix  but  not  the  calcified  part.    (E.  A.  Schafer.) 

the  outer  or  peripheral  part  being  covered  with  a  layer  of  columnar  nu- 
cleated cells  called  odontoblasts.  The  odontoblasts  possibly  form  the 
dentine,  while  the  remainder  of  the  papilla  forms  the  tooth-pulp.  The 
method  of  the  formation  of  the  dentine  from  the  odontoblasts  is  said  to 
be  as  follows :  The  cells  elongate  at  their  outer  part,  and  these  processes 
are  directly  converted  into  the  tubules  of  dentine  (fig.  79,  c),  and,  ac- 
cording to  some,  into  the  contained  fibrils  as  well.  The  continued  for- 
mation of  dentine  proceeds  by  the  elongation  of  the  odontoblasts,  and 
their  subsequent  conversion  by  a  process  of  calcification  into  dentine  tu- 
bules. The  most  recently  formed  tubules  are  not  immediately  calcified. 
The  dentine  fibrils  contained  in  the  tubules  are  said,  by  others,  to  be 
formed  from  processes  of  the  deeper  layer  of  odontoblasts,  which  are 
wedged  in  between  the  cells  of  the  superficial  layer  (fig.  79,  e)  which  form 
the  tubules  only.  There  are  several  theories  upon  these  points.  The 
matrix,  according  to  more  recent  views,  is  formed  by  a  calcification  of 
the  fibrous  connective  tissue  develojied  in  the  papilla. 

Since  the  papillse  are  to  form  the  main  portion  of  each  tooth,  i.e.,  the 


THE    STRUCTURE    OF   THE    ELEMENTARY    TISSUES. 


77 


dentine,  each  of  them  early  takes  the  shape  of  the  crown  of  the  tooth 
to  which  it  corresponds.  As  the  dentine  increases  in  thickness  the 
papilla?  diminish,  and  at  last  when  the  tooth  is  cut  only  a  small  amount 
of  the  papilla  remains  as  the  dental  pulp,  and  is  supplied  by  vessels  and 
nerves  which  enter  at  the  end  of  the  root.  The  shape  of  the  crown  of 
the  tooth  is  taken  by  the  corresponding  papilla,  and  that  of  the  single 
or  double  root  by  the  subsequent  constriction  below  the  crown,  or  by 
division  of  the  lower  part  of  the  papilla.  The  number  of  roots  being 
foreshadowed  by  the  number  of  arteries  going  to  the  papilla.     The  roots 


Fig.  80.— Vertical  transverse  section  of  the  dental  sac,  pulp,  etc.,  of  a  kitten.  «,  Dental  papilla 
or  pulp;  b,  the  cap  of  dentine  formed  upon  the  summit;  c,  its  covering  of  enamel;  d,  inner  layer  of 
epitheUum  of  the  enamel  organ;  e.  gelatinous  tissue;  /,  outer  epithelial  layer  of  the  enamel  organ; 
3,  inner  layer,  and  h.  outer  layer  of  dental  sac.     X  14.    (Thiersch.) 


are  not  completely  formed  at  the  time  of  the  eruption  of  the  teeth,  but 
subsequently.  ■• 

The  enamel  cap  is  found  later  on  to  consist  (fig.  80,  d,  e,f)  of  three 
parts  (1)  an  inner  membrane,  composed  of  a  layer  of  columnar  epithe- 
lium in  contact  with  the  dentine,  called  enamel  cells,  and  outside  of  these 
one  or  more  layers  of  small  polyhedral  nucleated  cells  {stratum  inter- 
medium of  Hannover) ;  (2)  an  outer  membrane  of  several  layers  of  epi- 
thelium; (3)  a  middle  membrane  formed  of  a  matrix  of  non-vascular, 
gelatinous  tissue,  containing  stellate  cells.  The  enamel  is  formed  by 
the  enamel  cells  of  the  inner  membrane,  by  the  elongation  of  their  distal 
extremities,  and  the  direct  conversion  of  their  ends  nearest  the  dentine 
papilla    into    enamel.      The   calcification    of  an  enamel  cell  or   prism 


78  HANDBOOK    OF    PHYSIOLOGY. 

takes  place  first  at  its  periphery,  the  centre  remaining  for  a  time  trans- 
jjarent.  The  cells  of  the  stratum  intermedium  are  used  for  the  regenera- 
tion of  the  enamel  cells,  but  these  and  the  middle  membrane  after  a 
time  disappear.  The  cells  of  the  outer  membrane  atrophy  early  and  dis- 
appear. 

The  cement  or  crusta  petrosa  is  formed  from  the  internal  tissue  of 
the  tooth  sac,  the  structure  and  function  of  which  are  identical  with 
those  of  the  osteogenetic  layer  of  the  periosteum,  or,  in  other  words,  os- 
sification in  membrane  occurs  in  it. 

The  outer  layer  or  portion  of  the  membrane  of  the  tooth  sac  forms 
the  fibrous  dental  per iodeum. 

This  periosteum,  when  the  tooth  is  fully  formed,  is  not  only  a  means 
of  attachment  of  the  tooth  to  its  socket,  but  also  in  conjunction  with 
the  indp  a  source  of  nourishment  to  it.  Additional  laminae  of  cement 
are  added  to  the  root  from  time  to  time  during  the  life  of  the  tooth,  as 
especially  well  seen  in  the  abnormal  condition  called  exostosis,  by  the 
process  of  calcification  taking  place  in  the  periosteum.  On  the  other 
hand  absorption  of  the  root  may  equally  occur  through  tlie  same  mem- 
brane. 

In  this  manner  the  first  set  of  teeth,  or  the  milk-teeth,  are  formed; 
and  each  tooth,  by  degrees  developing,  presses  at  length  on  the  wall  of 
the  sac  inclosing  it,  and,  causing  its  absorption,  is  cut,  to  use  a  familiar 
phrase. 

The  temimrary  or  milk-teeth  are  speedily  replaced  by  the  growth  of 
the  permanent  teeth,  which  push  their  way  up  from  beneath  them,  ab- 
sorbing in  their  progress  the  whole  of  the  root  of  each  milk-tooth,  and 
leaving  at  length  only  the  crown  as  a  mere  shell,  which  is  shed  to  make 
way  for  the  eruption  of  the  permanent  teeth. 

Each  temporary  tooth  is  replaced  by  a  tooth  of  the  permanent  set 
which  is  developed  from  a  small  sac  set  by,  so  to  speak,  from  the  sac  of 
the  temporary  tooth  which  precedes  it,  and  called  the  cavity  of  reserve 
(fig.  78,  c,  fp).  Thus  the  temporary  incisors  and  canines  are  succeeded 
by  the  corresponding  permanent  ones,  the  temporary  first  molar  by  the 
first  bicuspid,  the  temporary  second  molar  develops  two  offshoots,  one 
for  the  second  bicuspid,  the  other  for  the  permanent  first  molar.  The 
permanent  second  molar  is  budded  off  from  the  first  jiermanent  molar 
and  the  wisdom  from  the  permanent  second  molar. 

The  development  of  the  temporary  teeth  is  said  to  commence  about 
the  sixth  week  of  intra-uterine  life,  after  the  laying  down  of  the  bony 
structure  of  the  jaws.  Their  permanent  successors  begin  to  form  about 
the  sixteenth  week  of  intra-uterine  life. 

The  second  permanent  molars  are  believed  to  originate  about  the 
third  month  after  birth,  and  the  wisdom  teeth  about  the  third  year. 


THE    STRUCTURE    OF   THE    ELEMENTARY   TISSUES. 


79 


III.  Muscular  Tissue. 

There  are  two  chief  kinds  of  muscular  tissue,  differing  both  in  mi- 
nute structure  as  well  as  in  mode  of  action,  viz.,  (1.)  the  jAain  or  non- 
striated,  and  (2.)  the  striated. 

Unstriped  or  Plain  Muscle. 

Distribution. — Unstriped  muscle  forms  the  proper  muscular  coats 
(1.)  of  the  digestive  canal  from  the  middle  of  the  oesophagus  to  the  in- 
ternal sphincter  ani;  (2.)  of  the  ureters  and  urinary  bladder;  (3.)  of  the 
trachea  and  bronchi;  (4.)  of  the  ducts  of  glands;  (5.)  of  the  gall-blad- 
der; (6.)  of  the  vesiculffi  seminales;  (T.)  of  the  pregnant  uterus;  (8.)  of 
blood-vessels  and  lymphatics;  (9.)  of  the  iris,  and  some  other  parts  of 


Fig.  81.— A,  Unstriped  muscle  cells  from  the  mesentery  of  a  newt.  The  sheath  exhibits  trans- 
verse markings,  x  180.  B.  From  a  similar  preparation,  showing  that  each  muscle  cell  consists  of 
a  central  bundle  of  fibrils,  F  (contractile  part),  connected  with  the  intra-nuclear  network,  N,  and  a 
sheath  with  annular  thickenings,  St.  The  cells  show  varicosities  due  to  local  contraction,  and  on 
these  the  annular  thickenings  a,re  most  marked.     X  450.     (Klein  and  Noble  Smith.) 

the  eye.  This  form  of  tissue  also  enters  largely  into  the  composition 
(10.)  of  the  tunica  dartos^lhe  contraction  of  which  is  the  principal  cause 
of  the  wrinkling  and  contraction  of  the  scrotum  on  exposure  to  cold. 
Unstriped  muscular  tissue  occurs  largely  also  in  the  true  skin  generally, 
being  especially  abundant  in  the  interspaces  between  the  bases  of  the 
papillae.  Hence  when  it  contracts  under  the  influence  of  cold,  fear, 
electricity,  or  any  other  stimulus,  the  papillae  are  made  unusually  prom- 
inent, and  give  rise  to  the  peculiar  roughness  of  the  skin  termed  cutis 
anserina,  or  goose  skin.  It  occurs  also  in  the  superficial  portion  of  the 
cutis,  in  all  parts  where  hairs  occur,  in  the  form  of  flattened  roundish 
bundles,  which  lie  alongside  the  hair-follicles  and  sebaceous  glands. 
They  pass  obliquely  from  without  inward,  embrace  the  sebaceous  glands, 
and  are  attached  to  the  hair-follicles  near  their  base. 

Structure. — Uustriated  muscles  are  made  up  of  elongated,  spindle- 
shaped,  nucleated  cells  (fig.  81),  which  in  their  perfect  form  are  flat, 
from  about  j-^Vo  to  -gVorr  of  ^^i  inch  broad  (7  to  8/^),  and  -^  to  3-^  of  an 
inch  (jJ^  to  -^mm)  in  length — very  clear,  granular,  and  brittle,  so  that 


80 


HANDBOOK    OF    PHYSIOLOGY. 


when  they  break  they  often  have  abruptly  rounded  or  square  extremities. 
Each  cell  of  these  consists  of  a  fine  sheath,  probably  elastic;  of  a  central 
bundle  of  fibrils  representing  the  contractile  substance;  and  of  an  ob- 
long nucleus,  which  includes  within  a  membrane  a  fine  network  anasto- 
mosing at  the  poles  of  the  nucleus  with  the  contractile  fibrils.  The 
ends  of  fibres  are  usually  single,  sometimes  divided.  Between  the  fibres 
is  an  albuminous  cementing  material  or  endomysiwn  in  which  are  found 


Fig.  82.— Plexus  of  bundles  of  unstriped  muscle  cells  from  the  pulmonary  pleura  of  the  Guiuea-pig. 
X  IHO.    (Klein  and  Noble  Smith.)    A,  Branching  fibres;  B,  their  long  central  nuclei. 

connective-tissue  corpuscles,  and  a  few  fibres.  The  i)ervmy8ium  is  con- 
tinuous with  the  endomysium  in  the  fibrous  connective  tissue  surround- 
ing and  separating  the  bundles  of  muscle  cells. 


Striated  Muscle. 

Distribution. — Striated  or  striped  muscle  is  found  in  the  following 
situations.  It  constitutes  the  whole  of  the  muscular  apparatus  of  the 
skeleton,  of  the  walls  of  the  abdomen,  etc.,  the  whole  of  those  muscles 
which  are  under  the  control  of  the  will  and  hence  termed  voluntary,  as 
well  as  certain  other  muscles,  e.g.,  of  the  internal  ear  and  pharynx  not 
directly  under  the  control  of  the  will,  and  the  heart. 

Structure. — For  the  sake  of  description,  striated  muscular  tissue  may 
be  divided  into  two  classes,  (a.)  skeletal,  which  comprises  the  whole  of 
the  striated  muscles  of  the  body  except  (b.)  the  heart : — 

(a.)  Skeletal  Muscle. — In  the  majority  of  cases  a  skeletal  muscle 
is  inclosed  in  a  sheath  of  areolar  tissue  called  the  epimysium,  which  in 
some  cases  is  a  very  thick  and  distinct  investment,  while  in  other  cases 
it  is  much  thinner.  The  sheath  sends  in  partitions  which  serve  to  sup- 
port the  fasciculi  or  bundles  of  fibres,  of  which  the  muscle  is  made  up, 
forming  more  or  less  distinct  sheaths  for  them,  called  perimysium.     The 


THE    STRUCTURE    OF    THE    ELEMENTARY    TISSUES. 


81 


fibres  themselves  are  supported  in  their  fasciculus  b}-  a  scanty  amount 
of  areolar  tissue  containing  plasma  cells  and  termed  endomysiimu 
Within  the  areolar  tissue  supporting  the  fasciculi  and  between  the  fibres 
are  contained  the  blood-vessels  and  nerves  of  the  tissue. 

The  muscular  fibres  of  each  fasciculus  are  parallel  to  one  another, 
and  generally  speaking  so  are  the  fasciculi  themselves,  except  that  toward 

their  terminations  they  may  converge  to 
their  insertion  into  the  tendon  of  the 
muscle.  The  fasciculi  extend  throughout 
the  whole  length  of  the  muscle,  but  they 
vary  in  size  and  in  the  number  of  their  con- 


Fig.  83. 


Fig.  84. 


Fig.  83.— Transverse  section  through  muscular  fibres  of  human  tongue.  The  muscle-corpuscles 
are  indicated  by  their  deeply-stained  nuclei  situated  at  the  inside  of  the  sarcolemma.  Each  muscle- 
fibre  shows  "Cohnheim's  flelds,"  that  is,  the  sarcous  elements  in  transverse  section  separated  by 
clear  (apparently  linear)  interstitial  substance.     X  450.     (Klein  and  Noble  Smith.) 

Fig.  84.— Muscular  fibre  torn  across;  the  sarcolemma  still  connecting  the  two  parts  of  the  fibre. 
(Todd  and  Bowman.) 

tained  fibres,  both  in  different  muscles  and  also  in  the  same  muscle,  some 
muscles  having  coarse,  others  fine  fasciculi.  In  some  cases  it  would  seem 
that  the  perimysium  is  altogether  independent  of  the  external  sheath 
of  the  muscle.  As  to  the  fibres  of  which  the  bundles  are  made  up,  they 
have  a  distinct  elastic  sheath,  the  sarcolemma;  their  size  varies  consid- 
erably, their  cross-section  being  from  lOO.a  to  10/./,  and  as  regards  their 


Fig.  85.— Part  of  a  striped  muscle-fibre  of  a  water  beetle  prepared  with  absolute  alcohol.  A, 
barcolemma:  B,  Krause  s  memorane.  The  sarcolemma  shows  regular  bulgings.  Above  and  below 
Krause  s  membrane  are  seen  the  transparent  "lateral  discs."  The  chief  mass  of  a  muscular  com- 
partment is  occupied  by  the  contractile  disc  composed  of  sarcous  elements.  The  substance  of  the 
individual  sarcous  elements  has  collected  more  at  the  extremity  than  in  the  centre  ■  hence  this 
latter  is  more  trau.spareut  The  optical  effect  of  this  is  that  the  contractile  disc  appears  to  possess 
a  median  disc  (Disc  of  Hensen).  Several  nuclei  of  mu^^cle  corpuscles.  C  and  D,  are  shown,  and 
in  them  a  minute  network,     x  300.     (Klein  and  Noble  Smitli.; 


shape,  it  is  cylindrical  or  is  triangular,  quadrilateral,  or  pentangular  with 
rounded  angles.     In  length  the  fibres  seldom  exceed  an  inch  and  a  half 
6 


82 


IIANDLOOi:    OF    PHYSIOLOGY. 


(3.75  cm).  It  is  thus  evident  that  tlie  same  fibre  does  not  extend  from 
one  end  of  a  muscle  to  the  other,  and  indeed  it  is  known  that  in  a  fas- 
ciculus fibrils  are  joined  together  by  rounded  or  angular  extremities  in- 
vested with  their  proper  sheath  the  sarcolemma. 

Each  muscular  fibre  then  is  thus  constructed : — Externally  is  a  fine, 
transparent,  structureless  membrane,  the  sarcolemma,  which  in  the  form 
of  a  tubular  investing  sheath  forms  the  outer  wall  of  the  fibre  and  which 
contains  the  contractile  material  of  which  the  fibre  is  chiefly  made  up. 
Sometimes,  from  its  comparative  toughness,  the  sarcolemma  will  remain 
untorn,  when  by  extension  the  contained  part  can  be  broken  (fig.  84), 
and  its  presence  is  in  this  way  best  demonstrated.  The  fibres  are  of  a 
pale  yellow  color,  and  apparently  marked  by  fine  striae  which  pass  trans- 
versely round  them,  in  slightly  curved  or  wholly  parallel  lines.     The 


A 


Fig.  86.— A.  Portion  of  a  medium -sized  human  muscular  fibre.  X  800.  B.  Separated  bundles  of 
fibrils  equally  magnified;  a,  a,  larger,  and  6,  b,  smaller  collections;  c,  .still  smaller;  d,  d,  the  smallest 
whicli  could  be  detached,  possibly  representing  a  single  series  of  sarcous  element.    cShaipey.) 


sarcolemma  is  a  transparent  structureless  elastic  sheath  of  great  resist- 
ance which  surrounds  each  fibre  (fig.  84).  There  is  still  some  doubt  re- 
ffarding  the  nature  of  the  fibrils. 

A  striated  muscle  fibre,  when  examined  with  a  sufficiently  high 
power  of  the  microscope,  presents  the  following  appearances,  longitu- 
dinally :— 

(a.)  Alternate  darh  and  light  parallel  transverse  stripes,  to  which 
this  variety  of  muscle  owes  its  name,  the  depth  of  the  stripes  not 
always  being  the  same. 

(b.)  With  still  higher  powers  of  the  microscope,  the  bright  stripes 


THE    STRUCTURE    OF   THE    ELEMENTARY    TISSUES. 


83 


may  be  seen  to  be  divided  in  the  middle  line  by  other  very  fine  trans- 
verse dark  lines,  sometimes  called  Dohie's  line. 

(c.)  Each  dark  stripe  may  also  sometimes  be  seen  to  be  divided  by  a 
clear  line,  called  Henson's  disc. 

(d.)  Each  fibre  presents  an  appearance  of  longitudinal  striation  and 
after  hardening  in  alcohol  may  be  divided  by  teasing  with  needles  into 
longitudinal  fibrils,  more  or  less  cylindrical  or  angular,  which  are  named 
muscle  columns  or  sarcostyles,  and  extend  throughout  each  fibre.  Each 
of  these  appears  to  consist  of  short  columns  connected  together  by 
bright  intervals,  the  former  are  the  sarcous  elements  of  Bowman.  They 
may  possibly  be  further  longitudinally  striated^  and  so  made  up  of  finer 
fibrillar  still. 

After  treatment  with  reagents  the  fibre  may  be  split  up  into  trans- 
verse discs. 

(e.)  On  Transverse  Section. — The  fibre  presents  most  externally, 
the  outline  of  the  sarcolemma. 

(f.)  The  muscular  substance  proper  appears  to  be  mapped  out  into 


Fig.  87.— Three  muscular  fibres  running  longitudinally,  and  two  bundles  of  fibres  in  transverse  sec- 
tion, M,  from  the  tongue.    The  capillaries,  C,  are  injected,     x  150.    (Klein  and  Noble  Smith.) 


small  polygonal  areas  by  clear  lines  (fig.  83)  called  CoJinlieim's  fields,  the 
lines  giving  the  appearance  of  a  mesh  work.  The  lines  represent  the 
transverse  section  of  the  cementing  material  between  the  sarcostyles, 
which  is  called  sarcoj)lasm. 

(g.)  Immediately  within  the  sarcolemma  in  ordinary  muscle  or  in 
the  centre  of  the  fibre  as  in  the  muscle  of  some  insects,  are  seen  clear 
oval  nuclei  called  muscle  nuclei  or  muscle  corpuscle,  surrounding  which 
is  a  certain  amount  of  granular  protoplasm  (fig.  85). 

The  appearances  of  the  muscle  fibre  when  seen  under  the  micro- 
scope, cannot  be  said  to  be  yet  thoroughly  understood,  and  have  given 
rise  to  various  theories  as  to  the  structure  of  striped  muscle,  to  several 
of  which  it  will  be  as  well  to  allude. 

Muscle  Caskets  (Krause)  Theory. — According  to  this  view  a 
muscle  fibre  is  made  up  of  transverse  compartments,  bounded  laterally 
by  the  sarcolemma,  and  above  and  below  by  a  fine  membrane,  called 


84 


HAIfDBOOK    OF    PHYSIOLOGY. 


Krause's  membrane,  whicli  passes  from  side  to  side  from  the  sarcolemma 
across  the  light  stripe.  This  membrane  corresponds  to  Dobie's  line. 
The  transverse  compartments  are  divided  longitudinally  into  smaller 
ones  by  lines  which  correspond  with  the  boundaries  of  Cohnheim's  areas, 
and  each  such  compartment  is  termed  a  muscle  casket.  Within  the 
middle  part  of  the  casket  is  a  muscle  prism  made  up  of  darker  rods  of 
contractile  material  called  muscle  rods,  and  above  and  below  the  muscle 
prism  is  a  more  fluid  substance.  When  the  muscle  contracts,  the  fluid 
substance  is  pressed  more  between  the  muscle  rods,  causing  them  to  be 
further  away  from  one  another. 

Muscle  Reticulum  Theory, — According  to  the  views  of  certain 
observers  (Ketzius,  Melland,  Marshall,  van  Gehuchten,  and  Carnoy),  the 


Fig.  88 


Fisr.  88a. 


Fig.  88.— Transverse  section  of  one  of  the  truuk  muscles  of  the  Hippocampus,  stained  in  chloiide 
of  gold.    (Rollett.) 

Fig.  88a. — Portion  of  muscle-fibre  of  Dytiscus,  showing  network  very  plainly.  One  of  the  trans- 
verse networks  is  split  off,  and  some  of  the  longitudinal  bars  are  shown  broken  off.    (After  Melland.) 

part  of  fresh  muscle  which  is  stained  in  chloride  of  gold,  is  a  meshwork 
of  fibrils  which  corresponds  to  the  intracellular  meshwork  of  ordinary 
protoplasmic  cells,  i.e.,  the  spongioplasm,  and  is  the  part  which  is  the 
contractile  element  in  muscle.  The  meshwork  on  one  level  is  connected 
with  the  meshwork  on  another  level  by  means  of  longitudinal  fibres,  at 
the  junction  of  which  the  meshes  appear  more  or  less  knotted  (tigs.  88 
and  88a).  The  longitudinal  fibres  of  the  network  are,  according  to  this 
theory,  the  chief  agents  in  the  active  contraction.  The  transverse  mesh- 
work is  more  passively  elastic,  and  may  be  the  cause  of  the  speedy  relax- 
ation of  muscle  after  contraction  has  ceased.  The  material  filling  up 
the  meshwork  is  a  more  fluid  and  non-contractile  material. 

Eollett  has  minutely  criticised  the  idea  of  the  gold-staining  sub- 
stance of  the  fibre  being  the  contractile  portion.     His  views  are  the 


THE    STRUCTURE    OF   THE    ELEMENTARY   TISSUES. 


85 


follon'ing: — That  the  muscle-fibre  consists  of  longitudinal  fibrillse 
grouped  together  into  muscle  columns,  which  are  seen  in  the  transverse 
section  as  Cohnheim's  fields,  and  that  the  intercolumnar  material  is 
semi-fluid  sorcoplasm.  A  muscle  column  consists  of  segments  alter- 
nately thin  and  thick,  while  in  the  centre  of  the  thin  portion  is  a  dark 
enlargement  forming  a  dot,  these  dots  in  Cohnheim's  arrangement  cor- 
respond to  Krause's  membrane. 

In  fresh  muscle,  at  low  focus,  according  to  this  view,  the  muscle- 
columns  appear  dark  and  the  sarcoplasma  appears  light,  the  former  are 
in  a  line  with  the  granules.  At  high  focus,  the  reverse  is  the  case,  but 
the  dark  sarcoplasma  is  now  seen  in  line  with  two  rows  of  granules 
(fig.  89).  _ 

Also,  that  in  gold-stained  preparations,  the  dark  row  of  granules  are 
thicknesses  of  the  sarcoplasma  between  the  thin  segments  of  the  muscle 


ftfttttfftfft' 


n  I I  >  4 '  <'  '  I 

<  Mfff<''  "'"' '  '  " 

il  I  '  M  ■ .11'.-     I  M      ill 

(iM  I  I  .  I  I  M  .  I  .  I      ._,■..: 


tTTTTfHYT' 


Fig.  89. — Diagram  of  the  appearances  in  fresh  muscle-fibre.  A.  At  low  focus  (b)  the  muscle 
colunius  appear  dark  and  in  a  line  with  the  granules,  sarcoplasm  light.  At  high  focus  (a)  the  sarco- 
plasm  is  dark,  muscle  columns  light,  and  two  rows  of  granules  appear  in  a  line  with  the  sarcoplasm 
and  alternating  with  the  muscle  columns.    (Marshall,  after  Rollett.) 


columns,  whereas  the  two  rows  of  granules  do  not  correspond  with 
these,  but  alternate  with  them,  belonging  as  they  do  to  the  muscle 
columns,  and  not  to  the  sarcoplasm. 

Schiifer  has  thrown  considerable  light  ujion  the  controversy  by  hav- 
ing actually  observed  that  when  a  small  portion  of  the  living  wing- 
muscle  of  insects  is  teased  up  with  needles  in  a  small  drop  of  white  of 
egg,  the  sarcostyles  may  easily  be  separated  from  their  surrounding 
sarcoplasm,  and  may  be  actualUj  seen  to  contract,  whereas  the  sarcoplasm 
shows  no  such  property.  According  to  this  observer  such  a  sarcostyle 
may  be  examined  thus  isolated,  both  living  and  after  treatment  with 
various  reagents,  and  it  shows  alternate  bright  and  light  stripes,  the 
latter  being  bisected  by  a  line  which  corresponds  wtili  Krause's  mem- 
brane. Krause's  membrane  divides  the  sarcostyle  into  sarcomeres,  which 
contain  in  the  middle  the  strongly  refractive  disc-like  sarcous  element, 
and  above  and  below  it  hyaline  material,  which  is  bounded  by  Krause's 
membrane.  The  sarcous  substance  is  penetrated  by  canals,  which  ex- 
tend upward  and  downward  from  the  hyaline  substance  to  the  middle. 


86 


HAISTDBOOK    OF    PHYSIOLOGY. 


The  sarcous  substance  stains  with  hgematoxylin.  A  light  interval  may 
bisect  the  sarcous  substance  if  the  fibre  is  stretched,  which  corresponds 
with  Hensen's  disc. 

Appearances  under  Polarized  Light. — The  appearances  which 
muscle  presents  when  viewed  under  polarized  light  vary  according  as 
the  fibres  are  looked  at,  as  fresh  in  their  own  plasma,  or  as  hardened 
fibres  i^repared  and  mounted  in  Canada  balsam. 

The  whole  of  the  living  fibre  may  be  doubly  refracting,  the  isotro- 
pous  part  appearing  as  rows  of  dots  separating  transversely  the  princi- 
pal material  of  the  fibre.  Shortly,  according  to  Schafer,  it  may  be  said 
that  the  sarcoplasm  is  singly  refracting,  and  that  the  sarcostyle  is  in 
great  part  doubly  refracting.  In  a  fibre  which  is  extended,  after  it  has 
been  hardened  in  alcohol  and  mounted  in  Canada  balsam,  there  are 


n 
,,.„.iiiil 

hiiiiiiii) 
iiiiiiiiii 

IIIIIH 

llllllllllj 


WllUi) 


K 


H   - 


S.E. 


8.E. 


Fig.  90. 


Fig.  91. 


Fig.  90.— Sarcostyles  from  the  wing-muscles  of  a  wasp,  a,  a'.  Sarcostyles  stiowing  degrees  of 
retraction  (?  contraction),  b.  A  sarcostyle  extended  with  the  sarcous  elements  separated  into  two 
parts,    c.  Sarcostyles  moderately  extended  (semidiagrammatic).     cE.  A.  Schafer.) 

Fig.  91. — Diagram  of  a  sarcomere  in  a  moderately  extended  condition,  a,  and  in  a  contracted 
condition,  B.  k,  k,  Krause's  membranes;  h,  plane  of  Henson;  s.e.,  poriferous  sarcous  elea:er;t. 
(E.  A.  Schafer.) 


alternate  dark  and  light  bands,  the  former  corresponding  to  the  light 
intervals  as  seen  in  ordinary  light,  and  the  latter  to  the  various  elements. 
When  the  fibre  is  more  contracted  the  dark  line  becomes  narrower,  and 
the  anisotropous  intervals  broader,  but  there  is  no  interval  of  the  bands 
on  contraction.  It  appears  further  that  the  chromatic  portion  only  of 
the  sarcostyles  is  anisotroiDous,  and  the  sarcoplasm  and  the  remainder  of 
the  fibre  is  isotropous. 

{b.)  Heart  Muscle. — The  muscular  fibres  of  the  heart,  unlike  those 
of  most  of  the  involuntary  muscles,  are  striated;  but  although,  in  this 
respect,  they  resemble  the  skeletal  muscles,  they  have  distinguishing 
characteristics  of  their  own.  The  fibres  which  lie  side  by  side  are  united 
at  frequent  intervals  by  short  branches  (fig.  92).  The  fibres  are  smaller 
than  those  of  the  ordinary  striated  muscles,  and  their  striation  is  Ici-s 
marked.  No  sarcolemma  can  be  discerned.  The  muscle-corpuscles  r,re 
situate  in  the  middle  of  the  substance  of  the  fibre;  and  in  correspond- 


THE    STRUCTUEE    OF    THE    ELEMENTARY    TISSUES. 


87 


ence  with  these  the  fibres  appear  under  certain  conditions  subdivided 
into  oblong  portions  or  "cells/'  the  offsets  from  which  are  the  means  by 
which  the  fibres  branch  and  anastomose  one  with  another. 

It  should  be  noted,  however,  that  the  heart  muscular  fibres  are  not 
the  only  ones  which  branch,  since  the  fibres  of  the  tongue  of  the  frog, 
especially  where  they  are  attached  to  the  mucous  membrane,  present 
this  peculiarity;  branching  muscular  fibres  have  also  been  noted  in  the 
tongue,  and  in  the  facial  muscles  of  other  animals.  And  again,  in  the 
animals  in  which  two  kinds  of  skeletal  muscles  occur,  red  and  pale,  in 
the  red  muscles  the  fibres  are  much  less  distinctly  striated  transversely, 
whereas  their  longitudinal  striation  is  more  marked  than  in  the  pale 
variety.     They  are  also  finer  than  other  skeletal  muscles.     It  should  also 


m- 


m^?^- 


^Tr. 


Fig.  92.  Fig.  93.  • 

Fig.  92.— Muscular  fibre  cells  from  the  heart.     (E.  A.  Sehafer.) 

Fig.  93.— From  a  preparation  of  the  uerve-teriiiination  in  the  muscular  fibres  of  a  snake,    a, 
End  plate  seen  only  broad  surfaced,    b.  End  plate  seen  as  narrow  surface.     (Lingard  and  Klein.) 

be  added  that  in  these  red  muscles  the  sarcoplasm  is  much  developed, 
and  the  muscle  nuclei  are  very  numerous,  and  may  be  situated  in  the 
middle  of  the  fibre,  as  is  the  case  with  heart  muscle  fibres. 

Blood  and  Nerve  Supply. — Tlie  voluntary  muscles  are  freely  sup- 
plied with  blood-vessels;  the  capillaries  form  a  network  with  oblong 
meshes  around  the  fibres  on  the  outside  of  the  sarcolemma.  No  vessels 
penetrate  the  sarcolemma  to  enter  the  interior  of  the  fibre.  Xerves  also 
are  supplied  freely  to  muscles;  the  voluntary  muscles  receiving  them 
from  the  cerebro-spinal  system,  and  the  unstriped  muscles  from  the 
sympathetic  or  ganglionic  system. 

The  nerves  terminate  in  the  muscular  fibre  in  the  following  ways: — 
(1.)  In  unstriped  muscle,  the  nerves  first  of  all  form  a  plexus,  called 
the  ground  plexus  (Arnold),  corresponding  to  each  group  of  muscle 
bundles;  the  plexus  is  m.ade  by  the  anastomosis  of  the  i^rimitive  fibrils 
of  the  axis-cylinders.     From  the  ground  plexus,  branches  pass  oU,  and 


88  HAXDBOOK    OF    PHYSIOLOGY. 

again  anastomosing,  form  plexuses  which  correspond  to  each  muscle 
bundle — intennediari/ jjlexuscfs.  From  these  plexuses  branches  consist- 
ing of  primitive  fibrils  pass  in  between  the  individual  fibres  and  anas- 
tomose. These  fibrils  either  send  off  finer  branches,  or  terminate  them- 
selves in  the  nuclei  of  the  muscle  cells. 

(2.)  In  striped  muscle  the  nerves  end  in  motorial  end-plates,  having 
first  formed,  as  in  the  case  of  unstriped  fibres,  ground  and  intermediary- 


Fig.  94.— Two  striped  muscle-fibres  of  the  hyoglossus  of  frog,  a,  Nerve-end  plate;  5,  nerve- 
fibres  leaving  the  end-plate;  c,  nerve-fibres,  terminating  after  dividing  into  branches  d,  a  nucleus  in 
which  two  nerve-fibres  anastomose.    X  600.     (Arndt.) 

plexuses.  The  fibres  are,  however,  medullated,  and  when  a  branch  of 
the  intermediary  plexus  passes  to  enter  a  muscle-fibre,  its  primitive 
sheath  becomes  continuous  with  the  sarcolemma,  and  'the  axis-cylinder 
forms  a  network  of  its  fibrils  on  the  surface  of  the  fibre.  This  network 
lies  embedded  in  a  flattened  granular  mass  containing  nuclei  of  several 
kinds;  this  is  the  motorial  end-plate  (figs.  93  and  94).  In  batrachia, be- 
sides end-plates,  there  is  another  way  in  which  the  nerves  end  in  the  muscle 
fibres,  viz.,  by  rounded  extremities,  to  which  oblong  nuclei  are  attached. 


THE    STRUCTURE    OF   THE    ELEMENT ^RY    TISSUES.  89 

Development. — (1.)  Unstriped. — The  cells  of  unstriped  muscle 
are  derived  directly  from  embryonic  cells,  by  an  elongation  of  the  cell, 
and  its  nucleus;  the  latter  changing  from  a  vesicular  to  a  rod  shape. 

(3.)  Striped.— Formerly  it  was  supposed  that  striated  fibres  were 
formed  by  the  coalescence  of  several  cells,  but  recently  it  has  been 
proved,  that  each  fibre  is  formed  from  a  single  cell,  the  process  involv- 
ing an  enormous  increase  in  size,  a  multiplication  of  the  nucleus  by  fis- 
sion, and  a  differentiation  of  the  cell-contents.  This  view  differs  but 
little  from  another,  that  the  muscular  fibre  is  produced,  not  by  multi- 
plication of  cells,  but  by  arrangement  of  nuclei  in  a  growing  mass  of 
protoplasm  (answering  to  the  cell  in  the  theory  just  referred  to),  which 
becomes  gradually  differentiated  so  as  to  assume  tlie  characters  of  a 
fully  developed  muscular  fibre. 

Growth  of  Muscle. — The  growth  of  muscles  both  striated  and 
non-striated,  is  the  result  of  an  increase  both  in  the  iiumber  and  size 
of  the  individual  elements.  In  the  pregnant  uterus  the  fibre-cells  may 
become  enlarged  to  ten  times  their  original  length.  In  involution  of  the 
uterus  after  parturition  the  reverse  changes  occur,  accompanied  gener- 
ally by  some  fatty  infiltration  of  the  tissue  and  degeneration  of  the 
fibres. 

IV.  Nervous  Tissue. 

Nervous  tissue  is  found  under  the  microscope  to  consist  essentially 
of  two  main  elements,  namely,  of  nerve  fibres  and  nerve  cells. 

Nerve-Fibres. 

Varieties. — Nerve  fibres  are  of  two  chief  kinds,  medullated  or  white 
fibres,  and  non-mednUated  or  gray  fibres. 

Medullated  Fibres. — Each  medullated  nerve-fibre  is  made  up  of 
the  following  parts: — (1.)  An  external  sheath  called  the  primitive  nerve 
sheath,  or  nucleated  sheath  of  Schwann;  (2.)  An  intermediate  or  pack- 
ing substance  known  as  the  mednllari/  or  7m/eline  sheath,  or  white  sub- 
stance of  Schwann;  and  (3)  internally  the  axis-cylinder,  primitive 
band,  axis  band,  or  axial  fibre. 

Although  these  parts  can  be  made  out  in  nerves  examined  some 
time  after  death,  in  a  recent  specimen  the  contents  of  the  nerve-sheath 
appear  to  be  homogeneous.  But  by  degrees  they  undergo  changes  which 
show  them  to  be  composed  of  two  different  materials.  The  internal  or 
central  part,  occupying  the  axis  of  the  tube,  viz.,  the  axis-cylinder,  be- 
comes grayish,  while  the  outer,  or  cortical  portion  or  white  substance 
of  Schwann,  becomes  opaque  and  dimly  granular  or  grumous,  as  if  from 
a  kind  of  coagulation.  At  the  same  time  fhe  fine  outline  of  the  previ- 
ously transparent  cylindrical  tube  is  exchanged  for  a  dark  double  con- 


90 


HANDBOOK    OF    PHYSIOLOGY. 


tour  (fig.  95,  b),  the  outer  line  being  formed  by  the  sheath  of  the  fibre, 
the  inner  by  the  murgin  of  curdled  or  coagulated  medullary  substance. 
The  granular  material  shortly  collects  into  little  masses,  which  distend 
portions  of  the  tubular  membrane;  while  the  intermediate  spaces  col- 
laj)se,  giving  the  fibres  a  varicose,  or  beaded  iippearance  (fig.  95,  c  and 
d),  instead  of  the  previous  cylindrical  form.  The  whole  contents  of 
the  nerve-tubules  are  extremely  soft,  for  when  subjected  to  pressure 
they  readily  pass  from  one  j^'H't  of  the  tubular  sheath  to  another,  and 
often  cause  a  bulging  at  the  side  of  the  mem.brane.  They  also  readily 
escape,  on  pressure,  from  the  extremities  of  the  tubule,  in  the  form  of  a 
grumous  or  granular  material. 

The  external  nucleated  sheath  of  Schwann,  also  called  the  neu- 
rilenwia,  is  a  pellucid   membrane  forming  the  outer  investment  of  the 


Fig.  95. 


Fig.  96. 


Fig.  95.— Primitive  nerve.-flbres.  a.  A  perfecUy  fresh  tubule  with  a  single  dark  outline,  b.  A 
tubule  or  fibre  with  a  double  contour  from  commencing  post-mortem  change,  c.  The  changes 
further  advanced,  producing  a  varicose  or  beaded  appearance,  d.  A  tubule  or  fibre,  the  central 
part  of  which,  in  consequence  of  still  further  changes,  has  accumulated  in  separate  portions  within 
the  sheath  (Wagner). 

Fig.  96. — Two  nerve-fibres  of  sciatic  nerve,  a.  Node  of  Ranvier.  b.  Axis-cylinder,  c.  Sheath 
of  Schwann,  with  nuclei.     X  300.     (Klein  and  Noble  Smith.) 


nerve-fibre.  Within  this  delicate  structureless  membrane  nuclei  are 
seen  at  intervals,  surrounded  by  a  variable  amount  of  protoplasm.  The 
sheath  is  structureless,  like  the  sarcolemma,  and  the  nuclei  appear  to  be 
within  it :  together  with  the  protoplasm  which  surrounds  them  they  are 
the  relics  of  embryonic  cells,  and  from  their  resemblance  to  the  muscle 
corpuscles  of  striated  muscle  may  be  termed  nerve-corptiscles.  They  are 
easily  stained  with  logwood  and  other  dyes. 

The  medullary  or  myelin  sheath  or  white  substance  of  Schwann 
is  the  part  to  which  the  peculiar  opaque  white  aspect  of  medullated 
nerves  is  due.     The  thickness  of  this  layer  in  nerve-fibres  varies  consid- 


THE    STRUCTURE    OF   THE    ELEMENTARY    TISSUES. 


91 


erably,  at  oue  time  being  very  well  developed,  at  another  forming  but  a 
very  thin  investment  of  the  axis  cylinder.  It  is  a  semi-fluid,  fatty  sub- 
stance, and  in  the  fibre  possesses  a  double  contour.  It  is  said  to  be 
made  up  of  a  fine  reticulum  (Stilling,  Klein),  in  the  meshes  of  which  is 
embedded  the  bright  fatty  material.     It  stains  well  with  osmic  acid. 

According  to  McCarthy  this  sheath  is  composed  of  small  rods  radiat- 
ing from  the  axis-cylinder  to  the  external  sheath  of  SchAvann.  Some- 
times the  whole  space  is  occupied  by  them,  while  at  other  times  the 
rods  appear  shortened  and  compressed  laterally  into  bundles  embedded 
in  some  homogeneous  substance.  According  to  other  ob- 
servers the  sheath  is  made  up  of  segments  which  are 
either  cylindrical  or  funnel-shaped  {sections  of  Lanter- 
mann).  It  is  not  definitely  decided  that  these  divisions 
exist  naturallv  in  the  nerve-fibre.     In  nerves  hardened  in 


Fig.  yr.  Fig.  98. 

Fig.  97. — A  node  of  Ranvier  in  a  meduUated  nerve-fibre,  viewed  from  above.  The  medullary 
sheath  is  interrupted,  and  the  primitive  sheath  thickened.  Copied  from  Axel  Key  and  Retzius. 
X  750.    (.Klein  and  Noble  Smith.) 

Fig.  98. — Gray,  pale,  or  gelatinous  nerve-fibres.  A.  From  a  branch  of  the  olfactory  nerve  of  the 
sheep:  two  dark-bordered  or  white  fibres  from  the  fifth  pair  are  associated  with  the  pale  olfactory 
fibres.    B.  From  the  sympathetic  nerve,     x  450.     (Max  Schultze.) 

alcohol,  it  is  possible  to  demonstrate  a  very  chromatic  recticulum  in  the 
medullary  sheath,  which  is  supposed  to  be  of  a  horny  nature,  since  it 
offers  much  resistance  both  to  chemical  reagents  and  to  digestive  fluids 
{horuy  reiicuJum  or  neuro-kerafin  neticork). 

The  axis-cylinder  consists  of  a  large  number  of  ])vimitive  fibi-illcp. 
This  is  well  shown  in  the  cornea,  where  the  axis-cylinders  of  nerves 
break  up  into  minute  fibrils  which  form  terminal  networks,  and  also  in 
the  spinal  cord,  where  these  fibrillar  form  a  large  part  of  the  gray  matter. 
From  various  considerations,  such  as  its  invariable  presence  and  un- 
broken continuity  in  all  nerves,  though  the  primitive  sheath  or  the 
medullary  sheath  may  be  absent,  there  can  be  little  doubt  that  the  axis- 
cylinder  is  the  essential  part  of  the  fibre,  the  other  parts  having  the 
subsidiary  function  of  support  and  possibly  of  insulation. 


92 


HANDBOOK    OF    PHYSIOLOGY. 


Nodes  of  Ranvier. — At  regular  intervals  in  most  medullated  nerves 
the  nucleated  sheath  of  Schwann  possesses  annular  constrictions;  these 
are  called  nodes  of  Ranvier.  At  these  jjoints  (figs.  99,  101),  the  contin- 
uity of  the  medullary  white  substance  is  interrupted,  and  the  primitive 
sheath  comes  into  immediate  contact  with  the  axis-cylinder.  The  seg- 
ment of  the  fibre  between  two  nodes  is  termed  an  internode,  and  the 
length  of  the  interned es  varies  in  different  nerves;  their  average  is  said 
to  be  1  mm.  There  is  only  one  nerve  nucleus  to  each  internode.  At 
each  node  the  internodes  are  united  within  the  external  sheath  by  a 
band,  constricting  hand  of  Eanvier  (fig.  101),  and  this  stains  black  with 
silver  nitrate;  the  axis-cylinders  at  the  nodes  also  are  capable  of  being 


m.m.f.  .—- — -: 


.s.m.p. 


Fig.  99.— Transverse  section  of  the  ramus  visceralis  of  the  va^s  of  skate,    v.g.,  visceralis  ganglion ; 
m.m.f.,  median  medullated  fibres;  s.m.f.,  small  medullated  fibres.     (T.  W.  Shore.) 

stained  with  the  same  reagent,  and  so  a  node  of  Eanvier  when  stained 
with  silver  nitrate  is  marked  by  a  black  cross. 

Size. — The  size  of  the  nerve-fibres  varies  (fig.  99);  it  is  said  that 
the  same  fibres  may  not  preserve  the  same  diameter  through  their  whole 
length.  The  largest  fibres  are  found  within  the  trunks  and  branches  of 
the  spinal  nerves,  in  which  the  majority  measure  from  14.4/^  to  19//  in 
diameter.  In  the  so-called  visceral  nerves  of  the  brain  and  spinal  cord 
medullated  nerves  are  found,  the  diameter  of  which  varies  from  1.8/^.  to 
3.6,'j..  In  the  hypoglossal  nerve  they  are  intermediate  in  size,  and  gene- 
rally measure  7.2/j-  to  10.8,'j.. 

Non-medullated  Fibres. — The  fibres  of  the  second  kind  (fig.  98) 
which  are  also  called  fibres  of  Rernak,  constitute  the  principal  part  of 
the  trunk  and  branches  of  the  sympatlietic  nerves,  the  whole  of  the 


THE    STKUCTUEE    OF    THE    ELEMENTARY   TISSUES. 


93 


olfactory  nerve,  and  are  mingled  in  various  proportions  in  the  cerebro- 
spinal nerves.  They  differ  from  the  preceding  chiefly  in  their  fineness, 
being  only  about  ^  to  ^  as  large  in  their  course  within  the  trunks  and 


Fig.  100.— Transverse  section  of  the  sciatic  nerve  of  a  cat  about  x  100.— It  consists  of  bundles 
(FuniculO  of  nerve-fibres  ensheathed  in  a  fibrous  supporting-  capsule,  ephieuriuvi.  A;  eacii  bundle 
has  a  special  sheath  (not  sufficiently  marked  out  from  the  epineurium  in  tiie  figure) or  perhieurium 
B;  the  nerve-flbres  N  /  are  separated  from  one  another  by  endoneurium  ;  L,  lympn  spaces;  Ar, 
artery;  V,  vein;  F,  fat.    Somewhat  diagrammatic.     (V.  D.  Harris.) 

branches  of  the  nerves;  in  the  absence  of  the  double  contour;  in  their 
contents  being  apparently  uniform ;  and  in  their  having,  when  in  bun- 
dles, a  yellowish-gray  hue  instead  of  the  whiteness  of  the  cerebro-spinal 


Fig.  101.— Several  fibres  of  a  bundle  of  medullated  nerve-fibres  acted  upon  by  silver  nitrate  to 
show  pecuUar  Ijeliavior  of  nodes  of  Ranvier,  N,  toward  this  reagent.  The  silver  has  penetrated  at 
the  nodes,  and  has  stained  the  axis-cylinder,  M,  for  a  short  distance.  S,  the  white  substance. 
CKlein  and  Xoble  Smith.) 

nerves.  These  peculiarities  depend  on  their  not  possessing  the  outer 
layer  of  medullary  substance;  their  contents  being  composed  exclusively 
of  the  axis-cylinder.  Yet,  since  many  nerve-fibres  may  be  found  which 
appear  intermediate  in  character  between  these  two  kinds,  and  since  the 


94 


HANDBOOK    OF    PHYSIOLOGY. 


large  fibres,  as  they  approach  both  their  central  and  their  peripheral 
end,  lose  their  medullary  sheath  and  assume  many  of  the  other  charac- 
ters of  the  fine  fibres  of  the  sympathetic  system,  it  is  not  necessary  to 
suppose  that  there  is  any  material  difference  in  the  two  kinds  of  fibres. 
The  non-medullated  fibres  frequently  branch. 

It  is  worthy  of  note  that  in  the  foetus,  at  an  early  period  of  develop- 
ment, all  nerve-fibres  are  non-medullated. 

Nerve-trunks. — Each  nerve-trunk  is  composed  of  a  variable  num- 
ber of  difi'erent-sized  bundles  {fnnicidi)  of  nerve-fibres  which  have  a 
special  sheath  {perineurium).  The  funiculi  are  inclosed  in  a  firm  fibrous 
sheath  (epineuriuni);  this  sheath  also  sends  in  processes  of  connective 


Fig.  102.— Small  branch  of  a  muscular  nerve  of  the  frog,  near  its  termination,  showing  divisions 
of  the  fibres,     a,  into  two ;  6,  into  three.     X  350.    (Kolliker.) 


tissue  which  connect  the  bundles  together.  In  the  funiculi  between  the 
fibres  is  a  delicate  supporting  tissue  (the  endoneurium). 

There  are  numerous  lymph-spaces  both  beneath  the  connective  tissue 
investing  individual  nerve-fibres  and  also  beneath  that  which  surrounds 
the  funiculi. 

Every  nerve-fibre  in  its  course  proceeds  uninterruptedly  from  its 
origin  in  a  nerve-centre  to  near  its  destination,  whether  this  be  the 
periphery  of  the  body,  another  nervous  centre,  or  the  same  centre  whence 
it  issued. 

Bundles  of  fibres  run  together  in  the  nerve-trunk,  but  merely  lie  in 
apposition  to  each  other;  they  do  not  unite:  even  when  they  anas- 
tomose, there  is  no  union  of  fibres,  but  only  an  interchange  of  fibres 
between  the  anastomosing  funiculi.     Although  each  nerve-fibre  is  thus 


THE    STRUCTURE    OF   THE   ELEMENTARY   TISSUES. 


95 


single  and  undivided  through  nearly  its  whole  course,  yet  as  it  ap- 
proaches the  region  in  which  it  terminates,  individual  fibres  break  up 
into  several  subdivisions  before  their  final  ending. 

Plexuses. — At  certain  parts  of  their  course,  nerves  form  plexuses, 
in  which  they  anastomose  with  each  other,  as  in  the  case  of  the  brachial 
and  lumbar  plexuses.  The  objects  of  such  interchange  of  fibres  are: — 
(«),  to  give  to  each  nerve  passing  off  from  the  plexus,  a  wider  connection 
with  the  spinal  cord  than  it  would  have  if  it  proceeded  to  its  destina- 
tion without  such  communication  with  other  nerves.     Thus,  each  nerve 


Fig.  103. 


Fis.  104. 


Fig.  103.— Ganglion  nerve-corpuscles  of  different  shapes.    (Klein  and  Noble  Smith.) 

Fig.  104. — Different  forms  of  ganglion  cells.    A.  a.  round  ball-shaped  unipolar  cell  from  the 

human  Gasserian  ganglion.    A  X  "240.    a  X  80.    Two  cells  only  show  the  process/,-  b.  spindle-shaped; 

r,  multipolar  ganghou  cell  from  the  spinal  cord  of  the  ox.     x  80.    d.  D,  Purkinjee  ganglion  cells 

from  human  cerebellum  ;  ax,  axis-cyliuder  process  ;  p,  protoplasmic  process  ;  h,  h,  two  cells  sur- 

roimded  with  a  nucleated  sheath.    (Stohr.) 

by  the  wideness  of  its  connections  is  less  dependent  on  the  integrity  of 
any  single  portion,  whether  of  nerve-centre  or  of  nerve-trunk,  from 
which  it  may  spring,  {b)  Each  part  supplied  from  a  plexus  has  wider 
relations  with  the  nerve-centres,  and  more  extensive  sympathies;  and, 
by  means  of  the  same  arrangement,  groups  of  muscles  may  be  co-ordi- 
nated, every  member  of  the  group  receiving  motor  filaments  from  the 
same  parts  of  the  nerve-centre,  (c)  Any  given  part,  say  a  limb,  is  less 
dependent  upon  the  integrity  of  any  one  nerve. 

Nerve  Terminations. — As  medullated  nerve-fibres  approach  their 
terminations  they  lose  their  medullary  sheath  and  consist  then  merely 
of  axis-cylinder  and  j^rimitive  sheath.     They  then  lose  also  the  latter  and 


96  HANDBOOK    OF    PHYSIOLOGY. 

only  the  axis-cylinder  is  left  with  here  and  there  a  nerve-corpuscle  partly 
rolled  round  it.  Finally,  even  this  investment  ceases  and  the  axis- 
cylinder  breaks  up  into  its  elementary  fibrillae. 

Nerve-cells. 

Nerve-cells,  also  known  as  nerve-corpuscles,  comprise  the  second 
principal  element  of  nervous  tissue.  They  are  not  generally  present  in 
nerve-trunks,  but  are  found  in  collections  of  nervous  tissue  called  gavglia. 
They  vary  considerably  in  shape,  size,  and  structure  in  different  situations. 


Fig.  105.— An  isolated  sympathetic  ganglion  cell  of  man,  showing  sheath  with  nucleated-ceU 
lining,  B.  A.  Ganglion  cell,  with  nucleus  and  nucleolus.  C.  Branched  process.  D.  Unbranched 
process.     (Key  and  Retzius.)     x  750. 

Nerve-cells  are,  as  a  rule,  provided  with  very  large  round  nuclei  in 
which  one  or  more  nucleoli  are  very  marked.  The  protoplasm  of  the 
cells  is  granular,  but  may  be  striated  or  reticular.  They  often  contain 
deposits  of  yellowish-brown  pigment. 

a.  Some  nerve-cells  are  small,  generally  spherical  or  ovoid,  and  have 
a  regular  uninterrupted  outline.  These  single  nerve-cells  are  most  nu- 
merous in  the  sympathetic  ganglia;  each  is  inclosed  in  a  nucleated 
sheath,  h.  Others,  which  are  called  caudate  or  stellate  nerve-cells  (fig. 
103),  are  larger,  and  have  one,  two,  or  more  long  processes  issuing  from 
them,  the  cells  being  called  respectively  unipolar,  bipolar,  ov multipolar: 
which  processes  often  divide  and  subdivide,  and  appear  tubular  and 


THE    STRUCTURE   OF   THE   ELEMEXTARY    TISSUES.  97 

filled  with  the  same  kind  of  granular  material  that  is  contained  within 
the  cell.  Of  these  processes  some  appear  to  taper  to  a  point  and  ter- 
minate at  a  greater  or  less  distance  from  the  cell ;  some  appear  to  anas- 
tomose with  similar  offsets  from  other  cells;  while  generally  only  one 
process  from  each  cell  is  continuous  with  a  nerve-fibre,  the  prolongation 
from  the  cell  by  degrees  assuming  the  characters  of  the  nerve-fibre  with 
which  it  is  continuous.  This  is  known  as  the  axis-cylinder  process.  In 
bipolar-cells,  however,  one  pole  may  be  continuous  with  a  medullated 
fibre,  and  the  other  with  a  non-medullated  one,  or  both  poles  may  pass 
into  fibres  of  the  one  or  the  other  kind. 

Ganglion-cells  are  generally  inclosed  in  a  transparent  membranous 
capsule  similar  in  appearance  to  the  external  nucleated  sheath  of  nerve- 
fibres  :  within  this  capsule  is  a  layer  of  small  fiattened  cells. 

The  process  of  a  nerve-cell  which  becomes  continuous  Avith  a  nerve- 
fibre  is  always  unbranched  as  it  leaves  the  cell.  It  at  first  has  all  the 
characters  of  an  axis-cylinder,  but  soon  acquires  a  medullary  sheath, 
and  then  may  be  termed  a  nerve-fibre.  This  continuity  of  nerve-cells 
and  fibres  may  be  readily  traced  out  in  the  anterior  cornua  of  the  gray 
matter  of  the  spinal  cord.  In  many  large  branched  nerve-cells  a  distinctly 
fibrillated  appearance  is  observable;  the  fibrillar  are  probably  continuous 
with  those  of  the  axis-cylinder  of  a  nerve. 

Other  points  in  the  structure  of  nerve-cells  will  be  mentioned  under 
the  account  of  the  central  nervous  system. 

Nerve  Terminations. 

Nerve-fibres  terminate  perij^herally  in  many  parts  of  the  body  in  cer- 
tain special  end-organs  of  which  the  following  are  the  chief: 

Pacinian  Corpuscle. — The  Pacinian  bodies  or  corpuscles  (figs.  106 
and  107),  named  after  their  discoverer  Pacini,  also  called  corpuscles  of 
Vater,  are  little  elongated  oval  bodies,  situated  on  some  of  the  cerebro- 
spinal and  sympathetic  nerves,  especially  the  cutaneous  nerves  of  the 
hands  and  feet;  and  on  branches  of  the  large  sympathetic  plexus  nbout 
the  abdominal  aorta.  They  often  occur  also  on  the  nerves  of  the  mes- 
entery, and  are  especiall}^  well  seen  even  by  the  naked  eye  in  the  mesen- 
tery of  the  cat.  They  have  been  observed  also  in  the  pancreas,  lymphatic 
glands  and  thyroid  glands,  as  well  as  in  the  penis  of  the  cat.  Each  cor- 
puscle is  attached  by  a  narrow  pedicle  to  the  nerve  on  which  it  is  situ- 
ated, and  is  formed  of  several  concentric  layers  of  fine  membrane,  con- 
sisting of  a  hyaline  ground-membrane  with  connective  tissue  fibres,  each 
layer  being  lined  by  endothelii-im  (fig.  107);  through  its  pedicle  passes 
a  single  nerve-fibre,  which,  after  traversing  the  several  concentric  layers 
and  their  immediate  spaces,  enters  a  central  cavity  and,  gradually  losing 
its  dark  border  and  becoming  smaller,  terminates  at  or  near  the  distal 
7 


98 


HANDBOOK    OF    PHYSIOLOGY. 


end  of  the  cavity,  in  a  knob-like  enlargement  or  in  a  bifurcation.  The 
enlargement  commonly  found  at  the  end  of  the  fibre  is  said  by  Pacini 
to  resemble  a  ganglion  corpuscle;  but  this  observation  has  not  been  con- 
firmed. In  some  cases  two  nerves  have  been  seen  entering  one  Pacinian 
body,  and  in  others  a  nerve  after  jJfissing  unaltered  through  one  has 
been  observed  to  terminate  in  a  second  Pacinian  corpuscle.  The  physi- 
ological import  of  these  bodies  is  still 
obscure. 

The  corpuscles  of  Herbst  (fig. 
109)  are  closely  allied  to  Pacinian  cor- 
puscles, except  that  they  are  smaller 
and  longer  with  a  row  of  nuclei  around 
the  central  termination  of   the   nerve 


Fig.  106. 


Fig.  107 


Fig.  106. — Extremities  of  a  nerve  of  the  finger  with  Pacinian  corpuscles  attached,  about  the 
natural  size  ("adapted  from  Henle  and  Kolliker). 

Fig.  107. — Pacinian  corpuscle  of  the  cat's  mesentery.  The  stalk  consists  of  a  nerve-fibre  (N) 
vfith  its  thick  outer  slieath.  The  peripheral  capsules  of  the  Pacinian  coi-puscle  are  continuous  with 
tiie  outer  sheath  of  the  stalk.  The  intermediary  part  becomes  much  narrower  near  the  entrance  of 
the  axis-cylinder  into  the  clear  central  mass.  A  nook-shaped  termination  witli  the  end-bulb  (T)  is 
seen  in  the  upper  part.  A  blood-vessel  (V)  enters  the  Pacinian  corpuscle,  and  apjiroaches  the  end- 
bulb  ;  it  pos.sesses  a  sheath  which  is  the  continuation  of  the  peripheral  capsules  of  the  Pacinian 
corpuscle.    X  100.    (Klein  and  Noble  Smith.) 

in  the  core.  They  have  been  found  chiefly  in  the  tongues  of  ducks. 
The  capsules  are  nearer  together,  and  toward  the  centre  the  endo- 
thelial sheath  appears  to  be  absent. 

End-bulbs  are  found  in  the  conjunctiva,  in  the  glans  penis  and 
clitoris,  in  the  skin,  in  the  lips,  and  in  tendon ;  each  is  about  g^  inch  in 
diameter,  oval  or  spheroidal,  and  is  composed  of  a  medullated  nerve- 
fibre,  which  terminates  in  corpuscles  of  various  shapes,  with  a  capsule 


THE    STRUCTURE    OF   THE   ELEMENTARY   TISSUES. 


99 


containing  a  transparent  or  striated  mass  in  the  centre  of  which  ter- 
minates the  axis-cjliuder  of  the  nerve-fibre,  the  ending  of  which  is  some- 
what chihbed  (fig.  110). 

Touch-corpuscles  (fig.  Ill),  are  found  in  the  papilla  of  the  skin 


Fig.  108.— Summit  of  a  Pacinian  corpuscle  of  the  human  finger,  shoeing  the  endothelial  membranes 
hning  the  capsules,     x  220.     (Klein  and  Noble  Smith.) 

of  the  fingers  and  toes,  or  among  its  epithelium;  they  may  be  simple  or 
compound;  when  simple,  they  are  large  and  slightly  flattened  transpar- 
ent nucleated  ganglion  cells,  inclosed  in  a  capsule;  when  compound  the 


Fig.  110. 

Fig.  109. —A  corpuscle  of  Herbst,  from  the  tongue  of  a  duck,    a,  Medullated  nerve  cut  away. 
<Klein.) 

Fig.  110. — End-bulb  of  Krause.    a,  Medullated  nen'e  fibre.    6,  Capsule  of  corpuscle. 


capsule  contains  several  small  cells.  They  are  small  oblong  masses, 
about  -jI  0"  inch  long,  and  3  J^  inch  broad.  Some  regard  touch-cori3uscles 
as  little  else  than  masses  of  fibrous  or  connective  tissue,  surrounded  by 
elastic  fibres  and  formed,  according  to  Huxley,  by  an  increased  develo]!- 


100 


HANDBOOK    OF   PHYSIOLOGY. 


ment  of  the  primitive  sheaths  of  the  nerve-fibres  entering  the  papillas. 
Others,  however,  believe  that,  instead  of  thus  consisting  of  a  homogeneous 
mass  of  connective  tissue,  they  are  special  and  peculiar  bodies  of  lami- 


Fig.  111.— Papillae  from  the  skin  of  the  hand,  freed  from  the  cuticle  and  exhibiting  tactile  cor- 
puscles. A.  Simple  papilla  with  four  nerve-fibres :  a,  tactile  corpuscles  ;  b.  nerves  with  winding 
fibres  c  and  e.  b.  Papilla  treated  with  acetic  acid :  a,  cortical  layer  with  cells  and  fine  elastic  fila- 
ments; b,  tactile  corpuscle  with  transverse  nuclei:  c.  entering  nerve  wuth  neurilemma  or  perineu- 
rium ;  d  and  e,  nerve-fibres  winding  round  the  corpuscle,    x  350.    (KolUker.; 

nated  structure  directly  concerned  in  the  sense  of  touch.  They  do  not 
occur  in  all  the  papillse  of  the  parts  where  they  are  found,  and,  as  a  rule, 
in  the  papillae  in  which  they  are  present  there  are  no  blood-vessels.  Since 
these  bodies  in  which  the  nerve-fibres  end  are  only  met  with  in  the 
papillae  of  highly  sensitive  parts,  it  is  inferred  that  they  are  specially 


Fig.  112. 


Fig.  11.3. 


Fig.  112.— A  corpuscle  of  Grandry,  from  the  tongue  of  a  duck. 

Fig.  113. — A  touch-corpuscle  of  Meissner,  from  tlie  skin  of  the  human  hand. 


concerned  in  the  sense  of  touch,  yet  their  absence  from  the  papillse  of 
other  tactile  parts  shows  that  they  are  not  essential  to  this  sense. 

The  peculiar  way  in  which  the  medullated  nerve  winds  round  and 
round  the  corpuscle  before  it  enters  it  is  shown  in  fig.  111. 

It  loses  its  sheath  before  it  enters  into  the  interior,  and  then  its  axis- 
cylinder  branches  and  the  branches  coil  round  the  corpuscle  (fig.  Ill), 


THE   STRUCTURE   OF   THE    ELEMENTARY   TISSUES. 


101 


anastomosing  with  one  another  and  ending  in  pear-shaped  enlarge- 
ments. 

The  corpuscles  of  Grandy  (fig.  112)  form  another  variety,  and  have 
been  noticed  in  the  beaks  and  tongnes  of  birds.  They  consist  of  cor- 
puscles oval  or  spherical,  contained  within  a  delicate  nucleated  sheath, 
and  containing  several  cells,  two  or  more  compressed  vertically.  The 
cells  are  granular  and  transparent,  with  a  nucleus.  The  nerve  enters  on 
one  side  and,  laying  aside  its  medullary  sheath,  terminates  in  or  between 
the  cells. 

Nerve  terminations,  probably  sensory  in  function,  are  found  in  inter- 
muscular tissue  (figs.  114,  115),  and  also  in  tendon.     The  former  are 


r:^ 


Fig.  114. 


Fig.  115. 


Fig.  116. 


Fig.  114. — Termination  of  meduUated  nerve-flbres  in  tendon  near  the  muscular  insertion.   (Golgi.) 
Fig.  115.— One  of  the  reticulated  end-plates  of  fig.  114,  more  highly  magnified,     a,  Jledullated 

nerve-fibre  ;  6,  reticulated  end-plates.    (Golgi.) 

Fig.  116. — A  termination  of  a  meduUated  nerve-fibre  in  tendon,  lower  half  with  convoluted 

medullated  nerve-fibre.     (Golgi.) 


reticulated  end-plates,  and  the  latter  are  something  like  small  Pacinian 
corpuscles  (fig.  116). 

In  addition  to  the  special  end  organs,  sensory  fibres  may  terminate 
in  plexuses,  as  in  the  sub-epithelial  and  the  intra-epithelial  plexus  of 
the  cornea. 

The  terminations  of  the  nerves  of  special  sense  will  be  considered  in 
the  Chapter  on  the  Special  Senses. 

The  terminations  of  nerves  in  muscle,  both  striped  and  nnstriped, 
have  been  already  described. 

The  ending  of  nerves  in  the  cells  of  the  salivary  glands  which  has 
been  described  by  Pfliiger  will  be  noticed  further  on. 


CHAPTER  IT. 

THE    CHEMICAL   COMPOSITION    OP  THE  BODY. 

Of  the  known  chemical  elements  of  which  about  sixty-seven  have 
been  isolated  no  less  than  seventeen  combine,  in  larger  or  smaller  quan- 
tities, to  form  the  chemical  basis  of  the  animal  body. 

The  substances  which  contribute  the  largest  share  are  the  non-me- 
tallic elements,  Oxygen,  Carbon,  Hydrogen,  and  Nitrogen — oxygen  and 
carbon  making  up  altogether  about  85  per  cent  of  the  whole.  The  most 
abundant  of  the  metallic  elements  are  (7aZciM'///,  >S'o6?mm,  and  Po^«ss^ww^.* 

Few  of  the  elements,  however,  appear  free  or  uncombined  in  the  an- 
imal body.  They  are  generally  united  together  in  variable  proportions 
to  form  compounds.  The  only  elements  which  have  been  found  free 
in  the  body  are  oxygen,  nitrogen,  and  hydrogen,  the  first  two  in  the 
blood,  and  hydrogen  as  well  as  oxygen  and  nitrogen  in  the  intestinal  canal. 

It  was  formerly  thought  that  the  more  complex  compounds  built  up 
by  the  animal  or  vegetable  or^rn?/.y?;z  were  peculiar  and  could  not  be  made 
artificially  by  chemists,  and  under  this  idea  they  were  formed  into  a  dis- 
tinct class,  termed  organic.  This  idea  has  long  been  given  up,  but  the 
name  is  still  in  use  with  a  different  signification.  The  term  is  now 
applied  simply  to  the  compounds  of  the  element  carbon,  irrespective  of 
their  origin. 

A  large  number  of  the  animal  organic  compounds,  particularly  those 
of  the  albuminous  group,  are  characterized  by  their  complexity.  Many 
elements  enter  into  their  composition,  thereby  distinguishing  them  from 
simple  inorganic  compounds.  Many  atoms  of  the  same  element  occur 
in  each  molecule.  This  latter  fact  no  doubt  explains  the  reason  of  their 
instability.  Another  great  canse  of  the  instability  is  the  frequent  pres- 
ence of  nitrogen,  which  may  be  called  negative  or  undecided  in  its  affin- 
ities and  may  be  easily  separated  from  combination  with  other  elements. 

*  The  following  table  represents  the  relative  proportion   of   the  various  ele- 
ments. —  (Marshall. ) 

Oxygen  . 

Carhon 

Hydrogen 

Nitrogen 

Calcium 

Phosphorus 

Sulphur  . 

Sodium 

Chlorine 

102 


.     72.0 

Fluorine          .... 

.08 

.    .     13.5 

Potassium  .        .        ... 

.026 

.       9.1 

Iron         ..... 

.01 

.    .       2.5 

Magnesium          .         .         .    . 

.0012 

.       1.3 

Silicon 

.0002 

.    .       1.15 

(Traces  of   copper,  lead,  and 

.  1476 
.    .         .1 

.085 

aluminium) 

100. 

THE    CHEMICAL    COMPOSITIOX    OF   THE    BODY.  103 

Animal  tissues,  containing  as  they  do  these  orgauic  nitrog  ous  com- 
pounds, are  extremely  prone  to  undergo  decomposition.  They  also  con- 
tain much  water,  a  circumstance  very  favorable  to  the  breaking  up  of 
such  substances.  It  is  due  to  this  tendency  to  decomiDosition  that  we 
meet  with  so  large  a  number  of  decomposition  products  among  the  chem- 
ical substances  forming  the  basis  of  the  animal  body. 

The  various  substances  found  in  the  animal  organism  may  be  conven- 
iently considered  according  to  the  following  classification:  1.  Orgauio 
— a.  Nitrogenous  and  b.  Xon-Nitrogenous.     2.  Inorganic. 

Organic  Substances. 

Nitrogenous  organic  bodies  take  the  chief  part  in  forming  the  solid 
tissues  of  the  body,  and  are  found  also  to  a  considerable  extent  in  the 
circulating  fluids  (blood,  lymph,  chyle),  the  secretions  and  excretions. 
They  often  contain  in  addition  to  carbon,  hydrogen,  nitrogen,  and  oxy- 
gen, the  elements  sulphur  and  phosphorus;  but  although  the  composition 
of  most  of  them  is  approximately  known,  no  general  rational  formula 
can  at  present  be  given. 

It  will  be  convenient  to  give  an  account  of  the  Proteids  and  Gelatins 
in  this  Chapter,  as  these  constitute  the  most  imi3ortant  classes  of  nitro- 
genous organic  substances.  The  other  members  are  Decomposition  prod- 
ucts, the  chief  of  which  is  Urea,  found  for  the  most  part  in  the  urine; 
Ferments;  Pigments;  and  other  bodies  and  will  be  more  appropriately 
treated  of  later  on. 

Proteids  are  also  called  Albuminous  substances.  They  are  the  chief 
of  the  nitrogenous  org  mic  compounds  and  exist  in  both  plants  and  ani- 
mals, one  or  more  of  them  entering  as  an  essential  part  into  the  forma- 
tion of  all  living  tissue.  In  the  lympli,  chyle,  and  blood,  they  exist 
abundantly.  Very  little  is  known  with  any  certainty  about  their  chem- 
ical composition.  Not  a  single  member  of  the  class  has  yet  been  syn- 
thesized. Their  formula  is  unknown,  the  chemists  who  have  attemjjtcd 
to  construct  it  differing  very  greatly  among  themselves.  In  fact  the 
very  term  proteid  is  an  extremely  arbitrary  one.  It  simply  means  a 
body  which,  according  to  Hoppe-Seyler,  contains  in  its  molecule  the 
elements  carbon,  hydrogen,  nitrogen,  oxygen,  and  sulphur,  in  certain 
arbitrary  but  varying  amounts,  thus — Carbon,  from  51.5  to  5-4.5;  Hy- 
drogen, from  6.9  to  7.3;  Nitrogen,  from  15.2  to  17.;  Oxygen,  from 
20.9  to  23.5;  Sulphur,  from  .3  to  2. 

Properties  of  Proteids. — Proteids  are  for  the  most  part  amorphous 
and  non-crystallizable.  Certain  of  the  vegetable  proteids  have,  it  is 
said,  been  crystallized,  and  according  to  Hofmeister,  Qg^  albumin  is  also 
capable  of  crystallization.  They  possess  as  a  rule  no  power  (or  scarcely 
any)  of  passing  through  animal  membranes.     They  are  soluble,  but  un- 


104  HANDBOOK    OF    PHYSIOLOGY. 

dergo  alteration  in  composition  in  strong  acids  and  alkalies;  some  are 
soluble  in  water,  others  in  neutral  saline  solutions,  some  in  dilute  acids 
and  alkalies,  few  in  alcohol  or  ether.  Their  solutions  exercise  a  left- 
handed  action  on  polarized  light. 

The  hojie  that  it  may  be  possible  in  the  immediate  future  to  synthe- 
size proteids  is  rendered  all  the  weaker  because  of  the  extraordinary 
variety  of  compounds  obtained  by  the  decomposition  of  proteids  by  va- 
rious chemical  methods,  the  compounds  differing  according  to  the 
method  employed.  In  the  body  it  seems  clear  that  living  proteid  is 
built  up  by  the  food  supplied  to  it,  which  necessarily  contains  proteid 
derived  either  from  a  vegetable  or  an  animal  source;  how  this  process 
takes  place  we  are  yet  unable  to  say.  In  the  course  of  later  chapters  in 
this  book  we  shall  endeavor  to  trace  the  steps  of  the  breaking  up  of  pro- 
teid in  the  body,  but  we  may  anticipate  by  mentioning  that  it  is  now 
generally  believed  that  the  ultimate  products  of  this  decomposition  are 
urea,  a  body  the  formula  of  which  is  CO  (NH2)2,  carbon  dioxide  and 
water,  Avhile  the  intermediate  substances  or  by  products  are  glycin 
(C-^HslSiOa),  leucine  (CbHis  NOo),  uric  acid,  and  possibly  carbohydrate 
bodies.  When  proteid  material  is  decomposed  by  putrefaction,  by  the 
action  of  chemical  reagents,  e.^^r.,  acids,  alkalies,  or  by  heat,  various  bodies 
are  produced,  of  which  amido-acids  (acids  in  which  one  or  more  of  the 
hydrogen  atoms  of  the  radicle  of  the  acid  are  replaced  by  amidogen, 
N  Ha)  and  bodies  belonging  to  the  aromatic  or  benzene  series  predom- 
inate. Hence  it  comes  that  various  theories  of  the  way  in  which  pro- 
teids are  built  up  have  arisen.  The  one  which  has  appeared  to  have 
received  the  greatest  support  is  that  of  Latham.  This  observer  has 
suggested  that  proteid  may  he  considered  as  made  up  of  a  series  of 
cyan-aJcoliols,  (bodies  obtained  by  the  union  of  any  aldehyde  with  hy- 
drocyanic acid)  with  a  benzene  nucleus.  Taking  ordinary  ethyl  alcohol, 
CH3,CH2,OH,  as  the  type,  the  aldehyde  of  which  is  CHs.CHO,  the  cor- 
responding cyanalcohol  would  be  CH3,CH,CiSr,0H. 

Proteids  give  certain  general  chemical  reactions.  They  are  a  little 
varied  in  the  case  of  each  particular  substance.  The  chief  of  these  are 
as  follows: 

i.  Xantho-Proteic  Reaction.— A  solution  of  any  proteid  boiled 
with  strong  nitric  acid  becomes  yellow,  and  the  cooled  solu- 
tion is  darkened  on  the  addition  of  ammonia.  In  some  cases 
there  is  first  of  all  a  white  coagulum  thrown  down  with  the 
acid;  this  speedily  becomes  yellow  on  boiling. 

ii.  Biuret  (Piotrowski's)  Reaction.— With  a  trace  of  copper 
sulphate  and  an  excess  of  potassium  or  sodium  hydrate  they 
give  a  piirple  (or  rose  red);  with  ammonia  instead  of  the 
fixed  alkalies,  a  blue  coloration. 


THE    CHEMICAL    COMPOSITIOIS'    OF   THE    BODY.  105 

iii.  Millon's  Reaction. — With  Millon's  reagent  (a  solution  of 
metallic  mercury  in  strong  nitric  acid),  they  give  a  white  or 
pinkish  clotted  precipitate,  becoming  more  pink  or  red  on 
boiling.  This  test  is  said  to  be  due  to  the  presence  of  tyro- 
sine, an  aromatic  compound  in  the  proteid  molecule. 

iv.  Ammonium  Sulphate  Reaction. — They  are,  with  the  ex- 
ception of  j^eptone,  entirely  j^i'ecipitated  from  their  solu- 
tions by  saturation  w'ith  ammonium  sulphate. 

Many  of  the  jiroteids  give,  in  addition,  the  following  tests: 

V.  AVith  excess  of  acetic  acid,  and  potassium  ferrocyanide,  a  white 

precipitate. 
tI.  With  excess  of  acetic  acid  and  a  saturated  solution  of  sodium 

sulphate,  on  boiling,  a  white  precipitate.     This  test  is  often 

used  to  get  rid  of  all  traces  of  proteids,  except  peptones, 

from  solutions, 
yii.  Boiled  with  strong  hydrochloric  acid,  they  give  a  violet  red 

coloration, 
viii.  With  cane  sugar  and  strong  sulphuric  acid,  on  heating,  they 

give  ?k  purplish  coloration. 
ix.  They  are  precipitated  on  addition  of — citric  or  acetic  acid, 

and  picric  acid;  or  citric  or  acetic  acid,  and  sodium  tung- 

state;  or  citric  or  acetic  acid,  and  potassio-mercuric  iodide; 

and  with  many  other  metallic  salts  in  solution  and  by  alcohol. 

Varieties. — Proteids  are  divided  into  classes,  chiefly  on  the  basis  of 
their  solubilities  in  various  reagents.  Eacli  class,  however,  if  it  contains 
more  tlian  one  substance,  ma}'  often  be  distinguished  by  other  proper- 
ties common  to  its  members.  Not  every  one  of  the  proteids  enumerated 
is  contained  in  the  animal  tissues,  some  are  used  as  food. 

(1.)  Xative-AIbumins. — These  substances  are  soluble  in  water  and  in 
saline  solutions,  and  are  coagulated,  i.e.,  turned  into  coagulated  j^i'oteid, 
■on  heating. 

(2.)  Derived- Albumins. — These  are  soluble  in  acids  or  alkalies,  in- 
soluble in  saline  solutions  and  in  water,  and  not  coagulated  on  heating. 

(3.)  Globidins. — These  are  soluble  in  strong  or  in  weak  saline  solu- 
tions, in  dilute  acids  and  alkalies,  and  insoluble  in  water.  They  are 
•coagulated  on  heating. 

(4.)  Proteoses. — These  are  soluble  in  water  and  dilute  saline  solutions, 
precipitated  by  saturation  with  magnesium  sulphate  or  else  with  ammo- 
nium sulphate;  precipitated  but  not  coagulated  by  alcohol;  precipitated 
by  nitric  acid,  the  precipitate  being  dissolved  on  heating,  and  reappears 
on  cooling,  not  precipitated  by  heat. 

(5.)  Peptones. — These  are  soluble  in  water,  saline  solutions,  acids,  or 


100  HANDBOOK    OF   PHYSIOLOGY. 

alkalies;  not  iirecipitated  on  saturation  with  any  neutral  salt;  tiiey  are 
not  coagulated  on  heating. 

(6.)  Fibrin. — It  is  insoluble  in  water,  in  dilute  saline  solutions,  or 
in  dilute  acids  or  alkalies;  soluble  in  strong  saline  solutions  (partly)  and 
in  strong  acids;  soluble  to  a  certain  extent  in  strong  saline  solutions 
and  in  gastric  or  pancreatic  fluids. 

(7.)  Coagulated  Proteids. — These  are  of  two  classes,  either  coagulated 
by  (a)  action  ol  ferments,  or  (b)  heat.  These  are  soluble  only  in  gastric 
or  pancreatic  fluids,  forming  peptones. 

(8.)  Lardacein,  or  Amijloid  substance. — This  body  is  generally  in- 
soluble, even  in  gastric  or  pancreatic  fluids  at  ordinary  temperatures.  It 
gives  a  brown  coloration  with  iodine. 

Native- Albumins. — Of  native-albumins  there  are  three  varieties: 
(a)  egg  albumin;  (b)  serum-albumin;  and  (c)  cell-albumin. 

Egg  Albumin  is  contained  in  the  white  of  the  egg. 

When  in  solution  in  water  it  is  a  transparent,  frothy,  yellowish  fluid, 
neutral  or  slightly  alkaline  in  reaction.  It  gives  all  of  the  general  pro- 
teid  reactions. 

At  a  temperature  not  exceeding  40°  C.  it  is  dried  up  into  a  yellowish, 
transparent,  glassy  mass,  soluble  in  water.  At  a  temperature  of  70°  C. 
it  is  coagvlated,  i.e.,  changed  into  a  new  substance,  coagulated  proteid, 
which  is  quite  insoluble  in  water.  It  is  coagulated  also  by  the  prolonged 
action  of  alcohol;  by  strong  mineral  acids,  especially  by  nitric  acid,  also 
by  tannic  acid,  or  carbolic  acid;  by  ethers  the  coagulum  is  soluble  in 
caustic  sod;i. 

It  is  precipitated  without  coagulation,  i.e.,  forms  an  insoluble  com- 
pound with  the  reagent,  soluble  on  removal  of  the  salt  by  dialysis,  with 
either  mercuric  chloride,  lead  acetate,  copper  sulphate  or  silver  nitrate, 
the  precipitate  in  each  case  being  soluble  in  slight  excess  of  the  reagent. 

With  strong  nitric  acid  the  albumin  is  precipitated  at  the  point  of 
contact  with  the  acid  in  the  form  of  a  fine  white  or  yellow  ring. 

Serum- Albumin  is  contained  in  blood-serum,  lymph,  serous  and  syn- 
ovial fluids,  and  in  the  tissues  generalh';  it  may  be  prepared  from  serum 
after  removal  of  paraglobulin  by  saturation  with  magnesium  sulphate, 
by  a  further  saturation  with  sodium  sulphate.  It  appears  in  the  urine 
in  the  condition  known  as  albuminuria. 

It  gives  similar  reactions  to  egg-albumin,  but  differs  from  it  in  not 
being  coagulated  by  ether.  It  also  differs  from  egg-albumin  in  not  be- 
ing easily  precipitated  by  hydrochloric  acid,  and  in  the  precipitate  being 
easily  soluble  in  excess  of  that  acid.  Serum-albumin,  either  in  the  co- 
agulated or  precipitated  form,  is  more  soluble  in  excess  of  strong  acid 
than  egg-albumin. 

Derived'Albumins.— There  are  three  substances  belonging  to  this 
class,  a,  Acid-Albumin;  b.  Alkali- Albumin;  and  c,  Caseinogen. 


THE    CHEMICAL    COMPOSITIO^T    OF   THE    BODY.  107 

Acid-Albumin. — Acid-albumin  is  made  by  adding  small  quantities  of 
dilute  acid  (of  which  the  best  is  hydrochloric,  .4  per  cent  to  1  per  cent), 
to  either  egg-  or  serum-albumin  diluted  with  five  to  ten  times  its  bulk 
of  water,  and  keeping  the  solution  at  a  temperature  not  higher  than  50° 
C.  for  not  less  than  half  an  hour.  It  may  also  be  made  by  dissolving 
coagulated  native-albumin  in  strong  acid,  or  by  dissolving  any  of  the 
globulins  in  acids. 

It  is  not  coagulated  on  heating,  but  on  exactly  neutralizing  the  solu- 
tion a  fiocculent  precipitate  is  produced.  This  maybe  shown  by  adding 
to  the  acid-albumin  solution  a  little  aqueous  solution  of  litmus,  and  then 
adding,  drop  by  drop,  a  weak  solution  of  caustic  potash  from  a  burette, 
until  the  red  color  disappears.  The  precipitate  is  the  derived-albumin. 
It  is  soluble  in  dilute  acid,  dilute  alkalies  and  dilute  solutions  of  alka- 
line carbonates.  The  solution  of  acid-albumin  gives  the  proteid  tests. 
The  substance  itself  is  coagulated  by  strong  acids,  e.g.,  nitric  acid,  and 
by  strong  alcohol;  it  is  insoluble  in  distilled  water,  and  in  neutral  sa- 
line solutions;  it  is  precipitated  from  its  solutions  by  saturation  with 
sodium  chloride.  On  boiling  in  lime-water  it  is  partially  coagulated, 
and  a  further  precipitation  takes  i)laceon  addition  to  the  boiled  solution 
of  calcium  chloride,  magnesium  sulphate,  or  sodium  chloride. 

Alkali-Albumin.—li  solutions  of  native-albumin,  or  coagulated  or 
other  proteid,  be  treated  with  dilute  or  strong  fixed  alkali,  alkali-albu- 
min is  produced.  Solid  alkali-albumin  may  also  be  prepared  by  adding 
caustic  soda  or  potash,  drop  by  drop,  to  undiluted  egg-albumin,  until 
the  whole  forms  a  jelly.  This  jelly  is  soluble  in  dilute  alkalies  on  boil- 
ing. A  solution  of  alkali-albumin  gives  the  tests  corresponding  to  those 
of  acid-albumin.  It  is  not  coagulated  on  heating.  It  is  thrown  down 
on  neutralizing  its  solution,  except  in  the  presence  of  alkaline  phos- 
phates, in  which  case  the  solution  must  be  distinctly  acid  before  a  pre- 
cipitate falls. 

To  dilferentiate  between  Acid-  and  Alkali-Albumin,  the  following 
method  may  be  adopted.  Alkali-albumin  is  not  precipitated  on  exact 
neutralization,  if  sodium  phosphate  has  been  previously  added.  Acid- 
albumin  is  precipitated  on  exact  neutralization,  whether  or  not  sodium 
phosphate  has  been  pieviously  added. 

Caseinogen. — Caseinogen  is  the  chief  proteid  of  milk,  from  which  it 
may  be  prepared  by  the  following  process:  The  milk  should  be  diluted 
with  three  to  four  times  its  volume  in  water,  sufficient  dilute  acetic  acid 
should  then  be  added  to  render  the  solution  distinctly  acid,  and  the 
caseinogen  which  is  thrown  down  may  be  separated  by  filtration.  It  may 
then  be  washed  with  alcohol  and  afterward  with  ether,  to  free  it  from  fat. 

Caseinogen  may  also  be  prepared  by  adding  to  milk  an  excess  of 
crystallized  magnesium  sulphate  or  sodium  chloride,  either  of  which 
salt  causes  it  to  separate  out. 


108  HANDBOOK    OF    PHYSIOLOGY. 

Caseinogcn  gives  much  the  same  tests  as  alkali-albumin.  It  is  solu- 
ble in  dilute  acid  or  alkalies;  it  is  reprecipitated  on  neutralization,  but 
if  potassium  phosphate  be  present  the  solution  must  be  distinctly  acid 
before  the  caseinogen  is  deposited. 

Globulins. — The  globulins  give  the  general  proteid  tests;  are  insol- 
uble in  water;  are  soluble  in  dilute  saline  solutions;  are  soluble  in  acids 
and  alkalies  forming  the  corresponding  derived-albumin. 

Most  of  them  are  precipitated  from  their  solutions  by  saturation 
with  solid  sodium  chloride,  magnesium  sulphate,  or  other  neutral  salt. 
They  are  coagulated,  but  at  different  temperatures,  on  heating. 

Globulin  or  Crystallin. — It  is  obtained  from  the  crystalline  lens  by. 
rubbing  it  up  with  powdered  glass,  extracting  with  water  or  with  dilute 
saline  solution,  and  by  passing  through  the  extract  a  stream  of  carbon 
dioxide.  It  differs  from  other  globulins,  except  vitellin,  in  not  being 
precipitated  by  saturation  with  sodium  chloride. 

Myosin. — The  relation  of  myosin  to  living  muscle  will  be  considered 
under  the  head  of  the  physiology  of  muscle.  It  may  however  be  pre- 
jjared  from  dead  muscle  by  removing  all  fat,  tendon,  etc.,  and  washing 
repeatedly  in  water,  until  the  washing  contains  no  trace  of  proteids, 
mincing  it  and  then  treating  with  10  per  cent  solution  of  sodium  chlo- 
ride, or  similar  solution  of  ammonium  chloride  or  magnesium  sulphate, 
which  will  dissolve  a  large  portion  into  a  viscid  fluid,  which  filters  Avith 
•difficulty.  If  the  viscid  filtrate  be  dropped  little  by  little  into  a  large 
•quantity  of  distilled  water,  a  white  flocculcnt  precipitate  of  myosin  Avill 
•occur. 

It  is  soluble  in  10  per  cent  saline  solution;  it  is  coagulated  at  60°  C. 
into  coagulated  proteid;  it  is  soluble  without  change  in  very  dilute  acids; 
it  is  precipitated  by  picric  acid,  the  precipitate  being  redissolved  on  boil- 
ing; it  may  give  a  blue  color  with  ozonic  ether  and  tincture  of  guaiaciim. 

Paraglobulin.—VQ.Yiig\6h\\\m  is  contained  in  plasma  and  in  serum, 
in  serous  and  synovial  fluids,  and  may  be  precipitated  by  saturating 
plasma  after  removal  of  fibrinogen  or  serum  with  solid  sodium  chloride 
•or  magnesium  sulphate,  as  a  bulky  flocculent  substance  which  can  be 
removed  by  filtration. 

It  may  also  be  prepared  by  diluting  blood  serum  with  ten  volumes  of 
water,  and  passing  carbonic  acid  gas  rapidly  through  it.  The  fine  precip- 
itate may  be  collected  on  filter,  and  washed  with  water  containing  car- 
bonic acid  gas. 

It  is  very  soluble  in  dilute  saline  solutions  (5  to  8  per  cent),  from 
which  it  is  precipitated  by  carbonic  acid  gas  or  by  dilute  acids;  its  so- 
lution is  coagulated  at  70°  C;  even  dilute  acids  and  alkalies  convert  it 
into  acid-  or  alkali-albumin. 

Fibrinogen. — Fibrinogen  is  contained  in  blood-plasma,  from  which  it 
may  be  prepared  by  addition  of  sodium  chloride  to  the  extent  of  13  per 


THE   CHEMICAL   COMPOSITION    OF   THE    BODY.  i09^ 

cent.     It  may  also  be  prepared  from  hydrocele  fluid  or  from  other  serous 
transudation  by  a  similar  method. 

Its  general  reactions  are  similar  to  those  of  paraglobulin;  its  solution 
is  coagulated  at  53°-55°  C.  Its  characteristic  j^roperty  is  that,  under 
certain  conditions,  it  forms  fibrin. 

Vitellin. —  Vitellin  is  prepared  from  yolk  of  egg  by  washing  with 
ether  until  all  the  yellow  matter  has  been  removed.  The  residue  is- 
dissolved  in  10  per  cent  saline  solution,  filtered,  and  poured  into  a  large 
quantity  of  distilled  water.  The  23reci23itate  which  falls  is  impure  vitel- 
lin. It  gives  the  same  tests  as  myosin,  but  is  not  precipitated  on  satu- 
ration with  sodium  chloride;  it  coagulates  between  70°  and  83°  C. 

Globin. — Is  the  proteid  residue  of  haamoglobiu. 

Proteoses  are  intermediate  substances  of  the  digestion  of  other 
proteids,  tlie  ultimate  product  of  which  is  peptone. 

Peptones. — Pejatone  is  formed  by  the  action  of  the  digestive  iev- 
menti,  jjejjsi)!,  or  trypsin,  on  other  proteids,  and  on  gelatin.  They  wil 
be  considered  in  connection  Avith  the  physiology  of  digestion,  as  will  also 
the  intermediate  compounds. 

Fibrin. — Fibrin  can  be  obtained  as  a  soft,  Avhite,  fibrous,  and  very 
elastic  substance  by  whijDping  blood  with  a  bundle  of  twigs,  and  washing 
the  adhering  mass  in  a  stream  of  water  until  all  the  blood-coloring  mat- 
ter is  removed. 

Coagulated  proteids  are  formed  by  the  action  of  heat  or  of  fer- 
ments upon  other  proteids;  the  temperature  necessary  to  produce  coag- 
ulation varying  in  the  manner  previously  indicated.  They  may  also  be- 
produced  by  the  jDrolonged  action  of  alcohol  upon  proteids.  They  are 
soluble  in  strong  acids  or  alkalies;  slightly  so  in  dilute;  are  soluble  in 
digestive  fluids  (gastric  and  pancreatic).  Are  insoluble  in  saline  solu- 
tions. 

Lardacein  is  found  in  organs  which  are  the  seat  of  amyloid  degen- 
eration. It  is  insoluble  in  dilute  acids  and  very  slightly  in  gastric  juice 
at  the  temperature  of  the  body.  It  is  colored  brown  by  iodine  and  blu- 
ish-pink by  methyl  violet.  Lardacein  is  now  often  classed  under  the 
head  of  gelatins. 

Tlte  Gelatins  or  Nitrogenous  Bodies  otltcr  than  Proteids. — These  are 
nitrogenous  organic  bodies,  the  composition  of  which  does  not  include 
them  in  the  proteid  class  of  substances. 

Gelatin. — Gelatin  is  contained  in  the  form  of  co/Zf/i^p??,  its  anhydride, 
in  bone  (ossein),  teeth,  fibrous  connective  tissues,  tendons,  ligaments, 
etc.  It  may  be  obtained  by  prolonged  action  of  boiling  water  in  a 
Papin's  digester  or  of  dilute  acetic  acid  at  a  low  temperature  (15°  C). 

Properties. — The  percentage  composition  is  0,  23.21,  H.  7.15,  N,. 
18.32,  C,  50.76,  S,  0.56.     It  contains  more  nitrogen  and  less  carbon  than 


110  HAXDBOOK    OF    PHYSIOLOGY. 

proteids.  By  some  it  is  said  to  contiiin  no  sulphur.  It  is  amorphous, 
and  transparent  when  dried.  It  does  not  dialyse;  it  is  insoluble  in  cold 
water,  but  swells  up  to  about  six  times  its  volume:  it  dissolves  readily 
on  the  addition  of  very  dilute  acids  or  alkalies.  It  is  soluble  in  hot 
water,  and  forms  a  jelly  on  cooling,  even  when  only  1  per  cent  of  gelatin 
is  present.  Prolonged  boiling  in  dilute  acids,  or  in  water  alone,  destroys 
this  power  of  forming  a  jelly  on  cooling. 

A  fairly  strong  solution  of  gelatin — 2  per  cent  to  4  per  cent — gives 
the  following  reactions: 

(a)  With  proteid  tests:  (i.)  Xanthoproteic  test. — A  yellow  color  but 

no  previous  precipitate  with  nitric  acid,  becoming  darker  on  the 
addition  of  ammonia,  (ii.)  Biuret  test. — A  blue  color,  (iii.) 
Millon's  test. — A  pink  precipitate,  (iv.)  Potassium  ferrocy- 
anide  and  acetic  acid. — No  reaction,  (v.)  Boiling  with  sodium 
sulphate  and  acetic  acid.     No  reaction. 

(b)  Special  reactions:  (i.)  No  precipitate  with  acetic  acid,     (ii.)  No 

precipitate  with  hydrochloric  acid,     (iii.)  A  white  precipitate 
with  tannic  acid,  not  soluble  in  excess  or  in  dilute  acetic  acid, 
(iv.)  A  white  precipitate  with  mercuric  chloride,  unaltered  by 
excess  of  the  reagent,     (v.)  A  white  precipitate  with  alcohol, 
(vi.)  A  yellowish-white  precipitate  with  picric  acid,  dissolved 
on  heating  and  reappearing  on  cooling. 
Mucin.— Mucin  is  supposed  to  be  a  compound  of  a  proteid,  proba- 
bly a  globulin,  with  animal  gum,  and  is  the  characteristic  component  of 
mucus;  it  is  contained  also  in  foetal  connective  tissue,  in  tendons,  and 
salivary  glands.     It  can  be  obtained  from  mucus  by  diluting  it  with 
water,  filtering,  treating  the  insoluble  portion  with  weak  caustic  jilkali, 
and  reprecipitating  with  acetic  acid.     'J'he  mucins  derived  from  differ- 
ent sources  probably  have  different  compositions. 

Projjerties. — Mucin  has  a  ropy  consistency.  It  is  precipitated  by 
alcohol  and  by  mineral  acids,  but  dissolved  by  excess  of  the  latter.  It  is 
dissolved  by  alkalies  and  in  lime  water.  It  gives  the  proteid  reaction 
with  Millon's  reagent  and  with  nitric  acid.  Neither  mercuric  chloride 
nor  tannic  acid  gives  a  precipitate  with  it  (?).     It  does  not  dialyse. 

Elastin  is  found  in  elastic  tissue,  in  the  ligamenta  subflava,  liga- 
mentum  nucha?,  etc.  It  is  insoluble,  but  swells  up  both  in  cold  and  hot 
water.  Is  soluble  in  strong  caustic  soda.  It  is  precipitated  by  tannic 
acid;  does  not  gelatinize.  Gives  the  proteid  reactions  with  strong  nitric 
acid  and  ammonia,  and  imperfectly  with  Millon's  reagent.  Yields  leucin 
on  boiling  with  strong  sulphuric  acid. 

Chondrin  is  found  in  the  condition  of  chondrigen  in  cartilage. 
It  is  a  mixture  of  gelatin  with  a  mucin-like  substance,  and  is  obtained 
from  chondrigen  by  boiling. 

Properties. — It  is  soluble  in  hot  water,  and  in  solutions  of  neutral 


THE    CHEMICAL    COMPOSITIOX    OF    THE    BODY.  Ill 

salt,  e.g.,  sulphate  of  sodium,  in  dilute  mineral  acids,  caustic  potash,  aud 
soda.  Insoluble  in  cold  water,  alcohol,  and  ether.  It  is  precipitated 
from  its  solutions  by  dilute  mineral  acids  (excess  redissolves  it),  by- 
alum,  by  lead  acetate,  by  silver  nitrate,  and  by  chlorine  water.  On  boil- 
ing with  strong  hydrochloric  acid,  it  yields  grape-sugar  and  certain  ni- 
trogenous substances.  Prolonged  boiling  in  dilute  acids,  or  in  water, 
destroys  its  power  of  forming  a  jelly  on  cooling. 

Keratin  is  obtained  from  hair,  nails,  aud  dried  skin.  It  contains 
sulphur  evidently  only  loosely  combined. 

Nuclein. — Found  in  the  nuclei  of  cells,  also  in  milk,  and  yolk  of 
egg.  It  resembles  mucin  in  its  tests,  but  diliers  from  it  in  composition 
as  it  contains  phosphorus  in  its  molecule.  Some  of  the  bodies  which 
have  been  called  mucin,  are  really  compounds  of  nuclein  and  a  j)roteid, 
generally  a  globulin.     Such  is  the  mucinoid  substance  in  bile. 

Xon-nitrogenous  organic  bodies  consist  of 

(a)  Oils  and  Fats,  which  are  for  the  most  part  mixtures  of  paJmi- 
tin,  CsiHgoOe,  stearin  CstHuoOs,  and  oJein  C57H104O6,  in  different  pro- 
portions. They  are  formed  by  the  union  of  fatty  acid  radicals  with 
the  triatomic  alcohol.  Glycerin  C3H3(OH)3,  and  are  etherial  salts  of  that 
alcohol.  The  radicals  are  C18H35O,  CiellaiO,  and  CisHssO,  respectively. 
Human  fat  consists  of  a  mixture  of  palmitin,  stearin,  o-wH  olein,  of  which 
the  two  former  contribute  three-quarters  of  the  whole.  Olein  is  the 
only  liquid  constituent. 

Fats  are  insoluble  in  water  and  in  cold  alcohol;  soluble  in  hot  alco- 
hol, ether,  and  chloroform.  Colorless  and  tasteless;  easily  decomposed 
or  saponified  by  alkalies  or  super-heated  steam  into  glycerin  and  the  fatty 
acids. 

And  (b)  Carbohydrates,  which  are  bodies  composed  of  sis  or  twelve 
atoms  of  carbon  with  hydrogen  and  oxygen,  the  two  latter  elements  be- 
ing in  the  proportion  to  form  water.  There  are  three  main  classes  of 
carbohydrates. 

Atnyloses,  CeliioOs,  comprising  Starch,  Dextrin,  Glycogen,  etc.  Sac- 
cliaroses,  C12H22O11,  Saccharose,  or  Cane  sugar,  Lactose,  ]\Ialtose,  etc. 
Glucoses,  C6H12O6,  Dextrose  or  Grape  sugar,  Lsevulose  or  Fruit-sugar, 
Inosite,  etc. 

Of  these  the  most  important  are. 

Starch  (CeHioOa),  which  is  contained  in  nearly  all  plants,  and  in 
many  seeds,  roofs,  steins,  and  some  fruits.  It  is  a  soft  white  powder 
composed  of  granules  having  an  organized  structure,  consisting  of  gran- 
iilose  (soluble  in  water)  contained  in  a  coat  of  ceUuJose  (insoluble  in 
water) ;  the  shape  and  size  of  the  granules  varying  according  to  the 
source  whence  the  starch  has  been  obtained.  It  is  insoluble  in  cold 
water,  in  alcohol,  and  in  ether;  it  is  soluble  after  boiling  for  some  time, 
and  may  be  filtered,  in  consequence  of  the  swelling  up  of  the  granulose. 


112  HANDBOOK    OF    PHYSIOLOGY. 

wliicli  bursts  the  cellulose  coat,  and  becoming  free,  is  entirely  dissolved 
in  water.  This  solution  is  a  solution  of  soluble  starch  or  amydin.  It 
gives  a  blue  coloration  with  iodine,  which  disappears  on  heating  and 
returns  on  cooling.  It  is  converted  into  dextrine  and  grape-sugar  by 
diastase  or  by  boiling  with  dilute  acids. 

Glycogen,  which  is  contained  in  the  liver,  is  also  present  to  a  con- 
siderable extent  in  the  muscles  of  very  young  animals,  in  the  placenta, 
in  colorless  corpuscles,  and  in  embryonic  tissues.  It  is  freely  soluble  in 
Wivtor,  and  its  solution  looks  opalescent;  it  gives  a  port-wine  coloration 
with  iodine,  which  disappears  on  heating  and  returns  on  cooling.  It  is 
precipitated  by  basic  lead  acetate  and  insoluble  in  absolute  alcohol  and 
in  ether.  It  exists  in  the  liver  during  life,  but  very  soon  after  death  is 
changed  into  sugar.  It  is  converted  into  sugar  by  diastase  ferments,  or 
by  boiling  with  dilute  acids. 

Dextrin. — This  substance  is  made  in  commerce  by  heating  dry  po- 
tato-starch to  a  temperature  of  400°.  It  is  also  produced  in  the  process 
of  the  conversion  of  starch  into  sugar  by  diastase,  and  by  the  salivary 
and  pancreatic  ferments.  A  yellowish  amorphous  powder,  soluble  in 
water,  but  insoluble  in  absolute  alcohol  and  in  ether.  It  corresponds 
almost  exactly  in  tests  with  glycogen;  but  one  variety  (achroo-dextrine) 
does  not  give  the  port-wine  coloration  with  iodine. 

Cane  Sugar  or  Saccharose,  is  contained  in  the  juices  of  many 
plants  and  fruits,  and  is  as  a  rule  extracted  from  the  sugar  cane,  from 
beetroot,  or  from  the  majjle.  It  is  crystalline  and  is  precipitated  from 
concentrated  solutions  by  absolute  alcohol.  It  has  no  power  of  reduc- 
ing copper  salts  on  boiling.  It  is  dextro-rotatory  (see  Ajipendix).  lb 
is  not  subject  to  alcoholic  fermentation,  until  by  inversion  it  is  converted 
into  glucose,  it  chars  on  addition  of  sulj)huric  acid,  and  on  heating  with 
potassium  or  sodium  hydrate. 

Lactose  is  contained  in  milk.  It  is  less  soluble  in  water  than  glu- 
cose; not  sweet,  and  is  gritty  to  the  taste;  but  it  is  insoluble  in  absolute 
alcohol.  Undergoes  alcoholic  fermentation  with  extreme  difficulty;  gives 
the  tests  similar  to  glucose,  but  less  readily.    It  is  dextro-rotatory  -j-59°. 

Maltose  is  formed  in  the  conversion  of  starch  into  glucose  by  the 
saliva  and  pancreatic  fluids.  It  is  also  formed  by  the  action  of  malt 
upon  starch  by  the  ferment  diastase,  and  in  the  formation  of  glucose 
from  starch.  It  is  converted  into  dextrine  by  dilute  sulphuric  acid. 
It  is  dextro-rotatory;  ferments  with  yeast;  reduces  copper  salts,  and 
crystallizes  in  fine  needles. 

Glucose  occurs  widely  diffused  in  the  vegetable  kingdom,  in  diabetic 
urine,  in  the  blood,  etc.;  it  is  usually  obtained  from  grape-juice,  honey, 
beet-root  or  carrots.  It  really  is  a  mixture  of  two  isomeric  bodies,  Dex- 
trose or  grape-sugar,  which  turns  a  ray  of  polarized  light  to  the  right 
(_j_5G°),  and  Lcevulose  or  fruit-sugar,  which  turns  the  ray  to  the  left. 


THE   CHEMICAL    COMPOSITION    OF   THE    BODY.  113 

It  is  easily  soluble  in  water  and  in  alcohol;  not  so  sweet  as  cane- 
sugar;  the  relation  of  its  sweetness  to  that  of  cane-sugar  is  as  3  to  5. 
It  is  not  so  easily  charred  by  strong  sulphuric  acid  as  cane-sugar.  It  is 
not  entirely  soluble  in  alcohol.  It  undergoes  alcoholic  fermentation 
with  yeast. 

Dextrose  has  the  power  of  reducing  the  salts  of  silver,  bismuth, 
mercury,  and  copper,  either  to  the  form  of  the  metal  as  in  the  first  three 
cases,  or  to  the  form  of  the  sub-oxide  in  the  case  with  cujjrous  salts. 
Upon  this  property  the  chief  tests  for  the  sugar,  e.g.,  Trommer's  and 
Bottcher's,  depend  (see  Appendix).  When  boiled  with  potash,  glucic 
and  melanic  acids  are  formed,  and  a  yellowish  fluid  results  (Moore's 
test).  It  is  oxidized  by  the  action  of  nitric  acid  to  saccharic  acid.  It 
forms  compounds  with  acids  and  with  potash  and  lime.  It  undergoes 
alcoholic  fermentation  with  yeast,  and  lactic  acid  fermentation  with 
bacterina  lactis.  It  forms  caramel  when  strongly  heated,  and  is  also 
charred  with  strong  acids.  For  the  method  of  quantitative  estimation, 
etc.,  see  Appendix. 

Laevulose  is  one  of  the  products  of  the  decomposition  of  cane-sugar 
by  means  of  dilute  mineral  acids,  or  by  means  of  the  ferment  suverten 
in  the  alimentary  canal. 

It  reacts  to  the  same  test  as  glucose,  but  is  non-crystallizable,  and 
is  la^vo-rotatory  — 1060.  It  is  soluble  in  water  and  in  alcohol.  Its  com- 
pound with  lime  is  solid,  whereas  that  with  dextrose  is  not. 

Galactose  is  formed  from  lactose  by  the  action  of  dilute  mineral 
acids,  or  inverting  ferments.  It  undergoes  alcoholic  fermentation,  and 
reduces  copper  salts  to  the  suboxide. 

Inosite. — Inosite  is  a  non-fermentable  variety  of  glucose  occurring 
in  the  heart  and  voluntary  muscles,  as  well  as  in  beans  and  other  plants. 
It  crystallizes  in  the  form  of  large  colorless  monoclinic  tables,  which  are 
soluble  in  water,  but  insoluble  in  alcohol  or  ether,  Inosite  may  be  de- 
tected by  evaporating  the  solution  containing  it  nearly  to  dryness,  and 
by  then  adding  a  small  drop  of  solution  of  mercuric  nitrate,  and  after- 
ward evaporating  carefully  to  dryness,  a  yellowish-white  residue  is  ob- 
tained ;  on  further  cautiously  heating,  the  yellow  changes  to  a  deep  rose- 
color,  which  disappears  on  cooling,  but  reappears  on  heating.  If  the 
inosite  be  almost  pure,  its  solution  may  be  evaporated  nearly  to  dryness. 
After  the  addition  of  nitric  acid,  the  residue  mixed  with  a  little  ammonia 
and  calcium  chloride,  and  again  evaporated,  yields  a  rose-red  coloration. 

Certain  of  the  monatomic  Fatty  Acids  are  found  in  the  body,  viz., 
Formic  CHaOa,  acetic  C2H4O2,  and  propionic  CsHeOa,  present  ii^  sweat, 
but  normally  in  no  other  human  secretion.  They  have  been  found  else- 
where in  diseased  conditions.  Biitjiric  acid,  QiW^Oi/i^  found  in  sweat. 
Various  others  of  these  acids  have  been  obtained  from  blood,,  muscular 
juice,  fasces  and  urine. 
8 


114  HANDBOOK    OF    PHYSIOLOGY. 

Of  the  diatomic  fatty  acids,  one  acid,  Lactic  acid,  CsHeOs  exists  in 
a  free  state  in  muscle  ])lasma,  and  is  increased  in  quantity  by  muscular 
contraction,  is  never  contained  in  healthy  blood,  and  when  present  in 
abnormal  amount  seems  to  produce  rheumatism. 

Of  the  aromatic  series,  Benzoic  acid,  C3  HeOa,  is  always  found  in 
the  urine  of  herbivora,  and  can  be  obtained  from  stale  human  urine. 
It  does  not  exist  free  elsewhere. 

PlumoL — Phenyl  alcohol  or  carbolic  acid  exists  in  minute  quantity 
in  human  urine.     It  is  an  alcohol  of  the  aromatic  series. 

Inorganic  Principles. 

The  inorganic  ])roximate  principles  of  the  human  body  are  numer- 
ous. They  are  derived,  for  the  most  part,  directly  from  food  and  drink, 
and  pass  through  the  system  unaltered.  Some  are,  however,  decom- 
posed on  their  way,  as  chloride  of  sodium,  of  which  only  four-fifths  of 
the  quantity  ingested  are  excreted  in  the  same  form;  and  some  are 
newly  formed  within  the  body, — as,  for  example,  a  part  of  the  sulphates 
and  carbonates,  and  some  of  the  water. 

Much  of  the  inorganic  saline  matter  found  in  the  body  is  a  neces- 
sary constituent  of  its  structure, — as  necessary  in  its  way  as  albumin 
or  any  other  organic  principle;  another  part  is  important  in  regulat- 
ing or  modifying  various  jihysical  processes,  as  absorption,  solution,  and 
the  like;  while  a  part  must  be  reckoned  only  as  matter,  which  is,  so  to 
speak,  accidentally  present,  whether  derived  from  the  food  or  the  tis- 
sues, and  which  will,  at  the  first  opportunity,  be  excreted  from  the  body. 

Gases. — -The  gaseous  matters  found  in  the  body  are  Oxygen,  Hydro- 
fjen,  Nitrogen^  Carlmretted  and  ^^ulplinretted  hydrogen,  and  Carbonic 
acid.  The  first  three  have  been  referred  to.  Carburetted  and  sulphu- 
retted hydrogen  are  found  in  the  intestinal  canal.  Carbonic  acid  is  pres- 
ent in  the  blood  and  other  fluids,  and  is  excreted  in  large  quantities  by 
the  lungs,  and  in  very  minute  amount  by  the  skin.  It  will  be  specially 
considered  in  the  chapter  on  Respiration. 

Water,  the  most  abundant  of  the  proximate  principles,  forms  a  large 
proportion, — more  than  two-thirds  of  the  weight  of  the  whole  body. 
Its  relative  amount  in  some  of  the  principal  solids  and  fluids  of  the  body 
is  shown  in  the  following  table  (from  Robin  and  VerdeiPs) : — 


Quantity  of  Water  in  1000  Parts. 


Teeth     . 

Bones 

Cartilage 

Muscles 

Ligament^ 

Brain 

Blood     . 

Synovia 


100 

Bile 

130 

Milk  . 

550 

Pancreatic  juice 

750 

Urine 

768 

Ljniph 

789 

Gastric  juice     . 

795 

Perspiration 

805 

Saliva 

880 
887 
900 
936 
960 
975 
986 
995 


THE   CHEMICAL    COMPOSITIOX    OF   THE    BODY.  115 

The  importance  of  water  as  a  constituent  of  the  animal  body  may  be 
assumed  from  the  preceding  table,  and  is  shown  in  a  still  more  striking 
manner  by  its  withdrawal.  If  any  tissue,  as  muscle,  cartilage,  or  ten- 
don, be  subjected  to  heat  sufficient  to  drive  off  the  greater  jiart  of  its 
water,  all  its  characteristic  physical  2)roperties  are  destroyed ;  and  what 
was  previously  soft,  elastic,  and  flexible,  becomes  hard  and  brittle,  and 
horn}^  so  as  to  be  scarcely  recognizable. 

In  all  the  fluids  of  the  body — blood,  lymph,  etc., — water  acts  the  part 
of  a  general  solvent,  and  by  its  means  alone  circulation  of  nutrient  mat- 
ter is  possible.  It  is  the  medium  also  in  which  all  fluid  and  solid  ali- 
ments are  dissolved  before  absorjotion,  as  well  as  the  means  by  which  all, 
except  gaseous,  excretory  products  are  removed.  All  the  various  j)ro- 
cesses  of  secretion,  transudation,  and  nutrition,  depend  of  necessity  on 
its  presence  for  their  performance. 

The  greater  part,  by  far,  of  the  water  present  in  the  body  is  taken 
into  it  as  such  from  without,  in  the  food  and  drink.  A  small  amount, 
however,  is  the  result  of  the  chemical  union  of  hydrogen  with  oxygen  in 
the  blood  and  tissue.  The  total  amount  taken  into  the  body  every  day 
is  about  4^  lbs.;  while  an  uncertain  quantity  (perhaps  ^  to  f  lb.)  is 
formed  by  chemical  action  within  it. — (Dalton). 

The  loss  of  water  from  the  body  is  intimately  connected  with  excre- 
tion from  the  lungs,  skin,  and  kidneys,  and,  to  a  less  extent,  from  the 
alimentary  canal.  The  loss  from  these  various  orgaus  may  be  thus  ap- 
portioned (quoted  by  Dalton  from  various  observers). 

From  the  Alimentary  canal  (faeces) 4  per  cent. 

"         Lungs 30        " 

"         Skin  (perspiration) 30        " 

Kidneys  (urine) 46        " 

100 

Sodium  and  Potassium  Chlorides  are  present  in  nearly  all  parts  of 
the  body.  The  former  seems  to  be  especially  necessary,  judging  from 
the  instinctive  craving  for  it  on  the  part  of  animals  in  whose  food  it  is 
deficient,  and  from  the  diseased  condition  which  is  consequent  on  its 
withdrawal.  In  the  blood,  the  quantity  of  sodium  chloride  is  greater 
than  that  of  all  its  other  saline  ingredients  taken  together.  In  the 
muscles,  on  the  other  hand,  the  quantity  of  sodium  chloride  is  less  than 
that  of  the  chloride  of  potassium. 

Calcium  Fluoride,  in  minute  amount,  is  present  in  the  bones  and 
teeth,  and  traces  have  been  found  in  the  blood  and  some  other  fluids. 

Calcium,  Potassiwn,  Sodium,  and  Magnesium  Phosphates  are  found 
in  nearly  every  tissue  and  fluid.  In  some  tissues— the  bones  and  teeth 
— the  phosphate  of  calcium  exists  in  very  large  amount  and  is  the  jirin- 
cipal  source  of  that  hardness  of  texture  on  which  the  proper  perform- 
ance of  their  functions  so  much  depends.     The  phosphate  of  calcium  is 


116  HANDBOOK    OF   PHYSIOLOGY. 

intimately  incorporated  with  the  organic  basis  or  matrix,  but  it  can  be 
removed  by  acids  without  destroying  the  general  shape  of  the  bone; 
and,  after  the  removal  of  its  inorganic  salts,  a  bone  is  left  soft,  tough, 
and  flexible. 

Potassium  and  sodium  phosphates  with  the  carbonates,  maintain  the 
alkalinity  of  the  blood. 

Calcium  Carbonate  occurs  in  bones  and  teeth,  but  in  much  smaller 
quantity  than  the  phosphate.  It  is  found  also  in  some  other  parts. 
The  small  concretions  of  the  internal  ear  (otoliths)  are  composed  of 
crystalline  calcium  carbonate,  and  form  the  only  example  of  inorganic 
crystalline  matter  existing  as  such  in  the  body. 

Potassium  and  Sodium  Carbonates  are  found  in  the  blood,  and  some 
other  fluids  and  tissues. 

Potassium,  Sodium,  and  Calcium  Sulphates  are  met  with  in  small 
amount  in  most  of  the  solids  and  fluids. 

Silicon. — A  very  minute  quantity  of  silica  exists  in  the  urine,  and  in 
the  blood.  Traces  of  it  have  been  found  also  in  bones,  hair,  and  some 
other  parts. 

Iron. — The  especial  place  of  iron  is  in  haemoglobin,  the  coloring- 
matter  of  the  blood,  of  which  a  full  account  has  been  given  with  the 
chemistry  of  the  blood.  Peroxide  of  iron  is  found,  in  very  small  quan- 
tities, in  the  ashes  of  bones,  muscles,  and  many  tissues,  and  in  lymph  and 
chyle,  albumin  of  serum.,  fibrin,  bile,  milk  and  other  fluids;  and  a  salt 
of  iron,  probably  a  phosphate,  exists  in  the  hair,  black  pigment,  and 
other  deeply  colored  ejiithelial  or  horny  substances, 

Alumifiium,  Manganese,  Copper,  and  Lead. — It  seems  most  likely 
that  in  the  human  body,  C02:)per,  manganesium,  aluminium,  and  lead  are 
merely  accidental  elements,  which,  being  taken  in  minute  quantities 
with  the  food,  and  not  excreted  at  once  with  the  fseces,  are  absorbed  and 
deposited  in  some  tissue  or  organ,  of  which,  however,  they  form  no  nec- 
essary part.  In  the  same  manner,  arsenic,  being  absorbed,  may  be  de- 
posited in  the  liver  and  other  parts. 


CHAPTER  Y. 

THE   BLOOD 

The  blood  is  the  fluid  medium  by  means  of  which  all  the  tissues  of 
the  body  are  directly  or  indirectly  nourished;  by  means  of  it  also  such 
of  the  materials  which  result  from  the  metabolism  of  the  tissues  as  are 
of  no  further  use  in  the  economy^,  are  carried  to  the  excretory  organs  to 
be  removed  from  the  body.  It  is  a  somewhat  viscid  fluid,  and  in  man 
and  in  all  other  vertebrate  animals  with  the  exception  of  two,*  is  red 
in  color.  The  exact  shade  of  red  is  variable;  that  taken  from  the 
arteries,  from  the  left  side  of  the  heart  and  from  the  pulmonary  veins 
is  of  a  bright  scarlet  hue,  that  obtained  from  the  systemic  veins,  from 
the  right  side  of  the  heart,  and  from  the  pulmonary  artery,  is  of  a  much 
darker  color,  and  varies  from  bluish-red  to  reddish-black.  At  first 
sight,  the  red  color  appears  to  belong  to  the  whole  mass  of  blood,  but 
on  further  examination  this  is  found  not  to  be  the  case.  In  reality  blood 
consists  of  an  almost  colorless  fluid,  called  plasma  or  liquor  sanguinis, 
in  which  are  suspended  numerous  minute  rounded  masses  of  proto- 
plasm, called  blood  corpuscles,  which  are,  for  the  most  part,  colored, 
and  it  is  to  their  presence  in  the  fluid  that  the  red  color  of  the  blood  is 
due. 

Even  when  examined  in  very  thin  layers,  blood  is  opaque,  on  account 
of  the  different  refractive  powers  possessed  by  its  two  constituents,  viz., 
the  plasma  and  the  corpuscles.  On  treatment  with  chloroform  and 
other  reagents,  however,  it  becomes  transparent  and  assumes  a  lake 
color,  in  consequence  of  the  coloring  matter  of  the  corpuscles  having 
been  discharged  into  the  plasma.  The  average  specijic  gravity  of  blood 
at  15^  C.  (60''  F.)  varies  from  1055  to  1062.  A  rapid  and  useful  method 
of  estimating  the  specific  gravity  of  blood  has  been  employed  by  Lloyd 
Jones.  Drops  of  blood  are  taken  and  allowed  to  fall  into  fluids  of 
known  specific  gravity.  When  the  drop  neither  rises  nor  sinks  in  the 
fluid,  it  is  taken  to  be  of  the  same  specific  gravity  as  that  of  the  stand- 
ard fiuid.  The  reaction  of  blood  is  faintly  alkaline  and  the  taste  saltish. 
Its  temperature  varies  slightly,  the  average  being  37.8°  C.  (100°  F.). 
The  blood  stream  is  warmed  by  passing  through  the  muscles,  nerve  cen- 
tres, and  glands,  but  is  somewhat  cooled  on  traversing  the  capillaries  of 

*  The  amphioxus  and  the  leptocephalus. 
117 


118  HANDBOOK    OF    PHYSIOLOGY. 

the  skin.  Recently  drawn  blood  has  a  distinct  odor,  which  in  many 
cases  is  characteristic  of  the  animal  from  which  it  has  been  taken.  It 
may  be  further  developed  also  by  adding  to  blood  a  mixture  of  equal 
parts  of  sulphuric  acid  and  water. 

Quantity  of  the  Blood. — The  quantity  of  blood  in  any  animal 
under  normal  conditions  bears  a  fairly  constant  relation  to  the  body- 
weight.  The  methods  employed  for  estimating  it  are  not  so  simple  as 
might  at  first  sight  have  been  thought  For  example,  it  vvould  not  be 
possible  to  get  any  accurate  information  on  the  point  from  the  amount 
obtained  by  rapidly  bleeding  an  animal  to  death,  for  then  an  indefinite 
quantity  would  remain  in  the  vessels,  as  well  as  in  the  tissues;  nor,  on 
the  other  hand,  would  it  be  possible  to  obtain  a  correct  estimate  by  less 
rapid  bleeding,  as,  since  life  would  be  more  prolonged,  time  would  be 
allowed  for  the  passage  into  the  blood  of  lymph  from  the  lymphatic 
vessels  and  from  the  tissues.  In  the  former  case,  therefore,  we  should 
nnder-estimate,  and  in  the  latter  over-estimate  the  total  amount  of  the 
blood. 

Of  the  several  methods  which  have  been  employed,  the  most  accurate 
appears  to  be  the  following.  A  small  quantity  of  blood  is  taken  from 
an  animal  by  venesection;  it  is  defibrinated  and  measured,  and  used  to 
make  standard  solutions  of  blood.  The  animal  is  then  rapidl}^  bled  to 
death,  and  the  blood  which  escapes  is  collected.  The  blood-vessels  are 
next  washed  out  with  saline  solution  until  the  washings  are  no  longer 
colored,  and  these  are  added  to  the  previously  withdrawn  blood;  lastly 
the  whole  animal  is  finely  minced  with  saline  solution.  The  fluid  ob- 
tained from  the  mincings  is  carefully  filtered,  and  added  to  the  diluted 
blood  previously  obtained,  and  the  whole  is  measured.  The  next  step 
in  the  process  is  the  comparison  of  the  color  of  the  diluted  blood  with 
that  of  standard  solutions  of  blood  and  water  of  a  known  strength,  until 
it  is  discovered  to  what  standard  solution  the  diluted  blood  corresponds. 
As  the  amount  of  blood  in  the  corresponding  standard  solution  is  known, 
as  well  as  the  total  quantity  of  diluted  blood  obtained  from  the  animal, 
it  is  easy  to  calculate  the  absolute  amount  of  blood  which  the  latter  con- 
tained, and  to  this  is  added  the  small  amount  which  was  withdrawn  to 
make  the  standard  solutions.  This  gives  the  total  amount  of  blood 
Avhich  the  animal  contained.  It  is  contrasted  with  the  weight  of  the 
animal,  previously  known. 

The  result  of  many  experiments  shows  that  the  quantity  of  blood  in 
various  animals  averages  jV  to  -^^  of  the  total  body-weight. 

An  estimate  of  the  quantity  in  man  which  corresponded  nearly  with 
this  proportion,  has  been  more  than  once  made  from  the  following  data. 
A  criminal  was  weighed  before  and  after  decapitation;  the  difference  in 
the  weight  representing  the  quantity  of  blood  which  escaped.  The 
blood-vessels  of  the  head  and  trunk  were  then  washed  out  by  the  injec- 


'HE    BLOOD. 


119 


tion  of  water,  until  the  fluid  which  escaped  had  only  a  pale  red  or  straw 
color.  This  fluid  was  then  also  weighed;  and  the  amount  of  blood 
which  it  represented  was  calculated  by  comparing  the  proportion  of 
solid  matter  contained  in  it  with  that  of  the  first  blood  which  escaped 
on  decapitation.  Two  experiments  of  this  kind  gave  precisely  similar 
results.     (Weber  and  Lehmann.) 

It  should  be  remembered,  in  connection  with  these  estimations,  that 
the  quantity  of  the  blood  must  vary  very  considerably,  even  in  the  same 
animal,  with  the  amount  of  both  the  ingesta  and  egesta  of  the  period 
immediately  preceding  the  experiment;  it  has  been  found,  for  example, 
that  the  quantity  of  blood  obtainable  from  the  body  of  a  fasting  animal 
rarely  exceeds  a  half  of  that  which  is  present  soon  after  a  full  meal. 

Coagulation  of  the  Blood. 

One  of  the  most  characteristic  properties  which  the  blood  possesses 
is  that  of  dotting  or  coagulating.  This  phenomenon  may  be  observed 
under  the  most  favorable  conditions  in  blood  which  has  been  drawn 
into  an  open  vessel.     In  about  two  or  three  minutes,  at  the  ordinary 


Fig.  117.— Reticulum  of  fibrin,  from  a  drop  of  liuman  blood,  after  treatment  with  rosanilin. 

(Ranvier.) 

temperature  of  the  air,  the  surface  of  the  fluid  is  seen  to  become  semi- 
solid or  jelly-like,  and  this  change  takes  place,  in  a  minute  or  two  after- 
ward iit  the  sides  of  the  vessel  in  which  it  is  contained,  and  then  extends 
throughout  the  entire  mass.  The  time  which  is  occupied  in  these 
changes  is  about  eight  or  nine  minutes.  The  solid  mass  is  of  exactly 
the  same  volume  as  the  previously  liquid  blood,  and  adheres  so  closely 
to  the  sides  of  the  containing  vessel  that  if  the  latter  be  inverted  none 
of  its  contents  escape.  The  solid  mass  is  the  crassamentum  or  clot.  If 
the  clot  be  watched  for  a  few  minutes,  drops  of  a  light,  straw-colored 
fluid,  the  serum,  may  be  seen  to  make  their  appearance  on  the  surface, 


120  HANDBOOK    OF    PHYSIOLOGY, 

and,  as  they  become  more  and  more  numerous,  to  run  together,  form- 
ing a  complete  superficial  stratum  above  the  solid  clot.  At  the  same 
time  the  fluid  begins  to  transude  at  the  sides  and  at  the  under-surface 
of  the  clot,  which  in  the  course  of  an  hour  or  two  floats  in  the  liquid. 
The  first  drops  of  serum  appear  on  the  surface  about  eleven  or  twelve 
minutes  after  the  blood  has  been  drawn;  and  the  fluid  continues  to 
transude  for  from  thirty-six  to  forty-eight  hours. 

The  clotting  of  blood  is  due  to  the  development  in  it  of  a  substance 
called  fibrin,  which  appears  as  a  meshwork  (fig.  117)  of  fine  fibrils.  This 
meshwork  entangles  and  incloses  within  itself  the  blood  corpuscles. 
The  first  clot  formed,  therefore,  includes  the  whole  of  the  constituents 
of  the  blood  in  an  apparently  solid  mass,  but  soon  the  fibrinous  mesh- 
work begins  to  contract  and  the  serum  which  does  not  belong  to  the 
clot  is  squeezed  out.  When  the  whole  of  the  serum  has  transuded  the 
clot  is  found  to  be  smaller,  but  firmer  and  harder,  as  it  is  now  made  up 
of  fibrin  and  blood  corpuscles  only.  Thus  coagulation  rearranges  the 
constituents  of  the  blood ;  liquid  blood  being  made  up  of  plasma  and 
blood  corpuscles,  and  clotted  blood  of  serum  and  clot. 

Liquid  Blood. 


Plasma.  Corpuscles. 


Serum. 


Clot. 


Clotteil  Blood. 

Under  ordinary  circumstances  coagulation  occurs  before  the  red  cor- 
puscles have  had  time  to  subside;  and  thus  from  their  being  entangled 
in  the  meshes  of  the  fibrin,  the  clot  is  of  a  deep  red  color  throughout, 
probably  slightly  darker  at  the  most  dependent  part,  from  greater  accu- 
mulation of  red  corpuscles  there  than  elsewhere.  When,  however,  coag- 
ulation is  from  any  cause  delayed,  as  when  blood  is  kept  at  a  tempera- 
ture slightly  above  0°  C.  (32°  F,),  or  when  clotting  is  naturally  slow,  as 
is  the  case  with  horse's  blood,  or,  lastly,  in  certain  diseased  conditions, 
particularly  in  inflammatory  states,  time  is  allowed  for  the  colored  cor- 
puscles to  sink  to  the  bottom  of  the  fluid.  When  clotting  after  a  time 
occurs,  the  upper  layers  of  the  blood  are  free  of  colored  corpuscles  and 
consist  chiefly  of  fibrin.  This  forms  a  superficial  stratum  differing  in 
appearance  from  the  rest  of  the  clot,  and  is  of  a  grayish  yellow  color. 
This  is  known  as  the  bufi/  coat  or  crusta  phlogistica.  The  buffy  coat 
produced  in  the  manner  just  described,  commonly  contracts  more  than 
the  rest  of  the  clot,  on  account  of  the  absence  of  colored  corpuscles 


THE    BLOOD.  121 

from  its  moshes,  and  because  contraction  is  less  interfered  with  by  ad- 
hesion to  the  interior  of  the  containing  vessel  in  the  vertical  than  the 
horizontal  direction.  A  cup-like  appearance  of  the  buify  coat  results, 
and  the  clot  is  not  only  buUed  but  cupped  on  the  surface. 

Formation  of  Fibrin. — That  the  clotting  of  blood  is  due  to  the  grad- 
ual appearance  in  it  of  fibrin  may  be  easily  demonstrated.  For  example, 
if  recently  drawn  blood  be  whipped  with  a  bundle  of  twigs,  the  fibrin 
may  be  withdrawn  from  the  blood  before  it  can  entangle  the  blood  cor- 
puscles within  its  meshes,  as  it  adheres  to  the  twigs  in  stringy  threads 
almost  free  from  corpuscles ;  the  blood  from  which  the  fibrin  has  been 
withdrawn  no  longer  exhibits  the  power  of  spontaneous  coagulability. 
Although  these  facts  have  long  been  known,  the  closely  associated 
problem  as  to  the  exact  manner  in  which  fibrin  is  formed  is  by  no  means 
so  simple.  It  will  be  most  convenient  to  treat  of  the  question  step  by 
step. 

In  the  first  place  it  appears  that  under  the  ordinary  conditions  of 
ex^QTiniQwi,  the  fibrin  is  chiefii/,  if  not  entirely  derived  from  the  plasma  ; 
for  although  the  colorless  corpuscles  may  be  intimately  connected  with 
the  process,  as  will  be  shown  later  on,  yet  the  colored  corpuscles  take  no 
active  part  in  it.  This  statement  does  not  deny  the  possibility  that 
fibrin  may  sometimes  be  derived  from  the  colored  corpuscles.  Indeed, 
this  is  more  than  probable,  as  experiments  have  shown  that  if  a  little 
defibrinated  blood  be  added  to  serum,  the  haemoglobin  leaves  the  stroma 
of  the  colored  corpuscles  of  the  blood,  and  a  substance  arises  from  it 
called  stroma-fibrin,  indistinguishable  from  ordinary  fibrin,  and  the 
serum  is  clotted. 

But  normally  fibrin  is  derived  from  the  plasma. 

Pure  plasma  may  be  procured  by  delaying  coagulation  in  blood  by 
keeping  it  at  a  temperature  slightly  above  freezing  point,  until  the 
colored  corpuscles  have  subsided  to  the  bottom  of  the  containing  vessel: 
the  blood  of  the  horse  being  specially  suited  for  the  purposes  of  this 
experiment.  A  portion  of  the  colorless  supernatant  plasma,  if  decanted 
into  another  vessel  and  exposed  to  the  ordinary  temperature  of  the  air, 
will  coagulate  just  as  though  it  were  the  entire  blood,  producing  a  clot 
similar  in  all  respects  to  blood  clot,  except  that  it  is  almost  colorless 
from  the  absence  of  red  corpuscles.  If  some  of  the  plasma  be  diluted 
with  twice  or  three  times  its  bulk  of  normal  saline  solution,*  coagula- 
tion is  delayed,  and  the  stages  of  the  gradual  formation  of  fibrin  in  it 
may  be  conveniently  watched.  The  viscidity  which  precedes  the  com- 
plete coagulation  may  be  actually  seen  to  be  due  to  the  formation  of 
fibrin  fibrils — first  of  all  at  the  edge  of  the  fluid  containing  vessel,  and 
then  gradually  extending  throughout  the  mass. 

*  Normal  saline  solution  commonly  consists  of  a  .6  per  cent  solution  of  com- 
mon salt  (sodium  chloride)  in  water. 


122  HANDBOOK    OF    PHYSIOLOGY. 

If  a  further  portion  of  plasma_,  diluted  or  not,  be  whipped  with  a 
bundle  of  twigs,  the  fibrin  may  be  obtained  as  a  solid,  stringy  mass,  just 
in  the  same  way  as  from  the  entire  blood,  and  the  resulting  fluid  no 
longer  retuins  its  power  of  spontaneous  coagulability. 

It  is  not  indeed  necessary  that  the  plasma  shall  have  been  obtained 
by  the  jirocess  of  cooling  above  described,  as  if  it  had  been  separated 
from  the  corpuscles  in  any  other  way,  e.g.,  by  allowing  blood  to  flow 
direct  from  the  vessels  of  an  animal  into  a  vessel  containing  a  third  or 
a  fourth  of  its  bulk  of  a  saturated  solution  of  a  neutral  salt  (preferably 
of  magnesium  or  sodium  sulphate)  and  mixing  carefully,  will  answer 
the  purpose  and,  just  as  in  the  other  case  the  colored  corpuscles  will 
subside  leaving  the  clear  superstratum  of  (salted)  plasma.  In  order ' 
that  salted  plasma  may  coagulate,  however,  it  is  necessary  to  get  rid  of 
the  salts  by  dialysis,  or  to  dilute  it  with  several  times  its  bulk  of  water. 

The  second  question  which  must  be  considered  is,  from  what  mate- 
rials of  the  plasma  is  fibrin  formedf  If  plasma  be  saturated  with  solid 
magnesium  sulphate  or  sodium  chloride,  a  white,  sticky  precipitate  called 
by  Denis,  by  whom  it  was  first  obtained,  plasmine,  is  thrown  down, 
after  the  removal  of  which,  by  filtration,  the  plasma  will  not  spontane- 
ously coagulate.  Plasmine  is  soluble  in  dilute  neutral  saline  solutions, 
and  the  solution  of  it  speedily  coagulates,  producing  a  clot  composed  of 
fibrin.  Blood  plasma  therefore  contains  a  substance  without  which  it 
cannot  coagulate,  and  a  solution  of  which  is  spontaneously  coagulable. 
This  substance  is  very  soluble  in  dilute  saline  solutions,  and  is  not, 
therefore,  fibrin,  which  is  insoluble  in  these  fluids. 

But  there  is  distinct  evidence  that  plasmine  is  a  compound  body 
made  up  of  two  or  more  substances,  not  all  of  which  are  requisite  to 
form  a  clot,  and  that  it  is  not  mere  soluble  fibrin.  There  exists  in  all 
the  serous  cavities  of  the  body  in  health,  e.g.,  the  pericardium,  the  peri- 
toneum, and  the  pleura,  a  certain  small  amount  of  transparent  fluid, 
generally  of  a  pale  straw  color,  which  in  diseased  conditions  may  be 
greatly  increased.  It  somewhat  resembles  serum  in  appearance,  but  in 
reality  differs  from  it,  and  is  probably  closely  allied  to  plasma.  This 
serous  fluid  is  not,  as  a  rule,  spontaneously  coagulable,  but  may  be  made 
to  clot  on  the  addition  of  serum,  which  is  also  a  fluid  which  has  no 
tendency  of  itself  to  coagulate.  The  clot  produced  consists  of  fibrin, 
and  the  clotting  is  identical  with  the  clotting  of  plasma.  From  the 
serous  fluid  (that  from  the  inflamed  timica  vaginalis  testis  or  hydrocele 
fluid  is  mostly  used)  we  may  obtain,  by  half-saturating  it  with  .^olid 
sodium  chloride,  a  white  viscid  substance  as  a  precipitate  which  is 
called  fibrinogen.  If  fibrinogen  be  separated  by  filtration,  it  can  be  dis- 
solved in  water,  as  a  certain  amount  of  the  neutral  salt  used  in  precipi- 
tating it  is  entangled  with  the  precipitate,  and  is  sufficient  to  produce  a 
dilute  (6  to  8  per  cent)  saline  solution  in  which  fibrinogen,  being  a  body 


THE    BLOOD.  123 

of  the  globulin  class,  is  soluble.  The  solution  of  fibrinogen  has  no 
tendency  to  clot  of  itself,  but  if  blood-serum  be  added  to  a  solution  of 
fibrinogen,  the  mixture  clots. 

On  the  other  hand  from  blood-serum  may  be  obtained,  by  saturation 
with  one  of  the  neutral  salts  above-mentioned,  a  globulin  very  similar 
in  properties  to  fibrinogen,  which  is  called  senimglobuUn  or  paragJohu- 
lin,  and  it  m;iy  be  separated  by  filtration  and  dissolved  in  a  dilute  saline 
solution  in  a  manner  similar  to  fibrinogen. 

If  the  solutions  of  fibrinogen  and  paraglobulin  be  mixed,  the  mix- 
ture cannot  be  distinguished  from  a  solution  of  plasmine,  and  in  a  great 
majority  of  cases  firmly  clots  like  that  solution,  whereas  a  mixture  of 
the  hydrocele  fluid  and  serum,  from  which  these  bodies  have  been  re- 
spectively taken,  no  longer  manifests  the  like  jjroperty. 

In  addition  to  this  evidence  of  the  compound  nature  of  plasmine,  it 
may  be  further  shown  that,  if  sufficient  care  be  taken,  both  fibrinogen 
and  paraglobulin  may  be  separately  obtained  from  plasma:  the  one, 
fibrinogen,  as  a  flaky  precipitate  by  adding  carefully  13  per  cent  of 
crystalline  sodium  chloride  to  it;  and  the  other,  paraglobulin,  may  be 
precipitated,  after  the  removal  of  fibrinogen  by  filtration,  on  the  further 
addition  (above  20  per  cent  and  to  saturation)  of  the  same  salt  or  of 
magnesium  sulphate  to  the  filtrate.  It  is  evident,  therefore,  that  both 
these  substances  must  be  thrown  down  together  when  plasma  is  at  once 
saturated  with  sodium  chloride  or  magnesium  sulphate,  and  that  the 
mixture  of  the  two  corresponds  with  plasmine. 

So  far  it  has  been  shown  that  plasmine,  the  antecedent  of  fibrin,  to 
the  possession  of  which  blood  owes  its  power  of  coagulating,  is  not  a 
simple  body,  but  is  composed  of  at  least  two  factors — viz.,  fibrinogen 
and  paraglobulin;  there  is  reason  for  believing  that  yet  another  body 
is  precipitated  with  them  in  plasmine. 

It  was  at  one  time  thought  that  the  reason  why  hydrocele  fluid 
coagulated,  when  serum  was  added  to  it,  was  that  the  latter  fluid  sup- 
plied the  paraglobulin  which  the  former  lacked;  this,  however,  is  not 
the  case,  as  hydrocele  fluid  does  not  lack  this  body,  and  moreover,  if 
paraglobulin,  obtained  from  diluted  serum  by  passing  a  stream  of  car- 
bonic acid  gas  through  it,  be  added,  no  clotting  will  take  place.  But  if 
paraglobulin,  obtained  by  the  saturation  method,  be  added  to  hydrocele 
fluid,  clotting  soon  follows,  as  it  will  also  in  a  mixed  solution  of  fibrin- 
ogen and  paraglobulin,  both  obtained  by  the  saturation  method.  From 
this  it  is  evident  that  in  plasmine  there  is  something  more  than  the  two 
bodies  above  mentioned,  and  that  this  something  is  precipitated  with 
the  paraglobulin  by  the  saturation  method,  and  is  not  precipitated  by 
the  carbonic  acid  method. 

The  following  experiments  show  that  this  substance  is  of  the  nature 
of  a  ferment.     If  defibrinated  blood  or  serum  be  kept  in  a  stoppered 


124  HANDBOOK    OF    PHYSIOLOGY. 

bottle  with  its  own  bulk  of  alcohol  for  some  weeks,  all  the  proteids  are 
precipitated  in  a  coagulated  form ;  if  the  precipitate  be  then  removed 
by  filtration,  dried  over  sulphuric  acid,  finely  powdered,  and  then  sus- 
pended in  water,  a  watery  extract  may  be  obtained  by  further  filtration, 
containing  but  little  proteid.  Yet  a  little  of  this  watery  extract  will 
produce  coagulation  in  fluids,  e.g.,  hydrocele  fluid  or  diluted  plasma, 
which  are  not  sjiontaneously  coagulable,  or  which  coagulate  slowly  and 
with  difficulty.  It  will  also  cause  a  mixture  of  fibrinogen  and  paraglob- 
ulin  both  obtained  by  the  carbonic  acid  method  to  clot.  The  watery 
extract  aj)pears  to  contain  the  body  which  is  precipitated  with  tbe 
paraglobulin  by  the  saturation  method.  Its  active  properties  are  en- 
tirely destroyed  by  boiling.  The  amount  of  the  extract  added  does  not 
influence  the  amount  of  the  clot  formed,  but  only  the  rapidity  of  clot- 
ting, and  moreover  the  active  substance  contained  in  the  extract  evi- 
dently does  not  form  part  of  the  clot,  as  it  may  be  obtained  from  the 
serum  after  blood  has  clotted.  So  that  the  substance  contained  in  the 
aqueous  extract  of  blood  appears  to  belong  to  that  class  of  bodies  which 
promote  the  union  of,  or  cause  changes  in,  other  bodies,  without  them- 
selves entering  into  union  or  undergoing  change;  these  are  known  as 
jerments.  It  has,  therefore,  received  the  name  fibrin  ferment.  This 
ferment  is  developed  in  blood  soon  after  it  has  been  shed,  and  its 
amount  continues  to  increase  for  some  little  time  (p.  135). 

So  far  we  have  seen  that  plasmine  is  a  body  composed  of  three  sub- 
stances, viz.,  fibrinogen,  paraglobulin,  and  fibrin  ferment.  But  we  shall 
see  that  only  two  of  them  are  necessary  to  coagulation. 

Alex.  Schmidt,  to  whom  we  are  indebted  for  much  of  our  knowledge 
of  this  subject,  believed  that  the  three  substances  are  necessary  to  the 
production  of  a  clot.  He  thought  that  the  reason  why  coagulation  does 
not  occur  in  serum  which  contains  paraglobulin  and  the  fibrin  ferment 
is  that  serum  lacks  fibrinogen,  and  that  when  it  does  not  occur  in  fluids 
which  contain  fibrinogen,  joaraglobulin  or  the  ferment  or  both  are  want- 
ing. Schmidt's  view  is,  however,  quite  untenable  in  the  face  of  the  fact 
that  a  solution  of  pure  fibrinogen  will  clot  firmly  on  the  addition  of  a 
solution  of  fibrin  ferment,  and  that  the  complemental  proposition  is 
equally  true,  viz.,  that  a  mixture  of  paraglobulin  and  fibrin  ferment 
(such  as  exists  in  serum)  will  not  clot.  It  is  to  Hammersten  that  the 
credit  of  clearing  up  this  matter  is  due;  he  proved  that  paraglobulin  is 
not  an  essential  in  coagulation,  since  fibrin  is  formed  from  fibrinogen 
alone  by  the  action  of  fibrin  ferment;  so  that  the  ferment  which  is  pre- 
cipitated with  paraglobulin  is  essential  and  not  that  body  itself.  He 
showed,  however,  that  paraglobulin  possesses  the  property,  in  common 
with  many  other  bodies,  of  combining  with — or  decomposing,  and  so 
rendering  inert — certain  substances  which  have  the  power  of  preventing 
the  formation   or  precipitation  of  fibrin,  such  a  power  belonging  for 


THE    BLOOD.  125 

example  to  the  free  alkalies,  to  the  alkaline  carbonates,  and  to  certain 
salts.  He  considered  that  fibrinogen  is  probably  decomposed  into  fibrin 
with  the  production  of  some  other  substances;  or  that  it  may  possibly 
be  bodily  converted  into  it  under  the  action  of  the  ferment. 

It  is  now  generally  believed,  however,  that  the  presence  of  a  certain 
but  small  amount  of  salts,  especially  of  sodium  chloride,  and  according 
to  the  researches  of  Green,  of  calcitwi  siilphate,  is  necessary  for  coagu- 
lation, and  that  without  it  clotting  cannot  take  place. 

Certain  other  changes  besides  solidification  take  place  in  blood  when 
it  clots,  viz.: — its  temperature  rises  slightly,  it  becomes  less  alkaline, 
the  oxygen  is  diminished,  the  tension  of  carbonic  anhydride  rises,  and  a 
trace  of  ammonia  gas  is  given  off.  The  clotted  part  is  said  to  become 
electrically  negative  to  the  unclotted  part. 

Sources  of  the  Fibrin  Ferment. — Fibrin  ferment  cannot  be  obtained 
in  any  appreciable  amount  from  blood  which  is  allowed  to  flow  direct 
from  the  living  vessel  into  absolute  alcohol.  It  is  almost  certainly  a 
result  of  the  more  or  less  complete  disintegration  of  the  colorless  cor- 
puscles after  blood  is  shed,  or  of  the  intermediate  corpuscles  which  will 
be  described  later  on  under  the  name  of  hlood  platelets.  The  proofs  of 
this  may  be  briefly  summarized  as  follows: — (1)  That  all  strongly  coag- 
ulable  fluids  contain  these  corpuscles  almost  in  direct  proportion  to 
their  coagulability;  (2)  That  clots  formed  on  foreign  bodies,  such  as 
needles  projecting  into  the  interior  or  lumen  of  living  blood-vessels,  are 
preceded  by  an  aggregation  of  colorless  corjsuscles;  (3)  That  plasma  in 
which  these  corpuscles  happen  to  be  scanty,  clots  feebly;  (4)  That  if 
horse's  blood  be  kept  in  the  cold,  so  that  the  corpuscles  subside,  it  will 
be  found  that  the  lowest  stratum,  containing  chiefly  colored  corpuscles, 
will,  if  removed,  clot  feebly,  as  it  contains  little  of  the  fibrin  factors; 
whereas  the  colorless  plasma,  especially  the  lower  layers  of  it  in  which 
the  colorless  corpuscles  are  most  numerous,  will  clot  well,  but  if  filtered 
in  the  cold  will  not  clot  so  well,  indicating  that  when  filtered  nearly 
free  from  colorless  corpuscles  even  the  plasma  does  not  contain  sufficient 
of  all  the  fibrin  factors  to  produce  thorough  coagulation;  (5)  In  a  drop 
of  coagulating  blood  observed  under  the  microscojoe  the  fibrin  fibrils  are 
seen  to  start  from  the  colorless  corpuscles. 

Nature  of  the  Fibrin  Ferment. — Halliburton  has  brought  forward 
weighty  reasons  for  believing  fibrin  ferment  to  be  a  globulin.  Thus,  a 
solution  of  ferment  made  according  to  Schmidt's  method,  if  clear,  neu- 
tral, or  faintly  alkaline  in  reaction,  does  not  coagulate  on  boiling,  and 
gives  the  proteid  tests  faintly.  If  the  solution  be  concentrated,  these 
reactions  become  more  developed,  and  the  proteid  present  reacts  to  the 
test  for  globulins.  The  ferment  too  can  be  extracted  from  shreds  of 
fibrin  obtained  from  whipped  blood  by  the  method  usually  employed 
for  dissolving  globulins,  viz.,  by  an  8  per  cent  solution  of  sodium  chlor- 


126  HANDBOOK    OF    PHYSIOLOGY. 

ide,  .ind  when  the  globulin  is  removed  from  the  solution  thus  obtaiTied, 
the  ferment  uction  disappears  also.  A  globulin  (cell-globulin)  with 
similar  characters,  which  has  very  powerful  ferment  properties,  can  be 
obtained  from  the  cells  of  lymphatic  glands,  which  are  the  precursors 
of  the  colorless  corpuscles  of  the  blood.  Further,  the  ferment  action 
is  destroyed  at)  a  temperature  of  from  73°-75°  C.  (165°  F.),  or  if  in 
saline  solution  at  a  lower  temperature  still,  60°-65°  C.  (145°  F )  corre- 
sponding closely  with  the  coagulating  points  of  proteids  and  globulins 
respectively. 

The  explanation  of  the  clotting  of  blood  which  has  been  given  in  the  pre- 
ceding pages,  and  which  depends  chiefly  upon  the  researches  of  Alex.  Schmidt 
and  Hammersten,  supposes  that  it  is  one  of  the  fermentative  actions,  so  many 
of  which  are  believed  to  go  on  in  the  living  body.  Wooldridge  contested  this 
view  of  the  process.  His  researches  led  him  to  the  belief  that  coagulation  of 
the  blood  is  a  vital  process,  or  rather  that  it  is  the  last  act  of  vitality  displayed 
by  blood  plasma,  which  he  considered  to  be  living  protoplasm.  Some  of  the 
results  of  his  experiments  may  with  advantage  be  here  mentioned.  Firstly, 
he  showed  that  plasma  itself  contains  everything  that  is  necessary  for  coagula- 
tion. For  his  experiments  he  used  plasma  obtained  by  injecting  a  solution  of 
commercial  peptone  into  the  veins  of  an  animal  and  removing  blood  from  it 
immediately  afterward.  The  blood  so  obtained  does  not  readily  clot,  and  so 
allows  the  separation  of  the  blood -coi'puscles  from  the  plasma,  the  plasma  so 
obtained  being  called  ijeptone  plasma.  The  whole  of  the  corpuscular  elements 
were  removed  by  repeated  treatment  with  a  centrifugal  machine.  Peptone 
plasma  was  shown  to  clot  by  the  use  of  some  simple  mechanical  means,  e.g., 
filtering  through  a  clay  cell,  or  through  filter  paper,  or  on  neutralization  with 
acetic  acid,  or  carbonic  acid,  or  by  dilution  with  water  or  saline  solution. 
Thus  it  would  appear  that  if  the  colorless  blood  coriJuscles  aid  coagulation, 
their  influence  is  only  secondary. 

Secondly,  he  showed  that  the  imjjortant  precui-sor  of  clotting  in  this  pep- 
tone-plasma may  be  separated  from  it,  as  a  precipitate,  if  the  plasma  be  kept 
in  ice  for  some  time,  and  that  after  its  removal  the  plasma  contains  only  a 
little  fibrinogen  capable  of  clotting  by  the  action  of  fibrin  ferment.  If  the 
plasma  be  diluted  with  water  or  slightly  acidulated,  however,  the  fibrin  fer- 
ment is  able  to  produce  a  complete  clotting. 

In  peptone  plasma,  Wooldridge  stated  that  three  coagulable  bodies  exist, 
which  he  calls  A,  B,  and  C  fibrinogen,  and  which  are  closely  allied  to  one 
another.  C-fibrinogen  is  identical  with  the  body  which  has  been  hitherto  de- 
scribed as  fibrinogen,  is  present  in  very  small  amount,  and  clots  on  addition  of 
fibrin  ferment.  The  coagulable  matter  present  in  greatest  amount  is  B-fibrin- 
ogen,  which  clots  on  addition  of  lecithin,  or  of  lymph  corpuscles,  but  not  on 
the  addition  of  fibrin  ferment.  A-fibrinogen  is  separated  from  plasma  by 
cooling,  in  minute  regular  rounded  granules,  from  which,  if  watched  under 
tlie  microscope,  rounded  distinctly  biconcave  discs  are  seen  to  arise,  quite  in- 
distinguishable from  blood  plates;  it  is  not  coagulated  by  fibrin  ferment. 
Finally,  he  considered  that  when  blood  plasma  dies,  an  action  takes  place 
between  A-  and  B-fibrinogen,  which  are  both  compounds  of  profceid  and  leci- 
thin. The  essential  of  this  action  is  a  loss  of  lecithin  on  the  part  of  the  former 
and  a  gain  of  lecithin  on  the  part  of  the  latter,  with  the  result  of  the  produc- 


THE   BLOOD.  127 

tion  of  fibrin,  a  third  proteid-lecithin  compound,  while  other  substances  con- 
tained in  tlie  serum,  including  fibrin  ferment,  are  at  the  same  time  set  free. 
Thus,  fibrin  ferment,  a  body  which  can  convert  C-fibrinogen  into  fibrin,  is  not 
present  in  living  plasma,  but  is  a  result  of  its  disorganization  or  death.  As 
the  fibrinogen  which  can  be  clotted  by  the  ferment  is  only  j^resent  in  minimal 
amounts  in  living  plasma,  injection  of  a  solution  of  fibrin  ferment  or  of  shed 
blood  does  not  produce  intra- vascular  clotting,  whereas  injection  of  lymph 
corpuscles  from  lymphatic  glands  or  of  lecithin,  either  of  which  will  produce 
clotting  of  the  other  fibrinogens  which  form  the  bulk  of  the  coagulable  matter 
in  living  blood,  leads  to  extensive  intra- vascular  clotting. 

Conditions  affecting  Coagulation. —The  coagulation  of  the  blood 
is  hastened  by  the  following  means: — 

1.  Moderate  warmth,— from  about  37.8-49°  C.  (100°  to  120°  F.). 

2.  Rest  is  favorable  to  the  coagulation  of  blood.  Blood,  of  which 
the  whole  mass  is  kept  in  uniform  motion,  as  when  a  closed  vessel  com- 
pletely filled  with  it  is  constantly  moved,  coagulates  very  slowly  and 
imperfectly. 

3.  Contact  ivitli  foreign  matter,  QXi.(i  especially  multiplication  of  the 
points  of  contact.  Thus,  as  before  mentioned,  fibrin  may  be  quickly 
obtained  from  liquid  blood  by  stirring  it  with  a  bundle  of  small  twigs; 
and  even  in  the  living  body  the  blood  will  coagulate  upon  rough  bodies 
projecting  into  the  vessels. 

4.  The  free  access  of  air. — Coagulation  is  quicker  in  shallow  than  in 
tall  and  narrow  vessels. 

5.  The  addition  of  less  than  twice  the  bulk  of  water. 

The  blood  last  drawn  is  said,  from  being  more  watery,  to  coagulate 
more  quickly  than  the  first. 

The  coagulation  of  the  blood  is  retarded,  suspended,  or  pre- 
vented by  the  following  means: — 

1.  Coid  retards  coagulation;  and  so  long  as  blood  is  kept  at  a  tem- 
perature 0"^  C.  (32°  F.),  it  will  not  coagulate  at  all.  Freezing  the  blood, 
of  course,  prevents  its  coagulation;  yet  it  will  coagulate,  though  not 
firmly,  if  thawed  after  being  frozen;  and  it  will  do  so  even  after  it  has 
been  frozen  for  several  months.  A  higher  temperature  than -id"  C.  (120° 
F.)  retards  coagulation  by  coagulating  the  albumen  of  the  serum,  and' 

a  still  higher  one  above  56°  C.  (133°  F.)  prevents  it  altogether. 

2.  The  addition  of  water  in  greater  2>ro/)ortio?is  than  twice  the  bulk 
of  the  blood,  also  the  addition  of  syrup,  glycerine,  and  other  viscid  sub- 
stances. 

3.  Contact  with  living  tissues,  and  especially  with  the  interior  of  a 
living  blood-vessel.  Blood  may  be  kept  fluid  in  a  tortoise's  heart  after 
removal  from  the  body  for  several  days,  and  if  the  jugular  vein  of  a 
horse  be  ligatured  in  two  places  so  as  to  include  within  it  blood,  and 
then  be  removed  from  the  body  and  placed  in  a  cool  place,  the  contained 
blood  will  remain  unclotted  for  hours  or  even  days. 


128  HANDBOOK    OF    PHYSIOLOGY. 

4.  Tlte  addition  of  neutral  salts  in  the  proportion  of  2  or  3  per  cent 
and  upwurd.  When  added  in  hirge  jiroportion  most  of  these  saline  sub- 
stances 2^1'tJvent  coagulation  altogether.  Coagulation,  however,  ensues 
on  dilution  with  water.  The  time  during  which  blood  can  be  thus 
preserved  in  a  liquid  taste  and  coagulated  by  the  addition  of  water,  is 
quite  indefinite. 

5.  Imperfect  aeration, — as  in  the  blood  of  those  who  die  by  asphyxia. 
G.  In   inflamniatory  states  of  the  system  the  blood  coagulates  more 

slowly  aimough  more  firmly. 

7.  Coagulation  is  retarded  by  exclusion  of  the  blood  from  the  air,  as 
by  pouring   oil  on  the  surface,  etc.     In  vacuo,  the  blood   coagulates, 
quickly.     Receiving  blood  into  a  vessel,  well  smeared  inside  with   oil, 
fat,  or  vaseline,  is  said  also  to  retard  or  prevent  coagulation, 

8.  The  coagulation  of  the  blood  is  prevented  altogether  by  the  addi- 
tion of  strong  acids  and  caustic  alkalies. 

9.  The  injection  of  co^nmercial  peptone  containing  albumoses,  or  of 
various  digestive  ferments,  e.g.,  trypsin  or  pepsin,  into  the  vessels  of 
an  animal  appears  to  prevent  or  stay  coagulation  of  its  blood  if  it  be 
killed  soon  after.  The  secretion  of  the  mouth  of  the  leech,  and  possibly 
the  blood  squeezed  out  of  its  body  when  full,  also  prevents  the  clotting 
if  added  to  blood. 

It  is  stated  that  the  reason  why  blood  does  not  coagulate  in  the  living 
I'cssels  is,  that  the  factors  which  are  necessary  for  the  formation  of  fibrin 
are  not  in  the  exact  state  required  for  its  production,  and  that  at  any 
rate  the  fibrin  ferment  is  not  formed  or  is  not  free  in  the  living  blood, 
but  that  it  is  produced  (or  set  free)  at  the  moment  of  coagulation  by  the 
disintegration  of  the  colorless  (and  possibly  of  the  colored)  corpuscles. 
This  supposition  is  certainly  plausible,  and,  if  it  be  a  true  one,  it  must 
be  assumed  either  that  the  living  blood-vessels  exert  a  restraining  influ- 
ence upon  the  disintegration  of  the  corpuscles  in  sufficient  numbers  to 
form  a  clot,  or  that  they  render  inert  any  small  amount  of  fibrin  fer- 
ment, which  may  have  been  set  free  by  the  disintegration  of  a  few  cor- 
puscles; as  it  is  certain  firstly  that  corpuscles  of  all  kinds  must  from 
time  to  time  disintegrate  in  the  blood  without  causing  it  to  clot;  and, 
secondly,  that  shed  and  defibrinated  blood  which  contains  blood  corpus- 
cles, broken  down  and  disintegrated,  will  not,  when  injected  into  the 
vessels  of  an  animal,  under  ordinary  conditions,  produce  clotting.  There 
must  be  a  distinct  difference,  therefore,  if  only  in  amount,  between  the 
normal  disintegration  of  a  few  colorless  corpuscles  in  the  living  unin- 
jured blood-vessels  and  the  abnormal  disintegration  of  a  large  number 
which  occurs  whenever  the  blood  is  shed  without  suitable  precaution, 
or  when  coagulation  is  unrestrained  by  the  neighborhood  of  the  living 
uninjured  blood-vessels. 


THE   BLOOD.  139 


The  Blood  Corpuscles. 

There  are  two  principal  forms  of  corpuscles,  the  7'ed  and  the  white,  or, 
as  they  are  now  frequently  named,  the  colored  and  the  colorless.  In  the 
moist  state,  the  red  corpuscles  form  about  45  per  cent  by  weight,  of  the 
whole  mass  of  the  blood.  The  proportion  of  colorless  corpuscles  is  only 
as  1  to  500  or  600  of  the  colored. 

Red  or  Colored  Corpuscles. — Human  red  blood-corpuscles  are 
circular,  biconcave  discs  with  rounded  edges,  from  ^-j^^  to  :oVo  i'l^h  in 
diameter  6//  to  8/«,  and  y2oou  i^"'ch  or  about  2,'j.  in  thickness,  becoming 
flat  or  convex  on  addition  of  water.  When  viewed  singly  they  appear 
of  a  pale  yellowish  tinge;  the  deep  red  color  which  they  give  to  the 
blood  being  observable  in  them  only  when  they  are  seen  en  masse. 
They  are  composed  of  a  colorless,  structureless,  and  transparent  filmy 
framework  or  stroma,  infiltrated  in  all  parts  by  a  red  coloring  matter 
termed  hwmoglobin.  The  stroma  is  tough  and  elastic,  so  that,  as  the 
corpuscles  circulate,  they  admit  of  elongation  and  other  changes  of  form, 
in  adaptation  to  the  vessels,  yet  recover  their  natural  shape  as  soon  as 
they  escape  from  compression.  The  term  cell,  in  the  sense  of  a  bag  or 
sac,  although  sometimes  applied,  is  scarcely  applicable  to  the  red  blood 
corpuscle;  it  must  be  considered,  if  not  solid  throughout,  yet  as  having 
no  such  marked  difference  of  consistence  in  different  parts  as  to  justify 
the  notion  of  its  being  a  membranous  sac  with  fluid  contents.  The 
stroma  exists  in  all  parts  of  its  substance,  and  the  coloring-matter  uni- 
forml}'  pervades  this;  but  at  the  same  time  it  is  probable  that  the  con- 
sistence of  the  peripheral  part  of  the  protoplasm  is  more  solid  than  that 
of  the  more  central  mass. 

The  red  corpuscles  have  no  nuclei,  although,  in  their  usual  state,  the 
unequal  refraction  of  transmitted  light  gives  the  apisearance  of  a  cen- 
tral spot,  brighter  or  darker  than  the  border,  according  as  it  is  viewed 
in  or  out  of  focus.     Their  specific  gravity  is  about  1088. 

The  corpuscles  of  all  mammals  with  the  exception  of  the  camelidae 
are  circular  and  biconcave.  In  the  camelidae  they  are  oval  and  bicon- 
vex. In  all  mammals  the  corpuscles  are  non-nucleated,  and  in  all  other 
vertebrates  (birds,  reptiles,  amphibia,  and  fish),  the  corpuscles  are  oval 
biconvex  and  nucleated  (fig.  121). 

Varieties. — The  red  corpuscles  are  not  all  alike,  some  being  rather 
larger,  paler,  and  less  regular  than  others,  and  sometimes  flat  or  slightly 
convex,  with  a  shining  jiarticle  apparent  like  a  nucleolus.  In  almost 
every  specimen  of  blood  may  be  also  observed  a  certain  number  of  cor- 
puscles smaller  than  the  rest.  They  are  termed  microcytes,  or  hcema- 
tiihlasts,  and  are  probably  immature  corpuscles. 

It  is  necessary  to  take  notice  that  much  importance  is  attached  to 
9 


130  HANDBOOK    OF    PHYSIOLOGY. 

one  form  of  these  smaller  corpuscles  named  hlood  plates  by  Bizzozero 
(Blutpliittcben).  They  are  small,  more  or  less  rounded  or  slightly  oval 
granules,  slightly  if  at  all  colored,  and  about  one  third  the  size  of  ordi- 
nary colored  corpuscles.  From  them  it  is  supposed  the  fibrin  ferment  is 
specially  derived.  They  rapidly  undergo  change  in  blood,  after  it  has 
been  drawn.     They  may  form  masses  by  coalescing. 

A  peculiar  property  of  the  red  corpuscles,  which  is  exaggerated  iu 
inflammatory  blood,  may  be  here  again  noticed,  i.e.,  their  great  tendency 
to  iidhere  together  in  rolls  or  columns  (rouleaux),  like  piles  of  coins. 
These  rolls  quickly  fasten  together  by  their  ends,  and  cluster;  so  that, 
when  the  blood  is  spread  out  thinly  on  a  glass,  they  form  a  kind  of 
irregular  network,  with  crowds  of  corpuscles  at  the  several  points. cor- 
responding Avith  the  knots  of  the  net  (fig.  118).  Hence  the  clot  formed 
in  such  a  thin  layer  of  blood  looks  mottled  with  blotches  of  pink  upon 


Fig.  118.  Fig.  119. 

Fig.  118.— Red  corpuscles  in  rouleaux.    The  rounded  corpuscles  are  white  or  uncolored. 
Fig.  119.— Corpuscles  of  tlie  frog.    The  central  mass  consists  of  nucleated  colored  corpuscles. 
The  other  corpuscles  are  two  varieties  of  the  colorless  form. 

a  white  ground,  and  in  a  larger  quantity  of  blood  such  masses  help,  by 
the  consequent  rapid  subsidence  of  the  corpuscles,  in  the  formation  of 
the  buify  coat  already  referred  to. 

Action  of  Re-agents. — Considerable  light  has  been  thrown  on  the  physical 
and  chemical  constitution  of  red  blood-cells  by  studying  the  eflfects  produced 
by  mechanical  means  and  by  various  reagents :  the  following  is  a  brief  sum- 
mary of  these  re-actions  : — 

Pressure. — If  the  red  blood-cells  of  a  frog  or  man  are  gently  squeezed,  they 
exhibit  a  wrinkling  of  the  surface,  which  clearly  indicates  that  there  is  a 
supei-ficial  pellicle  partly  differentiated  from  the  softer  mass  within  ;  again,  if 
a  needle  be  rapidly  drawn  across  a  drop  of  blood,  several  corpuscles  will  be 
found  cut  in  two,  but  this  is  not  accompanied  by  any  escape  of  cell  contents ; 
the  two  halves,  on  the  contrary,  assume  a  rounded  form,  proving  clearly  that 
the  corpuscles  are  not  mere  membranous  sacs  with  fluid  contents  like  fat-cells. 

Fluids,     i.    Water. — When  water  is  added  gradually  to  frog's  blood,  the  oval 


THE   BLOOD. 


131 


disc-shaped  corpuscles  become  spherical,  and  gradually  discharge  their  haemo- 
globin, a  pale,  trausjjareiit  stroma  being  left  behind  ;  human  red  blood-cells 
change  from  a  discoidal  to  a  spheroidal  form,  and  discharge 
their  cell- contents,  becoming  quite  transparent  and  all  but  in- 
visible. 

ii.  Saline  solution  produces  no  appreciable  effect  on  the  red 
blood  cells  of  the  frog.     In  the  red  blood-cells  of  man  the  dis- 
coid shape  is  exchanged  for  a  spherical  one,  with  spinous  pro- 
jections, like  a  horse-chestnut  (fig.  120).     Their  original  forms  can  be  at  once 
restored  by  the  use  of  carbonic  acid. 

iii.  Acetic  acid  (dilute)  causes  the  nucleus  of  the  red  blood-cells  in  the  frog 
to  become  more  clearly  defined  ;  if  the  action  is  prolonged,  the  nucleus  becomes 
strongly  granulated,  and  all  the  coloring  matter  seems  to  be  concentrated  in  it, 


Fig.  120. 

Effect  of  saline 

solution. 


Fig.  131.— The  above  illustration  is  somewhat  altered  from  a  drawing  by  Gulliver,  in  the  Proceed. 
Zool.  Society,  and  exhibits  the  typical  charactei-s  of  the  red  blood-cells  in  the  main  divisions  of  the 
Vertebrata.  The  fractions  are  those  of  an  inch,  and  represent  the  average  diameter.  In  the  case 
of  the  oval  cells,  only  the  long  diameter  is  here  given.  It  is  remarkable,  that  although  the  size  of 
the  red  blood-cells  varies  so  much  in  the  different  classes  of  the  vertebrate  kingdom,  that  of  the 
white  corpuscles  remains  comparatively  uniform,  and  thus  they  are,  in  some  animals,  much  greater, 
in  others  much  less  than  the  red  corpuscle  existing  side  by  side  with  them. 


the  surrounding  cell-substance  and  outline  of  the  cell  becoming  almost  invisi- 
ble ;  after  a  time  the  cells  lose  their  color  altogether.  The  cells  in  the  figure 
(fig.  122)  represent  the  successive  stages  of  the  change.  A  similar  loss  of  color 
occurs  in  the  red  cells  of  human  blood,  which,  however,  from  the  absence  of 
nuclei,  seem  to  disappear  entirely. 

iv.  Alkalies  cause  the  red  blood-cells  to  swell  and  finally  to  disappear. 

V.  Chloroform  added  to  the  red  blood- cells  of  the  frog  causes  them  to  part 


J  32  HANDBOOK    OF    PHYSIOLOGY. 

with  their  haemoglobin ;  the  stroma  of  the  cells  becomes  gradually  broken  up. 
A  similar  effect  is  produced  on  the  human  red  blood-cell. 

vi.  Tannin. — When  a  2  per  cent  fresh  solution  of  tannic  acid  is  applied  to 
frog's  blood  it  causes  the  appearance  of  a  sharply-defined  little  knob,  project- 
ing from  the  free  surface  {Roberts'  macula)  :  the  coloring  matter  becomes  at 
the  same  time  concentrated  in  the  nucleus,  which  grows  more  distinct  (fig. 
123) .     A  somewhat  similar  effect  is  produced  on  the  human  red  blood  corpuscle. 

vii.  Magenta,  when  applied  to  the  red  blood-cells  of  the  frog,  produces  a 
similar  little  knob  or  knobs,  at  the  same  time  staining  the  nucleus  and  causing 
the  discharge  of  the  haemoglobin.  The  first  effect  of  the  magenta  is  to  cause 
the  discharge  of  the  hemoglobin,  then  the  nucleus  becomes  suddenly  stained, 
and  lastly  a  finely  granular  matter  issues  through  the  wall  of  the  corpuscle, 
becoming  stained  by  the  magenta,  and  a  macula  is  formed  at  the  point  of  es- 
cape.    A  similar  macula  is  produced  in  the  human  red  blood-cells. 

viii.  Boric  acid. — A  2  \)er  cent  solution  applied  to  nucleated  red  blood-cells 
(frog)  will  cause  the  concentration  of  all  the  coloring  matter  in  the  nucleus ; 
the  colored  body  thus  formed  gradually  quits  its  central  position,  and  comes  to 
be  partly,  sometimes  entirely,  protruded  from  the  surface  of  the  now  colorless 
cell  (fig.  124).     The  result  of  this  experiment  led  Briicke  to  distinguish  the 

0 

oo 


Fig.  122.  F'ig.  123.  Fig.  124.  Fig.  135. 

Effect  of  acetic  acid.      Effect  of  tannin.     Effect  of  boric  acid.     Effect  of  gases. 

colored  contents  of  the  cell  (zooid)  from  its  colorless  stroma  (cecoid) .  When 
applied  to  the  non-nucleated  mammalian  corpuscle  its  effect  merely  resembles 
that  of  other  dilute  acids. 

ix.  Ammonia. — Its  effects  seem  to  vary  according  to  the  degree  of  concen- 
tration. Sometimes  the  outline  of  the  corpuscles  becomes  distinctly  crenated  ; 
at  other  times  the  effect  resembles  that  of  boracic  acid,  while  in  other  cases 
the  edges  of  the  corpuscles  begin  to  break  up. 

Gases.  Carbonic  acid. — If  the  red  blood- cells  of  a  frog  be  first  exposed  to 
the  action  of  water-vapor  (which  renders  their  outer  pellicle  more  readily  per- 
meable to  gases),  and  then  acted  on  by  carbonic  acid,  the  nuclei  immediately 
become  clearly  defined  and  strongly  granulated  ;  when  air  or  oxygen  is  admitted 
the  original  appearance  is  at  once  restored.  The  upper  and  lower  cell  in  fig. 
125  show  the  effect  of  carbonic  acid  ;  the  middle  one  the  effect  of  the  re-admis- 
sion of  air.  These  effects  can  be  reproduced  five  or  six  times  in  succession. 
If,  however,  the  action  of  the  carbonic  acid  be  much  prolonged,  the  granula- 
tion of  the  nucleus  becomes  permanent ;  it  appears  to  depend  on  a  coagulation 
of  the  paraglobulin. 

Heat.— The  effect  of  heat  up  to  50^—60°  C.  (120—140°  F.)  is  to  cause  the 
formation  of  a  number  of  bud-like  processes  (fig.  126) . 

Electricity  causes  the  red  blood-corpuscles  to  become  crenated,  and  at  leugth 
mulberry -like.     Finally  they  recover  their  round  form  and  become  quite  pale. 

The  Colorless  Corpuscles. — In  human  blood  the  white  or  color- 
jess  corpuscles  or  leucocytes  are  nearly  spherical  masses  of  granular  pro- 


THE    BLOOD.  133 

toplasm  without  cell  wall.  The  granular  appearance  more  marked  in 
some  than  in  others  {vide  infra),  is  due  to  the  presence  of  particles 
probably  of  a  fatty  nature.  In  all  cases  one  or  more  nuclei  exist  in  each 
corpuscle.  The  size  of  the  corpuscle  average  gsVo  of  an  inch  (10/^)  in 
diameter. 

In  health,  the  proportion  of  white  to  red  corpuscles,  which,  taking 
an  average,  is  about  1  to  500  or  600,  varies  considerably  even  in  the 
course  of  the  same  day.  The  variations  appear  to  depend  chiefly  on  the 
amount  and  probably  also  on  the  kind  of  food  taken;  the  number  of 
leucocytes  being  very  considerably  increased  by  a  meal,  and  diminished 
again  on  fasting.  Also  in  young  persons,  during  pregnancy,  and  after 
great  loss  of  blood,  there  is  a  larger  proportion  of  colorless  blood  cor- 
puscles, which  probably  shows  that  they  are  more  rapidly  formed  under 
these  circumstances.  In  old  age,  on  the  other  hand,  their  proportion 
is  diminished. 

Varieties. — The  colorless  corpuscles  present  greater  diversities  of 
form  than  the  red  ones.     Two  chief  varieties  are  to  be  seen  in  human 


Fi~.  lir.— A.  Three  cnloi-eil  blood-corpuscles.    B.  Three  colorless  blood-coi-puscles  acted  on  by 
acetic  acid  ;  the  nuclei  are  very  clearly  visible,     x  900. 

blood;  one  which  contains  a  considerable  number  of  granules,  and  the 
other  which  is  paler  and  less  granular.  In  size  the  variations  are  great, 
for  in  most  specimens  of  blood  it  is  possible  to  make  out,  in  addition  to 
the  full-sized  varieties,  a  number  of  smaller  corpuscles,  consisting  of  a 
large  spherical  nucleus  surrounded  by  a  variable  amount  of  more  or  less 
granular  protoplasm.  The  small  corpuscles  are,  in  all  probability,  the 
undeveloped  form  of  the  others,  and  are  derived  from  the  cells  of  the 
lymph. 

Besides  the  above-mentioned  varieties,  Schmidt  decribes  another  form 
which  he  looks  upon  as  intermediate  between  the  colored  and  the  color- 
less forms,  viz.,  corpuscles  which  contain  red  granules  of  hfemoglobin  in 
their  protoplasm.  The  different  varieties  of  colorless  corpuscles  are 
especially  well  seen  in  the  blood  of  frogs,  newts,  and  other  cold-blooded 
animals. 

Amoeboid  movement. — The  remarkable  property  of  the  colorless 
corpuscles  of  spontaneously  changing  their  shape  was  first  demonstrated 
by  Wharton  Jones  in  the  blood  of  the  skate.  If  a  drop  of  blood  be  ex- 
amined with  a  high  power  of  the  microscope  on  a  warm  stage,  or,  in 
other  words,  under  conditions  by  which  loss  of  moisture  is  prevented, 

0 


134  HANDBOOK    OF    PHYSIOLOGY. 

and  at  the  same  time  the  temperature  is  maintained  at  about  that  of 
the  body  37°  C.  (98.5°  F.),  the  colorless  corpuscles  will  be  observed 
slowly  to  alter  their  shapes,  and  to  send  out  processes  at  various  parts 
of  their  circumference.  The  amoeboid  movement  which  can  be  demon- 
strated in  human  colorless  blood-corpuscles,  can  be  most  conveniently 
studied  in  the  newt's  blood.  The  processes  which  are  sent  out  from  the 
coriiuscle  are  either  lengthened  or  withdrawn.  If  lengthened,  the  pro- 
toijlasm  of  the  whole  corpuscle  flows  as  it  were  into  its  process,  and  the 
corpuscle  changes  its  position;  if  withdrawn,  protrusion  of  another  proc- 
ess at  a  different  point  of  the  circumference  speedily  follows.  The 
change  of  position  of  the  corpuscle  can  also  take  place  by  a  flowing 
movement  of  the  whole  mass,  and  in  this  case  the  locomotion  is  com- 
paratively rapid.  The  activity  both  in  the  jDrocesses  of  change  of  shape 
and  also  of  change  in  position,  is  much  more  marked  in  some  corpus- 
cles, viz.,  iu  the  granular  variety,  than  in  others.     Klein  states  that  in 


Fig.  138. — Human  colorless  blood-corpuscles,  showing  its  successive  changes  of  outline  within 
ten  minutes  when  kept  moist  on  a  warm  stage.     CSchofleld.) 

the  newt's  blood  the  changes  are  especialy  noticeable  in  a  variety  of  tbe 
colorless  corpuscle,  which  consists  of  a  mass  of  finely  granular  proto- 
plasm with  jagged  outline,  and  contains  three  or  four  nuclei,  or  in  large 
irregular  masses  of  protoplasm  containing  from  five  to  twenty  nuclei. 
Another  phenomenon  may  be  observed  to  occur  in  the  colorless  corpus- 
cles, viz.,  tlie  division  of  the  corjniscles.  A  cleft  takes  place  in  the  pro- 
toplasm at  one  point,  becomes  deeper  and  deeper,  and  then  by  the 
lengthening  out  and  attenuation  of  the  connection,  and  finally  by  its 
rupture,  two  corpuscles  result.  The  nuclei  have  previously  undergone 
division.  The  cells  so  formed  are  remarkably  active  in  their  movements. 
Thus  we  see  that  the  rounded  form  which  the  colorless  corpuscles  pre- 
sent in  ordinary  microscopic  specimens  must  be  looked  upon  as  the 
shape  natural  to  a  dead  corpuscle  or  to  one  whose  vitality  is  dormant 
rather  than  as  the  shape  proper  to  one  living  and  active. 

Action  of  reagents  upon  the  colorless  corpuscles. — Feeding  the  corpus- 
cles.— If  some  fine  pigment  granules,  e.g.,  powdered  vermilion,  be  added  to  a 
fluid  containing  colorless  blood-corijuscles,  on  a  glass  slide,  these  will  be 
observed,  under  the  microscope,  to  take  up  the  pigment.  In  some  cases 
colorless  corpuscles  have  been  seen  with  fragments  of  colored  ones  thus  em- 
bedded in  their  substance.  They  have  also  been  seen,  in  diseased  states,  to 
contain  micro-organisms,  e.g.,  bacilli,  and  according  to  some  pathologists  ai-e 
capable  of  destroying  them  (phagocytosis) .  They  may  too  take  up  other  for- 
eign matter  or  even  other  colorless  corpuscles.  This  property  of  the  colorless 
corpuscles  is  especially  interesting  as  helping  still  further  to  connect  them  with 


THE   BLOOD. 


135 


the  lowest  forms  of  animal  life,  and  to  connect  both  with  the  organized  cells  of 
which  the  higher  animals  are  composed. 

The  property  which  the  colorless  corpuscles  possess  of  passing 
through  the  walls  of  the  blood-vessels  will  be  described  later  on. 

Enumeration  of  the  blood-corpuscles. — Several  methods  are  employed  for 
counting  the  blo(xl -corpuscles,  most  of  them  depending  upon  the  same  princi- 
ple, i.e.,  the  dilution  of  a  minute  volume  of  blood  with  a  given  volume  of  a 
colorless  solution  similar  in  specific  gravity  to  blood  plasma,  so  that  the  size 
and  shape  of  the  corpuscles  is  altered  as  little  as  possible.  A  minute  quantity 
of  the  well-mixed  solution  is   then  taken,  examined  under  the  microscope, 


Healthy  bacillus 


Healthv  bacillus  — 


Healthy  bacillus 
Partially  digested  bacillus 


Partially  digested  leucocyte  . 
Nuclei  vacuolated 


Nucleus 
/it^^^>.   Bacillus  in  leucocyte 
fSj^'^     Partially  digested  leucocyte 

Foreign  matter 


Foreign  matter 


Leucocytes  ■ 


Particles  of  foreign  matter 

Particles  of  foreign  matter 
Particles  of  foreign  matter 


Fig.  129.— Macrophages  containing  bacilli  and  other  structures  supposed  to  be  imdergoing  digestion. 

(Buffer.) 

either  in  a  flattened  capillary  tube  (Malassez)  or  in  a  cell  (Hayem  &  Nachet, 
Govvers)  of  known  capacity,  and  the  number  of  corpuscles  in  a  measured  lengtli 
of  the  tube,  or  in  a  given  area  of  the  cell  is  counted.  The  length  of  the  tube 
and  the  area  of  the  cell  are  ascertained  by  means  of  a  micrometer  scale  in  the 
microscope  ocular ;  or  in  the  case  of  Gowers'  modification,  by  the  division  of 
the  cell  area  into  squares  of  known  size.  Having  ascertained  the  number  of 
corpuscles  in  the  diluted  blood,  it  is  easy  to  find  out  the  number  in  a  given 
volume  of  normal  blood,  Gowers'  modification  of  Hayem  &  Nachet's  instru- 
ment, called  by  him  Hccmacytomcter ,  consists  of  a  small  pipette  (a)  ,  which, 
when  filled  up  to  a  mark  on  its  stem,  holds  995  cubic  millimetres.  It  is  fur- 
nished witli  an  india-rubber  tube  and  glass  mouth-piece  to  facilitate  filling  and 
emptying  ;  a  capillary  tube  (B)  marked  to  hold  5  cubic  millimetres,  and  also 
furnished  with  an  india-rubber  tube  and  mouth-piece  ;  a  small  glass  jar  (d)  in 
which  the  dilution  of  the  blood  is  performed  ;  a  glass  stirrer  (e)  for  mixing 
the  blood  thoroughly,  (F)  a  needle,  the  length  of  which  can  be  regulated  by  a 
screw  ;  a  brass  stage  plate  (c)  carrying  a  glass  slide,  on  which  is  a  cell  one- 


136 


HANDBOOK    OF    I'HYSIOLOGY. 


fifth  of  a  millimetre  deep,  and  the  bottom  of  which  is  divided  into  one-tenth 
millimetre  squares.  On  the  top  of  tlie  cell  rests  the  cover-glass,  which  is  kept 
in  its  place  bj'  tlie  pressure  of  two  springs  proceeding  from  the  stage  plate  A 
standard  saline  solution  of  sodium  sulpliate,  or  similar  salt,  of  specific  gravity 
1025,  is  made,  and  995  cubic  millimetres  are  measured  by  means  of  the  pipette 
into  the  glass  jar,  and  with  this  five  cubic  millimetres  of  blood,  obtained  by 
pricking  the  finger  with  a  needle,  and  measured  in  the  capillary  pipette  (b) 
are  thoroughl3^  mixed  by  the  glass  stirring-rod.  A  drop  of  this  diluted  blood 
is  then  placed  in  the  cell  and  covered  with  a  cover-glass,  which  is  fixed  in 
position  by  means  of  the  two  lateral  springs.  The  layer  of  diluted  blood  be- 
tween the  slide  and  cover-glass  is  i  inch  thick.  The  preparation  is  then 
examined  under  a  microscope  with  a  power  of  about  400  diameters,  and  focussed 
until  the  lines  dividing  the  cell  into  squares  are  visible. 


Fig.  130.— Haemacytometer, 


After  a  short  delay,  the  red  corpuscles  which  have  sunk  to  the  bottom  of 
the  cell,  and  are  resting  on  the  squares,  are  counted  in  ten  squares,  and  the 
number  of  white  corpuscles  noted.  By  adding  together  the  numbers  counted 
in  ten  (one-tenth  millimetre)  squares,  and,  as  the  blood  has  been  diluted,  mul- 
tiplying by  ten  thousand,  the  number  of  corpuscles  in  one  cubic  millimetre  of 
blood  is  obtained.  The  average  number  of  corpuscles  per  each  cubic  millimetre 
of  healthy  blood,  according  to  Vierordt  and  Welcker,  is  5,000,000  in  adult 
men,  and  4,500,000  in  women. 

A  hgemacytometer  of  another  form,  and  one  that  is  much  used  at  the  present 
time,  is  known  as  the  Thoma-Zeiss  hasmacytometer.  It  consists  of  a  carefully 
graduated  pipette'  in  which  the  dilution  of  the  blood  is  done  ;  this  is  so  formed 
that  the  capillary  stem  has  a  capacity  equalling  one-hundredth  of  the  ball 
above  it.  If  the  blood  is  drawn  up  in  tlie  capillary  tube  to  the  line  marked  1 
(fig.  132)  the  saline  solution  may  afterward  be  drawn  up  the  stem  to  the  line 
101 ;  in  this  way  we  have  101  parts  of  which  the  blood  forms  1.  As  the  con- 
tents of  the  stem  can  be  displaced  unmixed  we  shall  have  in  the  mixture  the 


THE   BLOOD. 


137 


proper  dilution.  The  blood  and  the  saline  solution  are  well  mixed  by  shaking 
the  pipette,  in  the  ball  of  which  is  contained  a  small  glass  bead  for  the  pur- 
pose of  aiding  the  mixing.  The  other  part  of  the  instrument  consists  of  a 
glass  slide  (fig.  131)  upon  which  is  mounted  a  covered  disc,  vi,  accurately  ruled 
so  as  to  present  one  square  millimetre  divided  into  400  squares  of  one-twentieth 


M^Mi  lv\\\v\\\v»^^\s\\\Wl" 


ym^mMm//^ 


Fig.  131.— Thoma-Zeiss  Haemacytometer. 


of  a  riillimetre  each.  The  micrometer  thus  made  is  surrounded  by  another 
annul'^r  cell,  c,  which  has  such  a  height  as  to  make  the  cell  project  exactly 
one-tenth  millimetre  beyond  ?/i.  If  a  drop  of  the  diluted  blood  be  placed  upon 
tn,  and  c  be  covered  with  a  perfectly  flat  cover-glass,  the  volume  of  the  diluted 
blood  above  each  of  the  squares  of  the  micrometei",  i.e.,  above  each  -^-q,  will 
be  ^^'oo  <5f  ^  cubic  millimetre.  An  average  of  ten  or  more 
squares  are  then  taken,  and  this  number  multiplied  by  4000  X 100 
gives  the  number  of  corpuscles  in  a  cubic  millimetre  of  un- 
diluted blood. 


Chemical  Composition  of  the  Blood. 

Before  considering  the  cliemical  composition  of  the 
blood  as  a  whole,  it  will  be  convenient  to  take  in  order 
the  composition  of  the  various  chief  factors  which  have 
been  set  out  in  the  table  on  p.  120,  into  which  the  blood 
may  be  separated,  viz. : — (1.)  The  Plasma ;  (2.)  The 
Serum ;  (3.)   The  Corpuscles  ;  (4.)   The  Fibrin. 

(1.)  The  Plasma. — The  Plasma,  or  liquid  part  of 
the  blood,  in  which  the  corpuscles  float,  may  be  ob- 
tained free  from  colored  corpuscles  in  either  of  the  ways 
mentioned  below. 

In  it  are  the  fibrin  factors,  inasmuch  as  when  ex- 
posed to  the  ordinary  temperature  of  the  air  it  under- 
goes coagulation  and  splits  up  into  fibrin  and  serum. 
It  differs  from  the  serum  in  containing  fibrinogen,  but 
in  appearance  and  in  reaction  it  closely  resembles  that 
fluid;  its  alkalinity,  however,  is  less  than  that  of  the 
serum  obtained  from  it.  It  may  be  freed  from  white  corpuscles  by  filtra- 
tion at  a  temperature  below  5°  C.  (41°  F.)  or  by  the  centrifugal  machine. 

The  chief  methods  of  obtaining  plasma  free  from  corpuscles  may  be  here 
epitomized :  (1)  by  cold,  the  temperature  should  be  about  0°  C.  and  may  be 
two  or  three  degrees  higher,  but  not  lower.  (2)  The  addition  of  neutral  salts, 
in  certain  proportions,  either  solid  or  in  solution,  e.g.  of  sodium  sulphate,  if 
solid  1  part  to  13  parts  of  blood  ;  if  a  saturated  solution  1  part  to  6  parts  of 
blood ;  of  magnesium  sulphate,  of  a  23;?,  or  if  saturated  solution  1  part  to  4  of 


Fig.  132.— Thoma- 
Zeiss  Haemacy IO- 
meter. 


138 


HANDBOOK    OF    PHYSIOLOGY. 


blood.  (3)  A  third  way  is  to  mix  frog's  blood  with  an  equal  part  of  a  5>  of 
cane  sugar,  and  to  get  rid  of  the  corpuscles  by  filtration  ;  or  (4)  by  the  injec- 
tion of  commercial  peptone  into  the  veins  of  certain  mammals,  previous  to 
bleeding  them  to  death,  allowing  the  corpuscles  to  subside,  and  afterward 
subjecting  the  supernatant  plasma  to  the  action  of  a  centrifugal  machine ;  by 


Fig.  133. — Plan  and  section  of  centrifugal  machine,  a,  An  iron  socket  secured  to  top  of  table  b; 
c,  a  steel  spindle  carrjing  the  turntable  d,  and  turning  freely  in  a  :  e,  a  fla.<ge  round  turntable  d; 
p  F,  shallow  grooves  on  face  of  d,  in  which  the  test  tubes  are  fixed  by  clamp.,  g  g;  h,  a  pulley  fixed 
to  end  of  spindle  c,  and  turned  by  the  cord  k;  n  are  two  guide-pulleys  for  cord  k.     (Gamgee.) 


the  rapid  rotation  of  which  (fig.  133)  the  whole  of  the  remaining  solid  parti- 
cles, if  any,  is  driven  to  the  outer  end  of  the  test-tubes  in  which  the  plasma  is 
placed. 


Composition  of  Plasma. 


Water        .... 
Solids — 

Proteids : 

1.  Yield  of  fibrin 

2.  Other  proteids 
Extractives  of  fat  . 
Inorganic  salts 


4.05 

78.84 

5.66 

8  5 


902.9 


97.1 


1000 


THE   BLOOD.  139 

Salts  of  the  plasma. — in  1000  parts  of  plasma  there  are: — 

Sodium  chloride           .......  5.546 

Soda 1.533 

Sodium  phosphate       .......  .271 

Potassium  chloride .359 

"           sulphate .         .  .281 

Calcium  jjhosphate          ......  .298 

Magnesium  phosphate 218 

8. 505 

(2.)  The  Serum. — The  serum  is  the  liquid  part  of  the  blood  or  of 
the  plasma  which  remains  after  the  se^Jaratiou  of  the  clot.  It  is  a  trans- 
parent, yellowish,  alkaline  fluid,  with  a  specific  gravity  of  from  1025  to 
1032.  In  the  usual  mode  of  coagulation,  part  of  the  serum  remains  in 
the  clot,  and  the  rest,  squeezed  from  the  clot  by  its  contraction,  lies 
around  it.  Since  the  contraction  of  the  clot  may  continue  for  thirty-six 
or  more  hours,  the  quantity  of  serum  in  the  blood  cannot  be  even 
roughly  estimated  till  this  period  has  elapsed.  There  is  nearly  as  much, 
by  weight,  of  serum  as  there  is  clot  in  coagulated  blood. 

Serum  may  be  obtained  from  blood  corpuscles  by  allowing  blood  to 
clot  in  large  test  tubes,  and  subjecting  the  test  tubes  to  the  action  of  a 
centrifugal  machine  (tig.  133)  for  some  time. 

In  tabular  form  the  composition  may  be  thus  summarized.  In  1000 
parts  of  serum  *  there  are : — 

Water ,         .      about  900 

Proteids : 

a.   Serum-albumin         ...         .         .         ,         .         .  ^ 

(3.   Serum-globulin    .         .         .         .         .         .         ,         .  [■  80 

-y.   Fibrin  ferment         .......  ) 

Salts.  ■] 

Fats — including  fatty  acids,   cholesterin,   lecithin  ;    and  | 

some  soaps        .........  | 

Grape  sugar  in  small  amount )    ,„ 

Extractives — creatin,  creatinin,  urea,  etc.         .         .  h  --0 
Yellow  pigment,  which  is  independent  of  haemoglobin. 
Gases — small  amounts  of  oxygen,  nitrogen,  and  carbonic 

acid  .         .         .         .  " 

1000 

a.  Wafer. — The  water  of  the  serum  varies  in  amount  according  to 
the  amount  of  food,  drink,  and  exercise,  and  with  many  other  circum- 
stances. 

b.  Proteids. — a.  Serum  albumin  is  the  chief  proteid  found  in  serum. 
The  proportion  which  it  bears  to  serum-globulin,  the  otlier  proteid,  is 
as  3  to  4.5  in  human  blood. 

Serum-albumin  has  been  shown  by  Plalliburton  to  be  a  compound 
body    which  may  be  called   serine,  made  up  of  three  proteids,  which 

*  This  table  is  more  detailed  than  that  of  the  plasma  given  above.  The 
salts,  extractives,  etc. ,  are  the  same  in  both  serum  and  plasma,  but  the  proteids 
are  somewhat  different  in  nature  and  amount. 


140  HANDBOOK    OF    PHYSIOLOGY, 

coagulate  at  different  temperatures,  «  at  73°  C,  /3  at  77°  C,  and  y  at  84° 
C.  The  serine  is  coagulated  by  the  addition  of  strong  acids,  such  as 
nitric  and  hydrochloric;  by  long  contact  with  alcohol  it  is  precipitated. 
It  is  not  precipitated  on  addition  of  ether,  and  so  diifers  from  the  other 
native  albumin,  viz.,  e^^-albumin.  When  dried  at  40°  C,  (104°  F.) 
serum-albumin  is  a  brittle,  yellowish  substance,  soluble  in  water,  pos- 
sessing a  laevorotary  power  of  —  56°.  It  is  with  great  difficulty  freed 
from  its  salts.  It  is  precipitated  by  solutions  of  metallic  salts,  e.g.,  of 
mercuric  chloride,  copper  sulphate,  lead  acetate,  sodium  tungstate,  etc. 
If  dried  at  a  temperature  over  75°  C.  (167°  F.),  the  chief  part  of  the 
residue  is  insoluble  in  water,  having  been  changed  into  coagulated  pro- 
teid.  Serum-albumin  may  be  precipitated  from  serum,  from  which  the 
serum-globulin  has  been  previously  separated  by  saturation  with  mag- 
nesium sulj)hate,  by  further  saturation  with  sodium  sulphate,  sodium 
nitrate,  or  iodide  of  potassium. 

/?.  Serum-globulin  can  be  obtained  as  a  white  precipitate  from  cold 
serum  by  adding  a  considerable  excess  of  water  over  ten  times  its  bulk, 
and  passing  through  the  mixture  a  current  of  carbonic  acid  gas  or  by 
the  cautious  addition  of  dilute  acetic  acid.  It  can  also  be  obtained  by 
saturating  serum  with  either  crystallized  magnesium  sulphate,  or  sodium 
chloride,  nitrate,  acetate,  or  carbonate.  When  obtained  in  the  latter 
way,  precipitation  seems  to  be  much  more  complete  than  by  means  of 
the  former  method.  Serum-globulin  coagulates  at  75°  C.  (167°  F.). 
There  seems  to  be  more  globulin  in  the  serum  than  in  the  corresponding 
plasma,  and  supposing  Halliburton  is  correct  in  believing  the  fibrin  fer- 
ment to  belong  to  the  globulin  class,  its  presence  arising  from  the  dis- 
integration of  the  colorless  corpuscles  (cell-globulin)  would  account  for 
part  of  the  increase,  while  possibly  another  part  might  be  due,  as  sug- 
gested by  Hammersten,  to  the  fact  that  fibrinogen  splits  up  into  fibrin, 
leaving  a  globulin  residue  which  appears  in  the  serum. 

c.  The  salts  of  sodium  predominate  in  serum  as  in  plasma,  and  of 
these  the  chloride  generally  forms  by  far  the  largest  proportion. 

d.  Fats  are  present  partly  as  fatty  acids  and  partly  emulsified.  The 
fats  are  tri-olein,  tri-stearin,  and  fri-palmitln.  The  amount  of  fatty 
matter  varies  according  to  the  time  after,  and  the  ingredients  of,  a 
meal.     Of  cholesterin  and  lecitliiyi  there  are  mere  traces. 

e.  Grape  sugar  is  found  principally  in  the  blood  of  the  hepatic  vein, 
to  the  extent  of  about  two  parts  in  a  thousand. 

f.  The  extractives  vary  from  time  to  time;  sometimes  uric  and  hip- 
puric  acids  are  found  in  addition  to  urea,  creatin  and  creatinin.  Urea 
exists  in  proportion  from  ,02  to  .04  per  cent. 

g.  The  yellow  pigment  of  the  serum  and  the  odorous  matter  which 
gives  the  blood  of  each  particular  animal  a  peculiar  smell,  have  not  yet 
"been  exactly  differentiated.     The  former  is  probably  of  the  nature  of  a 


THE    BLOOD.  141 

lipochrome,  and  might  be  called  serum  lutein.  It  is  soluble  in  alcohol 
and  ether,  and  has  two  hazy  absorption  bands  toward  the  violet  end  of 
the  spectrum. 

(3.)  The  Corpuscles. — a.  Colored. — Analysis  of  a  thousand  parts 
of  moist  blood  corpuscles  shows  the  following  result: — 

Water 688 

Solids- 
Organic  303.88 

Mineral 8.13—312=1000 

Of  the  solids  the  most  important  is  Hcemoglohin,  the  substance  to 
which  the  blood  owes  its  color.  It  constitutes,  as  will  be  seen  from  the 
appended  Table,  more  than  90  per  cent  of  the  organic  matter  of  the 
corpuscles.  Besides  haemoglobin  there  are  proteid  and  fatty  matters, 
the  former  chiefly  consisting  of  globulins,  and  the  latter  of  cliolesterin 
and  lecithin. 

In  1000  parts  organic  matter  are  found: — 

Haemoglobin    .........     905.4 

Proteids 86.7 

Fats 7.9=1000 

Of  the  inorganic  salts  of  the  corpuscles,  with  the  iron  omitted — 
In  1000  parts  corpuscles  (Schmidt)  are  found: — 

Potassium  Chloride     -  .         .         .         .         .         .         .     3.679 

Potassium  Phosphate 2.343 

Potassium  sulphate         ........  132 

Sodium        .........  .633 

Calcium 094 

Magnesium         .         . .060 

Soda 341=7.282 

The  properties  of  hsemoglobin  will  be  considered  in  relation  to  the 
Gat-es  of  the  blood. 

b.  Colorless. — The  corpuscles  may  be  said  also  to  contain  fibrinogen, 
pnraglobulin,  and  fibrin-ferment.  In  consequence  of  the  difficulty  of 
obtaining  colorless  corpuscles  in  sufficient  number  to  make  an  analysis, 
little  is  accurately  known  of  their  chemical  composition;  in  all  proba- 
bility, however,  the  stroma  of  the  corpuscles  is  made  up  of  proteid  mat- 
ter, and  the  nucleus  of  nuclein,  a  nitrogenous  phosphorus-containing 
body  akin  to  mucin,  capable  of  resisting  the  action  of  the  gastric  juice. 
The  proteid  matter,  chiefiy  globulins  soluble  in  a  ten  per  cent  solution 
of  sodium  chloride,  the  solution  being  precipitated  on  the  addition  of 
water,  by  heat  and  by  the  mineral  acids.  The  stroma  couiwrn?,  fatty 
granules,  and  in  it  also  the  presence  of  glycogen  has  been  demonstrated. 
The  salts  of  the  corpuscles  are  chiefly  of  potassium,  and  of  these  the 
phosphate  is  in  greatest  amount. 

(4.)  Fibrin. — The  part  played  by  fibrin  in  the  formation  of  a  clot 
and  its  tests  have  been  already  described,  and  it  is  only  necessary  to 
consider  here  its  general  properties.     It  is  a  stringy  elastic  substance 


142  HANDBOOK    OF    PHYSIOLOGY. 

belonging  to  the  proteid  class  of  bodies.  Blood  contains  only  .2  per 
cent  of  fibrin.  It  can  be  converted  by  the  gastric  or  pancreatic  juice 
into  peptone.  It  possesses  the  power  of  liberating  the  oxygen  from 
solutions  of  hydric  peroxide  H2O2  or  ozonic  ether.  This  may  be  shown 
by  dipping  a  few  shreds  of  fibrin  in  tincture  of  guaiacum,  and  then 
immersing  them  in  a  solution  of  hydric  peroxide.  The  fibrin  becomes 
of  a  bluish  color,  from  its  having  liberated  from  the  solution  oxygen, 
which  oxidizes  the  resin  of  guaiacum  contained  in  the  tincture,  and 
thus  produces  the  coloration. 

The  Gases  of  the  Blood. 

The  gases  contained  in  the  blood  are  carbonic  acid,  oxygen,  and  ni- 
trogen, 100  volumes  of  blood  containing  from  50  to  60  volumes  of  these 
gases  collectively. 

Arterial  blood  contains  relatively  more  oxygen  and  less  carbonic  acid 
than  venous.  But  the  absolute  quantity  of  carbonic  acid  is  in  both 
kinds  of  blood  greater  than  that  of  the  oxygen. 

Oxygen.  Carbonic  Acid.         Nitrogen. 

Arterial  Blood  .         .         20  vol.  per  cent.       39  vol.  per  cent.       1  to  2  vols. 

Venous        " 

(fr(jm  muscles  at  rest)      8  to  12    "  "  46    "  "  1  to  2  vols. 

The  Extraction  of  the  Gases  from  the  Blood. — As  the  ordinary  air  pumps  are 
not  sufficiently  powerful  for  the  purpose,  the  extraction  of  the  gases  from  the 
blood  is  accomplished  by  means  of  a  mercurial  air-pump,  of  which  there  are 
many  varieties,  those  of  Ludwig,  Alvergnidt,  Geisslor,  and  Sprengel  being  the 
chief.  The  principle  of  action  in  all  is  much  the  same.  Ludwig's  pump, 
which  may  be  taken  as  a  type,  is  represented  in  fig.  134.  It  consists  of  two 
fixed  glass  globes,  C  and  F,  the  upper  one  communicating  by  means  of  the 
stop-cock  D,  and  a  stout  india-rubber  tube  with  another  glass  globe,  L,  which 
can  be  raised  or  lowered  by  means  of  a  pulley ;  it  also  communicates  by  means 
of  a  stop- cock,  B,  and  a  bent  glass  tube.  A,  with  a  gas  receiver  (not  repre- 
sented in  the  figure) ,  A,  dipping  into  a  bowl  of  mercury,  so  that  the  gas  may 
be  received  over  mercury.  The  lower  globe,  F,  cominunicates  with  C  by 
means  of  the  stop-cock,  E,  with  /  in  which  the  blood  is  contained  by  the  stop- 
cock, G,  and  with  a  movable  glass  globe,  31,  similar  to  L,  by  means  of  the 
stopcock,  H,  and  the  stout  india-rubber  tube,  K. 

In  order  to  work  the  pump,  L  and  31  are  filled  with  mercury,  the  blood  from 
which  the  gases  are  to  be  extracted  is  placed  in  the  bulb  I,  the  stopcocks,  H, 
E,  D,  and  B,  being  open,  and  G  closed.  M  is  raised  by  means  of  the  pulley 
until  F  is  full  of  mercury,  and  the  air  is  driven  out.  E  is  then  closed,  and 
L  is  raised  so  that  C  becomes  full  of  mercury,  and  the  air  driven  off.  B  is 
then  closed.  On  lowering  L  the  mercury  runs  into  it  from  C,  and  a  vacuum 
is  established  in  C.  On  opening  E  and  lowering  M,  a  vacuum  is  similarly 
established  in  i^;  if  C  be  now  opened,  the  blood  in  7  will  enter  ebullition,  and 
the  gases  will  pass  off  into  F  and  C,  and  on  raising  31  and  then  L,  the  stopcock 
B  being  opened,  the  gas  is  driven  through  A,  and  is  received  into  the  receiver 


THE    BLOOD. 


143 


over  mercury.     By  repeating  the  experiment  several  times  the  whole  of  the 
gases  of  the  specimen  of  blood  is  obtained,  and  may  be  estimated. 

A.  The  Oxygen  of  the  Blood. — It  has  been  found  that  a  very 
small  proportion  of  the  oxygen  which  can  be  obtained,  by  the  aid  of  the 
mercurial  pump  from  the  blood,  exists  in  a 
state  of  simple  solution  in  the  plasma.  If 
the  gas  were  in  simple  solution,  the  amount 
of  oxygen  in  any  given  quantity  of  blood, 
exposed  to  any  given  atmosphere,  ought  to 
vary  with  the  amount  of  oxygen  contained  in 
the  atmosphere.  Since,  speaking  generally, 
the  amount  of  any  gas  absorbed  by  a  liquid 
such  as  plasma  Avould  depend  upon  the  pro- 
portion of  the  gas  in  the  atmosphere  to 
which  the  liquid  is  exposed — if  the  propor- 
tion is  great,  the  absorption  will  be  great;  if 
small,  the  absorption  will  be  similarly  small. 
The  absorption  continues  until  the  propor- 
tions of  the  gas  in  the  liquid  and  in  the  at- 
mosphere are  equal.  Other  things  will,  of 
course,  influence  the  absorption,  such  as  the 
nature  of  the  gas  employed,  the  nature  of 
the  liquid  and  the  temperature,  but  ccfteris 
paribus,  the  amount  of  a  gas  which  a  liquid 
absorbs  depends  upon  the  proportion  —  the 
so-called  partial  pressure — of  the  gas  in 
the  atmosphere  to  which  the  liquid  is  sub- 
jected. And  conversely,  if  a  liquid  contain- 
ing a  gas  in  solution  be  exposed  to  an  atmo- 
sphere containing  none  of  the  gas,  the  gas 
will  be  given  up  to  the  atmosphere  until  the 
amount  in  the  liquid  and  in  the  atmosphere  becomes  equal, 
dition  is  called  a  condition  of  equal  tensions. 


Fig.  134.— Ludwig's  Mercurial 
Pump. 


This  con- 


The  condition  may  be  understood  by  a  simple  illustration.  A  large  amoimt 
of  carbonic  acid  gas  is  dissolved  in  a  bottle  of  water  by  exposing  the  liquid  to 
extreme  pressure  of  the  gas,  and  a  cork  is  placed  in  the  bottle  and  wired  down. 
The  gas  exists  in  the  waver  in  a  condition  of  tension,  and  therefore  exhibits 
a  tendency  to  escape  into  the  atmosphere,  in  order  to  relieve  the  tension  ;  this 
produces  the  violent  expulsion  of  the  cork  when  the  wire  is  removed,  and  if 
the  aerated  water  is  placed  in  a  glass  the  gas  will  continue  to  be  evolved  until 
it  has  almost  entirely  passed  into  the  atmosphei-e,  and  the  tension  of  the  gas 
in  the  water  approximates  to  that  of  tlie  atmosphere,  in  which,  it  should  be 
remembered,  the  carbon  dioxide  is,  naturally,  in  very  small  amount,  viz., 
.04  per  cent. 


144  HANDBOOK    OF    PHYSIOLOGY. 

The  oxygen  of  the  blood  does  not  obey  tliis  law  of  pressure.  For  if 
blood  which  contains  little  or  no  oxygen  be  exposed  to  a  succession  of 
atmospheres  containing  more  and  more  of  that  gas,  we  find  that  the 
absorption  is  at  first  very  great,  but  soon  becomes  relatively  very  small, 
not  being  therefore  regularly  in  proportion  to  the  increased  amount  (or 
tension)  of  the  oxygen  of  the  atmospheres,  and  that  conversely,  if  arte- 
rial blood  be  submitted  to  regularly  diminishing  pressures  of  oxygen,  at 
first  very  little  of  the  contained  oxygen  is  given  off  to  the  atmosphere, 
then  suddenly  the  gas  escapes  with  great  rapidity,  and  again  disobeys 
the  law  of  pressures. 

Very  little  oxygen  can  be  obtained  from  plasma  freed  from  blood 
corpuscles,  even  by  the  strongest  mercurial  air-pump,  neither  can  it  be 
made  to  absorb  a  large  quantity  of  that  gas;  but  the  small  quantity 
which  is  so  given  uj)  or  so  absorbed  follows  the  laws  of  absorption  ac- 
cording to  pressure. 

It  must  be,  therefore,  evident  that  the  chief  part  of  the  oxygen  is 
contained  in  the  corpuscles,  and  not  in  a  state  of  simple  solution.  The 
chief  solid  constituent  of  the  colored  corpuscles  is  hmmoglohm,  which 
constitutes  more  than  90  per  cent  of  their  bulk.  This  body  has  a  very 
remarkable  aiSnity  for  oxygen,  absorbing  it  to  a  very  definite  extent 
under  favorable  circumstances,  and  giving  it  up  when  subjected  to  the 
action  of  reducing  agents,  or  to  a  sufficiently  low  oxygen  pressure.  From 
these  facts  it  is  inferred  that  the  oxygen  of  the  blood  is  comhincd  wUli 
licemoglohin,  and  not  simply  dissolved;  but  inasmuch  as  it  is  compara- 
tively easy  to  cause  the  haemoglobin  to  give  up  its  oxygen,  it  is  believed 
that  the  oxygen  is  but  loosely  coynhined  with  the  substance. 

Haemoglobin. — Haemoglobin  is  a  crystallizable  body  which  consti- 
tutes by  far  the  largest  portion  of  the  colored  corpuscles.  It  is  intimately 
distributed  throughout  their  stroma,  and  must  be  dissolved  out  before 
it  will  undergo  crystallization.  Its  percentage  composition  is  C.  53.85; 
H.  7.32;  N.  1G.17;  0.  21.84;  S.  .03;  Fe.  .42;  and  if  the  molecule  be 
supposed  to  contain  one  atom  of  iron  the  formula  would  be  Ceoo,  Hgeo, 
Ni54,  Fe  S3  O179.  The  most  interesting  of  the  properties  of  haemoglobin 
are  its  powers  of  crystallizing  and  its  attraction  for  oxygen  and  other 
gases. 

Crystals. — The  haemoglobin  of  the  blood  of  various  animals  possesses 
the  power  of  crystallizing  to  very  different  extents  (hemoglobin).  In 
some  animals  the  formation  of  crystals  is  almost  spontaneous,  whereas 
in  others  it  takes  place  either  with  great  difficulty  or  not  at  all.  Among 
the  animals  whose  blood  coloring-matter  crystallizes  most  readily  are 
the  guinea-pig,  rat,  squirrel,  and  dog;  and  in  these  cases  to  obtain 
crystals  it  is  generally  sufficient  to  dilute  a  drop  of  recently-drawn  blood 
with  water  and  to  expose  it  for  a  few  minutes  to  the  air.  Light  seems 
to  favor  the  formation  of  the  crystals.     In  many  instances  other  means- 


THE    BLOOD. 


145 


must  be  adopted,  e.g.,  the  addition  of  alcohol,  ether,  or  chloroform,  rapid 
freezing,  and  then  thawing,  an  electric  current,  a  temperature  of  60°  C. 
(140°  F.),  the  addition  of  sodium  sulphate,  or  the  addition  of  decom- 
posing serum  of  another  animal. 

The  hemoglobin  of  human  blood  crystallizes  with  difficulty,  as  does 
also  that  of  the  ox,  the  pig,  the  sheep,  and  the  rabbit. 

The  forms  of  haemoglobin  crystals,  as  will  be  seen  from  the  appended 
figures,  differ  greatly. 

Haemoglobin  crystals  are  soluble  in  water.  Both  the  crystals  them- 
selves and  also  their  solutions  have  the  characteristic  color  of  arterial 
blood. 

A  dilute  solution  of  oxy-haemoglobin  gives  a  characteristic  appear- 
ance with  the  spectroscope.     Two  absorption  bands  are  seen  between 


Fig.  135.  Fig.  136. 

Fig.  135.— Crystals  of  oxy-haemoglobin— prismatic,  from  human  blood. 

Fig.  136.— Oxy-haemoglobin  crystals— tetrahedral,  from  blood  of  the  guinea-pig. 

the  solar  lines  d  (which  is  the  sodium  band  in  the  yellow)  and  e  (see 
plate),  one  in  the  yellow,  with  its  middle  line  some  little  way  to  the  right 
of  D,  is  very  intense,  but  narrower  than  the  other,  which  lies  in  the 
green  near  to  the  left  of  e.  Each  band  is  darkest  in  the  middle  and 
fades  away  at  the  sides.  As  the  strength  of  the  solution  increases  the 
bands  become  broader  and  deeper,  and  both  the  red  and  the  blue  ends 
of  the  spectrum  become  encroached  upon  until  the  bands  coalesce  to 
form  one  very  broad  band,  and  only  a  slight  amount  of  the  green  re- 
mains unabsorbed,  and  part  of  the  red;  on  still  further  increase  of 
strength  the  former  disappears. 

If  the  crystals  of  oxy-hsemoglobin  be  subjected  to  a  mercurial  air- 
pump  they  give  off  a  definite  amount  of  oxygen  (1  gramme  giving  off 
1.59  ccm.  of  oyxgen),  and  they  become  of  a  purple  color;  and  a  solution 
of  oxy-haemoglobin  may  be  made  to  give  up  oxygen,  and  to  become  pur- 
ple in  a  similar  manner. 

lO 


146 


HANDBOOK    OF    PHYSIOLOGY. 


This  change  may  be  also  effected  by  passing  through  the  solution  of 
blood  or  of  oxy-hfemoglobiu,  hydrogen  or  nitrogen  gas,  or  by  the  action 
of  reducing  agents,  of  which  Stokes's  fluid  *  or  ammonium  sulphide  are 
the  most  convenient. 

With  the  spectroscope,  a  solution  of  deoxidized  or  reduced  hcemoglohin 
is  found  to  give  an  entirely  different  appearance  from  that  of  oxidized 
haemoglobin.  Instead  of  the  two  bands  at  d  ami  e  we  find  a  single 
broader  but  fainter  band  occupying  a  position  midway  between  the  two, 
and  at  the  same  time  less  of  the  blue  end  of  the  spectrum  is  absorbed. 
Even  in  strong  solutions  this  latter  appearance  is  found,  thereby  differ- 
ing from  the  strong  solution  of  oxidized  haemoglobin  which  lets  through 
only  the  red  and  orange  rays;  accordingly  to  the  naked  eye  the  one 
(reduced  haemoglobin  solution)  appears  purple,  the  other  (oxy-h«moglo- 


Fig.  137.— Hexagonal  oxy -haemoglobin  crystals,  from  blood  of  squirrel.    On  these  hexagonal  plates 
prismatic  crystals  grouped  in  a  stellate  manner  not  unfrequently  occur  (after  Fuuke). 


bin  solution)  red.  The  deoxidized  crystals  or  their  solutions  quickly 
absorb  oxygen  on  exposure  to  the  air,  becoming  scarlet.  If  solutions 
of  blood  be  taken  instead  of  solutions  of  haemoglobin,  results  similar  to 
the  whole  of  the  foregoing  can  be  obtained. 

Venous  blood  never,  except  in  the  last  stages  of  asphyxia,  fails  to 
show  the  oxy-haemoglobin  bands,  inasmuch  as  the  greater  part  of  the 
haemoglobin  even  in  venous  blood  exists  in  the  more  highly  oxidized  con- 
dition. 

Action  of  Gases  on  Haemoglobin. — Carhonic  oxide  gas,  passed 
through  a  solution  of  haemoglobin,  causes  it  to  assume  a  cherry-red  color, 

*  Stokes's  Fluid  consists  of  a  solution  at  ferrous  sulphate,  to  which  ammonia 
has  been  added  and  sufficient  tartaric  acid  to  prevent  precipitation.  Auotlier 
reducing  agent  is  a  solution  of  stannous  chloride,  treated  in  a  way  similar  to 
the  ferrous  sulphate,  and  a  third  reagent  of  like  nature  is  an  aqueous  solution 
of  yellow  ammonium  sulphide,  NH4  HS. 


THE    BLOOD.  147 

and  to  present  a  slightly  altered  spectrum ;  two  bands  are  still  visible, 
but  are  slightly  nearer  the  blue  end  than  those  of  ox} -haemoglobin  (see 
plate).  The  amount  of  carbonic  oxide  taken  up  is  equal  to  the  amount 
of  the  oxygen  displaced.  Although  the  carbonic  oxide  gas  readily  dis- 
places oxygen,  the  reverse  is  not  the  case,  and  upon  this  property  de- 
pends the  dangerous  effect  of  coal-gas  poisoning.  Coal  gas  contains 
much  carbonic  oxide,  and  when  breathed,  the  gas  combines  with  the 
hemoglobin  of  the  blood,  and  produces  a  comjjound  which  cannot  easily 
be  reduced.  This  compound  (carb-oxy-hgemoglobin)  is  by  no  means  an 
oxygen  carrier,  and  death  may  result  from  suffocation  due  to  the  want 
of  oxygen  notwithstanding  the  free  entry  of  pure  air  into  the  lungs. 
Crystals  of  carbonic-oxide  haemoglobin  closely  resemble  those  of  oxy- 
hsemoglobin. 

Nitric  oxide  produces  a  similar  compound  to  the  carbonic-oxide 
hsemoglobin,  which  is  even  less  easily  reduced. 

Nitrous  oxide  reduces  oxy-ha?moglobin,  and  therefore  leaves  the  re- 
duced hgemoglobin  in  a  condition  to  actively  take  up  oxygen. 

Sulphuretted  Hydrogew. — If  this  gas  be  passed  through  a  solution  of 
oxy-haemoglobin,  the  haemoglobin  is  reduced  and  an  additional  band 
appears  in  the  red.  If  the  solution  be  then  shaken  with  air,  the  two 
bands  of  oxy-haemoglobin  replace  that  of  reduced  haemoglobin,  but  the 
band  in  the  red  persists. 

Methaemoglobin. — If  an  aqueous  solution  of  oxy-haemoglobin  is 
exposed  to  the  air  for  some  time,  its  spectrum  undergoes  a  change;  the 
two  D  and  e  bands  become  faint,  and  a  new  line  in  the  red  at  c  is  devel- 
oped. The  solution,  too,  becomes  brown  and  acid  in  reaction,  and  is  pre- 
cipitable  by  basic  lead  acetate.  This  change  is  due  to  the  decomposition 
of  oxy-haemoglobin,  and  to  the  production  of  metlicemoglohin.  On  add- 
ing ammonium  sulphide,  reduced  haemoglobin  is  produced,  and  on  shak- 
ing this  up  with  air,  oxy-hasmoglobin  is  rej^roduced.  Methaemoglobin 
is  probably  a  stage  in  the  deoxidation  of  oxy-haemoglobin.  It  appears 
to  contain  less  oxygen  than  oxy-haemoglobin,  but  more  than  reduced 
haemoglobin.  Its  oxygen  is  in  more  stable  combination,  however,  than 
is  the  case  with  the  former  compound. 

Estimation  of  Haemoglobin. — The  most  exact  method  is  by  the 
estimation  of  the  amount  of  iron  (dry  hemoglobin  containing  .42  per 
cent  of  iron)  in  a  given  specimen  of  blood,  but  as  this  is  a  somewhat 
complicated  process,  various  methods  have  been  proposed  which,  though 
not  so  exact,  have  the  advantage  of  simplicity.  In  Gower's  haemoglobin- 
ometer,  this  consists  in  comparing  the  color  of  a  given  small  amount 
of  diluted  blood  with  glycerine  jelly  tinted  with  carmine  and  picro-car- 
mine  to  represent  a  standard  solution  of  blood  diluted  one  hundred 
times.  The  amount  of  dilution  which  the  given  blood  requires  will 
thus  approximately  represent  the  quantity  of  haemoglobin  it  contains. 


148  HANDBOOK    OF    PHYSIOLOGY. 

But  of  the  several  varieties  of  haemoglobinometer  that  which  appears  to 
be  the  best  ada])ted  to  its  purpose  is  that  invented  by  Professor  Fleischl, 
of  Vienna.  In  this  instrument,  the  amount  of  hsemoglobin  in  a  solution 
of  blood  is  estimated  by  comparing  a  stratum  of  diluted  blood  with  a 
standard  solid  substance  of  uniform  tint  similar  spectroscopically  to  di- 
luted blood.  In  order  that  the  strength  of  color  in  the  standard  sub- 
stance may  be  varied,  the  red  tinted  glass  is  made  wedge-shaped.  This, 
which  is  called  the  comparison  wedge,  is  cemented  on  to  a  colorless 
plain  strip  of  glass,  and  is  mounted  in  a  frame  (fig.  138,  P)  made  to 
slide  in  a  V-shaped  groove,  on  the  under  surface  of  the  stage  of  the  in- 
strument.    The  comparison  wedge,  K,  is  so  placed  that  one  of  its  longi- 


Fif?  138.— Fleischl's  Haemoglobinometer. 

tudinal  edges  bisects  the  circular  stage-opening,  so  that  one-half  of  the 
latter  is  cut  off  by  the  red-tinted  wedge.  Into  the  stage-opening  fits 
a  small  circular  trough,  G,  having  a  glass  bottom,  and  divided  into  equal 
compartments  by  a  thin  lamina.  One  compartment,  a,  is  filled  in  the 
manner  to  be  presently  indicated  with  diluted  blood,  and  the  other,  a', 
with  water;  the  trough  is  so  placed  that  the  lamina  is  in  one  plane  with 
the  edge  of  the  wedge,  the  water  compartment  being  above  the  wedge 
and  the  blood  compartment  above  the  free  half  of  the  stage  opening. 
By  turning  the  screw  head,  T,  the  frame,  P,  with  the  wedge,  A",  may 
be  moved  backward  and  forward  until  a  position  is  found  where  the  in- 
tensity of  the  tints  due  to  the  stratum  of  blood  on  the  one  hand  and  the 
thickness  of  the  wedge  on  the  other  appears  to  be  equal.  The  required 
degree  of  dilution  is  obtained  by  the  use  of  small  cajiillary  tubes  of  a 
capacity  varying  from  6  to  8  cmm.  The  capillary  pipette  is  filled  with 
blood  and  is  held  over  the  blood  compartment  and  its  contents  thor- 


THE    BLOOD.  149 

oughly  washed  out  into  that  compartment,  and  the  blood  and  water  are 
mixed  with  a  wire.  Water  is  tlien  added  until  the  blood  compartment 
is  quite  full.  The  other  compartment  is  filled  with  Avater.  Light  is 
then  reflected  by  the  mirror,  >S,  so  as  to  illuminate  both  compartments. 
By  moving  K  by  means  of  the  milled  head,  T,  a  position  of  A' may  be 
found  corresponding  to  the  exact  intensity  of  the  light  passing  through 
the  two  compartments;  this  is  read  off  at  J/ on  the  scale  P,  the  division 
of  which  corresponds  to  standard  strengths  of  solutions  of  hgemoglobin. 
Distribution  of  Hemoglobin. — Hemoglobin  occurs  not  only  in  the 
red  blood-cells  of  all  vertebrata  (except  amphioxus  and  leptocephalus 
whose  blood-cells  are  all  colorless,)  but  also  in  similar  cells  in  many 
Worms;  moreover,  it  is  found  diffused  in  the  vascular  fluid  of  some 
other  worms  and  certain  Crustacea;  it  also  occurs  in  all  the  striated  mus- 
cles of  Mammals  and  Birds.  It  is  generally  absent  from  unstriated 
muscle  except  that  of  the  rectum.  It  has  also  been  found  in  Mollusca 
in  certain  muscles  which  are  specially  active,  viz.,  those  which  work  the 
rasp-like  tongue. 

Derivatives  of  Haemoglobin. 

Hasmatin. — By  the  action  of  heat,  or  of  acids  or  alkalies  in  the 
presence  of  oxygen,  hemoglobin  can  be  split  up  into  a  substance  called 
Hcematin,  which  contains  all  the  iron  of  the  hemoglobin  from  which  it 
was  derived,  and  a  proteid  residue.  Of  the  latter  it  is  impossible  to  say 
more  than  that  it  probably  consists  of  one  or  more  bodies  of  the  globu- 
lin class.  If  there  be  no  oxygen  present,  instead  of  hematin  a  body 
called  haemochromogen  is  produced,  which,  however,  will  speedily 
undergo  oxidation  into  hematin. 

Hematin  is  a  dark  brownish  or  black  non-crystallizable  substance  of 
metallic  lustre.  Its  percentage  composition  is  C.  64.30;  H.  5.50;  N. 
9.06;  Fe.  8.82;  0.  12.32;  which  gives  the  formula  Cgg,  H70,  Ng,  Feg, 
Oio  (Hoppe-Seyler).  It  is  insoluble  in  water,  alcohol,  and  ether;  solu- 
ble in  the  caustic  alkalies;  soluble  with  difficulty  in  hot  alcohol  to  which 
is  added  sulphuric  acid.  The  iron  my  be  removed  from  haematin  by 
heating  it  with  fuming  hydrochloric  acid  to  160°  C.  (320°  F.),  and  a 
new  body,  hasmatoporphyrin,  the  so-called  iron-free  hematin,  is  pro- 
duced. Hematoporphyrin  (Ces,  II-4,  Ns,  O12,  Hoppe-Seyler)  may  also  be 
obtained  by  adding  blood  to  strong  sulphuric  acid,  and  if  necessary 
filtering  the  fluid  through  asbestos.  It  forms  a  fine  crimson  solution, 
which  has  a  distinct  spectrum,  viz.,  a  dark  band  just  beyond  d,  and  a 
second  all  but  midway  d  and  e.  It  may  be  precipitated  from  its  acid 
solution  by  adding  water  or  by  neutralization,  and  when  redissolved 
in  alkalies  presents  four  bands,  a  pale  baud  between  c  and  d,  a  second 
between  d  and  e,  nearer  d,  another  nearer  e,  and  a  fourth  occupying 
the  chief  part  of  the  space  between  b  and  f. 


150  HANDBOOK    OF    PHYSIOLOGY. 

Hcematin  in  acid  solution. — If  an  excess  of  acetic  acid  is  added  to 
blood,  and  the  solution  is  boiled,  the  color  alters  to  brown  from  decom- 
position of  haemoglobin  and  the  setting  free  of  hsematin;  by  shaking 
this  solution  with  ether,  asolution  of  htematin  in  acid  solution  is  obtained. 
The  spectrum  of  the  ethereal  solution  (colored  plate)  shows  no  less  than 
four  absorption  bands,  viz.,  one  in  the  red  between  c  and  d,  one  faint 
and  narrow  close  to  d  and  then  two  broader  bands,  one  between  d  and 
E,  and  another  nearly  midway  between  b  and  f.  The  first  band  is  by 
far  the  most  distinct,  and  the  acid  aqueous  solution  of  hasmatin  shows 
it  plainly. 

Hmnatin  in  alkaline  solution. — If  a  caustic  alkali  is  added  to  blood 
and  the  solution  is  boiled,  alkaline  lia3matin  is  produced,  and  the  solu- 
tion becomes  olive  green  in  color.  The  absorption  band  of  the  new 
compound  is  in  the  red,  near  to  d,  and  the  blue  end  of  the  spectrum  is 


1^ 


n. 


Fig.  139.— Hasmatoklin  crj'stals.    (Frey.)  Fig.  140.— HEemin  crystals.     (Frey.) 


absorbed  to  a  considerable  extent.  If  a  reducing  agent  be  added,  two 
bands  resembling  those  of  oxy-hsemoglobin,  but  nearer  to  the  blue,  ap- 
pear; this  is  the  spectrum  of  reduced  hcematin,  or  haemochromogen. 
On  violently  shaking  the  reduced  hsematin  with  air  or  oxygen  the  two 
bands  are  replaced  by  the  single  band  of  alkaline  haematin. 

Haematoidin. — This  substance  is  found  in  the  form  of  yellowish 
crystals  (fig.  139)  in  old  blood  extravasations  and  is  derived  from  the 
haemoglobin.  Their  crystalline  form  and  the  reaction  they  give  with 
fuming  nitric  acid  seem  to  show  them  to  be  closely  allied  to  Bilirubin, 
the  chief  coloring  matter  of  the  bile,  and  in  composition  they  are  prob- 
ably either  identical  or  isomeric  with  it. 

Haemin. — One  of  the  most  important  derivatives  of  haematin  is 
haemin.  It  is  usually  called  Hifdrochlorate  of  Hcematin  (or  hydrochlor- 
ide), but  its  exact  chemical  composition  is  uncertain.  Its  formula  is 
said  to  be  Cos,  H70,  Ns,  Feo,  Oio,  3  Hcl,  and  it  contains  5.18  per  cent  of 
chlorine,  but  by  some  it  is  looked  upon  as  simply  crystallized  haematin. 
Although  difficult  to  obtain  in  bulk,  a  specimen  may  be  easily  made  for 
the  microscope  in  the  following  way: — A  small  drop  of  dried  blood  is 
finely  powdered  with  a  few  crystals  of  common  salt  on  a  glass  slide  and 


THE    BLOOD.  151 

spread  out;  a  cover  glass  is  then  placed  upon  it,  and  glacial  acetic  acid 
added  by  means  of  a  capillary  pipette.  The  blood  at  once  turns  of  a 
brownish  color.  The  slide  is  then  heated,  and  the  acid  mixture  evapo- 
rated to  dryness  at  a  high  temperature.  The  excess  of  salt  is  washed 
away  with  water  from  the  dried  residue,  and  the  specimen  may  then  be 
dried  and  mounted.  A  large  number  of  small,  dark,  reddish  black  crys- 
tals of  a  rhombic  shape,  sometimes  arranged  in  bundles,  will  be  seen  if 
the  slide  be  subjected  to  microscopic  examination  (fig.  140). 

The  formation  of  these  haemin  crystals  is  of  great  interest  and  im- 
portance from  a  medico-legal  point  of  view,  as  it  constitutes  the  most 
certain  and  delicate  test  we  have  for  the  presence  of  blood  (not  of  ne- 
cessity the  blood  of  man)  in  a  stain  on  clothes,  etc.  It  exceeds  in  deli- 
cacy even  the  spectroscopic  test.  Compounds  similar  in  composition  to 
hsemin,  but  containing  hydrobromic  or  hydriodic  acid,  instead  of  hydro- 
chloric, may  be  also  readily  obtained. 

B.  The  Carbon  Dioxide  Gas  in  the  Blood.— Of  this  gas  in  the 
blood  part  exists  in  a  state  of  simple  solution  in  the  plasma,  and  is  given 
up  in  vacuo  (35.2  per  cent),  and  the  rest  in  a  state  of  weak  chemical 
combination.  It  is  believed  that  the  latter  is  combined  with  the  sodium 
carbonate  in  a  condition  of  bicarbonate,  and  is  not  given  up  until  an  acid 
is  added  to  the  plasma  or  serum.  Some  observers  consider  that  part  of 
the  gas  is  associated  with  the  corpuscles.     (See  also  under  Resjnrafion.) 

C.  The  Nitrogen  in  the  Blood. — The  whole  of  the  small  quantity 
of  the  nitrogen  contained  in  the  blood  is  simply  dissolved  in  the  fluid 
plasma. 

Chemical  Composition  of  the  Blood  in  Bulk. — Analyses  of  the 
blood  as  a  whole  differ  slightly,  but  the  following  table  may  be  taken  to 
represent  the  average  composition : 

Water 784 

Solids- 
Corpuscles        .......      130 

Proteids  (of  serum)     .....  70 

Fibrin  (of  clot)         .         .         .         .         .         .         2. 2 

Fatty  matters  (of  serum)    ....  1.4 

Inorganic  salts  (of  serum)      ....         6 

Gases,  kreatin,  urea    and    other    extractive     )    «  . 

matter,  glucose  and  accidental  substances      ) 

216 

1000 

Variations  in  the  Composition  of  healthy  Blood. 

The  conditions  which  appear  most  to  influence  the  composition  of 
the  blood  in  health  are  these:  Sex,  Pregnancy,  Age,  and  Temperament. 
The  composition  of  the  blood  is  also,  of  course,  much  influenced  by  diet. 

1.  Sex. — The  blood  of  men  differs  from  that  of  women,  chiefly  in 


153  HANDBOOK    OF    PHYSIOLOGY. 

being  of  somewhat  higher  specific  gravity,  from  its  containiDg  a  relatively 
larger  quantity  of  red  corpuscles. 

2.  Pregnancy. — The  blood  of  pregnant  women  is  rather  lower  than 
the  average  specific  gravity,  from  deficiency  of  colored  corpuscles.  The 
quantity  of  the  colorless  corj^uscles,  on  the  other  hand,  and  of  fibrin,  is 
increased. 

3.  Age. — The  blood  of  the  foetus  is  very  rich  in  solid  matter,  and 
especially  in  colored  corpuscles;  and  this  condition,  gradually  diminish- 
ing, continues  for  some  weeks  after  birth.  The  quantity  of  solid  matter 
then  falls  during  childhood  below  the  average,  rises  during  adult  life, 
and  in  old  age  falls  again. 

4.  Temperament. — There  appears  to  be  a  relatively  larger  quantity  of 
solid  matter,  and  particularly  of  colored  cor]3uscles,  in  those  of  a  plethoric 
or  sanguineous  temperament. 

5.  Diet. — Such  differences  in  the  composition  of  the  blood  as  are  due 
to  the  temporary  presence  of  various  matters  absorbed  with  the  food  and 
drink,  as  well  as  the  more  lasting  changes  which  must  result  from  gen- 
erous or  poor  diet  respectively,  need  be  here  only  referred  to. 

6.  Effects  of  Bleeding.— 'The  result  of  bleeding  is  to  diminish  the 
specific  gravity  of  the  blood;  and  so  quickly,  that  in  a  single  venesection, 
the  portion  of  blood  last  drawn  has  often  a  less  specific  gravity  than  that 
of  the  blood  that  flowed  first.  This  is,  of  course,  due  to  absorption  of 
fluid  from  the  tissues  of  the  body.  The  physiological  import  of  this 
fact,  namely,  the  instant  absorption  of  liquid  from  the  tissues,  is  the 
same  as  that  of  the  intense  thirst  which  is  so  common  after  either  loss 
of  blood,  or  the  abstraction  from  it  of  watery  fluid,  as  in  cholera,  dia- 
betes, and  the  like. 

For  some  little  time  after  bleeding  the  want  of  colored  corpuscles  is 
well  marked,  but  with  this  exception,  no  considerable  alteration  seems 
to  be  produced  in  the  composition  of  the  blood  for  more  than  a  very 
short  time;  the  loss  of  the  other  constituents,  including  the  colorless 
corpuscles,  being  very  quickly  repaired. 

Variations  in  different  parts  of  the  Body. — The  composition  of  the 
blood,  as  might  be  expected,  is  found  to  vary  in  different  parts  of  the 
body.  Thus  arterial  blood  differs  from  venous;  and  although  its  com- 
position and  general  characters  are  uniform  throughout  the  whole  course 
of  the  systemic  arteries,  they  are  not  so  throughout  the  venous  system 
— the  blood  contained  in  some  veins  differing  remarkably  from  that  in 
others. 

Differences  between  Arterial  and  Vetious  Blood. — The  differences  be- 
tween arterial  and  venous  blood  are  these : — 

(a.)  Arterial  blood  is  bright  red,  from  the  fact  that  almost  all  its 
haemoglobin  is  combined  with  oyxgen  (Oxy-hsemoglobin,  or  scarlet  hae- 
moglobin), while  the  purple  tint  of  venous  blood  is  due  to  the  deoxida- 


THE    BLOOD.  153 

tion  of  a  certain  quantity  of  its  oxy-hfemoglobin,  and  its  consequent 
reduction  to  tlie  purple  variety  (Deoxidized,  or  purple  hgemoglobin). 

(b.)  Arterial  blood  coagulates  somewhat  more  quickly. 

(c.)  Arterial  blood  contains  more  oxygen  than  venous,  and  less  car- 
bonic acid. 

Some  of  the  veins  contain  blood  which  differs  from  the  ordinary 
standard  considerably.  These  are  the  Portal,  the  Hepatic,  and  the 
Splenic  veins. 

Portal  vein. — The  blood  which  the  portal  vein  conveys  to  the  liver 
is  supplied  from  two  chief  sources;  namely,  from  the  gastric  and  mes- 
enteric veins,  which  contain  the  soluble  elements  of  food  absorbed  from 
the  stomach  and  intestines  during  digestion,  and  from  the  splenic  vein; 
it  must,  therefore,  combine  the  qualities  of  the  blood  from  each  of  these 
sources. 

The  blood  in  the  gastric  and  mesenteric  veins  will  vary  much  ac- 
cording to  the  stage  of  digestion  and  the  nature  of  the  food  taken,  and 
can  therefore  be  seldom  exactly  the  same.  Speaking  generally,  and 
without  considering  the  sugar,  and  other  soluble  matters  which  may 
have  been  absorbed  from  the  alimentary  canal,  this  blood  appears  to  be 
deficient  in  solid  matters,  especially  in  colored  corpuscles,  owing  to  di- 
lution by  the  quantity  of  water  absorbed,  to  contain  an  excess  of  proteid 
matter,  and  to  yield  a  less  tenacious  kind  of  fibrin  than  that  of  blood 
generally. 

The  blood  from  the  splenic  vein  is  generally  deficient  in  colored  cor- 
puscles, and  contains  an  unusually  large  proportion  of  proteids.  The 
fibrin  obtainable  from  the  blood  seems  to  vary  in  relative  amount,  but 
to  be  almost  always  above  the  average.  The  proportion  of  colorless  cor- 
puscles is  also  unusually  large.  The  whole  quantity  of  solid  matter  is 
decreased,  the  diminution  aj)pearing  to  be  of  colored  corpuscles.  The 
plasma  is  said  to  be  colored  in  consequence  of  its  containing  dissolved 
hsematin. 

The  blood  of  the  portal  vein,  combining  the  peculiarities  of  its  two 
factors,  the  splenic  and  mesenteric  venous  blood,  is  usually  of  lower 
specific  gravity  than  blood  generally,  is  more  watery,  contains  fewer 
colored  corpuscles,  more  proteids,  and  yields  a  less  firm  clot  than  that 
yielded  by  other  blood,  owing  to  the  deficient  tenacity  of  its  fibrin. 

Guarding  (by  ligature  of  the  portal  vein)  against  the  possibility  of 
an  error  in  the  analysis  from  regurgitation  of  hepatic  blood  into  the 
portal  vein,  recent  observers  have  determined  that  hepatic  venous  blood 
contains  less  water,  proteids,  and  salts  than  the  blood  of  the  portal 
veins ;  but  that  it  yields  a  much  larger  amount  of  extractive  matter, 
in  which  is  one  constant  element,  namely,  grape-sugar,  which  is  found, 
whether  saccharine  or  farinaceous  matter  has  been  present  in  the  food 
or  not. 


154  HANDBOOK    OF   PHYSIOLOGY. 

Development  of  the  Blood-Corpuscles. 

The  first  formed  blood-corpuscles  of  the  human  embryo  differ  much 
in  their  general  characters  from  those  which  belong  to  the  later  periods 
of  intra-uterine,  and  to  all  periods  of  extra-uterine  life.  Their  manner 
of  origin  is  at  first  very  simple. 

Surrounding  the  early  embryo  is  a  circular  area,  called  the  vascular 
area,  in  which  the  first  rudiments  of  the  blood-vessels  and  blood-corpus- 
cles are  developed.  Here  the  nucleated  embryonal  cells  of  the  meso- 
blast,  from  which  the  blood-vessels  and  corpuscles  are  to  be  formed, 
send  out  processes  in  various  directions,  and  these  joining  together, 
form  an  irregular  meshwork.  The  nuclei  increase  in  number,  and  col- 
lect chiefly  in  the  larger  masses  of  protoplasm,  but  partly  also  in  the 


^J.'^:^5^^..^yfe^ 


W 


Fig.  141.— Part  of  the  network  of  developing  blood-vessels  in  the  vascular  area  of  a  guinea-pig. 
bl,  blood-corpnscle.s  becoming  free  in  an  enlarged  and  hoUowed-out  part  of  the  network  ;  o,  process 
of  protoplasm.    (E.  A.  Schafer.) 

processes.  These  nuclei  gather  around  them  a  certain  amount  of  the 
protoplasm,  and  becoming  colored,  form  the  red  blood-corpuscles.  The 
protoplasm  of  the  cells  and  their  branched  net-work  in  which  these 
corpuscles  lie  then  become  hollowed  out  into  a  system  of  canals  inclos- 
ing fluid,  in  which  the  red  nucleated  corpuscles  float.  The  corpuscles 
at  first  are  from  about  3  5V0  to  y-yo^  of  an  inch  (lO/Jt  to  16//)  in  diameter, 
mostly  spherical,  and  with  granualr  contents,  and  a  well-marked  nucleus. 
Their  nuclei,  which  are  about  xoVo  of  iin  inch  (5,^)  in  diameter,  are  cen- 
tral, circular,  very  little  prominent  on  the  surfaces  of  the  corpuscles, 
and  apparently  slightly  granular  or  tuberculated. 

The  corpuscles  then  strongly  resemble  the  colorless  corpuscles  of  the 
fully  developed  blood,  but  are  colored.  They  are  capable  of  amoeboid 
movement  and  multiply  by  division. 

AVhen,  in  the  progress  of  embryonic  development,  the  liver  begins  to 
be  formed,  the  multiplication  of  blood-cells  in  the  whole  mass  of  blood 
ceases,  and  new  blood-cells  are  produced  by  this  organ,  and  also  by  the 


THE   BLOOD. 


155 


lymphatic  glands,  thymus,  and  spleen.  These  are  at  first  colorless  and 
nucleated,  but  afterward  acquire  the  ordinary  blood-tinge,  and  resemble 
very  much  those  of  the  first  set.  They  also  multiply  by  division.  In 
whichever  way  produced,  however,  whether  from  the  original  formative 


Fig.  142.— Development  of  red  corpuscles  in  connective  tissue  cells.  From  the  subcutaneous 
tissue  of  a  new-born  rat.  h,  a  cell  containing  haemoglobin  in  a  diffused  form  in  the  protoplasm;  h\ 
one  containing  colored  globules  of  varying  size  and  vacuoles:  h",  a  cell  filled  with  colored  globules 
of  nearly  uniform  size  ;  /,  /'.  developing  fat  cells.    CE.  A.  Schafer.) 

cells  of  the  embryo,  or  by  the  liver  and  the  other  organs  mentioned 
above,  these  colored  nucleated  cells  begin  very  early  in  foetal  life  to  be 
mingled  with  colored  ;^ow-nucleated  corpuscles  resembling  those  of  the 
adult,  and  at  about  the  fourth  or  fifth  month  of  embryonic  existence 
are  completely  replaced  by  them. 


Fig.  143.— Further  development  of  blood-corpuscles  in  connective  tissue  cells  and  transforma- 
tion of  the  latter  into  capillary  blood-vessels,  a.  an  elongated  cell  with  a  cavity  in  the  protoplasm 
occupied  by  fluid  and  by  blood-corpuscles  which  are  still  globular;  b,  a  hollow  cell,  the  nucleus  of 
which  has  multiplied.  The  new  nuclei  are  arranged  around  the  wall  of  the  cavity,  the  corpuscles  in 
which  have  now  become  discoid:  c,  shows  the  mode  of  imion  of  a  "heemapoietic  ''  cell,  which,  in 
this  instance,  contains  only  one  corpuscle,  with  the  prolongation  (bl)  of  a  previously  existing  vessel; 
a  and  c,  from  the  new-born  rat;  b,  from  the  foetal  sheep.    (E.  A.  Schafer.) 

Origin  of  the  Mature  Colored  Corpuscles. — The  non-nucleated 
red  corpuscles  may  possibly  be  derived  from  the  nucleated,  but  in  all 
probability  are  an  entirely  new  formation.     Their  chief  origin  is: — 

From  the  medulla  of  bone. — It  has  been  shown  that  colored  corpuscles 
are  to  a  very  large  extent  derived  during  adult  life  from  the  large  pale 


156  HANDBOOK    OF    PHYSIOLOGY. 

cells  in  the  red  marrow  of  bones,  especially  of  the  ribs  (fig.  144).  These 
cells  become  colored  from  the  formation  of  hsemoglobin  chiefly  in  one 
part  of  their  protoplasm.  This  colored  part  becomes  separated  from  the 
rest  of  the  cell  and  forms  a  red  corpuscle,  being  at  first  cup- shaped,  but 
soon  taking  on  the  normal  appearance  of  the  mature  corpuscle.  It  is 
supposed  that  the  protoplasm  ma  grow  up  again  and  form  a  number  of 
red  corpuscles  in  a  similar  way. 

From  the  tissue  of  the  spleen. — It  is  probable  that  colored  as  well  as 
colorless  corpuscles  may  be  produced  in  the  spleen. 

From  Microcytes. — Hayem  describes  the  small  particles  (Microcytes), 
previously  mentioned  as  contained  in  the  blood,  and  which  he  calls 
hrematoblasts,  as  the  precursors  of  the  red  corpuscles.  They  acquire 
color,  and  enlarge  to  the  normal  size  of  red  corpuscles. 

From  the  uihite  corpuscles. — The  belief  that  the  red  corpuscles  are 
derived  from  the  white  is  still  very  general,  although  no  new  evidence 
has  been  recently  advanced  in  favor  of  this  view.  It  is,  however,  un- 
certain whether  the  nucleus  of  t-he  white  coj-puscle  becomes  the  red  cor- 

Fig.  144.  —Colored  nucleated  coi-puscles,  from  the  red  marrow  of  the  guinea-pig.    CE.  A.  Schafer.) 

puscle,  or  whether  the  whole  white  corpuscle  is  bodily  converted  into 
the  red  by  the  gradual  clearing  up  of  its  contents  with  a  disappearance 
of  the  nucleus.     Probably  the  latter  view  is  the  correct  one. 

During  foetal  life  and  possibly  in  some  animals,  e.g.,  the  rat,  which 
are  born  in  an  immature  condition,  for  some  little  time  after  birth,  the 
blood  discs  have  been  stated  by  Schafer  to  arise  in  the  connective  tissue 
cells  in  the  following  way.  Small  globules,  of  varying  size,  of  coloring 
matter  arise  in  the  protoplasm  of  the  cells,  and  the  cells  themselves 
become  branched,  their  branches  joining  the  branches  of  similar  cells. 
The  cells  next  become  vacuolated,  and  the  red  globules  are  free  "in  a 
cavity  filled  with  fluid  (fig.  143) ;  by  the  extension  of  the  cavity  of  the 
cells  into  their  processes  anastomosing  vessels  are  produced,  which  ulti- 
mately join  with  the  previously  existing  vessels,  and  the  globules,  now 
having  the  size  and  appearance  of  the  ordinary  red  corpuscles,  are 
passed  into  the  general  circulation.  This  method  of  formation  is  called 
ijitracellular. 

Without  doubt,  the  red  corpuscles  have,  like  all  other  parts  of  the 
organism,  a  tolerably  definite  term  of  existence,  and  in  a  like  manner 
die  and  waste  away  when  the  portion  of  work  allotted  to  them  has  been 
performed.  Neither  the  length  of  their  life,  however,  nor  the  fashion 
of  their  decay  has  been  yet  clearly  made  out.  It  is  generally  believed 
that  a  certain  number  of  the  colored  corpuscles  undergo  disintegration 


THE    BLOOD.  157 

in  the  spleen ;  and  indeed  corpuscles  in  various  degrees  of  degeneration 
have  been  observed  in  that  organ. 

Origin  of  the  Colorless  Corpuscles. — The  colorless  corpuscles  of 
the  blood  are  derived  from  the  lymph  corpuscles,  being,  indeed,  indis- 
tinguishable from  them;  and  these  come  chiefly  from  the  lymphatic 
glands.     Their  number  is  increased  by  division. 

Colorless  corpuscles  are  also  in  all  probability  derived  from  the 
spleen  and  thymus,  and  also  from  the  germinating  endothelium  of 
serous  membranes,  and  from  connective  tissue.  The  corpuscles  are  car- 
ried into  the  blood  either  with  the  lymph  and  chyle,  or  pass  directly 
from  the  lymphatic  tissue  in  which  they  have  been  formed  into  the 
neighboring  blood-vessels. 

Uses  of  the  Blood. 

1.  To  be  a  medium  for  the  reception  and  storing  of  matter,  e.g., 
oxygen  and  digested  food  material,  from  the  outer  world,  and  for  its 
conveyance  to  all  parts  of  the  body. 

2.  To  be  a  source  whence  the  various  tissues  of  the  body  may  take 
the  materials  necessary  for  their  nutrition  and  maintenance;  and  whence 
the  secreting  organs  may  take  the  constituents  of  their  various  secre- 
tions. 

3.  To  be  a  medium  for  the  absorption  of  refuse  matters  from  all  the 
tissues,  and  for  their  conveyance  to  those  organs  whose  function  it  is  to 
separate  them  and  cast  them  out  of  the  body. 

4.  To  warm  and  moisten  all  parts  of  the  body. 


CHAPTER  YL 

THE  CIRCULATION  OF  THE  BLOOD. 

The  blood  is  made  to  circulate  within  the  system  of  closed  tubes  in 
which  it  is  contained  by  means  of  the  alternate  contraction  and  relaxa- 
tion of  the  heart.  The  heart  is  a  hollow  muscular  organ  consisting  of 
four  chambers,  two  auricles  and  two  ventricles,  arranged  in  pairs.     On 


Pulmonary  artery  - 


Superior  cava  or  vein 
from  head  and  neck 

Right  auricle 
Inferior  vena  cava 

Right  ventricle 


Portal  circulation 


Second  renal 
circulation 


Pulmonary 
capillaries 


Pulmonary  veins 

Aorta 

Arteries  to  head  and 
neck 


Left  auricle 


._^  Left  ventricle 


Gastric  and  intestinal 

vessels 


.First  renal  circulation 


Systemic  capillaries 


Fig.  145. — Diagram  of  the  circulation. 

the  right  and  left  sides  is  an  auricle  joined  to  and  communicating  with 
a  ventricle,  but  the  chambers  on  the  right  side  do  not  directly  commu- 
nicate with  those  on  the  left  side.  The  blood  is  conveyed  away  from 
the  left  side  of  the  heart  (as  in  the  diagram,  fig.  145)  by  the  arteries, 
and  returned  to  the  right  side  of  the  heart  by  the  veins,  the  arteries  and 
veins  being  continuous  with  each  other  at  one  end  by  means  of  the 
heart,  and  at  the  other  by  a  fine  network  of  vessels  called  the  capillaries. 
From  the  right  side  of  the  heart  the  blood  passes  to  the  lungs 

158 


THE    CIRCULATION^    OF   THE    BLOOD.  159 

through  the  pulmonary  artery,  then  through  the  pulmonary  capillaries, 
and  through  the  pulmonary  veins  to  the  left  side  of  the  heart  (Fig.  145). 
Thus  there  are  two  circulations  through  which  the  blood  must  pass;  the 
one,  a  shorter  circuit  from  the  right  side  of  the  heart  to  the  lungs  and 
back  again  to  the  left  side  of  the  heart ;  the  other  and  larger  circuit, 
from  the  left  side  of  the  heart  to  all  parts  of  the  body  and  back  again  to 
the  right  side;  strictly  speaking,  however,  there  is  but  one  complete 
circulation,  which  may  be  diagrammatically  represented  by  a  double 
loop,  as  in  fig.  145,  in  which  there  is  one  continuous  stream,  the  whole 
of  which  must,  at  one  part  of  its  course,  pass  through  the  lungs.  Sub- 
ordinate to  the  circulations  through  the  lungs  and  through  the  system 
generally,  respectively  named  the  Pulmonary  and  Systemic,  it  will  be 
noticed  also  in  the  same  figure  that  a  portion  of  the  stream  of  blood 
having  been  diverted  once  into  the  capillaries  of  the  intestinal  canal, 
and  some  other  organs,  and  gathered  up  again  into  a  single  stream,  is  a 
second  time  divided  in  its  passage  through  the  liver,  before  it  finally 
reaches  the  heart  and  completes  a  revolution.  This  subordinate  stream 
through  the  liver  is  called  the  Portal  circulation.  A  somewhat  similar 
accessory  circulation  is  that  through  the  kidneys,  called  the  Renal  cir- 
culation. Such  then  is  the  outline  of  the  course  of  the  circulation. 
The  problems  in  connection  with  its  maintenance  cannot  be  well  under- 
stood without  a  more  detailed  knowledge  of  the  structure  and  mode  of 
action  of  the  heart,  and  of  the  structure  and  properties  of  the  blood- 
vessels.    These  subjects  will  now  be  considered  seriatim. 

The  Heart. 

The  heart  is  contained  in  the  chest  or  thorax,  and  lies  between  the 
right  and  left  lungs  (fig.  146),  inclosed  in  a  membranous  sac — the  Peri- 
cardium, which  is  made  up  of  two  distinct  parts,  an  external  fibrous 
membrane,  composed  of  closely  interlacing  fibres,  which  has  its  base 
attached  to  the  diaphragm  or  midriff,  the  great  muscle  which  forms  the 
floor  of  the  chest  tind  divides  it  from  the  abdomen — both  to  the  central 
tendon  and  to  the  adjoining  muscular  fibres,  while  the  smaller  and 
upper  end  is  lost  on  the  large  blood-vessels  by  mingling  its  fibres  with 
that  of  their  external  coats;  and  an  internal  serous  layer,  which  not  only 
lines  the  fibrous  sac,  but  also  is  reflected  on  to  the  heart,  which  it  com- 
pletely invests.  The  part  which  lines  the  fibrous  membrane  is  called 
the  parietal  layer,  and  that  inclosing  the  heart,  the  visceral  layer,  and 
these  being  continuous  for  a  short  distance  along  the  great  vessels  of 
the  base  of  the  heart,  form  a  closed  sac,  the  cavity  of  which  in  health 
contains  just  enough  fluid  to  lubricate  the  two  surfaces,  and  thus  to 
enable  them  to  glide  smoothly  over  each  other  during  the  movements 
of  the  heart.  The  vessels  passing  in  and  out  of  the  heart  receive  in- 
Testments  from  this  sac  to  a  greater  or  less  degree. 


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HANDBOOK    OF    PHYSIOLOGY. 


The  heart  is  situated  in  the  chest  behind  the  sternum  and  costal 
cartilages,  being  phiced  obliquely  from  right  to  left,  quite  two-thirds  of 
it  being  to  the  left  of  the  mid-sternal  line.  It  is  of  pyramidal  shape, 
with  the  apex  pointing  downward,  outward,  and  toward  the  left,  and  the 
base  backward,  inward,  and  toward  the  right.  It  rests  upon  the  dia- 
phragm, and  its  pointed  apex,  formed  exclusively  of  the  left  side  of  the 
heart,  is  in  contact  with  the  chest  wall,  and  during  life  beats  against  it 
at  a  point  called  the  apex  beat,  situated  in  the  fifth  left  intercostal 
space,  and  about  three  inches  from  the  mid-sternal  line.  The  heart  is, 
as  it  were,  suspended  in  the  chest  by  the  large  vessels  which  proceed 
from  its  base,  but,  excepting  at  this  part,  the  orgcin  itself  lies  free  within 
the  sac  of  the  pericardium.     The  part  which  rests  upon  the  diaphragm 


Right  luDg 


Pulmonary  artery 


Left  lung 


Diaphragm 


Fig.  146.— View  of  heart  and  lungs  in. situ.  The  front  portion  of  the  chest-wall,  and  the  outer 
orparietaHayers  of  the  pleurae  and  pericardium  have  been  removed.  The  lungs  are  partly  col- 
lapsed. 

is  flattened,  and  is  known  as  the  posterior  surface,  while  the  free  upper 
part  is  called  the  anterior  surface.  The  margin  toward  the  left  is  thick 
and  obtuse,  while  the  lower  margin  toward  the  right  is  thin  and  acute. 

On  examination  of  the  external  surface  the  division  of  the  heart  into 
parts  which  correspond  to  the  chambers  inside  of  it  may  be  traced,  for 
a  deep  transverse  groove  called  the  auricido-ventricular  groove  divides 
the  auricles  which  form  the  base  of  the  heart  from  the  ventricles  which 
form  the  remainder,  including  the  apex,  the  ventricular  portion  being 
by  far  the  greater;  and,  again,  the  inter-ventricular  groove  runs  between 
the  ventricles  both  front  and  back,  and  separates  the  one  from  the  other. 
The  anterior  groove  is  nearer  the  left  margin  and  the  posterior  nearer 
the  right,  as  the  front  surface  of  the  heart  is  made  up  chiefly  of  the 
right  ventricle  and  the  posterior  surface  of  the  left  ventricle.     In  the 


THE   CIRCULATION    OF   THE    BLOOD. 


161 


furrows  or  grooves  run  the  coronary  vessels,  which  supply  the  tissue  of 
the  heart  with  blood,  as  well  as  nerves  and  lymphatics  imbedded  in 
more  or  less  fatty  material. 

The  Chambers  of  the  Heart. — The  interior  of  the  heart  is  divided 
by  a  longitudinal  partition  in  such  a  manner  as  to  form  two  chief  cham- 
bers or  cavities — right  and  left.     Each  of  these  chambers  is  again  sub- 


Fig.  147. — The  right  auricle  and  ventricle  opened,  and  a  part  of  their  right  and  anterior  walls 
removed,  so  as  to  show  their  interior,  i^. — 1,  Superior  vena  cava  ;  2,  inferior  vena  cava  ;  2',  hepatic 
veins  cut  short ;  3,  right  auricle  ;  3',  placed  in  the  fossa  ovalis,  below  which  is  the  Eustachian  valve  ; 
3",  Is  placed  close  to  the  aperture  of  the  coronary  vein  ;  +,  +.  placed  in  the  auriculo-ventricular 

froove,  where  a  narrow  portion  of  the  adjacent  walls  of  the  auricle  and  ventricle  has  been  preserved ; 
,  4,  cavity  of  the  right  ventricle,  the  upper  figure  is  immediately  below  the  semihmar  valves  ;  4', 
large  columna  carnea  or  museuhis  papillaris  ;  .5,  5',  .5",  tricuspid  valve  ;  6,  placed  in  the  interior  of 
the  pulmonary  artery,  a  part  of  the  anterior  wall  of  that  vessel  having  been  removed,  and  a  narrow 
portion  of  it  preserved  at  its  couimencetnent,  where  the  semilunar  valves  are  attached  ;  7,  concavity 
of  the  aortic  arch  close  to  the  cord  of  the  ductus  arteriosus  ;  8,  ascending  part  or  sinus  of  the  arch 
covered  at  it.s  commencement  by  the  auricular  appendix  and  pulmonary  artery  ;  9,  placed  between 
the  innominate  and  left  carotid  arteries  ;  10,  appendix  of  the  left  auricle  ;  11,  11,  outside  of  the  left 
ventricle,  the  lower  figm-e  near  the  apex.     (AUen  Thomson.) 


divided  transversely  into  an  upper  and  a  lower  portion,  called  respect- 
ively, as  already  incidentally  mentioned,  auricle  and  ventricle,  which 
freely  communicate  one  with  the  other ;  the  aperture  of  communication, 
however,  is  guarded  by  valves,  so  disposed  as  to  allow  blood  to  pass 
freely  from  the  auricle  into  the  ventricle,  but  not  in  the  opposite  direc- 


162 


HANDBOOK   OF    PHYSIOLOGY. 


tion.     There  are  thus  four  cavities  in  the  heart — the  auricle  and  ventri- 
cle of  one  side  being  quite  separate  from  those  of  the  other  (fig.  147). 

Right  Auricle. — The  right  auricle  is  situated  at  the  right  part  of  the 
base  of  the  heart  as  viewed  from  the  front.  It  is  a  thin-walled  cavity 
of  more  or  less  quadrilateral   shape,  prolonged  at  one  corner  into  a 


Fig.  148.— The  left  auricle  and  ventricle  opened  and  a  part  of  their  anterior  and  left  walls  re- 
moved. J4  — The  puhnonary  artery  has  been  divided  at  its  commencement ;  the  opening  into  the 
left  ventricle  is  carried  a  short  distance  into  the  aorta  between  two  of  the  segments  of  the  semilunar 
valves  ;  and  the  left  part  of  the  auricle  with  its  appendix  has  been  removed.  The  riglit  auricle  is 
out  of  view.  1,  The  two  right  pulmonary  veins  cut  short :  their  openings  are  seen  within  the  aia-icle; 
1',  placed  within  the  cavity  of  the  auricle  on  the  left  side  of  the  septum  and  on  the  part  which  forms 
the  remains  of  the  valve  of  the  foramen  ovale,  of  which  the  erescentic  fold  is  seen  toward  the  left 
hand  of  1' ;  2,  a  narrow  portion  of  the  wall  of  the  auricle  and  ventricle  preserved  round  the  auriculo- 
ventricular  orifice  ;  3,  3',  the  cut  surface  of  the  walls  of  the  ventricle,  seen  to  become  very  much 
tliinner  towards  3",  at  the  apex  :  4,  a  small  part  of  the  anterior  wall  of  tin-  left  ventricle  which  has 
been  preseiwed  with  the  principal  anterior  columna  carnea  or  musciihis  i)aiiillaris  attached  to  it ; 
5,  5,  musculi  papUlares  ;  5',  the  left  side  of  the  septum,  between  the  two  ventricles,  within  the  cavity 
of  the  left  ventricle  ;  6,  6',  the  mitral  valve  ;  7,  placed  in  the  interior  of  the  aorta  near  its  conuneuce- 
ment  and  above  the  three  segments  of  its  semilunar  valve  which  are  hanging  loosely  together  ;  7', 
the  exterior  of  the  great  aortic  sinus  ;  8,  the  root  of  the  pulmonary  artery  and  its  semilunar  valves  ; 
8',  the  separated  portion  of  the  pulmonary  artery  remaining  attached  to  the  aorta  by  9,  the  cord  of 
the  ductus  arteriosus  ;  10,  the  arteries  rising  from  the  summit  of  the  aortic  arch.     (Allen  Thomson.) 


tongue-shaped  portion,  the  right  auricular  appendix,  which  slightly  over- 
laps the  exit  of  the  great  artery,  the  aorta,  from  the  heart. 

The  interior  is  smooth,  being  lined  with  the  general  lining  of  the 


THE    CIRCULATION    OF   THE    BLOOD.  163 

heart,  the  endocardium,  and  into  it  open  the  superior  and  inferior  venae 
cavse,  or  great  veins,  which  convey  the  blood  from  all  parts  of  the  body- 
to  the  heart.  The  former  is  directed  downward  and  forward,  the  latter 
upward  and  inward;  between  the  entrances  of  these  vessels  is  a  slight 
tubercle  called  tubercle  of  Lower.  The  opening  of  the  inferior  cava  is 
protected  and  partly  covered  by  a  membrane  called  the  Eustachian 
valve.  In  the  posterior  wall  of  the  auricle  is  a  slight  depression  called 
the  fossa  ovalis,  which  corresponds  to  an  opening  between  the  right  and 
left  auricles  which  exists  in  foetal  life.  The  right  auricular  appendix  is 
of  oval  form,  and  admits  three  fingers.  Various  veins,  including  the 
coronary  sinus,  or  the  dilated  portion  of  the  right  coronary  vein,  open 
into  this  chamber.  In  the  appendix  are  closely  set  elevations  of  the 
muscular  tissue  covered  with  endocardium,  and  on  the  anterior  wall  of 


Fig.  149.— Transverse  section  of  bullock's  heart  in  a  state  of  cadaveric  rigidity.    (Dalton.) 
6,  Cavity  of  right  ventricle,     a,  Cavity  of  left  ventricle. 

the  auricle  are  similar  elevations  arranged  parallel  to  one  another,  called 
miisculi  liectinati. 

Right  Ventricle. — The  right  ventricle  occuijies  the  chief  part  of  the 
anterior  surface  of  the  heart,  as  well  as  a  small  part  of  the  posterior 
surface :  it  .forms  the  right  margin  of  the  heart.  It  takes  no  part  in 
the  formation  of  the  apex.  On  section  its  cavity,  in  consequence  of  the 
encroachment  upon  it  of  the  septum  ventriculorum,  is  semilunar  or 
crescentic  (fig.  149);  into  it  are  two  openings,  the  auriculo-ventricular 
at  the  base  and  the  opening  of  the  pulmonary  artery  also  at  the  base, 
but  more  to  the  left;  the  part  of  the  ventricle  leading  to  it  is  called  the 
conus  arteriosus  or  infundibuluni ;  both  orifices  are  guarded  by  valves, 
the  former  called  tricuspid  and  the  latter  semilunar  or  sigmoid.  In 
this  ventricle  are  also  the  projections  of  the  muscular  tissue  called  co- 
lumncB  carnece  (described  at  length  p.  178). 

Left  Auricle. — The  left  auricle  is  situated  at  the  left  and  posterior 
part  of  the  base  of  the  heart,  and  is  best  seen  from  behind.  It  is  quad- 
rilateral, and  receives  on  either  side  two  pulmonary  veins.  The  auricu- 
lar appendix  is  the  only  part  of  the  auricle  seen  from  the  front,  and 
corresponds  with  that  on  the  right  side,  but  is  thicker,  and  the  interior 
is  more  smooth.  The  left  auricle  is  only  slightly  thicker  than  the  riglit. 
The  left  auriculo-ventricular  orifice  is  oval,  and  a  little  smaller  than 


164  HANDBOOK    OF    PHYSIOLOGY. 

that  on  the  right  side  of  the  heart.  There  is  a  slight  vestige  of  the 
foramen  between  the  auricles,  which  exists  in  foetal  life,  on  the  septum 
between  them. 

Left  Venli'icle. — Though  taking  part  to  a  comparatively  slight  ex- 
tent in  the  anterior  surface,  the  left  ventricle  occupies  the  chief  part  of 
the  posterior  surface.  In  it  are  two  openings  very  close  together,  viz. 
the  auriculo-ventricular  and  the  aortic,  guarded  by  the  valves  corre- 
sponding to  those  of  the  right  side  of  the  heart,  viz.  the  bicuspid  or 
mitral  and  the  semilunar  or  si(/7noid.  The  first  opening  is  at  the  left 
and  back  part  of  the  base  of  the  ventricle,  and  the  aortic  in  front  and 
toward  the  right.  In  this  ventricle,  as  in  the  right,  are  the  columnae 
carneae,  which  are  smaller  but  more  closely  reticulated.  They  are  chiefly 
found  near  the  apex  and  along  the  ^josterior  wall.  They  will  be  again 
referred  to  in  the  description  of  the  valves.     The  walls  of  the  left  ven- 


Fig.  150.— Network  of  muscular  fibres  from  the  heart  of  a  pig.    The  nuclei  of  the  muscle-corpus- 
cles are  well  shown.     X  450.      (Klein  and  Noble  Smith.) 

tricle,  which  are  nearly  half  an  inch  in  thickness,  are,  with  the  excep- 
tion of  the  apex,  twice  or  three  times  as  thick  as  those  of  the  right. 

Capacity  of  the  Chambers. — During  life  each  ventricle  is  capable 
of  containing  about  four  to  six  ounces  (about  180  grms.)  of  blood.  The 
capacity  of  the  auricles  after  death  is  rather  less  than  that  of  the  ven- 
tricles: the  thickness  of  their  walls  is  considerably  less.  The  latter 
condition  is  adapted  to  the  small  amount  of  force  which  the  auricles 
require  in  order  to  empty  themselves  into  their  adjoining  ventricles; 
the  former  to  the  circumstance  of  the  ventricles  being  partly  filled  with 
blood  before  the  auricles  contract. 

Size  and  Weight  of  the  Heart. — The  heart  is  about  5  inches 
long  (about  12.6  cm.),  34  inches  (8  cm.)  greatest  width,  and  2^  inches 
(6.3  cm.  )  in  its  extreme  thickness.  The  average  weight  of  the  heart  in 
the  adult  is  from  9  to  10  ounces  (about  300  grms.);  its  weight  gradually 
increasing  throughout  life  till  middle  age:  it  diminishes  in  old  age. 

Structure. — The  walls  of  the  heart  are  constructed  almost  entirely 
of  layers  of  muscular  fibres;  but  a  ring  of  connective  tissue,  to  which 
some  of  the  muscular  fibres  are  attached,  is  inserted  between  each  auri- 
cle and  ventricle,  and  forms  the  boundary  of  the  auriculo-ventricular 


THE    CIKCULATION    OF   THE   BLOOD.  165 

opening.  Fibrous  tissue  also  exists  at  the  origins  of  the  pulmonary 
artery  and  aorta. 

The  muscular  fibres  of  each  auricle  are  in  part  continuous  with  those 
of  the  other,  and  partly  separate;  and  the  same  remark  holds  true  for 
the  ventricles.  The  fibres  of  the  auricles  are,  however,  quite  separate 
from  those  of  the  ventricles,  the  bond  of  connection  between  them 
being  only  the  fibrous  tissue  of  the  auriculo-ventricular  openings. 

The  minute  structure  of  the  striated  muscular  fibres  of  the  heart 
has  been  already  described  (p.  86). 

Endocardium. — As  the  heart  is  clothed  on  the  outside  by  a  thin 
transparent  layer  of  pericardium,  so  its  cavities  are  lined  by  a  smooth 


Fig.  151.— Diagram  of  the  circulation  thi-ough  the  heart  CDalton). 

and  shining  membrane,  or  endocardium,  which  is  directly  continuous 
with  the  internal  lining  of  the  arteries  and  veins.  The  endocardium  is 
composed  of  connective  tissue  with  a  large  admixture  of  elastic  fibres; 
and  on  its  inner  surface  is  laid  down  a  single  tesselated  layer  of  flat- 
tened endothelial  cells.  Here  and  there  unstriped  muscular  fibres  are 
sometimes  found  in  the  tissue  of  the  endocardium. 

Valves. — The  arrangement  of  the  heart's  valves  is  such  that  the 
blood  can  pass  only  in  one  direction  (fig.  151). 

The  tricusjjid  valve  (5,  fig.  147)  presents  three  principal  cusps  or  sub- 
divisions, and  the  mitral  or  bicuspid  valve  has  f7V0  such  portions  (6,  fig. 
148).  But  in  both  valves  there  is  between  each  two  principal  portions 
a  smaller  one;  so  that  more  properly,  the  tricuspid  may  be  described  as 
consisting  of  six,  and  the  mitral  of  four,  portions.  Each  portion  is  of 
triangular  form.     Its  base  is  continuous  with  the  bases  of  the  neighbor- 


166  HANDBOOK    OF    PHYSIOLOGY. 

ing  portions,  so  as  to  form  an  annular  membrane  around  the  auriculo- 
ventricular  opening,  and  is  fixed  to  a  tendinous  ring  which  encircles  the 
orifice  between  the  auricle  and  ventricle  and  receives  the  insertions  of 
the  muscular  fibres  of  both.  In  each  principal  cusp  may  be  distin- 
guished a  central  part,  extending  from  base  to  apex,  and  including  about 
half  its  width.  It  is  thicker  and  much  tougher  than  the  border  pieces 
or  edges. 

While  the  bases  of  the  cusps  of  the  valves  are  fixed  to  the  tendinous 
rings,  their  ventricular  surface  and  borders  are  fastened  by  slender  ten- 
dinous fibres,  the  chordcB  tendinew,  to  the  internal  surface  of  tlie  walls  of 
the  ventricles,  the  muscular  fibres  of  which  project  into  the  ventricular 
cavity  in  the  form  of  bundles  or  columns — the  cohimnce  carnece.  These 
columns  are  not  all  alike,  for  while  some  are  attached  along  their  whole 
length  on  one  side,  and  by  their  extremities,  others  are  attached  only 
by  their  extremities;  and  a  third  set,  to  which  the  name  musculi  papil- 
lares  has  been  given,  are  attached  to  the  wall  of  the  ventricle  by  one 
extremity  only,  the  other  projecting,  papilla-like,  into  the  cavity  of  the 
ventricle  (4,  fig.  148),  and  having  attached  to  it  chords  tendinege.  Of 
the  tendinous  cords,  besides  those  which  j^ass  from  the  walls  of  the 
ventricle  and  the  musculi  j)apillares  to  the  margins  of  the  valves,  there 
are  some  of  especial  strength,  which  pass  from  the  same  parts  to  the 
edges  of  the  middle  and  thicker  portions  of  the  cusps  before  referred  to. 
The  ends  of  these  cords  are  spread  out  in  the  substance  of  the  valve, 
giving  its  middle  piece  its  peculiar  strength  and  toughness;  and  from 
the  sides  numerous  other  more  slender  and  branching  cords  are  given 
off,  which  are  attached  all  over  the  ventricular  surface  of  the  adjacent 
border-pieces  of  the  principal  portions  of  the  valves,  as  well  as  to  those 
smaller  portions  which  have  been  mentioned  as  lying  between  each  two 
principal  ones.  Moreover,  the  musculi  papillares  are  so  placed  that, 
from  the  summit  of  each,  tendinous  cords  proceed  to  the  adjacent  halves 
of  two  of  the  principal  divisions,  and  to  one  intermediate  or  smaller 
division,  of  the  valve. 

The  preceding  description  applies  equally  to  the  mitral  and  tricus- 
pid valve;  but  it  should  be  added  that  the  mitral  is  considerably  thicker 
and  stronger  than  the  tricuspid,  in  accordance  with  the  greater  force 
which  it  is  called  upon  to  resist. 

The  semilunar  valves  guard  the  orifices  of  the  pulmonary  artery  and 
of  the  aorta.  They  are  nearly  alike  on  both  sides  of  the  heart;  but  the 
aortic  valves  are  altogether  thicker  and  more  strongly  constructed  than 
the  pulmonary  valves,  in  accordance  with  the  greater  j^ressure  which 
they  have  to  withstand.  Each  valve  consists  of  three  parts  which  are  of 
semilunar  shape,  the  convex  margin  of  each  being  attached  to  a  fibrous 
ring  at  the  place  of  junction  of  the  artery  to  the  ventricle,  and  the 
concave  or  nearly  straight  border  being  free,  so  as  to  form  a  little  pouch 


THE    CIKCULATION    OF   THE    BLOOD.  167 

like  a  watch-pocket  (7,  fig.  148).  In  the  centre  of  the  free  edge  of  the 
pouch,  which  contains  a  fine  cord  of  fibrous  tissue,  is  a  small  fibrous 
nodule,  the  corpus  Arantii,  and  from  this  and  from  the  attached  border 
fine  fibres  extend  into  every  part  of  the  mid  substance  of  the  valve, 
except  a  small  lunated  space  just  within  the  free  edge,  on  each  side  of 
the  corpus  Arantii.  Here  the  valve  is  thinnest,  and  composed  of  little 
more  than  the  endocardium.  Thus  constructed  and  attached,  the  three 
semilunar  pouches  are  placed  side  by  side  around  the  arterial  orifice  of 
each  ventricle,  which  can  be  separated  by  the  blood  passing  out  of  the 
ventricle,  but  which  immediately  afterward  are  pressed  together,  so  as 
to  prevent  any  return  (6,  fig.  147,  and  7,  fig.  148).  This  will  be  again 
referred  to.  Opposite  each  of  the  semilunar  cusps,  both  in  the  aorta 
and  pulmonary  artery,  there  is  a  bulging  outward  of  the  wall  of  the 
vessel:  these  bulgings  are  called  the  sinuses  of  Valsalva. 

Structure. — The  valves  of  the  heart  are  formed  essentially  of  thick 
layers  of  closely  woven  connective  and  elastic  tissue,  over  which,  on 
every  part,  is  reflected  the  endocardium. 

The  Arteries. 

Distribution. — The  arterial  system  begins  at  the  left  ventricle  in  a 
single  large  trunk,  the  aorta,  wJiich  almost  immediately  after  its  origin 
gives  off  in  the  thorax  three  large  branches  for  the  supply  of  the  head, 
neck,  and  upper  extremities;  it  then  traverses  the  thorax  and  abdomen, 
giving  off  branches,  some  large  and  some  small,  for  the  supply  of  the 
various  organs  and  tissues  it  passes  on  its  way.  In  the  abdomen  it 
divides  into  two  chief  branches,  for  the  supply  of  the  lower  extremities. 
The  arterial  branches  wherever  given  off  divide  and  subdivide,  until  the 
calibre  of  each  subdivision  becomes  very  minute,  and  these  minute  ves- 
sels pass  into  capillaries.  Arteries  are,  as  a  rule,  placed  in  situations 
protected  from  pressure  and  other  dangers,  and  are,  with  few  exceptions, 
straight  in  their  course,  and  frequently  communicate  (anastomose  or 
inosculate)  with  other  arteries.  The  branches  are  usually  given  off  at 
an  acute  angle,  and  the  area  of  the  branches  of  an  artery  generally  ex- 
ceeds that  of  the  parent  trunk;  and  as  the  distance  from  the  origin  is 
increased,  the  area  of  the  combined  branches  is  increased  also.  After 
death,  arteries  are  usually  found  dilated  (not  collapsed  as  the  veins  are) 
and  empty,  and  it  was  to  this  fact  that  their  name  [apr-qpia,  the  wind- 
pipe) was  given  them,  as  the  ancients  believed  that  they  conveyed  air 
to  the  various  parts  of  the  body.  As  regards  the  arterial  system  of  the 
lungs,  the  pulmonary  artery  is  distributed  much  as  the  arteries  belong- 
ing to  the  general  systemic  circulation. 

Structure. — The  walls  of  the  arteries  are  composed  of  three  principal 
coats,  termed  («)  the  external  or  tunica  adventitia,  (6)  the  middle  or 
tunica  media,  and  (c)  the  internal  or  tunica  intima. 


168 


HANDBOOK    OF    PHYSIOLOGY. 


(a)  The  external  coat  or  tunica  advetititia  (figs.  152  and  153,  a),  tlie 
strongest  and  toughest  part  of  the  wall  of  the  artery,  is  formed  of 
areolar  tissue,  with  which  is  mingled  throughout  a  network  of  elastic 
fibres.  At  the  inner  part  of  this  outer  coat  the  elastic  network  forms  in 
most  arteries  so  distinct  a  layer  as  to  be  sometimes  called  the  external 
elastic  coat  (fig.  153,  e). 

(b)  The  middle  coat  (fig.  153,  m)  is  composed  of  both  muscular  and 
elastic  fibres,  with  a  certain  proportion  of  areolar  tissue.  In  the  larger 
arteries  (fig.  153)  its  thickness  is  comparatively  as  well  as  absolutely 
much  greater  than  in  the  small,  constituting,  as  it  does,  the  greater  part 

/         /I, 


Fig.  152. 


Fig.  153. 


Fig.  154. 


Fig.  152. — Minute  artery  viewed  in  longitudinal  section,  e,  Nucleated  endothelial  membrane, 
with  faint  nuclei  in  lumen,  looked  at  from  above  ;  i.  thin  elastic  tunica  intima  ;  wi,  muscular  coat 
or  tunica  media  ;  a,  tunica  adventitia.     (Klein  and  Noble  Smith.)      >  2.50. 

Fig.  153.— Transverse  section  through  a  large  branch  of  the  inferior  mesenteric  artery  of  a  pig. 
e.  Endothelial  membrane  ;  i,  tunica  elastica  interna,  no  subendothehal  layer  is  seen  ;  in,  muscular 
tunica  media,  containing  only  a  few  wavy  elastic  fibres  ;  e,  c.  tunica  elastica  externa,  dividing  the 
media  from  the  connective  tissue  adventitia,  a.    (Klein  and  Noble  Smith.)    X  350. 

Fig.  154.— Muscular  fibre-cells  from  human  arteries,  magnified  350  diameters.  (Kdlliker.)  a, 
Nucleus.     6,  aflbre-ceU  treated  with  acetic  acid. 


of  the  arterial  wall.  The  muscular  fibres  are  unstriped  (fig.  154),  and 
are  arranged  for  the  most  part  transversely  to  the  long  axis  of  the  artery 
(fig.  155,  m)\  while  the  elastic  element,  taking  also  a  transverse  direc- 
tion, is  disposed  in  the  form  of  closely  interwoven  and  branching  fibres, 
which  intersect  in  all  parts  the  layers  of  muscular  fibre.  In  arteries  of 
various  size  there  is  a  difference  in  ihe  proportion  of  the  muscular  and 
elastic  element,  elastic  tissue  preponderating  in  the  largest  arteries,  and 
unstriped  muscle  in  those  of  medium  and  small  size. 

(c)  The  internal  coat  is  formed  by  layers  of  elastic  tissue,  consisting 
in  part  of  coarse  longitudinal  branching  fibres,  and  in  part  of  a  very 
thin  and  brittle  membrane  which  possesses  little  elasticity,  and  is  thrown 
into  folds  or  wrinkles  when  the  artery  contracts.  This  latter  mem- 
brane, the  striated  or  fenestrated  coat  of  Henle,  is  peculiar  in  its  ten- 


THE    CIRCULATION    OF   THE   BLOOD.  169 

dency  to  curl  up,  when  peeled  olf  from  the  artery,  and  in  the  perforated 
and  streaked  appearance  which  it  presents  under  the  microscope.  Its 
inner  surface  is  lined  with  a  delicate  layer  of  elongated  endothelial  cells 
(fig.  153,  e),  which  make  it  smooth  and  polished,  and  furnish  a  nearly 
impermeable  surface,  along  which  the  blood  may  flow  with  the  smallest 
possible  amount  of  resistance  from  friction. 

Immediately  external  to  the  endothelial  lining  of  the  artery  is  fine 
connective    tissue,    suh-endothelial    layer,    with    branched    corpuscles. 


Fig.  155.— Transverse  section  of  aorta  through  internal  and  about  half  the  middle  coat. 

Thus  the  internal  coat  consists  of  three  parts,  {a)  an  endothelial  lining, 
{b)  the  sub-endothelial  layer,  and  (c)  elastic  layers. 

Vasa  Vasorum. — The  walls  of  the  arteries,  with  the  possible  exception 
of  the  endothelial  lining  and  the  layers  of  the  internal  coat  immediately 
outside  it,  are  not  nourished  by  the  blood  which  they  convey,  but  are, 
like  other  parts  of  the  body,  supplied  with  little  arteries,  ending  in 
capillaries  and  veins,  which,  branching  throughout  the  external  coat, 
extend  for  some  distance  into  the  middle,  but  do  not  reach  the  internal 
coat.     These  nutrient  vessels  are  called  vasa  vasorum. 

Nerves. — Most  of  the  arteries  are  surrounded  by  a  plexus  of  sympa- 
thetic nerves,  which  twine  around  the  vessel  very  much  like  ivy  round  a 
tree:  and  ganglia  are  found  at  frequent  intervals.  The  smallest  arter- 
ies and  capillaries  are  also  surrounded  by  a  very  delicate  network  of 


170  HAl^TDBOOK    OF    PHYSIOLOGY. 

similar  nerve-fibres,  many  of  which  appear  to  end  in  the  nuclei  of  the 
transverse  muscular  fibres  (fig.  156). 

The  Capillaries. 

Distrihidion. — In  all  vascular  textures  except  some  parts  of  the  cor- 
pora cavernosa  of  the  penis,  and  of  the  uterine  placenta,  and  of  the 
spleen,  the  transmission  of  the  blood  from  the  minute  branches  of  the 
arteries  to  the  minute  veins  is  effected  through  a  network  of  capillaries. 
They  may  be  seen  in  all  minutely  injected  preparations. 

The  point  at  which  the  arteries  terminate  and  the  minute  veins  com- 
mence, cannot  be  exactly  defined,  for  the  transition  is  gradual;  bat  the 


Fig.  156  —Ramification  of  nerves  and  termination  in  the  muscular  coat  of  a  small  artery  of  the 

frog.    (Arnold.) 

capillary  network  has,  nevertheless,  this  peculiarity,  that  the  small 
vessels  which  compose  it  maintain  the  same  diameter  throughout:  they 
do  not  diminish  in  diameter  in  one  direction,  like  arteries  and  veins; 
and  the  meshes  of  the  network  that  they  compose  are  more  uniform 
in  shape  and  size  than  those  formed  by  the  anastomoses  of  the  minute 
arteries  and  veins. 

Structure. — This  is  much  more  simple  than  that  of  the  arteries  or 
veins.  Their  walls  are  composed  of  a  single  layer  of  elongated  or  radi- 
ate, flattened  and  nucleated  cells,  so  joined  and  dovetailed  together  as 
to  form  a  continuous  transparent  membrane  (fig.  157).  Outside  these 
cells,  in  the  larger  capillaries,  there  is  a  structureless  or  very  finely 
fibrillated  membrane,  on  the  inner  surface  of  which  they  are  laid  down. 
In  some  cases  this  external  membrane  is  nucleated,  and  may  then  be 
regarded  as  a  miniature  representative  of  the  tunica  adventitia  of  arteries. 


THE    CIRCULATIOX    OF   THE   BLOOD,  171 

Here  and  there  at  the  junction  of  two  or  more  of  the  delicate  endothe- 
lial cells  which  compose  the  capillary  wall,  pseudo-stomata  may  be  seen. 
The  endothelial  cells  are  often  continuous  at  various  points  with  pro- 
cesses of  adjacent  connective-tissue  corpuscles.  Capillaries  are  sur- 
rounded by  a  delicate  nerve-plexus  resembling,  in  miniature,  that  of  the 
larger  blood-vessels. 

The  diameter  of  the  capillary  vessels  varies  somewhat  in  the  different 
textures  of  the  body,  the  most  common  size  being  about  -j^^th  of  an 
inch,  12/^1.  Among  the  smallest  may  be  mentioned  those  of  the  brain, 
and  of  the  follicles  of  the  mucous  membrane  of  the  intestines;  among 
the  largest,  those  of  the  skin,  and  especially  those  of  the  medulla  of 
bones. 

The  size  of  capillaries  varies  necessarily  in  different  animals  in  rela- 


Fig.  157.— CapiUary  blood-vessels  from  the  omentum  of  rabbit,  showing  the  nucleated  endothelial 
membrane  of  which  they  are  composed.     (Klein  and  Noble  Smith.) 

tion  to  the  size  of  their  blood  corpuscles :  thus,  in  the  Proteus,  the  capil- 
lary circulation  can  just  be  discerned  with  the  naked  eye. 

The /orm  of  the  capillary  network  presents  considerable  variety  in 
the  different  textures  of  the  body:  the  varieties  consisting  principally 
of  modifications  of  two  chief  kinds  of  mesh,  the  rounded  and  the  elon- 
gated. That  kind  in  which  the  meshes  or  interspaces  have  a  roundish 
form  is  the  most  common,  and  j^revails  in  those  parts  in  which  the 
capillary  iietAvork  is  most  dense,  such  as  the  lungs  (fig.  158),  most 
glands,  and  mucous  membranes,  and  the  cutis.  The  meshes  of  this 
kind  of  network  are  not  quite  circular  but  more  or  less  angular,  some- 
times presenting  a  nearly  regular  quadrangular  or  polygonal  form,  but 
being  more  frequently  irregular.  The  capillary  network  with  elongated 
meshes  is  observed  in  jiarts  in  which  the  vessels  are  arranged  among 
bundles  of  fine  tubes  or  fibres,  as  in  muscles  and  nerves.  In  such  parts, 
the  meshes  form  parallelograms,  the  short  sides  of  which  may  be  from 
three  to  eight  or  ten  times  less  than  the  long  ones;  the  long  sides  being 


172 


HANDBOOK    OF   PHYSIOLOGY. 


more  or  less  parallel  to  the  long  axis  of  the  fibre.  The  rounded  and 
elongated  meshes  vary  according  as  the  vessels  composing  them  are 
straight  or  tortuous. 

The  nunihei'  of  the  capillaries  and  the  size  of  the  meshes  in  different 
parts  determine  in  general  the  degree  of  vascularity  of  those  parts. 
The  capillary  network  is  closest  in  the  lungs  and  in  the  choroid  coat  of 
the  eye.  Tn  the  iris  and  ciliary  body,  the  interspaces  are  somewhat 
wider,  yet  very  small.  In  the  human  liver  the  interspaces  are  of  the 
same  size,  or  even  smaller  than  the  capillary  vessels  themselves.  In  the 
human  lung  they  are  smaller  than  the  vessels;  in  the  human  kidney, 
and  in  the  kidney  of  the  dog,  the  diameter  of  the  injected  capillaries, 
compared  with  that  of  the  interspaces,  is  in  the  proportion  of  one  to 


Fig.  158. 

Fig.  158. — Networlv  of  capillary  vessels  of  the  air-cells  of  the  horse's  lung  magnified,    a,  a, 
Capillaries  proceeding  from  6,  6,  terminal  brandies  of  the  pulmonary  artery.    (Frey.) 

Fig.  159. — Injected  capillary  vessels  of  muscle  seen  with  a  low  magnifying  power.      (Sharpey.) 

four,  or  of  one  to  three.  The  brain  receives  a  very  large  quantity  of 
blood;  but  its  capillaries  are  very  minute,  and  are  less  numerous  than 
in  some  other  parts.  In  the  mucous  membranes — for  example  in  the 
conjunctiva  and  in  the  cutis  vera,  the  capillary  vessels  are  much  larger 
than  in  the  brain,  and  the  interspaces  narrower, — namely,  not  more 
than  three  or  four  times  wider  than  the  vessels.  In  the  periosteum 
the  meshes  are  much  larger.  In  the  external  coat  of  arteries,  the  width 
of  the  meshes  is  ten  times  that  of  the  vessels. 

It  may  be  held  as  a  general  rule,  that  the  more  active  the  functions 
of  an  organ  are,  the  more  vascular  it  is.  Her.ce  the  narrowness  of  the 
interspaces  in  all  glandular  organs,  in  mucous  membranes,  and  in  grow- 
ing parts;  their  much  greater  width  in  bones,  ligaments,  and  other  very 
tough  and  comparatively  inactive  tissues:  and  the  usually  complete 
absence  of  vessels  in  cartilage,  and  such  parts  as  those  in  which,  proba- 
bly, very  little  vital  change  occurs  after  they  are  once  formed. 


THE    CIRCULATION    OF   THE   BLOOD.  173 


The  Veins. 


Distribution. — The  venous  system  begins  in  small  vessels  which  are 
slightly  larger  than  the  capillaries  from  which  they  spring.  These 
vessels  are  gathered  up  into  larger  and  larger  trunks  until  they  termi- 
nate (as  regards  the  systemic  circulation)  in  the  two  venae  cavse  and  the 
coronary  veins,  which  enter  the  right  auricle,  and  (as  regards  the  pul- 
monary circulation)  in  four  pulmonary  veins,  which  enter  the  left 
auricle.     The  total  capacity  of  the  veins  diminishes  as  they  approach 


<  .A' 
'ii 


^. 


Fig.  160. — Transverse  section  through  a  small  artery  aud  vein  of  the  mucous  membrane  of  a 
child's  epiglottis :  the  artery  is  thick  walled  and  the  vein  thin-walled,  a.  Artery,  the  'etter  is  placed 
in  the  hi  men  of  the  vessel,  e.  Endothelial  cells  with  nuclei  clearly  visible  ;  these  cells  appear  very 
thick  from  the  contracted  state  of  the  vessel.  Outside  it  a  double  wavy  line  jiarks  the  elastic 
tunica  iutiina.  m.  Tunica  media  consisting  of  unstriped  muscular  fibres  circularl>  arranged;  their 
nuclei  are  well  seen.  u.  Part  of  the  tunica  adventitia  showing  bundles  of  connective-tissue  fibre  in 
section,  with  the  circular  nuclei  of  the  connective-tissue  corpuscles.  This  coat  gradually  merges 
into  the  surrounding  connective-tissue,  v.  In  the  lumen  of  the  vein.  The  other  letters  indicate  tlie 
same  as  in  the  artery.  The  muscular  coat  of  the  vein  (m)  is  seen  to  be  much  thinner  than  that  of 
the  artery,     x  350.     (Klein  aud  Noble  Smith.) 

the  heart;  but,  as  a  rule,  their  capacity  exceeds  by  twice  or  three  times 
that  of  their  corresponding  arteries.  The  pulmonary  veins,  however, 
are  an  exception  to  this  rule,  as  they  do  not  exceed  in  capacity  the  pul- 
monary arteries.  The  veins  are  found  after  death  more  or  less  collapsed, 
and  often  contain  blood.  They  are  usually  distributed  in  a  superficial 
and  a  deep  set  which  communicate  frequently  in  their  course. 

Structure. — In  structure  the  coats  of  veins  bear  a  general  resemblance 
to  those  of  arteries  (fig.  160).  Thus,  they  possess  outer,  middle,  and 
internal  coats. 

The  outer  coat   is    constructed   of  areolar  tissue  like  that   of  the 


174 


HANDBOOK    OF   PHYSIOLOGY. 


arteries,  but  is  thicker.     In  some  veins  it  contains  muscular  fibre-cells, 
which  are  arranged  longitudinally. 

The  middle  coat  is  considerably  thinner  than  that  of  the  arteries;  it 
contains  circular  unstriped  muscular  fibres,  mingled  with  a  large  pro- 


rig.  161.— Diagram  showingvalves  of  veins,  a,  part  of  a  vein  laid  open  and  spread  out,  with  two 
pairs  of  valves,  b,  longitudinal  section  of  a  vein,  showing  the  apposition  of  the  edges  of  the  valves 
in  their  closed  state,  c,  portion  of  a  distended  vein,  exhibiting  a  swelling  in  the  situation  of  a  pair 
of  valves. 

portion  of  yellow  elastic  and  white  fibrous  tissue.  In  the  large  veins, 
near  the  heart,  namely  the  ?'ewfl?  caves  and  pulmonary  veins,  the  middle 
coat  is  replaced,  for  some  distance  from  the  heart,  by  circularly  arranged 
striped  muscular  fibres,  continuous  with  those  of  the  auricles. 


Fig.  162. — A,  vein  with  valves  open,    b,  vein  with  valves  closed:    stream  of  blood  passing  of?  by 

lateral  channel.    (Dalton.) 

The  internal  coat  of  veins  is  less  brittle  than  the  corresponding  coat 
of  an  artery,  but  in  other  respects  resembles  it  closely. 

Valves. — The  chief  influence  which  the  veins  have  in  the  circula- 
tion, is  effected  with  the  help  of  the  valves,  contained  in  all  veins;  sub- 
ject to  local  pressure  from  the  muscles  between  or  near  which  they  run. 


THE    CIRCULATIOX    OF   THE    BLOOD. 


175 


The  general  construction  of  these  valves  is  similar  to  that  of  the  semi- 
lunar valves  of  the  aorta  and  pulmonary  artery,  already  described;  but 
their  free  margins  are  turned  in  the  opposite  direction,  i.  e.,  toward  the 
heart,  so  as  to  prevent  any  movement  of  blood  backward.  They  are 
commonly  placed  in  pairs,  at  various  distances  in  different  veins,  but 
almost  uniformly  in  each  (fig.  161).  In  the  smaller  veins  single  valves 
are  often  met  with;  and  three  or  four  are  sometimes  placed  together,  or 
near  one  another,  in  the  largest  veins, 
such  as  the  subclavian,  and  at  their  junc- 
tion with  the  jugular  veins.  The  valves 
are  semilunar;  the  unattached  edge  be- 
ing in  some  examples  concave,  in  others 
straight.  They  are  composed  of  inexten- 
sile  fibrous  tissue,  and  are  covered  with 
endothelium  like  that  lining  the  veins. 
During  the  period  of  their  inaction,  when 
the  venous  blood  is  flowing  in  its  proper 
direction,  they  lie  by  the  sides  of  the  veins ; 
but  when  in  action,  they  come  together 
like  the  valves  of  the  arteries  (figs.  161  and 
162).  Their  situation  in  the  superficial 
veins  of  the  forearm  is  readily  discovered 
by  pressing  along  its  surface,  in  a  direc- 
tion opposite  to  the  venous  current,  i.e., 
from  the  elbow  toward  the  wrist;  when 
little  swellings  (fig.  161,  o)  appear  in  the 
position  of  each  pair  of  valves.  These 
swellings  at  once  disappear  when  the  pres- 
sure is  removed. 

Valves  are  not  equally  numerous  in  all 
veins,  and  in  many  they  are  absent  al- 
together. They  are  most  numerous  in 
the   veins   of   the  extremities,  and    more 

so  in  those  of  the  leg  than  the  arm.  They  are  commonly  absent  in 
veins  of  less  than  a  line  in  diameter,  and,  as  a  general  rule  there 
are  few  or  none  in  those  which  are  not  subject  to  muscular  pres- 
sure. Among  those  veins  which  have  no  valves  may  be  mentioned  the 
superior  and  inferior  vena  cava,  the  trunk  and  branches  of  the  portal 
vein,  the  hepatic  and  renal  veins,  and  the  pulmonary  veins;  those  in  the 
interior  of  the  cranium  and  vertebral  column,  those  of  the  bones,  and 
the  trunk  and  branches  of  the  umbilical  vein  are  also  destitute  of  valves. 

L>/mphatics  of  Arteries  and  Veins. — Lymphatic  spaces  are  present 
in  the  coats  of  both  arteries  and  veins;  but  in  the  tunica  adventitia  or 
external  coat  of  large  vessels  they  form  a  distinct  plexus  of  more  or  less 


Fig.  103.— Surface  view  of  an  artery 
from  tlie  mesentery  of  a  frog,  en- 
sheathed  iu  a  peri-vascular  lymphatic 
vessel,  a.  Theartery,  with  its  circular 
muscular  coat  (media)  indicated  by 
broad,  transverse  markings,  with  an 
imlication  of  the  adventitia  outside. 
I.  LjTiiphatic  vessel,  its  wall  is  a  sim- 
ple endothelial  membrane.  (Klein  and 
Xoble  Smith. 


176  HANDBOOK    OF    PHYSIOLOGY. 

tubular  vessels.  In  smaller  vessels  they  appear  as  sinous  spaces  lined 
by  endothelium.  Sometimes,  as  in  the  arteries  of  the  omentum,  mesen- 
tery, and  membranes  of  the  brain,  in  the  pulmonary,  hepatic,  and  splenic 
arteries,  the  spaces  are  continuous  with  vessels  which  distinctly  ensheath 
them — perivascular  lympliatic  sheaths  (fig.  163).  Lymph  channels  are 
said  to  be  present  also  in  the  tunica  media. 

The  Action  of  the  Heart. 

The  heart's  action  in  propelling  the  blood  consists  in  the  successive 
alternate  contraction  (systole)  and  relaxation  (diastole)  of  the  mus- 
cular walls  of  its  two  auricles  and  two  ventricles. 

Action  of  the  Auricles. — The  description  of  the  action  of  the 
heart  may  be  commenced  at  that  period  in  each  cycle  which  imme- 
diately precedes  the  beat  of  the  heart  against  the  chest  wall.  The  whole 
heart  is  then  in  a  passive  state;  the  auricles  are  gradually  filling  with 
blood  flowing  into  them  from  the  veins;  and  a  portion  of  this  blood  is 
passing  at  once  through  them  into  the  ventricles,  the  opening  between 
the  cavity  of  each  auricle  and  that  of  its  corresponding  ventricle  being, 
during  all  ilie  pause,  free  and  patent.  The  auricles,  however,  receiving 
more  blood  than  at  once  passes  through  them  to  the  ventricles,  become, 
near  the  end  of  the  pause,  fully  distended ;  and  at  the  end  of  the  pause, 
they  contract  and  expel  their  contents  into  the  ventricles. 

The  contraction  of  the  auricles  is  sudden  and  very  quick;  it  com- 
mences at  the  entrance  of  the  great  veins  into  them,  and  is  thence  prop- 
agated toward  the  auriculo-ventricular  opening;  but  the  last  part  which 
contracts  is  the  auricular  appendix.  The  reflux  of  blood  into  the  great 
veins  during  the  auricular  systole  is  resisted  not  only  by  the  mass  of 
blood  within  them,  but  also  by  the  simultaneous  contraction  of  the 
muscular  coats  with  which  the  large  veins  are  provided  near  their  en- 
trance into  the  auricles.  Any  slight  regurgitation  from  the  right  auri- 
cle is  limited  by  the  valves  at  the  Junction  of  the  subclavian  and  internal 
jugular  veins,  beyond  which  the  blood  cannot  move  backward;  and  the 
coronary  vein  is  preserved  from  it  by  a  valve  at  its  mouth. 

The  force  of  the  blood  propelled  into  the  ventricle  at  each  auricular 
systole  is  transmitted  in  all  directions,  but  being  insutficient  to  open  the 
semilunar  valves,  it  is  expended  in  distending  the  ventricle. 

Action  of  the  Ventricles. — The  dilatation  of  the  ventricles  which 
proceeds  during  the  chief  part  of  the  dilatation  of  the  auricles  is  com- 
pleted by  the  forcible  injection  of  the  contents  of  the  latter.  Thus 
distended,  the  ventricles  immediately  contract:  so  immediately,  indeed, 
that  their  systole  looks  as  if  it  were  continuous  with  that  of  the  auri- 
cles. The  ventricles  contract  much  more  slowly  than  the  auricles,  and 
in    their   contraction    probably    always    thoroughly    empty  themselves. 


THE    CIRCULATIOX    OF   THE   BLOOD.  177 

differing  in  this  respect  from  the  auricles,  in  which,  even  after  their 
complete  contraction,  a  small  quantity  of  blood  remains.  The  shape  of 
both  ventricles  during  systole  undergoes  an  alteration,  the  left  probably 
not  altering  in  length  but  to  a  certain  degree  in  breadth,  the  diameter 
in  the  plane  of  the  base  being  diminished.  The  right  ventricle  does 
actually  shorten  to  a  small  extent.  The  systole  has  the  effect  of  dimin- 
ishing the  diameter  of  the  base,  especially  in  the  plane  of  the  auriculo- 
ventricular  valves;  but  the  length  of  the  heart  as  a  whole  is  not  altered 
(Ludwig).  During  the  systole  of  the  ventricles,  too,  the  aorta  and  pul- 
monary artery,  being  filled  with  blood  by  the  force  of  the  ventricular 
action  against  considerable  resistance,  elongate  as  well  as  expand,  and 
the  whole  heart  moves  slightly  toward  the  right  and  forward,  twisting 
on  its  long  axis,  and  exposing  more  of  the  left  ventricle  anteriorly  than 
is  usually  in  front.  When  the  systole  ends  the  heart  resumes  its  former 
position,  rotating  to  the  left  again  as  the  aorta  and  pulmonary  artery 
contract.  After  the  whole  of  the  blood  has  been  expelled  from  the 
ventricles,  the  walls  are  believed  to  remain  contracted  for  a  short  period 
before  the  rapid  re-dilatation  of  the  chambers  begin. 

Action  of  the  Valves. — (1)  The  Auriciilo-Ventricular. — The  dis- 
tention of  the  ventricles  with  blood  continues  throughout  tlie  whole 
period  of  their  diastole.  The  auriculo-ventricular  valves  are  gradually 
brought  into  place  by  some  of  the  blood  getting  behind  the  cusps  and 
floating  them  up;  and  by  the  time  that  the  diastole  is  complete,  the 
valves  are  no  doubt  in  apposition,  the  completion  of  this  being  brought 
about  by  the  reflux  current  caused  by  the  systole  of  the  auricles.  This 
elevation  of  the  auriculo-ventricular  valves  is  materially  aided  by  the 
action  of  the  elastic  tissue  which  has  been  shown  to  exist  so  largely  in 
their  structure,  especially  on  the  ventricular  surface.  At  any  rate  at 
the  commencement  of  the  ventricular  systole  they  are  completely  closed. 
It  should  be  recollected  that  the  diminution  in  the  breadth  of  the  base 
of  the  heart  in  its  transverse  diameters  during  ventricular  systole  is 
especially  marked  in  the  neighborhood  of  the  auriculo-ventricular  rings, 
and  this  aids  in  rendering  the  auriculo-ventricular  valves  competent  to 
close  the  openings,  by  greatly  diminishing  their  diameter.  The  mar- 
gins of  the  cusps  of  the  valves  are  still  more  secured  in  apposition  with 
another,  by  the  simultaneous  contraction  of  the  musculi  papillares, 
whose  chords  tendineae  have  a  special  mode  of  attachment  for  this 
object.  The  cusps  of  the  auriculo-ventricular  valves  meet  not  by  their 
edges  only,  but  by  the  opposed  surfaces  of  their  thin  outer  borders. 

The  form  and  position  of  the  fleshy  columns  on  the  internal  walls  of 
the  ventricle  no  doubt  help  to  produce  the  obliteration  of  the  ventricu- 
lar cavity  during  contraction;  and  the  completeness  of  the  closure  may 
often  be  observed  on  making  a  transverse  section  of  a  heart  shortly 
after  death,  in  any  case  in  which  rigor  mortis  is  very  marked  (fig.  149). 


178  HANDBOOK    OF    PHYSIOLOGY. 

In  such  a  case  only  a  central  fissure  may  be  discernible  to  the  eye  in  the 
place  of  the  cavity  of  each  ventricle. 

If  there  were  only  circular  fibres  forming  the  ventricular  wall,  it  is 
evident  that  on  systole  the  ventricle  would  elongate;  if  there  were  only 
longitudinal  fibres,  the  ventricle  would  shorten  on  systole;  but  there 
are  both.  The  tendency  to  alter  in  length  is  thus  counterbalanced, 
and  the  whole  force  of  the  contraction  is  expended  in  diminishing  the 
cavity  of  the  ventricle;  or,  in  other  words,  in  expelling  its  contents. 

On  the  conclusion  of  the  systole  the  ventricular  walls  tend  to  expand 
by  virtue  of  their  elasticity,  and  a  negative  pressure  is  set  up,  which 
tends  to  suck  in  the  blood.  This  negative  or  suctional  pressure  on  the 
left  side  of  the  heart  is  of  the  highest  importance  in  helping  the  pul- 
monary circulation.  It  has  been  found  to  be  equal  to  23  mm.  of  mer- 
cury, and  is  quite  independent  of  the  aspiration  or  suction  power  of  the 
thorax  itself,  which  will  be  described  in  a  later  chapter. 

The  musculi  ]3apillares  prevent  the  anriculo-ventricular  valves  from 
being  everted  into  the  auricle.  For  the  chords  tendineae  might  allow 
the  valves  to  be  pressed  back  into  the  auricle,  were  it  not  that  Avhen  the 
wall  of  the  ventricle  is  brought  by  its  contraction  nearer  the  auriculo- 
ventricular  orifice,  the  musculi  papillares  more  than  compensate  for  this 
by  their  own  contraction — holding  the  chords  tiglit,  and,  by  pulliug 
down  the  valves,  adding  slightly  to  the  force  with  which  the  blood  is 
expelled. 

These  statements  apply  equally  to  the  auriculo-ventricular  valves  on 
both  sides  of  the  heart;  the  closure  of  both  is  generally  complete  every 
time  the  ventricles  contract.  But  in  some  circumstances  the  tricuspid 
yalve  does  not  completely  close,  and  a  certain  quantity  of  olood  is 
forced  back  into  the  auricle.  This  has  been  called  the  safety-valve  action. 
The  circumstances  in  which  it  usually  haj^pens  are  those  in  which  the 
vessels  of  the  lung  are  already  completely  full  when  the  right  ventricle 
contracts,  as,  e.g.,  in  certain  pulmonary  diseases,  in  very  active  exertions, 
and  in  great  efforts.  In  these  cases,  the  tricuspid  valve  does  not  com- 
pletely close,  and  the  regurgitation  of  the  blood  may  be  indicated  by  a 
pulsation  in  the  jugular  veins  synchronous  with  that  in  the  carotid 
arteries. 

It  has  been  shown  that  the  commencement  of  the  ventricular  systole 
precedes  the  opening  of  the  semilunar  valves  by  a  fraction  of  a  second. 
This  would  seem  to  show  that  the  intraventricular  j^ressure  does  not 
exceed  the  arterial  pressure  until  the  systole  has  actually  begun,  for  the 
opening  of  the  valves  takes  place  at  once  when  there  is  a  distinct  differ- 
ence in  favor  of  the  intraventricular  over  the  arterial  pressure,  and  con- 
tinues open  only  as  long  as  this  difference  continues.  When  the  arterial 
begins  to  exceed  the  intraventricular  pressure,  there  is,  as  it  were,  a 
reflux  of  blood  toward  the  heart,  and  the  valves  close.     The  dilatation 


THE    CIKCULATIOJT    OF   THE   BLOOD.  179 

of  the  arteries  is,  in  a  peculiar  manner,  adtiiited  to  bring  this  about. 
The  lower  borders  of  the  semilunar  valves  are  attached  to  the  inner 
surface  of  the  tendinous  ring,  which  is,  as  it  were,  inlaid  at  the  orifice 
of  the  artery,  between  the  muscular  fibres  of  the  ventricle  and  the 
elastic  fibres  of  the  walls  of  the  artery.  The  tissue  of  this  ring  is  tough, 
and  does  not  admit  of  extension  under  such  pressure  as  it  is  commonly 
exposed  to;  the  valves  are  equally  inextensile,  being,  as  already  men- 
tioned, formed  mainly  of  tough,  close-textured,  fibrous  tissue,  with 
strong  interwoven  cords.  Hence,  when  the  ventricle  propels  blood 
through  the  orifice  and  into  the  canal  of  the  artery,  the  lateral  pressure 
which  it  exercises  is  sufficient  to  dilate  the  walls  of  the  artery,  but  not 
enough  to  stretch  in  an  equal  degree,  if  at  all,  the  unyielding  valves  and 
the  ring  to  which  their  lower  borders  are  attached.  The  effect,  there- 
fore, of  each  such  propulsion  of  blood  from  the  ventricle  is,  that  the 
wall  of  the  first  portion  of  the  artery  is  dilated  into  three  pouches  behind 


Fig.  164.— Sections  of  aorta,  to  show  the  action  of  the  semilunar  valves,  a  is  intended  to  show 
the  valves,  represented  by  the  dotted  lines,  lying  near  the  arterial  walls,  represented  by  the  contin- 
uous outer  Hue.  b  Rafter  Hunter)  shows  the  arterial  wall  cUstended  into  three  pouches  uo,  and 
drawn  away  from  the  valves,  which  are  straightened  into  the  form  of  an  equilateral  triangle  as 
represented  by  the  dotted  lines. 

the  valves,  while  the  free  margins  of  the  valves  are  drawn  inward  toward 
its  centre  (fig.  16-i,  b).  Their  positions  may  be  explained  by  the  dia- 
grams, in  which  the  continuous  lines  represent  a  transverse  section  of 
the  arterial  wails,  the  dotted  ones  the  edges  of  the  valves,  firstly,  when 
the  valves  are  nearest  to  the  walls  (a),  as  in  the  dead  heart,  and,  sec- 
ondly, when,  the  walls  being  dilated,  the  valves  are  drawn  away  from 
them  (b). 

This  position  of  the  valves  and  arterial  walls  is  retained  so  long  as 
the  ventricle  continues  in  contraction:  but  as  soon  as  it  relaxes,  and  the 
dilated  arterial  walls  can  recoil  by  their  elasticity,  the  blood  is  forced 
backward  toward  the  ventricles  and  onward  in  the  course  of  the  circu- 
lation. Part  of  the  blood  thus  forced  back  lies  in  the  pouches  (sinuses 
of  Valsalva)  (a,  fig.  164.  b)  between  the  valves  and  the  arterial  walls; 
and  the  valves  are  by  it  pressed  together  till  their  thin  luuated  margins 
meet  in  three  lines  radiating  from  the  centre  to  the  circumference  of 
the  artery  (7  and  8,  fig.  148). 

The  contact  of  the  valves  in  this  position  and  the  complete  closure 


ISO  HAiNTDBOOK    OF    PHYSIOLOGY. 

of  the  arterial  orifice  are  secured  by  the  peculiar  construction  of  their 
borders  before  mentioned.  Among  the  cords  which  are  interwoven  in 
the  substance  of  the  valve  are  two  of  greater  strength  and  prominence 
than  the  rest;  of  which  one  extends  along  the  free  border  of  each  valve, 
and  the  other  forms  a  double  curve  or  festoon  just  below  the  free 
border.  Each  of  these  cords  is  attached  by  its  outer  extremities  to  the 
outer  end  of  the  free  margin  of  its  valve,  and  in  the  middle  to  the 
corpus  Arantii;  they  thus  enclose  a  lunated  sjiace  from  a  line  to  a  line 
and  a  half  in  width,  in  which  space  the  substance  of  the  valve  is  much 
thinner  and  more  pliant  than  elsewhere.  When  the  valves  are  pressed 
down,  all  these  parts  or  spaces  of  their  surfaces  come  into  contact,  and 
the  closure  of  the  arterial  orifice  is  thus  secured  by  the  apposition  not 
of  the  mere  edges  of  the  valves,  but  of  all  those  thin  lunated  parts  of 
each  which  lie  between  the  free  edges  and  the  cords  next  below  them. 
These  parts  are  firmly  pressed  together,  and  the  greater  the  pressure 
that  falls  on  them  the  closer  and  more  secure  is  their  apposition.  The 
corpora  Arantii  meet  at  the  centre  of  the  arterial  orifice  when  the  valves 
are  down,  and  they  probably  assist  in  the  closure;  but  they  are  not 
essential  to  it,  for,  not  unfrequently,  they  are  wanting  in  the  valves  of 
the  pulmonary  artery,  which  are  then  extended  in  larger,  thin,  flapping 
margins.  In  valves  of  this  form,  also,  the  inlaid  cords  are  less  distinct 
than  in  those  with  corpora  Arantii;  yet  the  closure  by  contact  of  their 
surfaces  is  not  less  secure. 

Cardiac  Cycle. — Taking  72  as  the  average  number  of  cardiac  evolu- 
tions per  minute,  each  revolution  may  be  considered  to  occupy  f  of  a 
second,  or  about  .8,  which  may  be  approximately  distributed  in  the 
following  way: — 

Auricular  systole,  about    .  1  -|-  Auricular  diastole    .         .         .     .  7  =  .  8 
Ventricular  systole    "         .  3 -(- Ventricular  diastole     .         .  .5  — .8 

Period  of  joint  auricular 
and  ventricular  diastole  .4  -|-  Period  of  systole  of 

auricles  or  ventricles    .         .     .4  =  .8 

If  the  speed  of  the  heart  be  quickened,  the  time  occupied  by  each 
cardiac  revolution  is  of  course  diminished,  but  the  diminution  affects 
only  the  diastole  and  i^ause.  The  systole  of  the  ventricles  occujjies  very 
much  the  same  time,  whatever  the  pulse-rate. 

The  exact  period  in  which  the  several  valves  of  the  heart  are  in 
action  is  a  matter  of  some  uncertainty;  the  auriculo-ventricular  valves 
are  probably  closed  during  the  wliole  time  of  the  ventricular  contrac- 
tion, while,  during  the  dilatation  and  distention  of  the  ventricles,  they 
are  open.  The  semilunar  valves  are  only  certainly  open  during  the 
middle  period  of  the  ventricular  contraction. 


THE    CIRCULATION    OF   THE    BLOOD.  181 


The  Sounds  of  the  Heart. 


When  the  ear  is  placed  over  the  region  of  the  heart,  two  sounds  may 
be  heard  at  every  beat  of  the  heart,  which  follow  in  quick  succession, 
and  are  succeeded  by  a  jjoiise  or  period  of  silence.  The  first  sound  is 
dull  and  prolonged;  its  commencement  coincides  with  the  impulse  of 
the  heart  against  the  chest  wall,  and  just  precedes  the  pulse  at  the  wrist. 
The  second  is  shorter  and  sharper,  with  a  somewhat  flapping  character, 
and  follows  close  after  the  arterial  pulse.  The  periods  of  time  occupied 
respectively  by  the  two  sounds  taken  together  and  by  the  pause,  are 
nearly  equal.  Thus,  according  to  Walshe,  if  the  cardiac  cycle  be  divided 
into  tenths,  the  first  sound  occupies  y*^^;  the  second  sound  f-^;  the  first 
pause  (almost  imperceptible)  ^^;  and  the  second  pause -j^^-.  The  relative 
length  of  time  occupied  by  each  sound,  as  compared  with  the  other,  is 
a  little  uncertain.  The  diiference  may  be  best  appreciated  by  consider- 
ing the  different  forces  concerned  in  the  production  of  the  two  sounds. 
In  one  case  there  is  a  strong,  comparatively  slow,  contraction  of  a  large 
mass  of  muscular  fibres,  urging  forward  a  certain  quantity  of  fluid 
against  considerable  resistance;  while  in  the  other  it  is  a  strong  but 
shorter  and  sharper  recoil  of  the  elastic  coat  of  the  large  arteries — shorter 
because  there  is  no  resistance  to  the  flapping  back  of  the  semilunar  valves, 
as  there  was  to  their  opening.  The  sounds  may  be  expressed  by  the 
words  luhh — du}). 

The  events  which  correspond,  in  point  of  time,  with  i\\ki  first  sound, 
are  (1)  the  contraction  of  the  ventricles,  (2)  the  first  part  of  the  dilata- 
tion of  the  auricles,  (3)  the  tension  of  the  auriculo-ventricular  valves, 
(4)  the  opening  of  the  semilunar  valves,  and  (5)  the  propulsion  of  blood 
into  the  arteries.  The  sound  is  succeeded,  in  about  one-thirtieth  of  a 
second,  by  the  pulsation  of  the  facial  arteries,  and  in  about  one-sixth  of 
a  second,  by  the  pulsation  of  the  arteries  at  the  wrist.  The  second  sound, 
in  point  of  time,  immediately  follows  the  cessation  of  the  ventricular 
contraction,  and  corresponds  with  (a)  the  tension  of  the  semilunar 
valves,  {b)  the  continued  dilatation  of  the  auricles,  (r)  the  commencing 
dilatation  of  the  ventricles,  and  {d)  the  opening  of  the  auriculo-ventric- 
ular valves.  The  iMuse  immediately  follows  the  second  sound,  and 
corresponds  in  its  first  part  with  the  completed  distention  of  the  auri- 
cles, and  in  its  second  with  their  contraction,  and  the  completed  disten- 
tion of  the  ventricles ;  the  auriculo-ventricular  valves  being  all  the  time 
of  the  pause  open,  and  the  arterial  valves  closed. 

Causes. — The  exact  cause  of  the  first  sound  of  the  heart  is  not 
known.  Two  factors  probably  enter  into  it,  viz.,  firstly  tlie  vibration 
of  the  auriculo-ventricular  valves  and  of  the  chordae  tendineae.  This 
vibration  is  produced  by  the  increased  intraventricular  pressure  set  up 
when  the  ventricular  systole  commences,  which  puts  the  valves  on  the 


182 


HANDBOOK    OF    PHYSIOLOGY. 


stretch.  The  question  whether  this  stretched  condition  of  the  valve 
continues  throughout  tlie  whole  of  the  ventricular  systole  cannot  be 
definitely  settled,  but  if  it  does  not,  the  valvular  element  may  possibly 
take  part  in  the  j)roduction  of  the  first  part  of  the  first  sound  only.  It 
is  not  unlikely  too  that  the  vibration  of  the  ventricular  walls  themselves, 
and  of  the  aorta  and  pulmonary  artery,  all  of  which  parts  are  suddenly 
put  into  a  state  of  tension  at  the  moment  of  ventricular  contraction, 
may  have  some  part  in  producing  the  first  sound.  Secondly,  tlie  mus- 
cular sound  produced  by  contraction  of  the  mass  of  muscular  fibres 
which  form  the  ventricle.  Looking  ujion  the  contraction  of  the  heart 
as  a  single  contraction  and  not  as  a  series  of  contractions  or  tetanus,  it 
is  at  first  sight  difficult  to  see  why  there  should  be  any  muscular  sound 
at  all  when  the  heart  contracts,  as  contraction  of  a  single  muscle  does- 


Fig.  165. — Scheme  of  cardiac  cycle.    The  inner  circle  shows  the  events  which  occur  within  the 
heart;  the  outer  the  relation  of" the  sounds  and  pauses  to  these  events.    (Sharpey  and  Gairdner.j 

not  produce  sound.  It  has  been  suggested,  however,  that  it  arises  from, 
the  repeated  unequal  tension  produced  when  the  wave  of  muscular  con- 
tractions passes  along  the  very  intricately  arranged  fibres  of  the  ventric- 
ular walls.  The  valvular  element  is  probably  the  more  important  of 
the  two  factors. 

The  cause  of  the  second  sound  is  more  simple  than  that  of  the  first. 
It  is  entirely  due  to  the  vibration  consequent  on  the  sudden  closure  of 
the  semilunar  valves  when  they  are  pressed  down  across  the  orifices  of 
the  aorta  and  pulmonary  artery.  The  influence  of  these  valves  in  pro- 
ducing the  sound  was  first  demonstrated  by  Hope  who  experimented 
with  the  hearts  of  calves.  In  these  experiments  two  delicate  curved 
needles  were  inserted,  one  into  the  aorta,  and  another  into  the  pulmo- 
nary artery,  below  the  line  of  attachment  of  the  semilunar  valves,  and,, 
after  being  carried  upward  about  half  an  inch,  were  brought  out  again, 
through  the  coats  of  the  respective  vessels,  so  that  in  each  vessel  one 


THE    CIRCULATIOX    OF   THE    BLOOD.  183 

valve  was  included  between  the  arterial  walls  and  the  wire.  Upon  ap- 
plying the  stetlioscope  to  the  vessels,  after  such  an  operation,  the  second 
sound  had  ceased  to  be  audible.  Disease  of  these  valves,  when  sufficient 
to  interfere  with  their  efficient  action,  also  demonstrates  the  same  fact 
by  modifying  the  valvular  cause  of  the  second  sound  or  destroying  its 
distinctness. 

One  reason  that  the  second  sound  is  clearer  and  sharper  than  the  first 
may  be,  that  the  semilunar  valves  are  not  covered  in  by  the  thick  layer 
of  fibres  composing  the  walls  of  the  heart  to  such  an  extent  as  are  the 
auriculo-veutricular.  It  might  be  expected  therefore  that  their  vibra- 
tion would  be  more  easily  heard  by  means  of  a  stethoscope  applied  to 
the  walls  of  the  chest. 

The  contraction  of  the  auricles  which  takes  place  in  the  end  of  the 
pause  is  inaudible  outside  the  chest,  but  may  be  heard,  when  the  heart 
is  exposed  and  the  stethoscope  placed  on  it,  as  a  slight  sound  preceding 
and  continued  into  the  louder  sound  of  the  ventricular  contraction. 

The  Impulse  of  the   Heart. 

With  each  contraction  the  heart  may  be  felt  to  beat  with  a  slight 
shock  or  impulse  against  the  walls  of  the  chest.  The  force  of  the  im- 
pulse and  the  extent  to  which  it  may  be  perceived  beyond  this  point 
vary  considerably  in  different  individuals,  and  in  the  same  individual 
under  different  circumstances.  It  is  felt  more  distinctly,  and  over  a 
larger  extent  of  surface,  in  emaciated  than  in  fat  and  robust  persons, 
and  more  during  a  forced  expiration  than  in  a  deep  inspiration;  for,  in 
the  one  case,  the  intervention  of  a  thick  layer  of  fat  or  muscle  between 
the  heart  and  the  surface  of  the  chest,  and  in  the  other  the  inflation  of 
the  portion  of  lung  Avhich  overlaps  the  heart,  prevents  the  impulse  from 
being  full}^  transmitted  to  the  surface.  An  excited  action  of  the  heart, 
and  especially  a  hypertrophied  condition  of  the  ventricles,  will  increase 
the  impulse;  while  a  depressed  condition,  or  an  atrophied  state  of  the 
ventricular  walls,  will  diminish  it. 

Cause  of  the  Impulse. — During  the  j^eriod  which  precedes  the  ven- 
tricular systole  the  apex  of  the  heart  is  situated  upon  the  diaphragm  and 
against  the  chest-wall  in  the  fifth  intercostal  space.  When  the  ventri- 
cles contract,  their  walls  become  hard  and  tense,  since  to  expel  their 
contents  into  the  arteries  is  a  distinctly  laborious  action,  as  it  is  resisted 
by  the  elasticity  of  the  vessels.  It  is  to  this  sadden  hardening  that  the 
impulse  of  the  heart  against  the  chest-wall  is  due,  and  the  shock  of  the 
sudden  tension  may  be  felt  not  only  externally,  but  also  internally,  if 
the  abdomen  of  an  animal  be  opened  and  the  finger  be  placed  upon  the 
under  surface  of  the  diaphragm,  at  a  point  corresponding  to  the  under 
surface  of  the  ventricle.     The  shock  is  felt,  and  possibly  seen  more  dis- 


184 


HANDBOOK    OF    PHYSIOLOGY. 


tiuctly  because  of  the  partial  rotation  of  the  heart,  already  spoken  of, 
along  its  long  axis  toward  the  right.  The  movement  produced  by  the 
ventricular  contraction  against  the  chest-wall  may  be  registered  by  means 
of  an  instrument  called  the  cardiograj^li ,  and  it  will  be  found  to  corre- 


Tube  to  communicate 
with  tambour. 


Ivory      Tape  to  attach  the  instrument 
knob.  to  the  chest. 


Tympanum. 
Fig.  166. — Cardiograph.    (Sanderson's.) 


spond  almost  exactly  with  a  tracing  obtained  by  the  same  instrument 
applied  over  the  contracting  ventricle  itself. 

The  Cardiograph  (fig.  166)  consists  of  a  cup-shaped  metal  box  over  the  open 
front  of  which  is  stretched  an  elastic  India-rubber  membrane,  upon  which  is 
fixed  a  small  knob  of  hard  wood  or  ivory.  This  knob,  however,  may  be  at- 
tached, as  in  the  figure,  to  the  side  of  the  box  by  means  of  a  spring,  and  may 
be  made  to  act  upon  a  metal  disc  attached  to  the  elastic  membrane. 

Screw  to  regulate  elevation  of  lever. 


Writing  lever. 


Tambour. 


Tube  to  cardiograph. 


Fig.  167. — Marey's  Tambour,  to  which  the  movement  of  the  column  of  air  in  the  first  tympanum 
is  conducted  by  a  tube,  and  from  which  it  is  communicated  by  the  lever  to  a  revolving  cylinder,  so 
that  the  tracing  of  the  movement  of  the  impulse  beat  is  obtained. 

The  knob  (a)  is  for  application  to  the  chest-wall  over  the  place  of  the  great- 
est impulse  of  the  heart.  The  box  or  tympanum  communicates  by  means  of 
an  air-tight  tube  with  the  interior  of  a  second  tympanum,  in  connection  with 
which  is  a  long  and  light  lever  (a).  The  shock  of  the  heart's  impulse  being 
communicated  to  the   ivory  knob,  and  through  it  to  the  first  tympanum,  the 


THE    CIRCULATIOX    OF   THE    BLOOD. 


185 


effect  is,  of  course,  at  once  transmitted  by  the  column  of  air  in  the  elastic  tube 
to  the  interior  of  the  second  tympanum,  also  closed,  and  through  the  elastic 
and  movable  lid  of  the  latter  to  the  lever,  which  is  placed  in  connection  with 
a  registering  apparatus.  This  generally  consists  of  a  cylinder  or  drum  covered 
with  smoked  paper,  revolving  by  clock-work  with  a  definite  velocity.  The 
point  of  the  lever  writes  upon  the  paper,  and  a  tracing  of  the  heart's  impulse 
or  cardiogram  is  thus  obtained. 

By  placing  three  small  India-rubber  air  bags  or  cardiac  sounds  in  the  interior 
respectively  of  the  right  auricle  and  the  right  ventricle,  and  in  an  intercostal 
space  in  front  of  the  heart  of  living  animals  (horse),  and  placing  these  bags, 
by  means  of  long,  narrow  tubes,  in  communication  with  three  levers,  arranged 
one  over  the  other  in  connection  with  a  registering  apparatus  (fig.  168),  Chau- 
veau  and  Marey  have  been  able  to  rec(n-d  and  measure  with  much  accuracy  the 
variations  of  the  endocardial  pressure  and  the  comparative  duration  of  the 
contractions  of  the  amides  and  ventricles.     By  means  of  the  same  apparatus, 


Fig.  168. 


-Apparatus  of  MM.  Chauveau  and  Marey  for  estimating  the  variations  of  endocardial 
pressure,  and  production  of  impulse  of  the  heart. 


the  synchronism  of  the  impulse  with  the  contraction  of  the  ventricles,  is  also 
well  shown  ;  and  the  causes  of  the  several  vibrations  of  which  it  is  really  com- 
posed, have  been  demonstrated. 


In  the  tracing  (fig.  169),  the  intervals  between  the  vertical  lines  rep- 
resent periods  of  a  tenth  of  a  second.  The  parts  on  which  any  given 
vertical  line  falls  represent  simultaneous  events.  It  will  be  seen  that 
the  contraction  of  the  auricle,  indicated  by  the  marked  curve  at  a  in 
first  tracing,  causes  a  slight  increase  of  pressure  in  the  ventricle,  which 
is  shown  at  a'  in  the  second  tracing,  and  produces  also  a  slight  impulse, 
which  is  indicated  by  a  '  in  the  third  tracing.  The  closure  of  the  semi- 
lunar valves  causes  a  momentarily  increased  pressure  in  the  ventricle  at 
d',  affects  the  pressure  in  the  auricle  d,  and  is  also  shown  in  the  trac- 
ing of  the  impulse  d". 

The  large  curve  of  the  ventricular  and  the  impulse  tracings,  between 
a'  and  d',  and  a"  and  d",  are  caused  by  the  ventricular  contraction,  while 
the  smaller  undulations,  between  b  and  c,  b'  and  c',  b"  and  c",  are 


186 


HANDBOOK    OF    PHYSIOLOGY. 


caused  by  the  vibrations  consequent  on  the   tightening  and  closure  of 
the  auriculo-ventricular  valves. 

It  seems  by  no  means  certain  that  Marey's  curves  properly  represent 
the  variations  in  intraventricular  pressure.  Much  objection  has  been 
taken  to  his  method  of  investigation.  Firstly,  because  his  tambour  ar- 
rangement does  not  admit  of  both  positive  and  negative  pressure  being 
simultaneously  recorded.  Secondly,  because  the  method  is  only  applicable 
to  large  animals,  such  as  the  horse.  And  thirdly,  because  the  intraven- 
tricular changes  of  pressure  are  communicated  to  the  recording  tambour 
by  a  long  elastic  column  of  air;  and  fourthly,  because  the  tambour  ar- 
rangement has  a  tendency  to  record  inertia  vibrations.  II.  D.  Eolleston, 
who  has  pointed  out  the  above  imperfections  of  Marey's  method,  has  re- 
investigated the  subject  with  a  more  suitable  apparatus.     The  method 


Fig.  169.— Tracings  of  (1),  Intra-auricular.  and  (2),  Intra- ventricular  pressures,  and  (3),  of  the  im- 
pulse of  the  heart,  to  be  read  from  left,  to  right,  obtained  by  Chauveau  and  Marey's  apparatus. 


adopted  by  Rolleston  is  as  follows:  a  window  is  made  in  the  chest  of 
an  anesthetized  and  curarized  animal,  and  an  appropriately  curved  glass 
canula  introduced  through  an  opening  in  the  auricular  appendix. 
The  canula  is  then  passed  through  the  auriculo-ventricular  orifice  with- 
out causing  any  appreciable  regurgitation,  into  the  auricle,  or  it  may  be 
introduced  into  the  cavity  of  the  right  or  left  ventricle  by  an  opening 
made  in  the  apex  of  the  heart.  In  some  experiments  the  trocar  is 
pushed  through  the  chest  wall  into  the  ventricular  cavity.  The  appa- 
ratus is  filled  with  a  solution  of  leech  extract  in  .75  per  cent  saline  so- 
lution, or  with  a  solution  of  sodium  bicarbonate  of  specific  gravity  1083. 
The  animals  employed  were  chiefly  dogs.  The  movement  of  the  column 
of  blood  is  communicated  to  the  writing  lever  by  means  of  a  vulcanite 
piston  which  moves  with  little  friction  in  a  brass  tube  connected  with 
the  glass  canula  by  means  of  a  short  connecting  tube. 

When  the  lower  part  of  the  tube  (a)  is  placed  in  communication  with 
one  of  the  cavities  of  the  heart,  the  movements  of  the  piston  are  re- 


THE    CIRCULATION   OF   THE   BLOOD. 


187 


corded  by  means  of  the  lever  (c).  Attached  to  the  lever  is  a  section  of 
a  pulley  (h),  the  axis  of  which  coincides  with  that  of  the  steel  ribbon 
(e);  while,  firmly  fixed  to  the  piston,  is  the  curved  steel  piston  rod  (1), 
from  the  top  of  which  a  strong  silk  thread  (j)  passes  downward  into  the 
groove  on  the  pulley. 

This  thread  (j),  after  being  twisted  several  times  round  a  small  pin 
at  the  side  of  the  lever,  enters  the  groove  in  the  pulley  from  above  down- 
ward, and  then  passes  to  be  fixed  to  the  lower  part  of  the  curve  on  the 
piston-rod  as  shown  in  the  smaller  figure. 

The  rise  and  fall  of  the  lever  (c)  is  controlled  by  the  resistance  to 


Fig.  170.— Apparatus  for  recording  the  endocardial  pressure.    (Rolleston.) 


torsion  of  the  steel  ribbon  (e),  to  the  middle  of  which  one  end  of  the 
lever  is  securely  fixed  by  a  light  screw  clamp  (f).  At  some  distance 
from  this  clamp — the  distance  varying  with  the  degree  of  resistance 
which  it  is  desired  to  give  to  the  movements  of  the  lever — are  two  hold- 
ers (g.g')  which  securely  clamp  the  steel  ribbon. 

As  the  torsion  of  a  steel  wire  or  strip  follows  Hooke's  law,  the  tor- 
sion being  proportional  to  the  twisting  force — the  movements  of  the 
lever  point  are  proportional  to  the  force  employed  to  twist  the  steel  strip 
or  ribbon — in  other  words  to  the  pressures  which  act  on  the  piston  (b). 

To  make  it  possible  to  record  satisfactorily  the  very  varying  ventric- 
ular and  auricular  pressures,  the  resistance  to  torsion  of  a  steel  ribbon 
adapts  itself  very  conveniently. 


188 


HANDBOOK    OF    PHYSIOLOGY. 


This  resistance  can  be  varied  in  two  ways,  1st,  by  using  one  or  more 
pieces  of  steel  ribbon  or  by  using  strips  of  different  thicknesses;  or  2d, 
by  varying  the  distance  between  the  holders  (g.g)  and  the  central  part 
of  the  steel  ribbon  to  which  the  lever  is  attached. 

Eolleston's  conclusions  are  as  follows : — 

1.  That  there   is   no   distinct   and   separate   auricular  contraction 


Fig.  171. — Endocardial  pressure-curve  from  the  left  ventricle.  The  thorax  was  opened  and  a 
canula  introduced  through  the  apex  of  the  ventricle:  abscissa  is  line  of  atmospheric  pressure,  g 
to  D  represents  ventricular  contraction;  from  d  to  the  next  rise  at  g  represents  tlie  ventricular 
diastole.  The  notch  at  the  top  of  wliich  is  f  is  a  post-ventricular  rise  in  pressure  from  below  that 
of  the  atmosphere  and  not  a  pre-systolic  or  auricular  rise  in  pressure. 

marked  in  the  curves  obtained  from  either  right  or  left  ventricles,  the 
auricular  and  ventricular  rises  of  jiressure  being  merged  into  one  con- 
tinuous rise. 

2.  That  the  auriculo-ventricular  valves  are  closed  before  any  great 
rise  of  pressure  within  the  ventricle  above  that  which  results  from  the 
auricular  systole  {a,  fig.  172).     The  closure  of  the  valve  occurs  probably 


"Fig.  172.— Curve  with  dicrotic  summit  from  left  ventricle;  abscissa  shows  atmospheric  pressure. 


in  the  lower  third  of  the  rise  a  b  (fig.  172),  and  does  not  produce  any 
Tiotch  or  wave. 

3.  That  the  semilunar  valves  open  at  the  poi7it  in  the  ventricular 
systole,  situated  (at  g)  about  or  a  little  above  the  junction  of  the  mid- 
dle or  upper  third  of  the  ascending  line  (a  b),  and  the  closure  about  or 
a  little  before  the  shoulder  (d). 

4.  That  the  minimum  pressure  in  the  ventricle  may  fall  below  that 
of  the  atmosphere,  but  that  the  amount  varies  considerably. 


THE   CIRCULATIO^;    OF   THE   BLOOD. 


189' 


Frequency  and  Force  of  the  Heart's  Action. 

The  heart  of  a  healthy  adult  man  contracts  about  72  times  in  a 
minute;  but  many  circumstances  cause  this  rate,  which  of  course  cor- 
responds with  that  of  the  arterial  pulse,  to  vary  even  in  health.  The 
chief  are  age,  temiDcrament,  sex,  food  and  drink,  exercise,  time  of  day,, 
posture,  atmospheric  pressure,  temperature;  as  follows: — 

(1.)  Age. — The  frequency  of  the  heart's  action  gradually  diminishes 
from  the  commencement  to  near  the  end  of  life,  but  is  said  to  rise 
again  somewhat  in  extreme  old  age,  thus: — 


Before   birth  the  average   number  of 
pulsations  per  minute  is    150 

Just  after  birth      .       from  140  to  130 

During  the  first  year             130  to  115 

During    the      second 

year          .         .         .             115  to  100 

Durina:  the  third  vear            100  to  90 


About     the     seventh 

year 
About  the   fourteenth 

year 
In  adult  age 
In  old  age 
In  decrepitude    . 


from    90  to     85. 


85  to 
80  to 
70  to 

75  to 


80 
70' 
60 
65. 


(2.)  Temperament  and  Sex. — In  j^ersons  of  sanguine  temperament,, 
the  heart  acts  somewhat  more  frequently  than  in  those  of  the  phleg- 
matic; and  in  the  female  sex  more  frequently  than  in  the  male. 

(3  and  4.)  Food  and  Drink.  Exercise. — After  a  meal  the  heart's 
action  is  accelerated,  and  still  more  so  during  bodily  exertion  or  mental 
excitement;  it  is  slower  during  sleep. 

(5.)  Diurnal  Variation. — In  health  the  pulse  is  most  frequent  in  the 
morning,  and  becomes  gradually  slower  as  the  day  advances :  and  this 
diminution  of  frequency  is  both  more  regular  and  more  rapid  in  the 
evening  than  in  the  morning. 

(6.)  Postvre. — The  pulse,  as  a  general  rule,  especially  in  the  adult 
male,  is  more  frequent  in  the  standing  than  in  the  sitting  posture,  and 
in  the  latter  than  in  the  recumbent  position;  the  ditference  being 
greatest  between  the  standing  and  the  sitting  postures.  The  effect  of 
change  of  posture  is  greater  as  the  frequency  of  the  pulse  is  greater, 
and,  accordingly,  is  more  marked  in  the  morning  than  in  the  evening. 
By  supporting  the  body  in  different  positions,  without  the  aid  of  mus- 
cular effort  of  the  individual,  it  has  been  j^roved  that  the  increased  fre- 
quency of  the  pulse  in  the  sitting  and  standing  positions  is  dependent 
upon  the  muscular  exertion  engaged  in  maintaining  them;  the  usual 
effect  of  these  postures  on  the  jjulse  being  almost  entirely  prevented 
when  the  usually  attendant  muscular  exertion  was  rendered  unnecessary. 

(7.)  Atmospheric  Pressure. — The  frequency  of  the  pulse  increases  in 
a  corresponding  ratio  with  the  elevation  above  the  sea. 

(8.)  Temperature. — The  rapidity  and  force  of  the  heart's  contrac- 
tions are  largely  influenced  by  variations  of  temperature.  The  frog's 
heart,  when  excised,  ceases  to  beat  if  the  temperature  be  reduced  to- 


190  HANDBOOK    OF    PHYSIOLOGY. 

0°  C.  (32°  F.).  "When  heat  is  graduully  ajjplied  to  it,  both  the  speed 
and  force  of  the  contractions  increase  till  they  reach  a  maximum.  If 
the  temperature  is  still  further  raised,  the  beats  become  irregular  and 
feeble,  and  the  heart  at  length  stands  still  in  a  condition  of  "  heat- 
rigor."  Similar  effects  are  produced  in  warm-blooded  animals.  In  the 
rabbit,  the  number  of  heart-beats  is  more  than  doubled  when  the  tem- 
perature of  the  air  was  maintained  at  40".5  C.  (105°  F.).  At  45°  C.  (113° 
— 114°  F.),  the  rabbit's  heart  ceases  to  beat. 

In  health  there  is  observed  a  nearly  uniform  relation  between  the 
frequency  of  the  beats  of  the  heart  and  of  the  respirations;  the  propor- 
tion being,  on  an  average,  1  respiration  to  3  or  4  beats.  The  same  rela- 
tion is  generally  maintained  in  the  cases  in  which  the  action  of  the  heart 
is  naturally  accelerated,  as  after  food  or  exercise;  but  in  disease  this 
relation  may  cease.  In  many  affections  accompanied  with  increased 
frequency  of  the  heart's  contraction,  the  respiration  is,  indeed,  also 
iiccelerated,  yet  the  degree  of  its  acceleration  may  bear  no  definite  pro- 
portion to  the  increased  number  of  the  heart's  actions:  and  in  many 
other  cases,  the  heart's  contraction  becomes  more  frequent  without  any 
accompanying  increase  in  the  number  of  respirations;  or,  the  respiration 
alone  may  be  accelerated,  the  number  of  pulsations  remaining  station- 
ary, or  even  falling  below  the  ordinary  standard. 

The  Force  of  the  Cardiac  Action. 

(a.)  Ventricular. — The  force  of  the  left  ventricular  systole  is  more 
than  double  that  exerted  by  the  contraction  of  the  right  ventricle:  this 
difference  results  from  the  walls  of  the  left  ventricle  being  about  twice 
or  three  times  as  thick  as  those  of  the  right.  And  the  difference  is 
adapted  to  the  greater  degree  of  resistance  which  the  left  ventricle  has 
to  overcome,  comj)ared  with  that  to  be  overcome  by  the  right:  the 
former  having  to  propel  blood  through  every  part  of  the  body,  the  latter 
only  through  the  lungs.  The  actual  amount  of  the  intraventricular 
pressures  during  systole  in  the  dog  has  been  found  to  be  2.4  inches  (60 
mm.)  of  mercury  in  the  right  ventricle,  and  C  inches  (150  mm.)  in  the 
left. 

During  diastole  there  is  in  the  right  ventricle  a  negative  or  suction 
pressure  of  about  |  of  an  inch  (  —  17  to  —16  mm.),  and  in  the  left  ven- 
tricle from  2  inches  to  |  of  an  inch  (  —  52  to  —  20  mm.).  Part  of  this 
fall  in  pressure,  and  possibly  the  greater  part,  is  to  be  referred  to  the  in- 
fluence of  respiration;  but  without  this  the  negcitive  pressure  of  the  left 
ventricle  caused  by  its  active  dilatation  is  about  equal  to  |-  of  an  inch 
(20  mm.  )of  mercury. 

The  right  ventricle  is  undoubtedly  aided  by  this  suction  power  of 
the  left,  so  that  the  whole  of  the  work  of   sonductmg  the  pulmonary 


THE    CIRCULATION    OF   THE    BLOOD.  191 

circLilutiou  does  not  fall  upon  the  right  side  of  the  heart,  but  is  assisted 
by  the  left  side. 

(b.)  Auricular. — The  maximum  pressure  within  the  right  auricle  is 
equal  to  about  i  of  an  inch  (^U  mm.)  of  mercury,  and  is  probably  some- 
what less  in  the  left.  It  has  been  found  that  during  diastole  the  j^res- 
sure  within  both  auricles  sinks  considerably  below  that  of  the  atmos- 
phere; and  as  some  fall  in  pressure  takes  place,  even  when  the  thorax 
of  the  animal  operated  upon  has  been  opened,  a  certain  proportion  of 
the  fall  must  be  due  to  active  auricular  dilatation  independent  of  respi- 
ration in  the  right  auricle,  this  negative  pressure  is  equal  to  about 
— 10  mm. 

In  estimating  the  work  done  by  any  machine  it  is  usual  to  express 
it  in  terms  of  the  unit  of  work.  In  England,  the  unit  of  work  is  the 
foot-jjound,  and  is  defined  to  be  the  energy  expended  in  raising  a  unit 
of  weight  (1  lb.)  through  a  unit  of  height  (1  ft.) :  in  France,  the  kilo- 
firnm-metre.  The  work  done  by  the  heart  at  each  contraction  can  be 
readily  found  by  multiplying  the  weight  of  blood  expelled  by  the  ven- 
tricles by  the  height  to  which  the  blood  rises  in  a  tube  tied  into  an 
artery.  This  height  is  probably  about  9  ft.  3.21  metres  in  man.  Tak- 
ing the  weight  of  blood  expelled  from  the  left  ventricle  at  eacli  systole 
at  6  oz.,  i.e.,  |  lb.,  we  have  9  X  f  =  3.375  foot-pounds,  or  3.21  X  180  grms. 
or  578  gram-metres,  as  the  Avork  done  by  the  left  ventricle  at  each  sys- 
tole; and  adding  to  this  the  work  done  by  the  right  ventricle  (about 
one-fourth  that  of  the  left)  we  have  3.375  +  -822  =  4.19  foot-pounds,  or 
722  gram-metres  as  the  work  done  by  the  heart  at  each  contraction. 

Blood  Pressure. 

The  subject  of  blood-pressure  has  been  already  incidentally  men- 
tioned more  than  once  in  the  preceding  pages,  the  time  has  now  arrived 
for  it  to  receive  more  detailed  consideration. 

That  the  blood  exercises  pressure  upon  the  walls  of  the  vessels  con- 
taining it,  is  due  to  the  following  facts: — 

Firstly,  that  the  heart  at  each  contraction  forcibly  injects  a  consid- 
erable amount  of  blood,  viz.,  4  to  G  oz.  (120  to  130  grms.)  suddenly  and 
quickly  into  the  arteries. 

Secondly,  that  the  arteries  are  already  full  of  blood  at  the  com- 
mencement of  the  ventricular  systole,  since  there  is  not  sufficient  time 
between  the  heart  beats  for  the  blood  to  pass  into  the  veins. 

Thirdly,  that  the  arteries  are  highly  distensible  and  stretch  to  ac- 
commodate the  extra  amount  of  blood  forced  into  them ;  and 

Fourthly,  ihac  there  is  a  distinct  resistance  interposed  to  the  pas- 
sage of  the  blood  from  the  arteries  into  the  veins,  from  the  enormous 
number  of  minute  vessels,  small  arteries  (arterioles)  and  capillaries  into 


192  HANDBOOK    OF    PHYSIOLOGY. 

which  the  main  artery  has  been  ultimately  broken  np.  The  sectional 
area  of  tlie  capillaries  is  several  hundred  times  that  of  the  aorta,  and 
the  friction  generated  by  the  passage  of  the  blood  through  these  minute 
channels  opposes  a  considerable  hindrance  or  resistance  in  its  course. 
The  resistance  thus  set  up  is  called  peripheral  resistance.  The  fric- 
tion is  greater  in  the  arterioles  where  the  current  is  comparatively  rapid 
than  in  the  cajDillaries  where  it  is  slow. 

That  the  blood  exerts  considerable  pressure  upon  the  arterial  walls 
in  keeping  them  in  a  stretched  or  distended  condition,  may  be  readily 
shown  by  puncturing  any  artery;  the  blood  is  instantly  projected  with 
great  force  tlirough  the  opening,  and  the  jet  rises  to  a  considerable 
height,  the  exact  level  of  which  varies  with  the  size  of  the  artery  .expe- 
rimented with.  If  a  large  artery  be  punctured,  the  blood  may  be  pro- 
jected upward  for  many  feet,  whereas  if  a  small  artery  be  similarly  dealt 
with  the  jet  does  not  rise  to  such  a  height.  Another  marked  feature  of 
the  jet  of  blood  from  a  cut  artery,  particularly  well  marked  if  the  vessel 
be  a  large  one,  and  near  the  heart,  is  the  jerky  character  of  the  outflow. 
If  the  artery  be  cut  across,  the  jet  issues  with  force,  chiefly  from  the 
central  end,  unless  there  is  considerable  anastomosis  of  vessels  in  the 
neighborhood,  when  the  jet  from  the  joeripheral  end  may  be  as  forcible 
and  as  intermittent  as  that  from  the  other  end.  The  intermittent  flow 
in  the  arteries  which  is  due  to  the  intermittent  action  of  the  heart,  and 
which  represents  the  systolic  and  diastolic  alterations  of  blood  pressure, 
may  be  felt  if  the  finger  be  placed  upon  a  sufficiently  superficial  artery. 
The  finger  is  apparently  raised  and  lowered  by  the  intermittent  systolic 
distention  of  the  vessel,  occurring  at  each  heart  beat.  This  intermittent 
distention  of  the  artery  is  what  is  known  as  the  Pulse,  to  the  further 
consideration  of  which  we  shall  persently  return,  but  we  may  say  here, 
that  in  a  normal  condition  the  pulse  is  a  characteristic  of  the  arterial, 
and  is  absent  from  the  venous  fiow.  At  the  same  time  it  must  be  recol- 
lected that  in  the  veins  the  blood  exercises  a  pressure  on  its  containing 
vessel,  but  as  we  shall  see  presently  this  is  small  when  compared  with 
the  arterial  blood-pressure.  As  might  be  expected,  therefore,  the  blood 
is  not  expelled  with  so  much  force  if  a  vein  be  punctured  or  cut,  and 
further,  the  flow  from  the  cut  vein  is  continuous  and  not  intermittent, 
and  the  greater  amount  of  blood  comes  from  the  peripheral  and  not 
from  the  central  end  as  is  the  case  when  an  artery  is  severed. 

The  result  produced  by  the  experiment  of  cutting  or  puncturing  a 
blood  vessel  may  be  modified  by  introducing  into  the  vessel  a  glass 
tube  of  a  calibje  corresponding  to  that  of  the  vessel,  and  allowing  the 
blood  to  rise  in  it.  If  the  vessel  be  an  artery,  the  blood  will  rise 
several  feet,  according  to  the  distance  of  the  vessel  from  the  heart,  and 
when  it  has  reached  its  highest  point  will  be  seen  to  oscillate  with 
the  heart's  beats.     This  experiment  shows  that  the  pressure  which  the 


THE    CIRCULATIOX    OF   THE    BLOOD. 


193 


blood  exerts  upon  the  walls  of  the  contained  artery,  equals  the  pres- 
sure of  a  column  of  blood  of  a  certain  height;  in  the  case  of  the  rab- 
bit's carotid  it  is  equal  to  3  feet  of  blood,  or  rather  more  than  3  feet  of 
water.  In  the  case  of  the  vein,  if  a  similar  experiment  be  performed, 
blood  will  rise  in  the  tube  for  an  inch  or  two  only. 

The  usual  method  of  estimating  the  amount  of  blood  pressure  differs 
somewhat  from  the  foregoing  simple  experiment.  Instead  of  a  simple 
straight  tube  of  glass  inserted  into  the  vessel,  a  U-shaped  tube  contain- 


Fig.  Ii3.— Diaprram  of  mercurial  kymograph,  a,  revolving  cylinder,  worked  by  a  clOCk-work 
arrangement  contained  in  the  box  (b),  the  speed  being  regulated  by  a  fan  above  the  box;  cylinder 
supported  by  an  upright  (6),  and  capable  of  being  raised  or  lowered  by  a  screw  (a),  by  a  handle 
attached  to  it:  d,  c,  e,  represent  mercurial  manometer,  a  somewhat  different  form  of  which  is 
s.iown  in  next  figure. 

ing  mercury,  or  a  mercurial  manometer  is  employed,  and  the  artery 
is  made  to  communicate  with  it  by  means  of  a  small  canula  which  is 
inserted  into  the  vessel,  and  a  connecting  tube,  an  arrangement  being 
made  whereby  the  canula,  tubes,  etc.,  are  filled  with  a  saturated  saline 
solution  to  prevent  the  clotting  of  blood  when  it  is  allowed  to  pass  from 
the  artery  into  the  apparatus.  The  passage  of  blood  is  prevented  during 
the  arrangement  of  the  details  of  the  experiment  by  a  pair  of  clamp  or 
bull-dog  forceps!  The  free  end  of  the  U-tube  of  mercury  contains  a 
very  fine  glass  piston,  the  bulbous  end  of  whicli  floats  upon  the  surface 
of  the  mercury,  rising  with  its  rise  and  oscillating  with  its  oscillations. 
13 


194 


HANDBOOK    OF    PHYSIOLOGY. 


As  soon  iis  there  is  free  communication  between  the  artery  and  the  tube 
of  mercury,  the  blood  rushes  out  and  puslies  before  it  the  column  of 
mercury.  The  mercury  will  therefore  rise  in  the  free  limb  of  the  tube, 
and  will  continue  to  do  so  until  a  point  is  reached  which  corresponds  to 
the  mean  pressure  of  the  blood-vessel  used.  The  blood-pressure  is  thus 
communicated  to  the  upper  part  of  the  mercurial  column;  and  the 
depth  to  which  the  latter  sinks,  added  to  the  height  to  which  it  rises  in 
the  other,  will  give  the  height  of  the  mercurial  column  which  the  blood- 
pressure  balances;  the  weight  of  the  saline  solution  being  subtracted. 
For  the  estimation  of  the  amount  of  blood  pressure  at  any  given  mo- 
ment, no  further  apparatus  than  this,  which  is  called  Poiseuilles's  h(B- 


Fig.  174. — Ludwig's  Kymograph.  The  manometer  is  shown  iu  lig.  173,  D.  C.  E.  The  mercury 
which  partially  fills  tlie  tube  su]jports  a  float  in  form  of  a  piston,  nearly  filling  the  tube;  a  vvu'e  is 
fixeil  to  the  float,  and  tlie  writing  style  or  pen  is  guided  by  passing  through  the  bra.ss  cap  of  the 
tube  fixed  to  the  wire;  the  ijressure  is  communicated  to  the  mercury  by  means  of  a  flexible  metal 
tube  filled  with  fluid. 

mad i/namometer, is  necessary;  but  for  noting  the  variation.'^  of  pressure 
iu  the  arterial  system,  as  well  as  its  absolute  amount,  the  instrument  is 
usually  combined  with  a  recording  apparatus,  in  this  form  called  a 
kymograph  (fig.  173). 

The  recording  apparatus  "consists  of  a  revolving  cylinder  (fig.  173, 
A),  which  is  moved  by  clockwork,  and  the  speed  of  which  is  capable  of 
regulation.  The  cylinder  is  covered  with  glazed  paper  blackened  in  the 
fiame  of  a  lump,  and  the  mercurial  mauometer  is  so  fixed  (fig,  173,  D) 
that  its  float  provided  with  a  style  writes  on  the  cylinder  as  it  revolves. 
There  are  many  ways  in  which  the  mercurial  manometer  may  be  varied; 
in  fig.  174  is  seen  a  form,  which  is  known  as  Ludwig's  Kymograph,  In 
order  to  obviate  the  necessity  of  a  large  quantity  of  blood  entering  the 
tube  of  the  apparatus,  it  is  usual  to  have  some  arrangement  by  means 


THE   CIRCULATION    OF   THE   BLOOD.  195 

of  which  the  mercury  may  be  made  to  rise  in  the  tube  of  the  manometer 
to  the  level  corresponding  to  the  mean  pressure  of  the  artery  experi- 
mented with,  so  that  the  writing  style  simply  records  the  variations  of 
the  blood  pressure  above  and  below  the  mean  pressure.  This  is  done  by 
causing  the  saline  solution,  generally  a  saturated  solution  of  sodium 
carbonate  or  sulphate,  to  fill  the  apparatus  from  a  bottle  suspended  at  a 
height,  and  capable  of  being  raised  or  lowered  as  required  for  the  pur- 
pose, or  by  injecting  the  saline  solution  into  the  tube  by  means  of  a 
syringe.  The  canula  inserted  and  tied  into  the  artery  may  be  of  two 
kinds.  In  one  case  a  fine  glass  tube  is  used  with  the  end  drawn  out  and 
cut  so  that  its  end  is  oblique,  and  provided  with  a  shoulder  to  prevent 
its  coming  out  easily,  the  peripheral  end  of  the  cut  artery  being  tied  to 
obviate  the  escape  of  blood.  By  this  means,  the  j^ressure  communicated 
to  the  column  of  mercury  is  the  forward  and  not  the  lateral  pressure  of 
blood,  or  a  T-canula  may  be  employed  and  may  be  tied  into  the  two 
ends  of  a  divided  artery,  and  the  free  arm  of  the  T  piece  being  made 


Fig.  irs. — Normal  tracing:  of  arterial  pressure  in  the  rabbit  obtained  with  the  mercurial  kyrno- 
graph.  The  smaller  undulations  correspond  with  the  heart  beats;  the  larger  curves  with  the  respi- 
ratory movements.     cBurdon-Sanderson.) 

to  communicate  with  the  manometer.  This  communicates  the  lateral 
blood  2)ressure. 

As  soon  as  the  experiment  is  completed,  the  writing  float  is  seen  to 
oscillate  in  a  regular  manner,  and  a  curve  of  blood  pressure  is  traced 
upon  the  smoked  paper  by  the  style  (or,  if  a  continuous  roll  of  unsmoked 
paper  be  used  instead,  by  an  inked  pen),  when  a  figure  similar  to  fig. 
175  will  be  obtained. 

This  indicates  two  main  variations  of  the  blood  pressure;  the  smaller 
excursions  of  the  lever  corresponds  with  the  systole  and  diastole  of  the 
heart,  and  the  large  curves  correspond  with  the  respirations,  being  called 
the  respiratory  undulations  of  blood  pressure,  to  which  attention  will 
be  directed  in  the  next  chapter.  Of  course,  the  undulations  spoken  of 
are  only  seen  in  records  of  arterial  blood  pressure;  they  are  more  clearly 
marked  in  the  arteries  nearer  the  heart  than  in  those  more  remote,  in 
the  smaller  arteries  the  amount  of  the  pressure  as  well  as  the  indication 
of  the  systolic  rise  of  pressure,  being,  comparatively  speaking,  small. 

In  order  to  record  the  undulations  of  arterial  pressure,  for  some  pur- 
poses it  is  better  to  use  Fick's  Spring  Kymograph  than  the  mercurial 
manometer.     Two  forms  of  this  instrument  are  shown  in  figs.  176  and 


196 


HANDBOOK    OF    PHYSIOLOGY. 


177.  It  consists  of  a  hollow  C-spring,  filled  with  fluid,  the  interior  of 
which  is  made  to  communicate  with  the  artery  by  means  of  a  flexible 
metal  tube  and  canula.  In  response  to  the  pressure,  transmitted  to 
its  interior,  the  spring  tends  to  straighten  itself,  and  the  movement 
thus  produced  is  communicated  by  means  of  a  lever  to  a  writing  style 
and  so  to  a  recording  apparatus.  This  instrument  obviates  the  errors 
which  might  be  caused  by  the  inertia  of  the  mercury  in  the  mercurial 
manometer;  it  also  shows  in  more  detail  the»variations  of  the  blood 
pressure  in  the  vessel  during  and  after  each  individual  beat  of  the  heart. 


Fig.  1?6. — A  form  of  Pick's  Spring  Kymograph,  a,  Tube  to  be  counected  with  artery;  c,  hollow 
spring,  the  movement  of  which  moves  b,  the  writing  lever;  e,  .screw  to  regulate  height  of  b;  d,  out- 
side protective  spring;  g,  screw  to  fix  on  the  u  right  of  the  support. 


In  fig.  178  is  seen  a  tracing  taken  with  Fick's  Kymograph  from  an 
artery  of  a  dog. 

As  regards  the  actual  amount  of  blood  pressure,  from  observations 
which  have  been  made  by  means  of  the  mercurial  manometer,  it  has 
been  found  that  the  pressure  of  blood  in  the  carotid  of  a  rabbit  is  capa- 
ble of  supporting  a  column  of  2  to  3.5  inches  (50  to  90  mm.)  of  mercury, 
in  the  dog  4  to  7  inches  (100  to  175  mm.),  in  the  horse  5  to  8  inches 
(152  to  200  mm.),  and  in  man  the  pressure  is  estimated  to  be  about  the 
same. 

To  measure  the  absolute  amount  of  this  pressure  in  any  artery,  it  is 
necessary  merely  to  multiply  the  area  of  its  transverse  section  by  the 
height  of  the  column  of  mercury  which  is  already  known  to  be  sup- 


THE    CIKCULATIOX    OF   THE    BLOOD. 


197 


ported  by  the  blood-pressure  in  any  part  of  the  arterial  system.  The 
weight  of  a  column  of  mercury  thus  found  will  represent  the  pressure 
of  the  blood.  Calculated  in  this  way,  the  blood-pressure  in  the  human 
aorta  is  equal  to  4  lbs.  4  oz.  avoirdupois;  that  in  the  aorta  of  the  horse 
being  11  lb.  9  oz.;  and  that  in  the  radial  artery  at  the  human  wrist  only 
4  drs.  Supposing  the  muscular  power  of  the  right  ventricle  to  be  only 
one-half  that  of  the  left,  the  blood-pressure  in  the  pulmonary  artery  will 
be  only  2  lb.  2  oz.  avoirdupois.  The  amounts  above  stated  represent  the 
arterial  tension  to  the  time  of  the  ventricular  contraction. 


Fig.  1((.—Fick's  Kymograpli,  improved  by  Hering  (after  McKendrick).  a,  Hollow  spring  filled 
with  alcohol,  bearing  lever  ai-raiisenient  b,  d,  c.  to  which  is  attached  the  marker  e;  the  rod  c  passes 
downward  into  the  tube/,  containing  castor  oil,  which  offers  resistance  to  the  oscillations  of  c;  g, 
syringe  for  filling  the  leaden  tube  b  with  saturated  sulphate  of  sodium  solution,  and  to  apply  suffi- 
cient pressure  as  to  prevent  the  blood  from  passing  into  the  tube  h  at  i,  the  canula  inserted  into 
the  vessel;  I,  abscissa-marker,  which  can  be  applied  U>  the  moving  surface  by  turning  the  screw  in; 
fc,  screw  for  adjusting  the  whi>le  apparatus  to  the  moving  surface:  o,  screw  for  elevating  or  de- 
pressing by  a  rack  and  pinion  movement  the  Kymograph;  u,  screw  for  adjusting  the  position  of 
the  tube  /. 

The  blood-pressure  is  greatest  in  the  left  ventricle  and  at  the  begin- 
ning of  the  aorta,  and  decreases  toward  the  capillaries.  It  is  greatest  in 
the  arteries  cit  the  period  of  the  ventricular  systole.  The  blood-pressure 
gradually  lessens  then  as  we  proceed  from  the  arteries  near  the  heart  to 
those  more  remote,  and  again  from  these  to  the  capillaries,  and  thence 
along  the  veins  to  the  right  auricle.  The  blood-pressure  in  the 
veins  is  nowhere  very  great,  but  is  greatest  in  the  small  veins,  while  in 
the  large  veins  toward  the  heart  the  pressure  becomes  7iegative,  or,  in 
other  words,  when  a  vein  is  put  in  connection  with  a  mercurial  man- 


198  HANDBOOK    OF    PHYSIOLOGY. 

ometer  the  mercury  will  falliu  the  arm  furthest  away  from  the  vein  aiid 
will  rise  in  the  arm  nearest  the  vein,  the  action  being  that  of  suction 
rather  than  pressure  forward.  In  the  large  veins  of  the  neck  the  ten- 
dency to  suck  in  air  is  especially  marked,  and  is  the  cause  of  death  in 
some  surgical  operations  in  that  region.  The  amount  of  pressure  in  the 
brachial  vein  is  said  to  suj^port  9  mm.  of  mercury,  whereas  the  pressure 
in  the  veins  of  the  neck  is  about  equal  to  a  negative  pressure  of  rather 
more  than  -^  inch  or  —  about  i  to  ^  inch  or  —  3  to  —  8  mm. 

The  variations  of  venous  pressure  during  systole  and  diastole  of  the 
heart  are  very  slight,  and  a  distinct  pulse  is  never  seen  in  veins  except 
under  extraordinary  circumstances.  From  observations  upon  the  web 
of  the  frog's  foot,  the  tongue  and  mesentery  of  the  frog,  the  tails  of 
newts,  and  small  fishes  (Roy  and  Brown),  as  well  as  upon  the  skin  of 
the  finger  behind  the  nail  (Kries),  by  careful  estimation  of  the  amount 
of  pressure  required  to  empty  the  vessels  of  blood  under  various  condi- 
tions, it  appears  that  the  blood-pressure  is  subject  to  variations  in 
the  capillaries,  apparently  following  the  variations   of   that   of   the 


Fig.  178. — Normal  arterial  tracing  obtained  with  Tick's  kymograph  in  the  dog. 
(Burdon-Sanderson . ) 

arteries;  and  that  up  to  a  certain  jjoint,  as  the  extra  vascular  pressure  is 
increased,  so  does  the  pulse  in  the  arterioles,  capillaries,  and  venules  be- 
come more  and  more  evident.  The  pressure  in  the  first  case  (web  of 
the  frog's  foot)  has  been  found  to  be  equal  to  about  i  to  f  inch  or  14  to 
20  mm.  of  mercury;  in  other  experiments  to  be  equal  to  about  |  to  ^  of 
the  ordinary  arterial  pressure. 

The  arterial  blood-pressure  may  be  made  to  vary  by  variations  of 
either  of  the  two  chief  factors  upon  which  the  pressure  in  the  vessels 
depends,  viz.,  the  cardiac  contractions  and  the  peripheral  resistance. 
Thus,  increase  of  blood-pressure  may  be  brought  about  by  either  (a)  a 
more  frequent  or  more  forcible  action  of  the  heart,  or  (b)  by  increase  of 
the  peripheral  resistance;  and  on  the  other  hand,  diminution  of  the 
blood-pressure  may  be  produced,  either  by  (a)  a  diminished  force  or  fre- 
quency of  the  contractions  of  the  heart,  or  by  (b)  a  diminished  periphe- 
ral resistance.  These  different  factors,  however,  although  varying  con- 
stantly, are  so  combined  that  the  general  arterial  pressure  remains  fairly 
constant;  for  example,  the  heart  may,  by  increased  force  or  frequency 
of  its  contractions,  distinctly  increase  the  blood-pressure,  but  this  in- 
creased action  is  almost  certainly  followed  by  diminished  peripheral 


THE    CIRCULATION    OF   THE    BLOOD.  199 

resistance,  and  thus  the  two  altered  conditions  may  balance,  with  the 
result  of  brinoing  back  the  blood-pressure  to  what  it  was  before  the 
heart  began  to  beat  more  rapidly  or  more  forcibly. 

It  will  be  clearly  seen  that  the  circulation  of  the  blood  within  the 
blood-vessels  must  depend  upon  the  dimijiution  of  the  pressure  from 
the  heart  to  the  capillaries,  and  from  the  capillaries  to  the  veins,  the 
blood  flowing  in  the  direction  of  least  resistance;  we  shall  presently  see 
further  that  the  general  or  local  flow  also  depends  upon  the  relations 
between  the  heart's  action  and  the  peripheral  resistance,  general  or  local. 

The  Arterial  Flow. 

The  character  of  the  flow  of  blood  through  the  arterial  system  de- 
pends to  a  very  considerable  extent  upon  the  structure  of  the  arterial 
walls,  and  particularly  upon  the  elastic  tissue  which  is  so  highly  devel- 
oped in  them. 

The  elastic  tissue  first  of  all  guards  the  arteries  from  the  suddenly 
exerted  pressure  to  which  they  are  subjected  at  each  contraction  of  the 
ventricles.  In  every  such  contraction  as  is  above  seen  the  contents  of 
the  ventricles  are  forced  into  the  iuteries  more  quickly  than  they  can 
be  discharged  through  the  capillaries.  The  blood,  therefore,  being,  for 
an  instant,  resisted  in  its  onward  course,  a  part  of  the  force  with  which 
it  was  impelled  is  directed  against  the  sides  of  the  arteries;  under  this 
force  their  elastic  walls  dil.ite,  stretching  enough  to  receive  the  blood, 
and,  as  they  stretch,  becomiiig  more  tense  and  more  resisting.  Thus, 
by  yielding  they  break  the  shock  of  the  force  impelling  the  blood.  On 
the  subsidence  of  the  pressure,  when  the  ventricles  cease  contracting, 
the  arteries  are  able,  by  the  same  elasticity,  to  resume  their  former  cali- 
bre; the  elastic  tissue  also  equalizes  the  current  of  blood  by  maintaining 
pressure  on  it  in  the  arteries  during  the  period  at  which  the  ventricles 
are  at  rest  or  are  dilating.  If  the  arteries  were  rigid  tubes,  the  blood, 
instead  of  flowing,  as  it  does,  in  a  constant  stream,  would  be  propelled 
through  the  arterial  system  in  a  series  of  jerks  corresponding  to  the 
ventricular  contractions,  with  intervals  of  almost  complete  rest  during 
the  inaction  of  the  ventricles.  But  in  the  actual  condition  of  the  ves- 
sels, the  force  of  the  successive  contractions  of  the  ventricles  is  expended 
partly  in  the  direct  propulsion  of  the  blood,  and  partly  in  the  dilatation 
of  the  elastic  arteries;  and  in  the  intervals  between  the  contractions  of 
the  ventricles,  the  force  of  the  i*ecoil  is  employed  in  continuing  the  on- 
ward flow.  Of  course  the  pressure  exercised  is  equally  difl'used  in  every 
direction,  and  the  blood  tends  to  move  backward  as  well  as  onward;  all 
movement  backward,  however,  is  prevented  by  the  closure  of  the  semi- 
lunar valves,  which  takes  place  at  tlie  very  commencement  of  the  recoil 
of  the  arterial  walls. 


200  HANDBOOK    OF    PHYSIOLOGY. 

Thus  by  the  exercise  of  the  ehisticity  of  the  arteries,  all  the  force  of 
the  ventricles  is  expended  upon  the  circulation;  for  that  part  of  the 
force  which  is  used  up  or  rendered  potential  in  dilating  the  arteries  is 
restored  or  made  active  or  kinetic,  in  full  when  they  recoil.  There  is 
no  loss  of  force;  neither  is  there  any  gain,  for  the  elastic  walls  of  the 
artery  cannot  originate  any  force  for  the  propulsion  of  the  blood — they 
only  restore  that  which  they  received  from  the  ventricles.  It  is  by  this 
equalizing  influence  of  the  successive  branches  of  every  artery  that  at 
length  the  intermittent  accelerations  produced  in  the  arterial  current 
by  the  action  of  the  heart,  cease  to  be  observable,  and  the  jetting  stream 
is  converted  into  the  continuous  and  equable  movement  of  the  blood 
which  we  see  in  the  capillaries  and  veins.  In  the  production  of  a  con- 
tinuous stream  of  blood  in  the  smaller  arteries  and  capillaries,  the  re- 
sistance which  is  offered  to  the  blood-stream  in  these  vessels  is  a  neces- 
sary agent.  Were  there  no  greater  obstacle  to  the  escape  of  blood  from 
the  larger  arteries  than  exists  to  its  entrance  into  them  from  the  heart, 
the  stream  would  be  intermittent,  notwithstanding  the  elasticity  of  walls 
of  the  arteries. 

By  means  of  the  elastic  and  muscular  tissue  in  their  walls  again  the 
arteries  are  enabled  to  dilate  and  contract  readily  in  correspondence 
with  any  temporary  increase  or  diminution  of  the  total  quantity  of 
blood  in  the  body;  and  within  a  certain  range  of  diminution  of  the 
quantity,  still  to  exercise  due  pressure  on  their  contents.  The  elastic 
tissue  further  assists  in  restoring  the  normal  channel  after  diminution 
of  its  calibre,  whether  this  has  been  caused  by  a  contraction  of  the  mus- 
cular coat,  or  by  the  temporary  application  of  a  compressing  foi'ce  from 
without.  This  action  is  well  shown  in  arteries  which,  having  contracted 
by  means  of  their  muscular  element,  after  death  regain  their  average 
potency  on  the  cessation  of  post-mortem  rigidity. 

The  office  of  the  muscular  coat  also  is  employed  to  adjust  the  flow 
of  the  blood  locally,  to  regulate  the  quantity  of  blood  to  be  received  by 
each  part  or  organ,  and  to  adjust  it  to  the  requirements  of  each,  accord- 
ing to  various  circumstances,  but,  chiefly,  according  to  the  activity  with 
which  the  functions  of  each  are  at  different  times  performed.  The 
amount  of  work  done  by  each  organ  of  the  body  varies  at  different  times, 
and  the  variations  often  quickly  succeed  each  other,  so  that,  as  in  the 
brain,  for  example,  (luring  sleep  and  waking,  within  the  same  hour  a 
part  may  be  now  very  active  and  then  inactive.  In  all  its  active  exer- 
cise of  function,  such  a  part  requires  a  larger  supply  of  blood  than  is 
sufficient  for  it  during  the  times  when  it  is  comparatively  inactive.  It 
is  evident  that  the  heart  cannot  regulate  the  supply  to  each  part  at  dif- 
ferent periods;  neither  could  this  be  regulated  by  any  general  and  uni- 
form contraction  of  the  arteries;  but  it  may  be  regulated  by  the  power 
which  the  arteries  of  each  part  have,  in  their  muscular  tissue,  of  con- 


THE   CIKCULATION    OF   THE    BLOOD.  201 

tracting  so  as  to  diminish,  and  of  passively  dilating  or  yielding  so  as  to 
permit  an  increase  of,  the  supply  of  blood,  according  to  the  requirements 
of  the  part  to  which  they  are  distributed.  And  thus,  while  the  ventri- 
cles of  the  heart  determine  the  total  quantity  of  blood,  to  be  sent  onward 
at  each  contraction,  and  the  force  of  its  propulsion,  and  while  the  large 
and  merely  elastic  arteries  distribute  it  and  equalize  its  stream,  the 
smaller  arteries,  in  addition,  regulate  and  determine,  by  means  of  their 
muscular  tissue,  the  proportion  of  the  whole  quantity  of  blood  which 
shall  be  distributed  to  each  part. 

This  regiilating  function  of  the  arteries  is  governed  and  directed  by 
the  nervous  system  in  the  way  to  be  presently  described. 

The  muscular  element  of  the  middle  coat  also  co-operates  with  the 
•elastic  in  adapting  the  calibre  of  the  vessels  to  the  quantity  of  blood 
which  they  contain.  For  the  amount  of  fluid  in  the  blood-vessels  varies 
very  considerably  even  from  hour  to  hour,  and  can  never  be  quite  con- 
.stant;  and  Avere  the  elastic  tissue  only  present  the  pressure  exercised 
by  the  walls  of  the  containing  vessels  on  the  contained  blood  would  be 
sometimes  very  small,  and  sometimes  inordinately  great.  The  presence 
of  a  muscular  element,  however,  provides  for  a  certain  uniformity  in  the 
amount  of  pressure  exercised;  and  it  is  by  this  adaptive,  iiniform,  gen- 
tle, muscular  contraction,  that  the  normal  tone  of  the  blood-vessels  is 
maintained.  Deficiency  of  this  tone  is  the  cause  of  the  soft  and  yield- 
ing pulse,  and  its  unnatural  excess  of  the  hard  and  tense  one. 

The  elastic  and  muscular  contraction  of  an  artery  may  also  be  re- 
garded as  fulfilling  a  natural  jiurpose  when,  the  artery  being  cut,  it  first 
limits  and  then,  in  conjunction  with  the  coagulated  fibrin,  arrests  the 
escape  of  blood.  It  is  only  in  consequence  of  such  contraction  and  co- 
agulation that  we  are  free  from  danger  through  even  very  slight  wounds; 
for  it  is  only  when  the  artery  is  closed  that  the  processes  for  the  more 
permanent  and  secure  prevention  of  bleeding  are  established.  But  there 
:appears  no  reason  for  supposing  that  the  muscular  coat  assists,  to  more 
•than  a  very  small  degree,  in  propelling  the  onward  current  of  blood. 

The  Pulse. 

The  most  characteristic  feature,  then,  of  the  arterial  flow,  is  its  in- 
termittency,  and  this  intermittent  flow  is  seen  or  felt  as  the  Pulse. 

The  pulse  is  generally  described  as  an  expansion  of  the  artery  pro- 
duced by  the  wave  of  blood  set  in  motion  by  the  injection  of  blood  at 
each  ventricular  systole  into  the  already  full  aorta.  As  the  force  of  the 
left  ventricle,  however,  is  not  expended  in  dilating  the  aorta  only,  the 
wave  of  blood  jsasses  on,  expanding  the  arteries  as  it  goes,  running  as  it 
were  on  the  surface  of  the  more  slowly  travelling  blood  already  con- 
tained in  them,  and  producing  the  pulse  as  it  proceeds. 


202 


HANDBOOK    OF   PHYSIOLOGY. 


The  distention  of  each  artery  increases  both' its  length  and  its  diam- 
eter. In  their  elongation,  the  arteries  change  their  form,  the  straight 
ones  becoming  slightly  curved,  and  those  already  curved  becoming  more 
so;  but  they  recover  their  previous  form  as  well  as  their  diameter  when 
the  ventricular  contraction  ceases,  and  their  elastic  walls  recoil.  The 
increase  of  their  (iurves  which  accomijanies  the  distention  of  arteries, 
and  the  succeeding  recoil,  may  be  well  seen  in  the  prominent  temporal 
artery  of  an  old  person.  In  feeling  the  pulse,  the  finger  cannot  distin- 
guish the  sensation  produced  by  the  dilatation  from  that  produced  by 
the  elongation  and  curving;  that  which  it  perceives  most  plainly,  how- 
ever, is  the  dilatation,  or  return,  more  or  less,  to  the  cylindrical  form,  of 
the  artery  which  has  been  partially  flattened  by  the  finger. 


Fig.  179.— Marey's  Sphygmograph,  modifled  by  Mahomed. 


The  pulse— due  to  any  given  beat  of  the  heart — is  not  perceptible- 
at  the  same  moment  in  all  the  arteries  of  the  body.  Thus,  it  can  be 
felt  in  the  carotid  a  very  short  time  before  it  is  perceptible  in  the  radial 
artery,  and  in  this  vessel  again  before  it  occurs  in  the  dorsal  artery  of 
the  foot.  The  delay  in  the  beat  is  in  proportion  to  the  distance  of  the 
artery  from  the  heart,  but  the  difference  in  time  between  the  beat  of 
any  two  arteries  probably  never  exceeds  I  to  -^  of  a  second. 

A  distinction  must  be  carefully  made  between  the  passage  of  the 
wave  along  the  arteries  and  the  arterial  fiow  itself.  Both  wave  and 
current  are  present;  but  the  rates  at  which  they  travel  are  very  different, 
that  of  the  wave  1G,5  to  ,33  feet  per  second  (5  to  10  metres),  being  twenty 
or  thirty  times  as  great  as  that  of  the  current. 

The  Sphygmograph,— Much  light  has  been  thrown  on  what  may 
be  called  the  form  of  the  pulse  wave  by  the  sphygmograph  (figs.  179 
and  182).  The  principle  on  which  it  acts  will  be  seen  on  reference  to- 
figs. 

The  small  button  replaces  the  finger  in  the  act  of  taking  the  pulse,. 


THE   CIRCULATION    OF   THE    BLOOD. 


203 


and  is  made  to  rest  lightly  on  the  artery,  the  pulsations  of  which  it  is 
desired  to  investigate.  The  up-and-down  movement  of  the  button  is 
communicated  to  the  lever,  to  the  hinder  end  of  which  is  attached  a 
slight  spring,  which  allows  the  lever  to  move  up,  at  the  same  time  that 


Fig.  180.— Diagram  of  the  lever  of  the  Sphjgmograph. 

it  is  just  strong  enough  to  resist  its  making  any  sudden  jerk,  and  in  the 
interval  of  the  beats  also  to  assist  in  bringing  it  back  to  its  original 
position.  For  ordinary  purposes  the  instrument  is  bound  on  the  wrist 
(fig.  181). 

It  is  evident  that  tlie  beating  of  the  pulse  with  the  reaction  of  the 
spring  will  cause  an  up-and-down  movement  of  the  lever,  the  pen  of 
which  will  write  the  effect  on  a  smoked  card,  which  is  made  to  move  by 
clockwork  in  the  direction  of  the  arrow\  Thus  a  tracing  of  the  pulse 
is  obtained,  and  in  this  way  much  more  delicate  effects  can  be  seen  than 
can  be  felt  on  the  application  of  the  finger. 


Fig.  181.— The  Sphygmograph  applied  to  the  arm. 

Two  forms  of  sphygmograph  are  shown  in  figs.  179,  182,  viz. ,  a  modifica- 
tion of  the  original  instrument  of  Marey  and  Dudgeon's.  Marey's  instrument, 
and  indeed  all  modifications  of  it,  .suffer  from  the  defect  that  tliere  is  no  ade- 
quate method  of  measuring  tlie  pressure  exercised  by  the  button  of  the  instru- 
ment upon  the  artery,  and  that  it  is  difiicult  to  be  certain  of  tlie  exact  position 
it  occupies  over  the  artery.  Dudgeon's  sphygmograph,  although  very  conven- 
ient to  use,  is,  according  to  Roy  and  Adami,  even  less  satisfactory,  and  the 
tracings  obtained  by  it  are  so  disfigured  by  inertia  vibrations  as  to  render 
them  more  or  less  worthless.  "The  mechanical  construction  of  the  instrument 
is  such  as  to  render  great  inertia  vibrations  unavoidable. "     These  authors  have 


204 


HANDBOOK    OF    PHYSIOLOGY. 


invented  an   instrument  called  a  sphygmometer,  in  which  these  defects  of   th: 
sphygmograph  are  corrected. 


Fis-  182.— Dudgeon's  Sphj'gmograph. 


Tlie  principle  of  the  sphygmometer  of  Roy  and  Adami  is  shown  in  the  dia- 
gram (fig.   183). 

The  apparatus  consists  of  a  box  (a)  which  is  moulded  to  fit  over  the  end  of 
the  radius  so  as  to  bridge  over  the  radial  artery.  Within  this  is  a  flexible  bag 
(6)  filled  with  water,  and  connected   by  a  T  tube  with  a  rubber  bag  (h)  and 


Fig.  183.— Diagrammatic  sectional  representation  of  the  sphygmometer  (Roy  and  Adami) .  a, 
Box  in  which  the  portion  of  the  artery  is  inclosed;  b,  thin-walled  india-rubber  bag  filled  with  water, 
and  communicating  through  tap,  c,  with  manometer  and  thick-walled  rubber  bag,  h;  d.  piston  con- 
nected by  rod,  e,  with  recording  lever,/:  jr.  spiral  spring  attached  to  axis  of  lever,  and  by  which 
the  pressure  in  b,  against  the  piston,  d,  is  counterbalanced;  k,  skin  and  subcutaneous  tissue;  w,  end 
of  radius  seen  in  section;  ii,  radial  artery  seen  in  section. 


THE   CIRCULATIOIn^    OF   THE    BLOOD.  205 

mercurial  manometer.  The  fluid  in  the  box  may  be  raised  to  any  desired 
pressure,  and  may  then  be  shut  off  by  tap  (c) .  At  the  upper  part  of  the  box  is 
a  circular  opening,  and  resting  upon  (b)  is  a  flat  button  (d) ,  which  by  means 
of  a  short  light  rod(e)  communicates  the  movement  of  (6)  to  the  lever  (/).  To 
the  axis  of  rotation  of  this  lever  is  a  spiral  watch-spring  (g)  which  can  be  tight- 
ened at  will,  so  that  the  lever  can  be  made  to  take  a  vertical  position  at  any 
desired  hydrostatic  pressure  within  the  box.  The  movements  of  the  lever  are 
recorded  upon  a  piece  of  blackened  glazed  paper  made  to  move  in  a  vertical 
direction  past  it.  When  in  use,  the  box  is  fixed  upon  the  end  of  the  radius  by 
an  appropriate  holder,  and  the  pressure  is  raised  to  any  desired  height  to  which 
the  lever  is  adapted  by  tightening  or  slackening  the  spring.  The  tap  (c)  is 
then  closed.  The  pressure  within  the  box  acts  in  all  directions,  and  is  correctly 
indicated  by  the  manometer. 

The  tracing  of  the  pulse  (sphygmogram),  obtained  by  the  use  of 
the  sphygniograph,  differs  somewhat  according  to  the  artery  upon  which 
it  is  applied,  but  its  general  characters  are  much  the  same  in  all  cases. 
It  consists  of:— A  sudden  upstroke  (fig.  1984,  a),  which  is  somewhat 


Fig.  184.— Diagram  of  pulse  tracing,    a,  Upstroke;  b,  down-stroke:  c,  pre-dicrotic  wave;  d,  di- 
crotic ;  E,  post-dicrotic  wave. 

higher  and  more  abrupt  in  the  pulse  of  the  carotid  and  of  other  arteries 
near  the  heart  than  in  the  radial  and  other  arteries  more  remote;  and 
a  gradual  decline  (b),  less  abrupt,  and  therefore  taking  a  longer  time 
than  (a).  It  is  seldom,  however,  that  the  decline  is  an  uninterrupted 
fall;  it  is  usually  marked  about  half-way  by  a  distinct  notch  (c),  called 
the  dicrotic  notch,  which  is  caused  by  a  second  more  or  less  marked 
ascent  of  the  lever  at  that  point  by  a  second  wave  called  the  dicrotic 
wave  (d)  ;  not  unfrequeutly  (in  which  case  the  tracing  is  said  to  have  a 
double  apex)  there  is  also  soon  after  the  commencement  of  the  descent 
a  slight  ascent  previous  to  the  dicrotic  notch:  this  is  called  the  p7-e- 
dicrotic  wave  (c),  and  in  addition  there  may  be  one  or  more  slight  ascents 
after  the  dicrotic,  called  post-dicrotic  (e). 

The  explanation  of  these  tracings  presents  some  difficulties,  not, 
however,  as  regards  the  two  primary  factors,  viz.,  the  upstroke  and 
downstroke,  because  they  ;ire  universally  taken  to  mean  the  sudden  in- 
jection of  blood  into  the  already  full  arteries,  and  the  gradual  fall  of 
the  lever  signifying  the  recovery  of  the  arteries  by  their  recoil.     These 


206  HANDBOOK    OF    PHYSIOLOGY. 

points  may  be  demonstnited  on  a  system  of  elastic  tubes,  with  a  syringe 
to  pump  in  water  at  regular  intervals,  just  as  well  as  on  the  radial 
artery,  or  on  the  more  complicated  system  of  tubes  in  which  the  heart, 
the  arteries,  the  capillaries  and  veins  are  represented,  which  is  known 
as  an  arterial  schema.     If  we  place  two  or  more  sphygmographs  upon 


Tig.  185.— Diagram  of  the  formation  of  the  pulse-tracing,    a,  Percussion  wave;  b,  tidal  wave;  c, 

dicrotic  wave.     (Mahomed.) 

such  a  system  of  tubes  at  increasing  distances  from  the  pump,  we  may 
demonstrate  first,  that  the  rise  of  the  lever  commences  earliest  in  that 
nearest  the  pump,  and  secondly,  that  it  is  higher  and  more  sudden, 
while  at  a  longer  distance  from  the  pump  the  wave  is  less  marked,  and 
a  little  later.  So  in  the  arteries  of  the  body  the  wave  of  blood  gradu- 
ally gets  less  and  less  as  we  approach  the  periphery  of  the  arterial  sys- 
tem, and  is  lost  in  the  capillaries,  according  to  Mahomed.     By  the 


Fig.  186.— Anacrotic  pulse  from  a  case  of  aortic  aneurism,  a,  Anacrotic  wave  (or  percussion  wave); 
B,  tidal  or  pre-dicrotic  wave,  continued  rise  in  tension  (or  higher  tidal  wave). 

sudden  injection  of  blood  two  distinct  waves  are  produced,  which  are 
called  the  tidal  and  percussion  waves.  The  tidal  wave  occurs  whenever 
fluid  is  injected  into  an  elastic  tube  (fig.  185,  b),  and  is  due  to  the  ex- 
pansion of  the  tube  and  its  more  gradual  collapse.  The  percussion  wave 
occurs  (fig.  185,  a)  when  the  impulse  imparted  to  the  fluid  is  more  sud- 


THE   CIRCULATION    OF   THE    BLOOD.  207 

■den;  this  causes  an  abrupt  upstroke  of  the  lever,  which  then  falls  until 
it  is  again  caught  up  perhaps  by  the  tidal  wave  which  begins  at  the 
same  time  but  is  not  so  quick. 

In  this  way,  generally  speaking,  the  apex  of  the  upstroke  is  double, 
the  second  upstroke,  the  so-called  pre-dicrotic  elevation  of  the  lever, 
representing  the  tidal  wave.  The  double  apex  is  most  marked  in  trac- 
ings from  large  arteries,  especially  when  their  tone  is  deficient.  In 
tracings  from  arteries  of  medium  size,  e.g.,  the  radial,  on  the  other  hand, 
the  upstroke  is  usually  single.  In  this  case  the  percussion-impulse  is 
not  sufficiently  strong  to  jerk  up  the  lever  and  produce  an  effect  distinct 
from  that  of  the  tidal  wave  which  immediately  follows  it,  and  which 
continues  and  completes  the  distention.  In  cases  of  feeble  arterial  ten- 
sion, however,  the  percussion-impulse  may  be  traced  by  the  sphygmo- 
_graph,  not  only  in  the  carotid  pulse,  but  also  to  a  less  extent  in  the 
radial. 

The  interruptions  in  the  downstroke  are  called  the  catacrotic  waves, 
to  distinguish  them  from  an  interruption  in  the  upstroke,  called  the 
anacrotic  wave,  occasionally  met  with  in  cases  in  which  the  pre-dicrotic 
or  tidal  wave  is  higher  than  the  percussion  wave. 

There  is  considerable  difference  of  opinion  both  as  to  whether  the 
dicrotic  wave  is  present  in  health,  and  also  as  to  its  cause.  The  balance 
of  opinion,  however,  appears  to  be  in  favor  of  the  belief  that  the  dicrotic 
wave  to  a  greater  or  lesser  degree  is  present  in  health;  in  certain  condi- 
tions not  necessarily  diseased,  it  becomes  so  marked  as  to  be  quite  plain 
to  the  unaided  finger.  Such  a  pulse  is  called  dicrotic.  Sometimes  the 
•dicrotic  rise  exceeds  the  initial  upstroke,  and  the  pulse  is  then  called 
hyper-dicrotic. 

As  to  the  cause  of  dicrotism,  one  opinion  (1)  is  that  it  is  due  to  a 
recovery  of  pressure  during  the  elastic  recoil,  in  consequence  of  a  rebound 
from  the  periphery.  It  may  indeed  be  produced  on  a  schema  by  ob- 
structing the  tube  at  a  little  distance  beyond  the  spot  where  the  sphyg- 
mograph  is  placed.  Against  this  view,  however,  is  the  fact  that  the 
notch  appears  at  about  the  same  point  in  the  downstroke  in  tracings 
from  the  carotid  as  from  the  radial,  and  not  first  in  the  radial  tracing, 
as  it  should  do,  if  this  theory  was  correct,  since  that  artery  is  nearer  the 
periphery  than  the  carotid,  and  as  it  does  in  the  corresponding  experi- 
ment with  the  arterial  schema  when  the  tube  is  obstructed.  (2)  The 
generally  accepted  notion  among  clinical  observers,  is  that  the  dicrotic 
wave  is  due  to  the  rebound  from  the  aortic  valves  which  causes  a  second 
wave;  but  the  question  cannot  be  considered  settled,  and  the  presence 
of  marked  dicrotism  in  cases  of  hemorrhage,  of  ansemia  and  of  other 
weakening  conditions,  as  well  as  in  cases  of  diminished  pressure  within 
the  arteries,  would  imply  that  it  may,  at  any  rate  sometimes,  be  due  to 
the  altered  specific  gravity  of  the  blood  within  the  vessels,  either  directly 


208 


HANDBOOK    OF    PHYSIOLOGY. 


or  througli  the  indirect  effect  of  these  conditions  on  the  tone  of  thj 

arterial  walls. 

Waves  may  be  produced  in  any  elastic  tube  when  a  fluid  is  being 

driven  through  it  with  an  intermittent  force,  such  waves  being  called 

waves  of  oscillation  (M,  Foster).  Their  origin  has  received  various  ex- 
planations. In  an  arterial  schema  they 
vary  with  the  specific  gravity  of  the 
fluid  used,  and  with  the  kind  of  tub- 
ing, and  maybe  therefore  supposed  to 
vary  in  the  body  with  the  condition  of 
the  blood  and  of  the  arteries. 

Some  consider  the  secondary  waves 
in  the  downstroke  of  a  normal  tracing 
to  be  oscillation  waves;  but,  as  just 
mentioned,  even  if  this  be  the  case,  as 
is  most  likely  with  post-dicrotic  waves, 
the  dicrotic  wave  itself  is  almost  cer- 
tainly due  to  the  rebound  from  the 
aortic  valves. 

The  anacrotic  notch  is  usually  as- 
sociated with  disease  of  the  arteries, 
e.g.,  in  atheroma  and  aneurism.  The 
dicrotic  notch  is  called  diastolic  or 
aortic,  and  in  point  of  time  indicates 
the  closure  of  the  aortic  valves. 

Of  the  three  main  parts  then  of  a 
pulse-tracing,  viz.,  the  percussion  wave, 
the  tidal,  and  the  dicrotic,  the  percus- 
sion wave  is  produced  by  sudden  and 
forcible  contraction  of  the  heart,  per- 
haps exaggerated  by  an  excited  action, 
and  may  be  transmitted  much  more 
rapidly  than  the  tidal  wave,  and  so  the 
two  may  be  distinct;  frequently,  how- 
ever, they  are  inseparable.  The  di- 
crotic wave  may  be  as  great  or  greater 
than  the  other  two. 
According  to  Mahomed,  the  distinctness  of  the  three  waves  depends 

upon  the  following  conditions:  — 

HhQ percussion  wave  is  increased  by: — 1.  Forcible  contraction  of  the 

Heart;  2.  Sudden  contraction  of  the  Heart;  3.   Large  volume  of  blood; 

4.  Fulness  of  vessel;  and  diminished  by  the  reversed  conditions. 

The  fidal  wave  is  increased  by: — I.  Slow  and  prolonged  contraction 

of  the  Heart;  2.  Large  volume  of  blood;  3.  Comparative  emptiness  of 


Fig.  187. — Diagrams  of  pulse  curves 
witli  exaggeration  of  one  or  other  of  the 
three  waves.  A ,  percussion ;  B,  tidal;  C, 
dicrotic.  1.  Percussion  wave  very  marked; 
2,  tidal  wave  sudden;  3.  dicrotic  pulse  curve; 
4  and  .5,  the  tidal  wave  very  exaggerated, 
from  high  tension,     (Mahomed.) 


THE    CIRCULATION    OF   THE    BLOOD. 


209 


vessels;  4.  Diminished  outflow  or  slow  capillary  circulation;  and  dimin- 
ished by  the  reverse  conditions. 

The  dicrotic  wave  is  increased  by : — 1.  Sudden  contraction  of  the 
Heart;  2.  Low  blood  pressure;  3.  Increased  outflow  or  rapid  capillary 
circulation;  4.  Elasticity  of  the  aorta;  5.  Relaxation  of  muscular  coat; 
and  diminished  by  the  reversed  conditions. 

In  the  use  of  the  sphygmograph  care  must  be  taken  as  to  the  careful 
regulation  of  the  pressure.  If  the  pressure  be  too  great,  the  characters 
of  the  pulse  may  be  almost  entirely  obscured,  or  the  artery  may  be 
entirely  obstructed,  and  no  tracing  is  obtained ;  and  on  the  other  hand. 


B 


Fig.  188. — A,  Kormal  pulse-tracing  from  radial  of  healthy  adult,  obtained  by  the  sphygmometer. 
B,  From  same  artery,  with  the  same  extra-ai-terial  pressure,  taken  durmg  acute  nasal  catarrh. 

if  the  pressure  be  too  slight,  a  very  small  part  of  the  characters  may  be 
reuresented  on  the  tracing. 


It  is  necessary  to  mention  that  Roy  and  Adami,  by  comparison  of  tracings 
of  intra-ventricular  pressure  with  pulse-tracings  obtained  by  the  sphygmometer, 
have  come  to  the  following  conclusions,  difiering  from  Mahomed  (whose  de- 
scription has  been  chiefly  followed  in  the  text)  in  several  particulars.  The 
pulse  tracing  obtained  from  the  radial  of  a  healthy  man  is  represented  in  the 
diagram  (fig.  188) .  in  which  the  different  parts  of  the  tracings  are  marked  out. 

These  may  be  thus  described  : — 

(1)  Upstroke,  which  may  vary  both  in  rapidity  and  in  height;  the  height 
varies  with  the  volume  of  blood  expelled  at  each  systole,  with  the  amount  of 
peripheral  resistance,  and  with  the  degree  of  rigidity  of  the  arterial  walls  ;  the  ra- 
pidity depends  upon  the  rapidity  of  the  outflow  from  heart.  (2)  The  second  part, 
usually  called  the  percussion  wave,  is  believed  by  these  authors  to  be  due  to 
14 


310  HANDBOOK    OF    PHYSIOLOGY. 

the  contraction  of  the  papillary  muscles,  and  is  hence  called  by  them  papillary 
wave,  and  corresponds  with  the  distance  between  the  top  of  the  upstrcjke  and 
pre-dicrotic  notch  (3  in  fig.  188).  (3)  The  outflow-remainder  wave.,  or  tidal 
or  jire-dicrotic  wave  (2  to  3) .  During  this  wave  tlie  outflow  from  the  ventricle 
ends.  (4)  The  dicrotic  notch,  due  to  the  inertia  of  the  blood.  (5)  The  post- 
dicrotic  wave,  also  due  to  inertia.  (6)  The  rounded  shoulder,  which  lies  be- 
tween the  post-dicrotic  wave  and  the  lowest  point  of  the  tracing.  (7)  In  trac- 
ings taken  near  the  heart,  a  small  notch  and  short  jjositive  wave,  corresponding 
in  time  with  the  commencement  of  the  ventricular  systole. 


The  Capillary  Flow. 

It  is  in  the  capillaries  that  the  chief  resistance  is  offered  to  the  prog- 
ress of  the  blood;  for  in  them  the  friction  of  the  blood  is  greatly  in- 


Fig.  189.— Capillaries  (C.)  in  the  web  of  the  frog's  foot  connecting  a  small  artery  (A)  with  a 
small  vein  V  (after  Allen  Thomson). 

creased  by  the  enormous  multiplication  of  the  surface  with  which  it  is 
brought  in  contact. 

When  the  capillary  circulation  is  examined  in  any  transparent  part 
of  a  full-grown  living  animal  by  means  of  the  microsco^^e  (tig.  189),  the 
blood  is  seen  to  flow  with  a  constant  equable  motion ;  the  red  blood- 
corpuscles  moving  along,  mostly  in  single  file,  and  bending  in  various 
ways  to  accommodate  themselves  to  the  tortuous  course  of  the  capillary, 
but  instantly  recovering  their  normal  outline  on  reaching  a  wider  vessel. 

At  the  circumference  of  the  stream  in  the  larger  capillaries,  but 
sepecially  well  marked  in  the  small  arteries  and  veins,  in  contact  with 
the  walls  of  the  vessel,  and  adhering  to  them,  there  is  a  layer  of  liquor 
sanguinis  which  appears  to  be  motionless.  The  existence  of  this  still 
layer,  as  it  is  termed,  is  inferred  both  from  the  general  fact  that  such 
an  one  exists  in  all  fine  tubes  traversed  by  fluid,  and  from  what  can  be 
seen  in  watching  the  movements  of  the  blood-corpuscles.  The  red 
corpuscles  occupy  the  middle  of  the  stream  and  move  with  comparative 
rapidity;  the  colorless  corpuscles  run  much  more  slowly  by  the  walls  of 
the  vessel;  while  next  to  the  wall  there  is  often  a  transparent  space  in 
which  the  fluid  appears  to  be  at  rest;  for  if  any  of  the  corpuscles  hap- 


THE   CIRCULATION^"   OF   THE    BLOOD. 


211 


pen  to  be  forced  within  it,  they  move  more  slowly  than  before,  rolling 
lazily  along  the  side  of  the  vessel,  and  often  adhering  to  its  wall.  Part 
of  this  slow  movement  of  the  colorless  corpuscles  and  their  occasional 
stoppage  may  be  due  to  their  having  a  natural  tendency  to  adhere  to 
the  walls  of  the  vessels.  Sometimes^,  indeed,  when  the  motion  of  the 
blood  is  not  strong,  many  of  the  white  corpuscles  collect  in  a  capillary 
vessel,  and  for  a  time  entirely  prevent  the  passage  of  the  red  cor2)uscles. 
When  the  peripheral  resistance  is  greatly  diminished  by  the  dilata- 
tion of  the  small  arteries  and  capillaries,  so  much  blood  passes  on  from 
the  arteries  into  the  capillaries  at  each  stroke  of  the 
heart,  that  there  is  not  sufficient  remaining  in  the 
arteries  to  distend  them.  Thus,  the  intermittent 
current  of  the  ventricular  systole  is  not  converted 
into  a  continuous  stream  by  the  elasticity  of  the 
arteries  before  the  capillaries  are  reached;  and  so  in- 
termittency  of  the  flow  occurs  both  in  capillaries 
and  veins  and  a  pulse  is  produced.  The  same  phe- 
nomenon may  occur  when  the  arteries  become  rigid 
from  disease,  and  when  the  beat  of  the  heart  is  so 
slow  or  so  feeble  that  the  blood  at  each  cardiac  sys- 
tole has  time  to  pass  on  to  the  capillaries  before  the 
next  stroke  occurs;  the  amount  of  blood  sent  at  each 
stroke  being  insufficient  to  pro^Derly  distend  the 
elastic  arteries. 

It  was  formerly  supposed  that  the  occurrence 
of  any  transudation  from  the  interior  of  the  capil- 
laries into  the  midst  of  the  surrounding  tissues  was 
confined,  in  the  absence  of  injury,  strictly  to  the 
fluid  part  of  the  blood;  in  other  words,  that  the 
corpuscles  could  not  escape  from  the  circulating 
stream,  unless  the  wall  of  the  containing  blood-vessel 
was  ruptured.  It  is  true  that  an  English  physiologist,  Augustus  Waller, 
affirmed,  in  1846,  that  he  had  seen  blood-corpuscles,  both  red  and  white, 
pass  bodily  through  the  wall  of  the  capillary  vessel  in  which  they  were 
contained  (thus  confirming  what  had  been  stated  a  short  time  previously 
by  Addison);  and  that,  as  no  opening  could  be  seen  before  their  escape, 
so  none  could  be  observed  afterward— so  rapidly  was  the  part  healed. 
But  these  observations  did  not  attract  much  notice  until  the  phenome- 
non of  escape  of  the  blood-corpuscles  from  the  capillaries  and  minute 
veins,  apart  from  mechanical  injury,  were  re-discovered  by  CohnheiiU 
in  1867. 

Cohnheim's  experiment  demonstrating  the  passage  of  the  corpuscles 
through  the  wall  of  the  blood-vessel  is  performed  in  the  following  man- 
ner.    A  frog  is  urarized,  that  is  to  say,  paralysis  is  produced  by  ejecting 


Fig.  190.— A  large  ca- 
pillary from  the  frog's 
mesentery  eight  hours 
after  irritation  had 
been  set  up,  sho-sving 
emigration  of  leuco- 
cytes, o.  Cells  in  the 
act  of  traversing  the 
capillary  wall;  b,  some 
already'escaped. 

(Frey.) 


212  HAXDBOOK    OF    PHYSIOLOGY. 

under  the  skin  a  minute  quantity  of  the  poison  called  urari;  and  the 
abdomen  having  been  ojoened,  a  portion  of  small  intestine  is  drawn  out, 
and  its  transparent  mesentery  spread  out  under  a  microscope.  After 
a  variable  time,  occupied  by  dilatation,  folloviang  contraction  of  the 
minute  vessels  and  accompanying  quickening  of  the  blood-stream,  there 
ensues  a  retardation  of  the  current,  and  blood-corpuscles,  both  red  and. 
white,  begin  to  make  their  way  through  the  capillaries  and  small  veins. 

The  process  of  diapedesis  of  the  red  corpuscles,  which  occurs  under 
circumstances  of  impeded  venous  circulation,  and  consequently  increased 
blood-pressure,  resembles  closely  the  migration  of  the  leucocytes,  with 
the  exception  that  they  are  squeezed  through  the  wall  of  the  vessel,  and 
do  not,  like  them,  work  their  way  through  by  amoeboid  movement. 

Various  explanations  of  these  remarkable  phenomena  have  been 
suggested.  Some  believe  that  pseudo-stomata  between  contiguous  endo- 
thelial cells  provide  the  means  of  escape  for  the  blood-corpuscles.  But 
the  chief  share  in  the  process  is  probably  to  be  found  in  the  vital  en- 
dowments with  respect  to  mobility  and  contraction  of  the  parts  con- 
cerned— both  of  the  corpuscles  and  of  the  capillary  wall  itself. 

The  circulation  through  the  capillaries  must,  of  necessity,  be  largely 
influenced  by  that  which  occurs  in  the  vessels  on  either  side  of  them — 
in  the  arteries  or  the  veins;  their  intermediate  position  causing  them  to 
feel  at  once,  so  to  speak,  any  alteration  in  the  size  or  rate  of  the  arterial 
or  venous  blood-stream.  Thus,  the  aj^parent  contraction  of  the  cnpilla- 
ries,  on  the  application  of  certain  irritating  substances,  and  during  fear, 
and  their  dilatation  in  blushing  may  be  referred  primarily  to  the  action 
of  the  small  arteriss.  But  however  greatly  the  capillaries  may  be  in- 
fluenced by  the  arterial  and  venous  flow,  and  by  the  condition  of  the 
parts  which  surround  and  support  them,  they,  too,  must  be  looked  upon 
not  as  mere  passive  channels  for  the  passage  of  blood,  but  as  possessing 
endowments  of  their  own  relation  to  the  circulation.  The  capillary 
wall  is  actively  living  and  contractile;  and  there  is  no  reason  to  doubt 
that,  as  such,  it  must  have  some  influence  in  connection  with  the  blood- 
current. 

The  Venous  Flow. 

The  blood-current  in  the  veins  is  maintained  (a)  primarily  by  the  vis 
a  tergo  of  the  contraction  of  the  left  ventricle;  but  very  effectual  assist- 
ance to  the  flow  is  afforded  (b)  by  th  ■  action  of  the  muscles  capable  of 
pressing  on  the  veins  with  valves,  as  well  as  (c)  by  the  suction  action  of 
the  heart. 

The  effect  of  muscular  pressure  upon  the  circulation  may  be  thus 
explained.  When  pressure  is  applied  to  any  part  of  a  vein,  and  the 
current  of  blood  in  it  is  obstructed,  the  portion  behind  the  seat  of  pres- 
sure becomes  swollen  and  distended  as  far  back  as  the  next  pair  of 


THE   CIRCULATIOX    OF   THE    BLOOD.  213 

valves,  which  are  in  consequence  closed.  Thus,  whatever  force  is  exer- 
cised by  the  pressure  of  the  muscles  on  the  veins,  is  distributed  partly 
in  pressing  the  blood  onward  in  the  proper  course  of  the  circulation, 
and  partly  in  pressing  it  backward  and  closing  the  valves  behind. 

The  circulation  might  lose  as  much  as  it  gains  by  such  an  action,  if 
it  were  not  for  the  numerous  communications,  one  with  another;  for 
through  these,  the  closing  up  of  the  venous  channel  by  the  backward 
pressure  is  prevented  from  being  any  serious  hindrance  to  the  circula- 
tion, since  the  blood,  of  which  the  onward  course  is  arrested  by  the 
closed  valves,  can  at  once  pass  through  some  anastomosing  cliannel,  and 
proceed  on  its  way  by  another  vein.  Thus,  therefore,  the  effect  of  mus- 
cular pressure  upon  veins  which  have  valves,  is  turned  almost  entirely 
to  the  advantage  of  the  circulation;  the  pressure  of  the  blood  onward 
is  all  advantageous,  and  the  pressure  of  the  blood  backward  is  prevented 
from  being  a  hindrance  by  the  closure  of  the  valves  and  the  anastomoses 
of  the  veins. 

In  the  web  of  the  bat's  wing,  the  veins  are  furnished  with  valves, 
and  possess  the  remarkable  property  of  rhythmical  contraction  and 
dilatation,  whereby  the  current  of  blood  within  them  is  distinctly  accel- 
erated. The  contraction  occurs,  on  an  average,  about  ten  times  in  a 
minute;  the  existence  of  valves  preventing  regurgitation,  the  entire 
effect  of  the  contractions  was  auxiliary  to  the  onward  current  of  blood. 
Analogous  phenomena  have  been  observed  in  other  animals. 

The  Velocity  of  the  Flow. 

The  velocity  of  the  blood-current  at  any  given  point  in  the  various 
divisions  of  the  circulatory  system  is  inversely  proportional  to  their  sec- 
tional area  at  that  point.  If  the  sectional  area  of  all  the  branches  of  a 
vessel  united  were  always  the  same  as  that  of  the  vessel  from  which  they 
arise,  and  if  the  aggregate  sectional  area  of  the  capillary  vessels  were 
equal  to  that  of  the  aorta,  the  mean  rapidity  of  the  blood's  motion  in  the 
capillaries  would  be  the  same  as  in  the  aorta;  and  if  a  similar  corre- 
spondence of  capacity  existed  in  the  veins  and  arteries,  there  would  be 
an  equal  correspondence  in  the  rapidity  of  the  circulation  in  them.  But 
the  arterial  and  venous  systems  may  be  represented  by  two  truncated 
cones  with  their  apices  directed  toward  the  heart;  the  area  of  their 
united  base  (the  sectional  area  of  the  capillaries)  being  400 — 800  times 
as  great  as  that  of  the  truncated  apex  representing  the  aorta.  Thus 
the  velocity  of  blood  in  the  capillaries  is  not  more  than  jJ-^-  of  that  in 
the  aorta. 

In  the  Arteries. — The  velocity  of  the  stream  of  blood  is  greater  in 
the  arteries  than  in  any  other  part  of  the  circulatory  system,  and  in  them 
it  is  greatest  in  the  neighborhood  of  the  heart,  and  during  the  ventricu- 


214 


HANDBOOK    OF    PHYSIOLOGY. 


lar  systole.  The  rate  of  movement  diminishes  during  the  diastole  of 
the  ventricles,  and  in  the  parts  of  the  arterial  system  most  distant  from 
the  heart.  Chauveau  has  estimated  the  r.apidity  of  the  blood -stream  in 
the  carotid  of  the  horse  at  over  20  inches  per  second  during  the  heart's 
systole,  and  nearly  6  inches  during  the  diastole  (530-150  mm.). 

Estimation  of  the  Velocity. — Various  instruments  have  been  devised  for 
mesuring  the  velocity  of  the  blood-stream  in  the  arteries.  Ludwig's  Stromuhr 
(fig.  191)  consists  of  a  U-shaped  glass  tube  dilated  at  a  and  a',  the  ends  of 
which,  h  and  i,  are  of  known  calibre.  The  bulbs  can  be  filled  by  a  common 
opening  at  k.  The  instrument  is  so  contrived  that  at  b  and  b'  the  glass  part  is 
firmly  fixed  into  metal  cylinders,  attached  to  a  circu- 
lar horizontal  table,  c  c',  capable  of  horizontal  move- 
ment on  a  similar  table  d  d'  about  the  vertical  axis 
mai'ked  in  figure  by  a  dotted  line.  The  opening  in  c  e  , 
when  the  instrument  is  in  position,  as  in  fig.,  cor- 
responds exactly  with  those  in  d  d' ;    but  if   c  c'  be 


Fig.  191. 


Fig.  192. 


Fig.  191. — Ludwig's  Stromuhr. 

Fig.  192. — Diagram  of  Chauveau's  Instrument,  o.  Brass  tube  for  introduction  into  the  lumen  of 
the  artery,  and  containing  an  index  needle,  which  passes  through  the  elastic  membrane  in  its  side. 
and  moves  by  the  impulse  of  the  blood-current,  c.  Graduated  scale,  for  measuring  the  extent  of 
the  oscillations  of  the  needle. 


turned  at  right  angles  to  its  present  position,  there  is  no  communication  be- 
tween h  and  a,  and  i  and  a' ,  but  h  communicates  directly  with  i ;  and  if 
turned  through  two  right  angles  c'  communicates  with  d,  and  c  with  d',  and 
there  is  no  direct  communication  between  h  and  i.  The  experiment  is  jier- 
formed  in  the  following  way  : — The  artery  to  be  experimented  upon  is  divided 
and  connected  with  two  canulae  and  tubes  which  fit  it  accurately  with  h  and 
i — h  the  central  end,  and  i  the  peripheral ;  the  bulb  a  is  filled  with  olive  oil  up 
to  a  point  rather  lower  than  Tc,  and  a'  and  the  remainder  of  a  is  filled  with 
defibrinated  blood  ;  the  tube  on  k  is  then  carefully  clamped  :  the  tubes  d  and 
d  are  also  filled  with  defibrinated  blood.  When  everything  is  ready,  the  blood 
is  allowed  to  flow  into  a  through  /;,  and  it  pushes  before  it  tJie  oil,  and  that 
the  defibrinated  blood  into  the  artery  through  i.  and  replaces  it  in  o  ;  when  the 
blood  reaches  the  former  level  of  the  oil  in  a',  the  disc  c  C'  is  turned  rapidly 
through  two  right  angles,  and  the  blood  flowing  through  d  into  a'  again  dis- 


THE   CIRCULATION    OF   THE    BLOOD.  215 

places  the  oil  which  is  driven  into  a.  This  is  repeated  several  times,  and  the 
duration  of  the  experiment  noted.  The  capacity  of  a  and  a'  is  known  ;  the 
diameter  of  the  artery  is  also  known  by  its  corresponding  with  the  canulae  of 
known  diameter,  and  as  the  number  of  times  a  has  been  filled  in  a  given  time 
is  known,  the  velocity  of  the  current  can  be  calculated. 

Chauveau's  instrument,  fig.  192,  consists  of  a  thin  brass  tube,  a  in  one  side 
of  which  is  a  small  perforation  closed  by  thin  vulcanized  india-rubber.  Pass- 
ing through  the  rubber  is  a  fine  lever,  one  end  of  which,  slightly  flattened, 
extends  into  the  lumen  of  the  tube,  while  the  other  moves  over  the  face  of  a 
dial.  The  tube  is  inserted  into  the  interior  of  an  artery,  and  ligatures  applied  to 
fix  it,  so  that  the  movement  of  the  blood  may,  in  flowing  through  the  tube,  be 
indicated  by  the  movement  of  the  outer  extremity  of  the  lever  on  the  face  of 
the  dial. 

The  HcemafocJi077ieter  of  Vierordt,  and  the  instrument  of  Lortet,  resemble  in 
principle  that  of  Chauveau. 

In  the  Capinaries.— The  observation  of  Hales,  E.  H.  Weber,  and  Val- 
entin agree  very  closely  as  to  the  rate  of  the  blood-current  in  the  capil- 
laries of  the  frog;  and  the  mean  of  their  estimates  gives  the  velocity  of 
the  systewic  capillary  circulation  at  abont  one  inch  (25  mm.)  per  min- 
ute. The  velocity  in  the  capillaries  of  warm-blooded  animals  is  greater. 
In  the  dog  gV  to  yfo-  inch  (.5  to  .75  mm.)  a  second.  This  may  seem 
inconsistent  with  the  facts,  which  show  that  the  whole  circulation  is 
accomplished  in  about  half  a  minute.  But  the  whole  length  of  capillary 
vessels,  through  which  any  given  portion  of  blood  has  to  pass,  probably 
does  not  exceed  from  g^th  to  -gi^th  of  an  inch  (.5  mm.);  and  therefore 
the  time  required  for  each  quantity  of  blood  to  traverse  its  own  appointed 
portion  of  the  general  capillary  system  will  scarcely  amount  to  a  second. 

In  the  Veins. — The  velocity  of  the  blood  is  greater  in  the  veins  than 
in  the  capillaries,  but  less  than  in  the  arteries:  this  fact  depending ui:)on 
the  relative  capacities  of  the  arterial  and  venous  systems.  If  an  accurate 
estimate  of  the  proportionate  areas  of  arteries  and  the  veins  correspond- 
ing to  them  could  be  made,  we  might,  from  the  velocity  of  the  arterial 
current,  calculate  that  of  the  venous.  A  usual  estimate  is,  that  the  ca- 
pacity of  the  veins  is  about  twice  or  three  times  as  great  as  that  of  the 
arteries,  and  that  the  velocity  of  the  blood's  motion  is,  therefore,  about 
twice  or  three  times  as  great  in  the  arteries  as  in  the  veins,  8  inches 
(200  mm.)  a  second.  The  rate  at  which  the  blood  moves  in  the  veins 
gradually  increases  the  nearer  it  approaches  the  heart,  for  the  sectional 
area  of  the  venous  trunks,  compared  with  that  of  the  branches  opening 
into  them,  becomes  gradually  less  as  the  trunks  advance  toward  the  heart. 

Of  the  Circulation  as  a  Wlwle. — It  would  appear  that  a  portion  of 
blood  ca7i  traverse  the  entire  course  of  the  circulation,  in  the  horse,  in 
half  a  minute.  Of  course  it  would  require  longer  to  traverse  the  vessels 
of  the  most  distant  part  of  the  extremities  than  to  go  through  those  of 
the  neck;  but  taking  an  average  length  of  vessels  to  be  traversed,  and 


216  HANDBOOK    OF    PHYSIOLOGY. 

assuming,  as  we  may,  that  the  movement  of  blood  in  the  human  subject 
is  not  slower  than  in  the  horse,  it  may  be  concluded  that  half  a  minute 
represents  the  average  rate. 

Satisfactory  data  for  these  estimates  are  afforded  by  the  results  of 
experiments  to  ascertain  the  rapidity  with  which  poisons  introduced  into 
the  blood  are  transmitted  from  one  part  of  the  vascular  system  to  an- 
other. The  time  required  for  the  passage  of  a  solution  of  potassium 
ferrocyanide,  mixed  with  the  blood,  from  one  jugular  vein  (through  the 
right  side  of  the  heart,  the  pulmonary  vessels,  the  left  cavities  of  the 
heart,  and  the  general  circulation)  to  the  jugular  vein  of  the  opposite 
side,  varies  from  twenty  to  thirty  seconds.  The  same  substance  was 
transmitted  from  the  jugular  vein  to  the  great  saphena  in  twenty  sec- 
onds; from  the  jugular  vein  to  the  masseteric  artery  in  between  fifteen 
and  thirty  seconds;  to  the  facial  artery,  in  one  experiment,  in  between 
ten  and  fifteen  seconds;  in  another  experiment  in  between  twenty  and 
twenty-five  seconds;  in  its  transit  from  the  jugular  vein  to  the  metatar- 
sal artery,  it  occupied  between  twenty  and  thirty  seconds,  and  in  one 
instance  more  than  forty  seconds.  The  result  was  nearly  the  same 
whatever  was  the  rate  o£  the  heart's  action. 

In  all  these  experiments,  it  is  assumed  that  the  substance  injected 
moves  with  the  blood,  and  at  the  same  rate,  and  does  not  move  from 
one  part  of  the  organs  of  circulation  to  another  by  diffusing  itself 
through  the  blood  or  tissues  more  quickly  than  the  blood  moves.  The 
assumption  is  sufficiently  probable  to  be  considered  nearly  certain,  that 
the  times  above  mentioned,  as  occupied  in  the  passage  of  the  injected 
substances,  are  those  in  which  the  portion  of  blood,  into  which  each 
was  injected,  was  carried  from  one  part  to  another  of  the  vascular  system. 

Another  mode  of  estimating  the  general  velocity  of  the  circulating 
blood,  is  by  calculating  it  from  the  quantity  of  blood  supposed  to  be 
contained  in  the  body,  and  from  the  quantity  which  can  pass  through 
the  heart  in  each  of  its  actions.  But  the  conclusions  arrived  at  by  this 
method  are  less  satisfactory.  For  the  total  quantity  of  blood,  and  the 
capacity  of  the  cavities  of  the  heart,  have  as  yet  been  only  approximately 
ascertained.  Still  the  most  careful  of  the  estimates  thus  made  accord 
very  nearly  with  those  already  mentioned;  and  it  may  be  assumed  that 
the  blood  may  all  pass  through  the  heart  in  from  twenty-five  to  fifty 
seconds. 

Local  Peculiarities  of  the  Circulation. 

The  most  remarkable  peculiarities  attending  the  circulation  of  blood 
through  different  oi'gans  are  observed  in  the  cases  of  the  brain,  the  erec- 
tile organs,  the  hings,  the  liver,  and  the  kidneys. 

In  the  Brain. — For  the  due  performance  of  its  functions  the  brain 
requires  a  large  supply  of  blood.     This  object  is  effected  through  the 


THE    CIRCULATIOX    OF   THE    BLOOD.  217 

number  and  size  of  its  arteries,  the  two  internal  carotids,  and  the  two 
vertebrals.  It  is  further  necessary  that  the  force  with  which  this  blood 
is  sent  to  the  brain  should  be  less,  or  at  least  should  be  subject  to  less 
variation  from  external  circumstances  than  it  is  in  other  parts,  and  so 
the  large  arteries  are  very  tortuous  and  anastomose  freely  in  the  circle 
of  Willis,  which  thus  insures  that  the  supply  of  blood  to  the  brain  is 
uniform,  though  it  may  by  an  accident  be  diminished,  or  in  some  way 
changed,  through  one  or  more  of  the  principal  arteries.  The  transit  of 
the  large  arteries  through  bone,  especially  the  carotid  canal  of  the  tem- 
poral bone,  may  prevent  any  undue  distention;  and  uniformity  of  sup- 
ply is  further  insured  by  the  arrangement  of  the  vessels  in  the  pia 
mater,  in  which,  previous  to  their  distribution  to  the  substance  of  the 
brain,  the  large  arteries  break  up  and  divide  into  innumerable  minute 
branches  ending  in  capillaries,  which,  after  frequent  communication 
Avith  one  another,  enter  the  brain,  and  carry  into  nearly  every  part  of  it 
uniform  and  equable  streams  of  blood.  The  arteries  are  also  enveloped 
in  a  special  lymphatic  sheath.  The  arrangement  of  the  veins  within 
the  cranium  is  also  peculiar.  The  large  venous  trunks  or  sinuses  are 
formed  so  as  to  be  scarcely  capable  of  change  of  size;  and  composed, 
as  they  are,  of  the  tough  tissue  of  the  dura  mater,  and,  in  some  instances 
bounded  on  one  side  by  the  bony  cranium,  they  are  not  compressible  by 
any  force  which  the  fulness  of  the  arteries  might  exercise  through  the 
substance  of  the  brain;  nor  do  they  admit  of  distention  when  the  flow 
of  venous  blood  from  the  brain  is  obstructed. 

The  general  uniformity  in  the  supply  of  blood  to  the  brain,  which 
is  thus  secured,  is  well  adapted,  not  only  to  its  functions,  but  also  to  its 
condition  as  a  mass  of  nearly  incompressible  substance  placed  in  a  cav- 
ity with  unyielding  walls.  These  conditions  of  the  brain  and  skull  for- 
merly appeared,  indeed,  enough  to  justify  the  opinion  that  the  quantity 
of  blood  in  the  brain  must  be  at  all  times  the  same.  But  it  was  found 
that  in  animals  bled  to  death,  without  any  aperture  being  made  in  the 
cranium,  the  brain  became  pale  and  anaemic  like  other  parts.  And  in 
death  from  strangling  or  drowning,  there  was  congestion  of  the  cerebral 
vessels;  while  in  death  by  prussic  acid,  the  quantity  of  blood  in  the 
cavity  of  the  cranium  was  determined  by  the  position  in  which  the  ani- 
mal was  placed  after  death,  the  cerebral  vessels  being  congested  when 
the  animal  was  suspended  with  its  head  downward,  and  comparatively 
empty  when  the  animal  was  kept  suspended  by  the  ears.  Thus,  it  was 
concluded,  although  the  total  volume  of  the  contents  of  the  cranium  is 
probably  nearly  always  the  same,  yet  the  quantity  of  blood  in  it  is  liable 
to  variation,  its  increase  or  diminution  being  accompanied  by  a  simul- 
taneous diminution  or  increase  in  the  quantity  of  the  cerebro-spinal 
fluid,  which,  by  readily  admitting  of  being  removed  from  one  part  of 
the  brain  and  spinal  cord  to  another,  and  of  being  rapidly  absorbed,  and 


218  HANDBOOK    OF   PHYSIOLOGY. 

as  readily  effused,  would  serve  as  a  kind  of  suj^plemental  fluid  to  the 
other  contents  of  the  cranium,  to  keep  it  uniformly  filled  in  case  of 
variations  in  their  quantity.  And  there  can  be  no  doubt  that,  although 
the  arrangements  of  the  blood-vessels,  to  which  reference  has  been  made, 
insure  to  the  brain  an  amount  of  blood  which  is  tolerably  uniform,  yet, 
inasmuch  as  with  every  beat  of  the  heart  and  every  act  of  respiration 
and  under  many  other  circumstances,  the  quantity  of  blood  in  the  cav- 
ity of  the  cranium  is  constantly  varying,  it  is  plain  that,  were  there 
not  provision  made  for  the  possible  displacement  of  some  of  the  contents 
of  the  unyielding  bony  case  in  which  the  brain  is  contained,  there  would 
be  often  alternations  of  excessive  pressure  with  insufficient  supply  of 
blood. 

Chemical  Composition  of  Cerebro-spinal  Fluid. — The  cerebro-spinal  fluid  is 
transparent,  colorless,  not  viscid,  with  a  saline  taste  and  alkaline  reaction,  and 
is  not  affected  by  heat  or  acids.  It  contains  981-984  parts  water,  sodium 
chloride,  traces  of  potassium  chloride,  of  sulphates,  carbonates,  alkaline  and 
earthy  phosphates,  minute  ti'aces  of  urea,  sugar,  sodium  lactate,  fatty  matter, 
cholesterin,  and  albumen  (Flint). 

In  Erectile  Structures. — The  instances  of  greatest  variation  in  the 
quantity  of  blood  contained,  at  different  times,  in  the  same  organs,  are 
found  in  certain  structures  which,  under  ordinary  circumstances,  are 
soft  and  flaccid,  but,  at  certain  times,  receive  an  unusually  large  quan- 
tity of  blood,  become  distended  and  swollen  by  it,  and  pass  into  the  state 
which  has  been  termed  erection.  Such  structures  are  the  corpora  caver- 
nosa and  corpus  spongiosiim  of  the  penis  in  the  male,  and  the  clitoris  in 
the  female;  and,  to  a  less  degree,  the  nipple  of  the  mammary  gland  in 
both  sexes.  The  corpus  cavernosum  penis,  which  is  the  best  example 
of  an  erectile  structure,  has  an  external  fibrous  membrane  or  sheath ;  and 
from  the  inner  surface  of  the  latter  are  prolonged  numerous  fine  lamellae 
which  divide  its  cavity  into  small  compartments  looking  like  cells  when 
they  are  inflated.  Within  these  is  situated  the  plexus  of  veins  upon 
which  the  peculiar  erectile  property  of  the  organ  mainly  depends.  It 
consists  of  short  veins  which  very  closely  interlace  and  anastomose  with 
each  other  in  all  directions,  and  admit  of  great  variations  of  size,  col- 
lapsing in  the  passive  state  of  the  organ,  but,  for  erection,  capable  of  an 
amount  of  dilatation  which  exceeds  beyond  comparison  that  of  the 
arteries  and  veins  which  convey  the  blood  to  and  from  them.  The 
strong  fibrous  tissue  lying  in  the  intervals  of  the  venous  plexuses,  and 
the  external  fibrous  membrane  or  sheath  with  which  it  is  connected, 
limit  the  distention  of  the  vessels,  and,  during  the  state  of  erection,  give 
to  the  penis  its  condition  of  tension  and  firmness.  The  same  general 
condition  of  vessels  exists  in  the  corpus  spongiosum  urethra?,  but  around 
the  urethra  the  fibrous  tissue  is  much  weaker  than  around  the  body  of 
the  penis,  and  around  the  glans  there  is  none.     The  venous  blood  is 


THE    CIRCULATION    OF   THE    BLOOD.  219 

returned  from  the  plexuses  by  comparatively  small  veins;  those  from, 
the  glans  and  the  fore  part  of  the  urethra  empty  themselves  into  the 
dorsal  veins  of  the  penis;  those  from  the  cavernosum  pass  into  deeper 
veins  which  issue  from  the  corjsora  cavernosa  at  the  crura  penis;  and 
those  from  the  rest  of  the  urethra  and  bulb  pass  more  directly  into  the 
plexus  of  the  veins  about  the  prostate.  For  all  these  veins  one  condi- 
tion is  the  same;  namely,  that  they  are  liable  to  the  pressure  of  muscles 
when  they  leave  the  penis.  The  muscles  chiefly  concerned  in  this  action 
are  the  erector  penis  and  accelerator  urinse.  Erection  results  from  the 
distention  of  the  venous  plexuses  with  blood.  The  j)rincipal  exciting 
cause  in  the  erection  of  the  penis  is  nervous  irritation,  originating  in 
the  part  itself,  or  derived  from  the  brain  and  spinal  cord.  The  nervous 
influence  is  communicated  to  the  penis  by  the  pudic  nerves,  which  ram- 
ify in  its  vascular  tissue;  and  after  their  division  in  the  horse  the  penis 
is  no  longer  capable  of  erection. 

This  influx  of  the  blood  is  the  first  condition  necessary  for  erection, 
and  through  it  alone  much  enlargement  and  turgescence  of  the  penis 
may  ensue.  But  the  erection  is  probably  not  complete,  nor  maintained 
for  any  time  except  when,  together  with  this  influx,  the  muscles  already 
mentioned  contract,  and,  by  compressing  the  veins,  stop  the  eiSux  of 
blood,  or  prevent  it  from  being  as  great  as  the  influx. 

It  appears  to  be  only  the  most  perfect  kind  of  erection  that  needs 
the  help  of  muscles  to  compress  the  veins;  and  none  such  can  materially 
assist  the  erection  of  the  nipples,  or  that  amount  of  turgescence,  just 
falling  short  of  erection,  of  which  the  spleen  and  many  other  parts  are 
capable.  For  such  turgescence  nothing  more  seems  necessary  than  a 
large  plexiform  arrangement  of  the  veins,  and  such  arteries  as  may  ad- 
mit, upon  occasion,  augmented  quantities  of  blood. 

The  circulation  in  the  Lungs,  Liver,  and  Kidneys  will  be  described 
under  their  respective  heads. 

The  Regulation  of  the  Blood-Flow. 

The  flow  of  blood  is  not  always  the  same,  but  varies: — 

(a.)  With  alterations  in  the  force  and  frequency  of  the  contractions 

of  the  heart ;  and 
(b.)  "With  variations  of  the  peripheral  resistance. 

It  is  obvious  that  the  flow  of  blood  may  be  increased  under  the 
following  circumstances: — 

(a.)  If  the  force  and  frequency  of  the  heart's  beats  be  increased,  and 
the  peripheral  resistance  be  (1)  unchanged,  or  be  (2)  diminished. 

(b.)  If  the  force  and  frequency  of  the  heart  be  unchanged,  and  the 
peripheral  resistance  be  diminished. 


220  HANDBOOK    OF    PHYSIOLOGY. 

And  niiiy  on  the  other  hand  be  diminished: — 

(c.)  If  the  force  and  frequency  of  the  heart's  beats  be  diminished, 
and  if  the  peripheral  resistance  be  (1)  unchanged,  or  be  (2)  in- 
creased. 

(d.)  If  the  force  and  frequency  of  the  heart's  beats  be  unchanged, 
and  the  peripheral  resistance  be  increased. 

When  the  force  and  frequency  of  the  heart's  contractions  are  in- 
creased and  at  the  same  time  the  peripheral  resistance  is  increased,  the 
flow  may  be  increased,  diminislied,  or  unchanged,  according  as  either  of 
the  two  factors,  one  of  which  tends  to  increase  the  flow,  and  the  other 
to  diminish  it,  is  more  markedly  increased,  or  if  they  are  balanced.  The 
complemental  proposition  is  also  true,  that  the  flow  may  be  increased, 
diminished,  or  unchanged,  when  the  force  and  frequency  of  the  heart's 
contractions  are  diminished,  and  the  peripheral  resistance  is  diminished. 

The  conditions  of  increased  flow  and  of  increase  of  blood  pressure 
are  not  the  same.  Indeed,  the  greatest  blood-flow  may  occur  when  the 
blood  pressure  is  low,  i.e.,  when  the  peripheral  resistance  is  diminished 
and  the  heart's  beat  is  increased  or  is  unchanged.  In  fact  there  is  only 
one  condition  in  which  increased  blood-flow  is  accompanied  by  increased 
blood-pressure,  viz.,  when  the  heart's  beat  is  increased  and  the  periphe- 
ral resistance  is  unchanged. 

It  will  be  necessary  now  to  consider  (a)  the  ivays  in  wliicli  the  force 
and  frequency  of  the  heart's  heats  are  regulated  ;  and  also  (b)  the  ways  in 
which  the  peri2)heral  resistance  is  increased  or  diminished.  We  shall 
afterward  be  in  a  better  position  to  discuss  the  variations  of  blood- 
pressure  produced  by  different  combinations  of  cardiac  and  arterial 
alterations. 

(«.)  The  force  and  frequency  of  the  contractions  of  the  heart 
may  be  considered  to  de^Dend  upon : 

1.  The  properties  and  condition  of  the  heart-muscle  itself; 

2.  The  influence  of  the  central  nervous  system ; 

3.  The  amount  of  the  blood  passing  into  the  heart's  cavities ; 

4.  The  amount  of  jjressure  to  be  overcome. 
Each  of  these  factors  must  be  considered  seriatim. 

1.  The  properties  of  the  heart-imiscle. —  It  has  already  been  pointed 
out  that  in  structure  the  mugcular  fibres  of  the  heart  differ  from  skele- 
tal muscle  on  the  one  hand,  and  from  unstriped  muscle  on  the  other, 
occupying,  as  it  were,  an  intermediate  position  between  the  two  vari- 
eties. The  heart-muscle,  however,  possesses  a  property  which  is  not 
possessed  by  either  skeletal  or  unstriped  muscle,  namely,  the  property 
of  rhythmical  contractility.  The  property  of  rhythmic  contraction 
is  shown  by  the  action  of  the  heart  within  the  body;  its  systole  is  fol- 
lowed by  its  diastole  in  regular  sequence  throughout  the  life  of  the 


THE    CIRCULATION    OF   THE    BLOOD. 


221 


individual.  The  force  aud  frequency  of  the  systole  may  vary  from  time 
to  time  as  occasion  requires,  but  there  is  no  interruption  to  the  action 
of  the  normal  heart,  or  any  interference  with  its  rhythmical  contrac- 
tions. Further,  we  find  that  in  an  animal  rapidly  bled  to  death,  the  heart 
continues  to  beat  for  a  time,  varying  in  duration  with  the  kind  of  ani- 
mal experimentally  dealt  with,  and  in  the  entire  absence  of  blood  within 
the  heart-chambers;  and  still  further,  if  the  heart  of  an  animal  be  re- 
moved from  the  body,  it  still,  for  a  varying  time,  continues  its  alternate 
systolic  and  diastolic  movements.  Thus  we  see  that  the  power  of 
rhythmic  contraction  depends  neither  upon  connection  with  the  central 


•c.s.d/. 


Fig.  193.  Fig.  193  B. 

Fig.  193.— The  heart  of  a  frog  (Rana  esculenta)  from  the  front.  V,  Ventricle;  Ad,  right  auricle; 
As,  left  auricle;  B.  bulbus  arterio-us,  dividiug  into  right  and  left  aortae.    (Ecker.) 

Fig.  193  B.— The  heart  of  a  frog  (Rana  esculenta)  from  the  back.  s.  v..  Sinus  venosus  opened  ; 
c.  s.  .s-.,  left  vena  cava  superior;  c.  s.  d.,  right  vena  cava  superior;  c.  i..  vena  cava  inferior  ;  r.  p.. 
vena  pulmonales;  A.d.,  right  auricle;  A.s.,  left  auricle;  A.p.,  opening  of  communication  between  tlie 
right  auricle  and  the  sinus  venosus,     X  2^-3-    (Ecker.) 


nervous  system,  nor  yet  upon  the  stimulation  produced  by  the  presence 
of  blood  within  its  chambers — it  is  automatic.  The  cause  of  this 
rhythmic  power  has  been  the  subject  of  much  discussion  and  experi- 
mental observation.  Up  to  a  comparatively  short  time  ago,  the  remark- 
able property  of  the  heart  to  continue  its  rhythmical  contractions  after 
removal  from  the  body  was  believed  to  be  connected  in  some  way  or 
other  with  the  presence  of  collections  of  nerve  cells,  or  ganglia  in  sev- 
eral parts  of  its  tissue.  Although  this  idea,  as  we  shall  presently  see,  has 
now  been  almost  universally  given  up,  it  may  be  as  well  to  describe 
shortly  these  ganglia  in  this  place;  they  have  been  studied  more  partic- 
ularly in  the  heart  of  the  frog,  of  the  tortoise,  and  of  other  cold-blooded 
animals. 


222 


HANDBOOK    OF   PHYSIOLOGY. 


In  the  frog's  heart  (fig.  193)  these  ganglia  consist  of  three  chief 
groups.  The  first  group  is  situated  in  the  wall  of  the  sinus  venosus  at 
the  junction  of  the  Sinus  with  the  auricles  (Remak's);  the  second  group 
is  placed  near  the  junction  between  the  auricles  and  rentricle  (Bidder's); 
and  the  third  in  the  septum  between  the  auricles  (v.  BezokVs). 

The  nerve  cells  of  which  these  ganglia  are  composed  are  generally 
unipolar,  and  seldom  bipolar:  sometimes  two  cells  are  said  to  exist  in 
the  same  envelope,  constituting  the  ticin  cells  of  Dogiel.  The  cells 
are  large,  and  have  very  large  round  nuclei  and  nucleoli  (fig.  195). 
Ganglion  cells  have  not  been  found  in  the  ventricle  of  the  frog's 
heart  below  the  auriculo-ventricular  groove. 

As  regards  the  automatic  movements 
of  the  heart  removed  from  the  body  our 
chief  knowledge  has  been  derived  from 
the  stud^  of  the  hearts  of  the  frog  and 
tortoise 


IT 


Fig.  19*. 

Fig.  194. — Course  of  the  nerves  in  the  auricular  partition  waU  of  the  heart  of  a  frog.  d.  Dorsal 
branch;  v.  ventral  branch,      (lacker.) 

Fig.  195.— Isolated  nerve-cells  from  the  frogs  heart.  I.  Usual  form.  n.  Twin  cell.  C,  Capsule; 
K,  nucleus;  K',  nucleolus;  P,  process.      (Trom  Ecker.^ 

If  removed  from  the  body  entire,  the  frog's  heart  will  continue  to 
beat  for  many  hours  and  even  days,  and  the  beat  has  no  apparent  differ- 
ence from  the  beat  of  the  heart  before  removal;  it  will  take  place,  as  we 
have  mentioned,  without  the  presence  of  blood  or  other  fluid  within  its 
chambers.  Xot  only  is  this  the  case,  but  the  auricles  and  ventricle  may 
be  cut  off  from  the  sinus,  and  both  parts  continue  to  pulsate,  and  fur- 
ther the  auricles  may  be  divided  from  the  ventricle  with  the  same  result. 
If  the  heart  be  divided  lengthwise,  its  parts  will  continue  to  pulsate 
rhythmically,  and  the  auricles  may  be  cut  up  into  pieces,  and  the  pieces 
will  continue  their  movements  of  rhythmical  contraction. 

It  will  be  thus  seen  that  the  rhythmical  movements  appear  to  be 
more  marked  in  the  parts  supplied  by  the  ganglia,  as  the  apical  portion 
of  the  ventricle,  in  which  ganglia  have  not  been  found,  does  not,  under 
ordinary  circumstances,  possess  the  power  of  automatic  movement. 

It  has,  however,  been  shown  by  C-askell  that  the  extreme  apex  of  the 


THE    CIRCULATION    OF   THE    BLOOD.  233 

ventricle  of  the  heart  of  the  tortoise,  wliich  contains  no  ganglia,  may 
under  appropriate  stimuli  be  made  to  contract  rhythmically.  This 
proves  that  the  muscular  tissue  of  the  heart  itself  is  capable  of  rhyth- 
mical contraction  indeiDcndent  of  the  ganglia.  Thus  it  seems  probable 
that  the  rhythmic  contractility  of  the  heart  is  a  power  inherent  in  the 
muscular  tissue,  which  is  quite  independent  as  far  as  its  commencement, 
at  any  rate,  is  concerned  of  nerve  influence. 

The  heart-muscle  exhibits  another  property  which  distinguishes  it 
from  ordinary  skeletal  muscle,  viz.,  the  way  in  which  it  reacts  to  stimuli. 
The  latter  as  will  be  described  at  greater  length  in  its  appropriate  place, 
reacts  slightly  to  a  slight  stimulus  above  the  minimal,  and  with  an  in- 
crease of  the  strength  of  the  stimuli  will  give  increasingly  ample  con- 
tractions until  the  maximum  contraction  is  reached;  in  the  case  of  the 
heart- beats  this  is  not  so,  since  the  ininimum  stimulus  tvhich  has  any 
effect  is  followed  hy  tlte  maximum  contraction;  in  other  words  the  weak- 
est effectual  stimulus  brings  out  as  great  a  beat  as  the  strongest.  There 
is  another  great  difference  between  the  contraction  of  the  heart  and  of 
skeletal  muscle,  viz.,  the  inability  of  the  former  to  enter  into  a  state  of 
tetanus  under  the  influence  of  stimuli  repeated  very  rapidly.  If  the 
heart  be  stimulated  by  a  series  of  rapid  interrupted  induction  shocks, 
there  is  no  summation  of  the  contractions,  as  there  would  be  supposing 
an  ordinary  skeletal  muscle  were  stimulated  in  the  same  way.  This 
phenomenon  is  said  to  be  due  to  the  following  fact,  viz.,  that  in  order  to 
produce  an  extra  contraction  of  the  excised  frog's  heart,  the  stimulus 
must  be  applied  during  diastole  or  period  of  rest  or  relaxation,  and  in 
that  case  the  next  contraction  happens  at  an  earlier  period  than  if  the 
stimulus  were  not  ajjplied.  If  applied  during  the  systole,  the  stimulus 
has  scarcely  any  effect;  the  period  during  which  the  muscle  is  refractory 
to  stimuli  is  much  longer  in  the  case  of  the  heart  than  in  the  case  of 
other  muscles.  In  order  to  produce  a  tetanus  in  skeletal  muscle,  the 
second  stimulus  must  be  sent  into  the  muscle  before  it  has  had  time  to 
recover  from  the  effect  of  the  first  stimulus  and  relax,  and  so  on  with 
the  third,  fourth,  and  other  stimuli.  If,  as  we  may  suppose,  the  same 
conditions  for  the  production  of  tetanus  are  necessary  in  heart-muscle, 
the  reasons  of  the  impossibility  of  producing  tetanus,  i.e.  that  a  stim- 
ulus applie  during  contraction  is  ineffectual,  are  sufficiently  obvious. 
It  appears,  however,  that  if  the  stimuli  are  sufficiently  strong  and  rap- 
idly repeated,  the  refractory  period  during  which  the  muscle  is  prac- 
tically insensible  to  stimuli  diminishes,  and  a  very  rapid  repetition  of 
the  beats  occurs,  which  may  even  develop  the  appearance  of  an  incom- 
plete, but  never  of  complete  tetanus. 

In  connection  with  the  rhythmic  contraction  of  muscle,  it  is  neces- 
sary to  allude  briefly  to  what  is  known  as  Stannius'  experiment. 
This  experiment  consisted  originally  of  applying  a  tight  ligature  to  the 


224  HANDBOOK    OF    PHYSIOLOGY. 

heart  between  the  sinus  and  the  auricles,  the  effect  of  which  is  to  stop 
the  beat  of  the  heart  below  the  ligature,  while  the  sinus  and  the  veins 
leading  into  it  continue  to  beat.  If  a  second  ligature  be  a^jplied  at  the 
junction  of  the  auricles  and  ventricle,  the  ventricle  may  begin  to  beat 
slowly,  while  the  auricles  continue  quiescent.  In  both  cases  the  quies- 
cent parts  of  the  heart  may  be  made  to  give  single  contractions  in 
response  to  mechanical  stimulation.  A  considerable  amount  of  discussion 
has  arisen  as  to  the  explanation  of  these  phenomena.  It  was  suggested 
that  the  action  of  the  ligature  is  to  stimulate  some  inhibitory  nervous 
mechanism  in  the  sinus,  whereby  the  auricles  and  ventricle  can  no 
longer  continue  to  contract,  but  this  suggestion  must  certainly  be  given 
up  if  the  present  theory  as  to  the  functions  of  the  nerve  ganglia  be  cor- 
rect. It  may  be  that  the  effect  of  Stannius'  ligature  is  simply  an  exam- 
ple of  what  has  been  called  by  Gaskell  UocTcing.  The  explanation  of 
this  term  is  as  follows : — it  appears  that  under  normal  conditions  the 
wave  of  contraction  in  the  heart  starts  at  the  sinus  and  travels  down- 
Avard  over  the  auricles  to  the  ventricle,  the  irritability  of  the  muscle 
and  the  power  of  rhythmic  contractility  being  greatest  in  the  sinus,  less 
in  the  auricles  and  still  less  in  the  ventricle,  while  under  ordinary  con- 
ditions the  apical  portion  of  the  ventricle  exhibits  very  slight  irritability 
and  still  less  power  of  spontaneous  contraction.  Thus  it  may  be  sup- 
posed that  the  wave  of  contraction  beginning  at  the  sinus  is  more  or 
less  blocked  by  a  ring  of  muscle  of  lower  irritability  at  its  junction  with 
the  auricles,  and  again  the  wave  in  the  auricles  is  similarly  delayed  in 
its  passage  over  to  the  ventricle  by  a  ring  of  lesser  irritability,  and  thus 
the  wave  of  contraction  starting  at  the  sinus  is  broken  as  it  were  both 
at  the  auricles  and  at  the  ventricle.  By  an  arrangement  of  ligatures,  or 
better,  of  a  system  of  clamps,  one  part  of  the  heart  may  be  isolated  from 
the  other  portion,  and  the  contraction  when  stimulated  by  an  induction 
shock  may  be  made  to  stop  in  the  portion  of  the  heart-muscle  in  which 
it  begins.  It  is  not  unlikely  that  the  contraction  of  one  portion  of  the 
heart  acts  as  a  stimulus  to  the  next  portion,  and  that  the  sinus  contrac- 
tion generally  begins  first,  since  the  sinus  is  the  most  irritable  to  stimuli, 
and  possesses  the  power  of  rhythmic  contractility  to  the  most  highly 
developed  degree.  It  must  not  be  thought,  however,  that  the  wave  of 
contraction  is  incapable  of  passing  over  the  heart  in  any  other  direction 
than  from  the  sinus  downward;  it  has  been  shown  that  by  application 
of  approprinte  stimuli  at  appropriate  instants,  the  natural  sequence  of 
beats  may  be  reversed,  and  the  contraction  starting  at  the  arterial  part 
of  the  ventricle  may  pass  upward  to  the  auricles  and  then  to  the  sinus 
in  order. 

An  exceedingly  interesting  fact  with  regard  to  the  passage  of  the 
wave  in  any  direction  has  been  made  out  by  partial  division  of  the  mus- 
cular fibres  at  any  point,  whereby  one  part  of  the  wall  of  the  heart  is 


THE   CIRCULATION    OF    THE    BLOOD.  225 

left  connected  with  the  other  parts  by  a  small  portion  of  undivided 
muscular  tissue,  and  the  wave  of  contraction  then  being  only  able  to 
pass  to  the  next  portion  of  the  wall  every  second  or  third  beat.  Thus 
division  of  the  muscle  has  much  the  same  effect  as  partial  clamping  it 
in  the  same  position,  or  of  a  ligature  similarly  applied,  but  not  tied 
tightly.  It  may,  therefore,  be  suggested  that  Stannius'  ligature  acts  as 
a  partial  or  complete  block,  and  prevents  the  stimulus  of  the  sinus-beat 
from  passing  further  down  the  heart,  but  that  the  parts  below  the  liga- 
ture may  be  made  to  contract  by  stimuli  applied  to  them  directly. 
Nearly  all  the  information  to  be  obtained  as  to  the  phenomena  of  the 
contraction  of  heart-muscle  apart  from  the  rhythmic  action  of  the 
organ  itself,  may  be  obtained  from  a  heart  to  which  a  Stannius'  ligature 
has  been  applied;  indeed,  the  eifect  of  minimal  stimuli,  the  effect  of 
rapidly  repeated  shocks,  and  the  refractory  period  of  heart-muscle  may 
all  be  studied  from  a  heart  in  this  condition. 

The  velocity  of  the  wave  of  contraction  in  frog's  heart-muscle  has 
been  shown  to  be  f  to  |  inch,  or  10-15  cm.  a  second. 

In  pointing  out  the  differences  between  the  phenomena  of  contrac- 
tion in  skeletal  and  heart-muscle,  the  similarities  between  the  two  are 
not  to  be  overlooked;  thus  it  has  been  shown  that  the  effect  of  cold, 
heat,  fatigue,  and  other  influences  have  very  much  the  same  effect  in 
both  cases. 

2.   The  inftuence  of  the  central  nervous  system. 

The  heart  is  capable  of  automatic  rhythmic  movement,  as  has  been 
clearly  shown  by  its  behavior  when  removed  from  the  body,  and  it  has 
been  shown  further  that  there  is  reason  for  believing  that  the  power 
resides  in  the  inherent  property  of  its  muscle  fibres  themselves.  While 
in  the  body,  however,  the  heart's  beats  are  under  control  of  the  central 
nervous  system.  To  this  nervous  control,  we  must  next  direct  our  at- 
tention. The  influence  which  is  exerted  by  the  central  nervous  system 
appears  to  be  of  two  kinds,  firstly,  i^i  the  direction  of  slowing  or  inhibit- 
ing the  heats,  and  secondly,  in  the  direction  of  accelerating  or  augment- 
ing the  l>eats.  The  influence  of  the  first  kind  is  brought  to  bear  upon 
the  heart  through  the  fibres  of  the  vagi  nerves,  and  that  of  the  second 
kind  through  the  sympathetic  fibres. 

Influence  of  the  Vagi. — It  has  long  been  known,  indeed  ever  since 
the  experiments  of  the  Bros.  Weber  in  1845,  that  stimulation  of  one  or 
both  vagi  produces  slowing  of  the  beats  of  the  heart.  It  has  since  been 
shown  in  all  of  the  vertebrate  animals  experimented  with,  that  this  is 
the  normal  action  of  vagus  stimulation.  Moreover,  section  of  one  nerve, 
or  at  any  rate  of  both  vagi,  produces  acceleration  of  the  pulse,  and  stim- 
ulation of  the  distal  or  peripheral  end  of  the  divided  nerve  produces 
normally  slowing  or  stopping  of  the  heart's  beats. 

It  appears  that  any  kind  of  stimulus  produces  the  same  effect,  either 
15 


226 


HANDBOOK    OF    I'll  VSIOLOfi  Y. 


cliemical,  mechanical,  electrical,  or  thermal,  but  that  of  these  the  most 
potent  is  a  rapidly  interrupted  induction  current.  A  certain  amount  of 
confusion  has  arisen  as  to  the  effect  of  vagus  stimulation  in  conse- 
quence of  the  fact  that  within  the  trunk  of  the  nerve  is  contained,  in 
some  animals,  fibres  of  the  sympathetic,  and  it  depends  to  some  extent 
upon  the  exact  position  of  the  application  of  the  stimulus,  us  to  the 
exact  effect  produced.  Speaking  generally,  however,  excitation  of  any 
part  of  the  trunk  of  the  vagus  produces  inhibition,  the  stimulus  being 
particularly  potent  if  applied  to  the  termination  of  the  vagi  in  the 
heart  itself,  where  they  enter  the  substance  of  the  organ  at  the  situation 
of  the  sinus  ganglia.  The  stimulus  may  be  applied  to  either  vagus  with 
effect,  although  it  is  frequently  more  potent  if  applied  to  the  nerve  on 
the  right  side.  The  effect  of  the  stimulus  is  not  immediately  seen;  one 
or  more  beats  may  occur  before  stoppage  of  the  heart  takes  place,  and 
slight  stimulation  may  produce  only  slowing  and  not  complete  stoppage 


"^^lifiiififi 


Fig.  196. — Tracing  showing  the  actions  of  the  vagus  on  the  heart.  Aur.,  Auricular;  vent.,  ven- 
tricular tracing.  The  part  between  perpendicular  lines  indicates  period  of  vagus  stimulation.  C.S 
indicates  that  the  secondary  coil  was  H  cm.  from  the  primary.  The  part  of  tracing  to  the  left 
shows  the  i-egular  contractions  of  moderate  height  before  stimulation.  During  stinuilation,  and  for 
some  time  after,  the  beats  of  auricle  and  ventricle  are  arrested.  After  they  commence  again  they 
are  single  at  first,  but  soon  acquire  a  much  greater  amplitude  than  before  the  application  of  the 
stimulus.     (From  Bruntou,  after  Gaskell.) 


of  the  heart.  The  stoppage  may  be  due  either  to  prolongation  of  the 
diastole,  as  is  usually  the  case,  or  to  diminution  of  the  systole.  Vagus 
stimulation  inhibits  the  spontaneous  beats  of  the  heart  only,  it  does  not 
do  away  with  the  irritability  of  the  heart-muscle,  since  mechanical  stim- 
ulation may  bring  out  a  beat  during  the  still-stand  caused  by  vagus 
stimulation.  The  inhibition  of  the  beats  varies  in  duration,  but  if  the 
stimulation  be  a  prolonged  one,  the  beats  may  reappear  before  the  cur- 
rent is  shut  off.  When  the  beats  reappear,  the  first  few  are  usually 
feeble,  and  may  be  auricular  only;  after  a  time  the  contractions  become 
more  and  more  strong,  and  very  soon  exceed  both  in  amplitude  and. 
frequency  those  which  occurred  before  the  application  of  the  stimulus 
(fig.  196). 

Influence  of  the  Sympathetic. — The  influence  of  the  sympathetic 
may  be  considered,  to  a  certain  extent,  as  the  reverse  of  that  of  the 
vagus.     Stimulation  of  the  sympvithetic,  even  of  one  side,  produces  ac- 


THE    CIRCULATION    OF   THE    BLOOD. 


227 


celerutiou  of  the  heart-beats,  and  according  to  certain  observers,  section 
of  the  same  nerve  produces  slowing.  The  acceleration  produced  by  stim- 
ulation of  the  sympathetic  fibres  is  accompanied  by  increased  force,  and 
so  the  action  of  the  nerve  is  more  properly  termed  augmentor.  The 
action  of  the  sympathetic  differs  from  that  of  the  vagus  in  several  par- 
ticulars besides  the  augmentation  which  is  produced :  firstly,  the  stimulus 
required  to  produce  any  effect  must  be  more  powerful  than  is  the  case 
with  the  vagus  stimulation;  secondly,  a  longer  time  lapses  before  the 
effect  is  manifest;  and  thirdly,  the  augmentation  is  followed  by  exhaus- 
tion, the  beats  being  after  a  time  feeble  and  less  frequent. 

Origin  of  the  cardiac  nerve-fibres. — The  fibres  of  the  sympa- 
thetic system,  which  influence  the  heart-beat  in  the  frog,  leave  the 
spinal  cord  by  the  anterior  root  of  the  third  spinal  nerve,  and  pass 
thence  by  the  ramus  communicans  to  the  third  spinal  ganglion,  thence 
to  the  second  spinal  ganglion,  and  thence  by  the  annulus  of  Vieussens 


Fig.  197. — Tracing  showing  diminished  amplitude  and  slowing  of  the  pulsations  of  the  auricle 
and  ventricle  without  complete  stoppage  during  irritation  of  the  vagus.  (From  Brunton,  after 
Gaskell.) 


(round  the  subclavian  artery)  to  the  first  spinal  ganglion,  and  thence  in 
the  main  trunk  of  the  sympathetic,  to  near  the  exit  of  the  vagus  from 
the  cranium,  where  it  joins  that  nerve  and  runs  down  to  the  heart  within 
its  sheath,  forming  the  joint  vago-sympathetic  trunk. 

In  the  dog,  the  augmentor  fibres  leave  the  corfl  by  the  second  and 
third  dorsal  nerves,  and  possibly  by  anterior  roots  of  two  or  more  lower 
nerves,  passing  by  the  rami  communicantes  to  the  ganglion  stellatum, 
or  first  thoracic  ganglion,  thence  by  the  annulus  of  Vieussens  to  the 
inferior  cervical  g.nglion  of  the  sympathetic  fibres  from  the  annulus,  or 
from  the  inferior  cervical  ganglion  proceed  to  the  heart. 

From  the  fact  that  the  augmentor  fibres  are  joined  to  the  vagus 
trunk,  it  may  be  understood  that  the  effect  of  the  stimulation  of  the 
vagus  in  the  frog  is  not  in  all  cases  purely  inhibitory,  but  may  be  aug- 
mentor, according  to  the  position  where  the  stimulus  is  applied,  the 
intensity  of  the  stimulus,  and  the  condition  of  the  heart;  if  it  is  beating 
strongly  a  slight  vagus  stimulation  will  produce  immediate  inhibition. 

The  fibres  of  the  vagus  which  pass  to  the  heart  arise  in  the  medull.i 


228  HANDBOOK    OF   PHYSIOLOGY. 

oblongata,  in  the  floor  of  the  fourth  ventricle,  and  in  a  nucleus  of  gray 
matter,  the  exact  position  of  which  will  be  indicated  in  a  future  chapter. 
It  has  been  found  that  stimulation  of  this  nucleus,  which  is  called  the 
cardio-inhibitory  centre,  produces  inhibition  of  the  heart-beat. 

Thus  there  is  no  doubt  that  the  vagi  nerves  are  simply  the  media  of 
an  inhibitory  or  restraining  influence  over  the  action  of  the  heart,  which 
is  conveyed  through  them  from  the  centre  in  the  medulla  oblongata 
which  is  always  in  operation.  The  restraining  influence  of  the  centre 
in  the  medulla  may  be  reflexly  increased  by  stimulation  of  almost  any 
afferent  nerve,  particularly  of  the  abdominal  sympathetic,  so  as  to  pro- 
duce slowing  or  stoppage  of  the  heart,  through  impulses  from  it  passing 
down  the  vagi.  As  an  example  of  this  reflex  stimulation,  the  well- 
known  effect  on  the  heart  of  a  violent  blow  on  the  ei^igastrium  may  be 
referred  to.  The  stojjpage  of  the  heart's  action  in  this  case  is  due  to 
the  conveyance  of  the  stimulus  by  flbres  of  the  sympathetic  (afferent) 
to  the  medulla  oblongata,  and  its  subsequent  rcjiectioii  through  the  vagi 
(efferent)  to  the  muscular  substance  of  the  heart.  It  is  possible  that  the 
power  of  the  medullary  inhibitory  centre  may  in  a  similar  manner  be 
reflexly  lessened  so  as  to  produce  accelerated  action  of  the  heart. 

In  the  mammal  the  fibres  in  the  vagus,  by  means  of  which  inhibitory 
influences  are  conveyed  to  the  heart,  are  derived  from  the  spinal  acces- 
sory nerve,  since  when  that  nerve  is  divided  certain  fibres  of  the  vagus 
trunk  degenerate,  and  afterwards  stimulation  of  the  vagus  trunk  no 
longer  produces  inhibition.  The  spinal  accessory  fibres  are  fine  medul- 
lated  fibres,  2,'j-  to  3,a  in  diameter,  and  may  be  traced  to  the  heart,  and 
lose  their  medulla  in  the  ganglia  of  that  organ.  The  fibres  of  the  vagus 
traceable  into  the  heart  muscle,  have  been  found  to  be  both  niedullated 
and  non-medullated  when  they  enter;  they  pass  out  of  Remak's  ganglion 
more  generally  as  niedullated  nerves,  forming  the  nerve-fibres  of  the 
septum,  but  after  these  septal  fibres  issue  from  Bidder's  ganglia,  they 
enter  the  ventricle  ag  non-medullated  nerves,  in  the  frog  at  any  rate, 
but  in  mammals  a  few  fibres  are  niedullated.  The  sympathetic  fibres, 
on  the  other  hand,  reach  the  heart  as  non-medullated  fibres,  having  lost 
their  medulla  in  the  sympathetic  ganglia. 

The  course  of  the  augmentor  fibres  in  the  spinal  cord  is  not  known, 
but  it  is  thought  that  in  all  probability  they  are  connected  with  an  aug- 
mentor centre  in  the  medulla.  The  circulation  of  venous  blood  appears 
to  stimulate  the  inhibitory  centre,  and  of  highly  oxygenated  the  aug- 
mentor centre. 

In  addition  to  direct  and  reflex  stimulation  it  is  almost  certain  that 
impulses  passing  down  from  the  cerebrum  may  have  a  similar  effect. 

Other  Influences  Affecting  the  Heart-Beat. — Alteration  of  tempera- 
ture.—The  effect  of  cold  is  to  slow  the  heart-beats,  and  if  the  heart  be 
cooled  down  to  3°  C.  (38°  F.)  it  will  stop  beating.     The  heart  may  be 


THE    CIRCULATION   OF   THE    BLOOD.  229 

frozen,  and  when  thawed  will  continue  its  spontaneous  beats.  The 
elfect  of  heat  is  to  quicken  and  shorten  the  heart-beats,  but  at  a  moder- 
ate temperature,  20°  C.  (68°F.),  the  contractions  are  increased  in  force. 
At  or  below  40°  C.  (104°  F.)  the  contractions  are  so  rapid  as  to  pass  into 
heart-rigor;  this  may  be  stopi^ed  by  cooling. 

Poisons  and  other  chemical  substances.— A  large  number  of 
chemical  substances  have  a  distinct  effect  upon  the  cardiac  contractions. 
Of  these  the  most  imj^ortant  are  atroinn  and  inuscarin. 

Atropin  produces  considerable  augmentation  of  the  heart-beats,  and 
when  acting  upon  the  heart  prevents  the  results  of  vagus  stimulation. 

Muscarin  (obtained  from  various  species  of  poisonous  fungi)  pro- 
duces marked  slowing  of  the  heart-beats,  and,  in  larger  doses,  stoppage 
of  the  heart.  It  produces  a  similar  effect  to  that  of  prolonged  vagus 
stimulation,  and  as  in  that  case  the  effect  can  be  removed  by  the  action 
of  atropin. 

Digitalin  (the  active  principle  of  digitalis  purpurea),  slows  the  heart 
and  appears  to  act  by  stimulating  the  vagi.  Later  on  the  muscle  is  also 
more  excitable.  Veratrin  and  aconifin  have  a  similar  effect.  Nicotine 
prevents  the  effect  of  vagus  stimulation. 

Methods  of  investigating  the  Heart-beat. 

(1)  The  simplest  foi-m  of  an  apjmratus  to  be  used  for  recording  the  contrac- 
tions of  the  frog's  heart  consists  of  a  small  closed  cylindrical  box  fixed  to  a 
stand.  At  the  bottom  of  the  box  are  two  tubes  by  means  of  which  water  at 
various  temperatures  may  be  made  to  circulate  through  it,  one  tube  being  the 
inlet  and  the  other  the  outlet,  and  they  are  connected  with  india-rubber,  suit- 
able for  the  purpose  of  conducting  water  to  and  from  the  apparatus.  The  lever 
is  made  of  a  piece  of  glass  rod  which  is  softened  and  drawn  out  in  the  flame 
of  the  blow-pipe  a  very  fine  thread,  leaving  a  small  piece  unaltered  to  act  as 
a  counterpoise.  The  lever  is  then  passed  through  a  piece  of  cork  and  through 
this  cork  a  fine  needle  is  inserted  at  right  angles  to  the  lever.  The  needle  is 
made  to  rest  on  a  support  attached  above  one  side  of  the  box  in  such  a  way 
that  the  lever  has  free  movement  up  and  down.  Another  small  piece  of  cork 
is  passed  along  the  lever  arm  and  is  adjusted  and  cut  so  that  its  point  directed 
downward  can  rest  upon  the  frog's  heart,  which  is  removed  from  the  body  and 
placed  upon  the  top  of  the  box  in  serum  or  defibrinated  blood.  In  this  way 
the  contractions  of  the  auricles  and  ventricle  are  communicated  to  the  lever, 
and  this  may  be  made  to  write  upon  a  recording  cylinder. 

(2)  The  variations  of  endocardial  pressure,  M-hich  correspond,  of  course, 
with  the  various  phases  of  the  cardiac  cycle,  may  be  recorded  by  a  modifica- 
tion of  the  ordinary  mercurial  manometer.  The  apparatus  is  best  used  with  a 
large  frog  (Rana  esculenta),  and  the  heart  is  exposed  in  the  usual  manner,  the 
pericardium  opened.  A  cut  is  made  into  the  bulb,  and  by  this  means  a  double 
or  perfusion  canula  (fig.  198)  is  passed  into  the  ventricle,  a  ligature  is  passed 
round  the  heart,  and  the  canula  is  tied  in  tightly.  The  vessels  are  then  di- 
vided beyond  the  ligature,  and  the  canula,  with  the  heart  attached,  is  removed. 
To  one  stem  of  the  canula  a  tube  is  attached,  communicating  with  a  reservoir 


230 


HANDBOOK    OF   PHYSIOLOGY. 


of  a  solution  of  dried  blood  iu  .0  saline  solution,  and  filtered,  which  is  capa- 
ble of  being  raised  or  lowered  in  temperature  by  being  surrounded  by  a  metal 
box  which  contains  hot,  cold,  or  iced  water.  Attached  to  the  other  end  is  a 
similar  tube,  which  communicates  by  a  T  piece  with  a  small  mercurial  man- 
ometer, provided  with  a  writing  style,  and  also  with  a  vessel  into  which  the 
serum  is  received.  The  apparatus  being  arranged  so  that  the  movements  of 
the  mercury  can  be  recorded  by  the  float  and  the  writing  style  on  a  slowly 
revolving  drum,  and  after  some  serum  has  been  allowed  to  pass  freely  through 
the  ventricle,  both  tubes  are  clipped,  the  second  one  beyond  the  T  piece,  and 
the  alterations  in  the  pressure  are  recorded.  The  effects  of  fluids  at  various 
temperatures  and  of  poisons  may  be  recorded  in  the  manner  indicated  above. 

(3)  By  Roy's  Tonometer  (fig.  199)  the  alterations  in  volume  which  a  frog's 
heart  undergoes  during  contrac- 
tion are  recorded  by  the  follow- 
ing means :  A  small  bell -jar, 
open  above,  but  provided  with  a 
firmly  fitting  cork,  in  which  is 
fixed  a  double  canula,  is  ad- 
justable by  a  smoothly  ground 
base  upon  a  circular  brass  plate, 


Fig.  198. 


Fig.  199. 


Fig.  198.— Kronecker's  Perfusion  Canula,  for  supplying  Fluids  to  the  interior  of  the  Frog's 
Heart.  It  consists  of  a  double  tube,  one  outside  the  other;  the  end  view  is  shown  in  the  engraving. 
The  inner  tube  branches  out  to  the  left:  thus,  when  the  ventricle  is  tied  to  the  outer  tulie  of  the  can- 
ula, a  current  of  liquid  can  be  made  to  pass  into  the  heart  by  one  tube  and  out  through  the  other. 

Fig.  199.— Roy's  Tonometer. 


about  2  to  3  inches  in  diameter.  The  junction  is  made  complete  by  greas- 
ing the  base  with  lard.  In  the  plate,  which  is  fixed  to  a  stand  adjustable  on 
an  upright,  are  two  holes,  one  in  the  centre,  a  large  one  about  one-third 
of  an  inch  in  diameter,  to  which  is  fixed  below  a  brass  grooved  collar, 
about  half  an  inch  deep ;  the  other  hole  is  the  opening  into  a  pipe  provided 
with  a  tap  (stopcock) .  The  opening  provided  with  the  collar  is  closed  at  the 
lower  part  with  a  membi-ane  of  animal  tissue,  which  is  loosely  tied  by  means 
of  a  ligature  around  the  groove  at  the  lower  edge  of  the  collar.  To  this  mem- 
brane a  piece  of  cork  is  fastened  by  sealing-wax,  from  which  passes  a  wire, 
which  can  be  attached  to  a  lever,  fixed  on  a  stage  below  the  apparatus. 

When  using  the  apparatus,  the  bell-jar  is  fixed  by  means  of  lard,  and  the 
jar  is  filled  with  olive  oil.  In  the  way  above  described,  the  heart  of  a  large 
frog  is  prepared  and  the  canula  fixed  in  the  cork  is  firmly  tied  into  the  heart ; 
the  tubes  of  the  canula  communicating  with  the  reservoir  of  serum  on  the 


THE    CIRCULATIOX    OF   THE    BLOOD.  231 

one  hand,  and  with  a  vessel  to  contain  the  serum  after  it  has  run  through  on 
the  other.  The  canula  with  heart  attaclied  is  passed  into  the  oil,  and  the 
cork  firmly  secured.  By  these  means  the  lever  will  be  found  to  be  adjusted  to 
a  convenient  elevation.  The  lever  is  allowed  to  write  on  a  moving  drum,  and 
serum  is  passed  through  at  various  temperatures.  After  a  short  time  the  heart 
may  stop  beating ;  but  two  wires  are  arranged,  the  one  in  the  canula,  the 
other  projecting  from  the  plate  in  such  a  way  that  the  heart  can  be  moved 
against  them  by  shifting  the  position  of  the  bell-jar  a  little.  The  wires  act  as 
electrodes,  and  can  be  made  to  communicate  with  an  induction  apparatus,  so 
that  single  induction  shocks  can  be  sent  into  the  heart  to  produce  contractions, 
and  if  need  be,  by  means  of  the  trigger  key,  at  one  definite  point  in  the  revo- 
lution of  the  recording  cylinder. 

Electrical  Phenomena  of  the  Heart-beat. — The  phenomena  of 
the  natural  beat  of  the  heai't  are  generally  considered  to  indicate  that 
the  systolic  coutraction  is  a  single  and  not  a  tetanic  one.  The  electrical 
changes  support  this  view.  During  the  contraction  a  distinct  electrical 
change  occurs  which  is  similar  to  that  which  happens  in  skeletal  muscle 
with  each  contraction.  It  has  been  demonstrated  that  a  stanniused 
frog  heart  undergoes  two  changes  or  phases  as  regards  its  electrical  con- 
dition, the  first  immediately  before  the  contraction,  in  which  the  excited 
part  becomes  negative  to  the  other  parts,  contraction  following  the 
wave  of  excitation,  and  the  second  during  relaxation,  in  which  the  cur- 
rent flows  in  an  opposite  way. 

The  Metabolism  of  the  Heart. — Whatever  view  may  be  taken  of 
the  nature  of  the  rhythmic  cardiac  contractions,  it  will  be  genemlly 
acknowledged  that  the  contractions  cannot  long  be  maintained  without 
a  due  supply  of  blood  or  of  a  similar  nutritive  fluid.  Some  very  re- 
markable facts  have  been  made  out  about  this,  in  the  case  of  the  frog's 
heart.  For  instance,  it  has  been  shown  that  normal  saline  solution  is 
insufficient  to  maintain  the  contractions,  and  that  in  experiments  in 
which  it  is  necessary  to  maintain  the  beats  for  any  length  of  time  failing 
serum  or  saline  solution  of  dried  blood,  the  solution  should  contain 
some  serum-albumin,  and  that  there  should  also  be  present  some  potas- 
sium chloride,  and  Dr.  Kinger  has  com];)osed  a  nutritive  fluid  which 
contains  chlorides  of  sodium,  potassium,  and  calcium  in  small  amounts, 
which  is  able  to  maintain  the  normal  beats  of  the  heart.  It  is  therefore 
very  reasonable  to  suppose  that  the  amount  and  quality  of  the  blood 
supplied  to  the  human  heart  has  the  greatest  influence  in  maintaining 
the  force  and  frequency  of  the  rhythmic  activity.  The  view  that  is 
taken  at  present  of  the  action  of  the  heart  is  one  propounded  by  Gaskell, 
viz.,  that  in  heart  muscle  as  in  protoplasm  generally,  the  metabolic  pro- 
cesses are  those  of  anabolism  or  building  up,  which  takes  place  during 
the  diastole  of  the  heart,  that  vagus  stimulation  helps  on  this  process, 
iind  of  catabolism  or  discharge,  which  is  manifested  in  the  contraction 
of  the  heart,  and  which  is  accelerated  by  stimulation  of  the  sympathetic 


232 


HANDBOOK    OF    PHYSIOLOGY. 


fibres.  That  vagus  stimulation  is  therefore  ultimately  beneficial  to  the 
contractions.  The  electrical  currents  set  up  on  the  stimulation  of  the 
vagus  and  of  the  sympathetic  are  in  opposite  directions,  and  so  if  Gas- 
kell's  contention  is  correct  that  the  negative  variation  of  the  muscle 
current  occurring  on  sympathetic  stimulation  is  a  sign  of  catabolism,  the 
result  of  vagus  stimulation,  viz.,  a  positive  variation  of  the  muscle  cur- 
rent, may  be  supposed  to  indicate  the  complementary  condition  of  ana- 
bolism. 

3.  The  Amount  of  Blood  Passing  into  the  Heart's  Cavities. — It  is  found 
that  in  the  body  at  any  rate  the  amount  of  blood  which  passes  into  the 
cavities  of  the  heart  distinctly  affects  the  strength  of  its  beat.  Thus  if 
from  any  cause  the  blood  is  diminished  the  contractions  become  much 


Fig.  200.— Plethysmograph.  By  means  of  this  apparatus,  the  alteration  in  volume  of  the  arm, 
E,  which  is  inclosed  in  a  glass  tube,  a,  filled  with  fluid,  the  opening  through  which  it  passes  being 
firmly  closed  by  a  thick  gutta-percha  band,  f,  is  communicated  to  the  lever,  d,  and  registered  by  a 
recording  apparatus.  The  fluid  in  a  communicates  with  that  in  b,  the  upper  limit  of  which  is 
above  that  in  a.  The  chief  alterations  in  volume  are  due  to  alteration  in  the  blood  contained  in  the 
arm.  When  the  volume  is  increased,  fluidpasses  out  of  the  glass  cylinder,  and  the  lever,  d,  also  is 
raised,  and  when  a  decrease  takes  place  the  fluid  returns  again  from  b  to  a.  It  will  therefore  be 
evident  that  the  apparatus  is  capable  of  recording  alterations  of  blood-pressure  in  the  arm.  Appa- 
ratus founded  upon  the  same  principle  have  been  used  for  recording  alterations  in  the  volume  of 
the  spleen  and  kidney. 


more  feeble,  although  they  may  possibly  be  increased  in  rapidity.  Simi- 
larly with 

4.  Ihe  Amount  of  Pressure  to  he  Overcome. — If  the  aortic  pressure  is 
too  low  the  muscle  contractions  of  the  heart  is  not  so  powerful  or  effec- 
tive as  if  the  pressure  is  normal,  whereas  too  great  arterial  pressure  may 
be  sufficient  to  delay  if  not  to  stop  altogether  the  heart's  beats,  dilata- 
tion of  its  cavities  taking  place  and  a  condition  of  asi/stolism  (Beau) 
resulting. 

Another  condition  sometimes  forgotten  should  be  added  as  influenc- 
ing the  potency  of  the  cardiac  contraction,  viz.,  the  heart  must  have 
sufficient  room  to  contract,  it  must  not  be  unduly  pressed  upon. 

(b.)  The  Peripheral  Resistance. — The  regulation  of  the  amount 
of  resistance  to  the  passage  of  blood  at  the  perijjhery  is  principally  done 


THE   CIRCULATION"   OF   THE    BLOOD.  233 

by  the  alteration  of  the  calibre  of  the  arterioles.  This  regulating  power 
is  chiefly  invested  in  the  nervous  system.  Its  influence  is  exerted  upon 
the  muscular  coat  of  the  arteries  and  not  upon  the  elastic  element,  which 
possesses,  as  must  be  obvious,  rather  j^hysical  than  vital  properties. 
The  muscular  tissue  in  the  walls  of  the  vessels  increases  in  amount  rel- 
atively to  the  other  coats  as  the  arteries  grow  smaller,  so  that  in  the 
arterioles  it  is  developed  out  of  all  proportion  to  the  other  elements; 
in  fact,  in  passing  from  capillary  vessels,  made  up  as  we  have  seen  of 
endothelial  cells  with  a  ground  substance,  the  first  change  which  occurs 
as  the  vessels  become  larger  (on  the  side  of  the  arteries)  is  the  appear- 
ance of  muscular  fibres.  Thus  the  nervous  system  is  more  powerful  in 
regulating  the  calibre  of  the  smaller  than  of  the  larger  arteries. 

It  was  long  ago  shown  by  Claude  Bernard  that  if  the  cervical  sym- 
pathetic nerve  is  divided  in  a  rabbit,  the  blood-vessels  of  the  correspond- 
ing side  of  the  head  and  neck  become  dilated.  This  effect  is  best  seen 
in  the  ear,  which  if  held  up  to  the  light  is  seen  to  become  redder,  and 
the  arteries  are  seen  to  become  larger.  The  whole  ear  is  distinctly 
warmer  than  the  opposite  one.  This  effect  is  produced  by  removing 
the  arteries  from  the  influence  of  the  central  nervous  system,  which  in- 
fluence normally  passes  down  the  divided  nerve;  for  if  the  peripheral 
end  of  the  divided  nerve  {i.e.,  that  farthest  from  the  brain)  be  stimulated, 
the  arteries  which  were  before  dilated  return  to  their  natural  size,  and 
the  parts  regain  their  primitive  condition.  And,  besides  this,  if  the 
stimulus  is  very  strong  or  very  long  continued,  the  point  of  normal  con- 
striction is  passed,  and  the  vessels  become  much  more  contracted  than  nor- 
mal. The  natural  condition,  which  is  about  midway  between  extreme  con- 
traction and  extreme  dilatation,  is  called  the  natural  tone  of  an  artery; 
if  this  is  not  maintained,  the  vessel  is  said  to  have  lost  tone,  or  if  it  is 
exaggerated,  the  tone  is  said  to  be  too  great.  The  effects  described  as 
having  been  produced  by  section  of  the  cervical  sympathetic  and  by 
subsequent  stimulation  are  not  peculiar  to  that  nerve,  as  it  has  been 
found  that  for  every  part  of  the  body  there  exists  a  nerve  the  division 
of  which  produces  the  same  effects,  viz.,  dilatation  of  the  vessels;  such 
may  be  cited  as  the  case  with  the  sciatic,  the  splanchnic  nerves,  and  the 
nerves  of  the  brachial  plexus:  when  these  are  divided,  dilatation  of  the 
blood-vessels  in  the  parts  supplied  by  them  takes  place.  It  appears, 
therefore,  that  nerves  exist  which  have  a  distinct  control  over  the  vas- 
cular supply  of  every  part  of  the  body.  These  nerves  are  called  vaso- 
motor; they  run  now  in  cerebro-spinal,  now  in  the  sympathetic  nerve- 
trunks. 

Vaso-motor  centres. — Experiments  by  Ludwig  and  others  show 
that  the  vaso-motor  fibres  come  primarily  from  a  nucleus  of  gray  matter, 
vaso-motor  centre,  in  the  bulb  or  medulla  oblongata,  being  situated 
in  the  floor  of  the  fourth  ventricle,  between  the  calamus  scriptorius  and 


234 


HANDBOOK    OF    PHYSIOLOGY. 


the  corfora  quadrigmnina.  Thence  the  vaso-motor  fibres  pass  down  in 
the  spinal  cord,  and  issuing  with  the  anterior  roots  of  the  spinal  nerves, 
traverse  the  various  ganglia  on  the  prae-vertebral  cord  of  the  sympathetic, 
and,  accompanied  by  branches  from  those  ganglia,  pass  to  their  des- 
tination. 

Secondary  or  subordinate  vaso-motor  centres  exist  in  the  spinal  cord, 
and  the  influence  exerted  by  the  chief  vaso-motor  centre  is  not  only  in 
constant  moderate  action,  but  may  be  altered  in  several  ways,  but  chiefly 
by  afferent  (sensory)  stimuli.  These  stimuli  may  act  in  two  ways,  either 
increasing  or  diminishing  the  usual  action  of  the  centre,  which  maintains 
a  medium  tone  of  the  arteries.  This  afferent  influence  upon  the  centre 
(augmenting  or  inhibiting)  is  well  shown  by  the  action  of  a  nerve  called 


Fie:.  201  .—Tracing  showing  the  effect  on  blood-pressure  of  stimulating  the  central  end  of  the 
Deprtssor  nerve  in  the  rabbit.  To  be  read  from  right  to  left.  T.  indicates  the  rate  at  which  the 
recording  surface  was  travelling,  the  intervals  corresjioiul  to  seconds:  C,  the  moment  of  entrance  of 
current;  O,  moment  at  which  it  was  shut  off.  Tlie  effect  is  some  time  in  developing  and  lasts  after 
the  current  has  been  taken  off.  The  larger  undulations  are  the  respiratory  nerves;  the  pulse  oscilla- 
tions are  very  small.     (Foster.) 

the  depressor,  the  existence  of  which  was  demonstrated  by  Cyon  and 
Ludwig. 

It  is  a  small  afferent  nerve  and  passes  up  from  the  heart  in  which  it 
takes  its  origin,  and  in  the  rabbit  goes  upward  in  the  sheath  of  the  su- 
perior laryngeal  briinch  of  the  vagus  or  with  that  branch  and  the  vagus 
itself,  communicating  by  filaments  with  the  inferior  cervical  ganglion 
as  it  proceeds  from  the  heart. 

If  during  a  blood-pressure  observation  in  a  rabbit  this  nerve  be  di- 
vided, and  the  central  end  {i.e.,  that  nearest  the  brain)  be  stimulated,  a 
remarkable  fall  of  blood-pressure  takes  place  (fig.  201). 

The  cause  of  the  fall  of  blood-pressure  is  found  to  proceed  from  the 
dilatation  of  the  vascular  district  within  the  abdomen  suiDplied  by  the 
splanchnic  nerves,  in  consequence  of  which  the  vessels  hold  a  much 
larger  quantity  of  blood  than  usual.  The  engorgement  of  the  splanch- 
nic area  very  greatly  diminishes  the  amount  of  blood  in  the  vessels  else- 


THE    CIRCULATIOX    OF   THE    BLOOD.  235 

where,  and  so  materially  diminishes  the  blood-pressure.  The  function 
of  the  depressor  nerve  is  presumed  to  be  that  of  conveying  to  the  vaso- 
motor centre  indications  of  such  conditions  of  the  heart  as  require  a 
diminution  of  the  tension  in  the  blood-vessels;  as,  for  example,  that  the 
heart  cannot,  with  sufficient  ease,  propel  blood  into  the  already  too  full 
or  too  tense  arteries  (p.  233). 

The  action  of  the  depressor  nerve  in  causing  an  inhibition  of  the 
vaso-motor  centre  illustrates  the  more  unusual  effect  of  afferent  impulses. 
As  a  rule,  the  stimulation  of  the  central  end  of  an  afferent  nerve  pro- 
duces a  reverse  or  pressor  effect,  and  increases  the  tonic  influence  of 
the  centre,  and  by  causing  constriction  of  the  arterioles,  either  locally  or 
generally,  raises  the  blood-pressure.  Thus  the  effect  of  stimulating  an 
afferent  nerve  may  be,  by  its  influence  on  the  vaso-motor  centre,  either 
to  dilate  or  to  constrict  the  arteries.  Stimulation  of  an  afferent  nerve 
too  may  produce  a  kind  of  paradoxical  effect,  causing  general  vascular 
constriction  and  so  general  increase  of  blood -pressure,  but  at  the  same 
time  local  dilatation  which  must  evidently  have  an  immense  influence 
in  increasing  the  flow  of  blood  through  the  part. 

The  vaso-motor  centre  may  not  only  be  reflexly  affected,  but  it  may 
also  be  affected  by  impulses  proceeding  to  it  from  the  cerebrum,  as  in 
the  case  of  hlusliing  from"  mind  disturbance,  or  of  pallor  from  sudden 
fear.  It  will  be  shown,  too,  in  the  chapter  on  Respiration  that  the  cir- 
culation of  venous  blood  may  directly  stimulate  the  centre  itself. 

Although  the  tone  of  the  arteries  is  influenced  by  the  centres  in  the 
cerebro-spinal  axis,  experiments  have  proved  that  this  is  not  the  only 
way  in  which  it  may  be  influenced.  Thus  the  dilatation  which  occurs 
after  section  of  the  cervical  sympathetic  in  the  first  experiment  cited 
above,  only  remains  for  a  short  time,  and  is  soon  followed — although  a 
portion  of  the  nerve  may  have  been  removed  entirely — by  the  vessels 
regaining  their  ordinary  calibre;  and  afterward  local  stimulation,  e.g., 
the  application  of  heat  or  cold,  will  cause  dilatation  or  constriction. 
This  is  probably  the  effect  of  the  direct  stimulation  of  the  muscle  of  the 
walls  of  the  vessels.  The  observations  upon  the  functions  of  the  vaso- 
motor nerves  themselves  appear  to  divide  them  into  four  classes:  (1) 
those  on  division  of  which  dilatation  occurs  for  some  time,  and  which 
on  stimulation  of  their  peripheral  ends  produce  constriction;  (2)  those 
on  division  of  which  momentary  dilatation  followed  by  constriction  oc- 
curs, with  dilatation  on  stimulation;  (3)  those  on  division  of  which  di- 
latation is  caused,  which  lasts  for  a  limited  time,  with  constriction  if 
stimulated  at  once,  but  dilatation  if  some  time  is  allowed  to  elapse  before 
the  stimulation  is  applied;  (4)  a  class,  division  of  which  produces  no 
effect  but  which,  on  stimulation,  cause  according  to  their  function  either 
dilatation  or  constriction.  A  good  example  of  this  fourth  class  is  afforded 
by  the  nerves  supplying  the  submaxillary  gland,  viz.,  the  chorda  tympani 


236  HANDBOOK    OF    PHYSIOLOGY. 

a,nd  the  sympathetic.  When  either  of  these  nerves  is  simply  divided, 
no  change  takes  place  in  the  vessels  of  the  gland;  but  on  stimulating 
the  chorda  tympani  the  vessels  dilate,  and,  on  the  other  hand,  when  the 
sympathetic  is  stimulated  the  vessels  contract.  The  nerves  acting  like 
the  chorda  tympani  in  this  case  are  called  vaso-dilators,  and  those 
like  the  symiwthetic  vaso-constrictors.  The  vaso-dilator  nerves  are 
believed  to  act  upon  the  bloud-vessels  just  in  the  same  way  as  the  vagus 
does  upon  the  heart,  they  are  vuso-inliibitory,  or  anabolic  nerves.  In 
the  same  way  the  vaso-constrictor  are  vaso-augmentor,  like  the  sympa- 
thetic heart  fibres,  or  in  other  words,  catabolic  nerves  to  the  blood-vessels. 
The  following  table  may  serve  as  summary  of  the  effect  of  the  altera-- 
Hon  of  the  'peripheral  resistance  upon  the  blood-pressure : — 

A.  An  increase  of  the  blood-pressure  may  be  produced: — 

(1.)  By  stimulation  of  the  vaso-motor  centre  in  the  medulla,  either 
a.   Directly,  as  by  carbonated  or  deoxygenated  blood. 
/?.  Indirectly,    by  impressions  descending  from   the   cerebrum, 

e.g.,  in  sudden  pallor. 
■y.  Reflexly,  by  stimulation  of   afferent  or  pressor  nerves  any- 
where, which  increases  the  action  of  the  centre. 
(2.)  By  stimulation  of  the  centres  in  spinal  cord. 

Possibly  directly  or  indirectly,  certainly  reflexly. 
(3.)   By  stimulation  of  each  vascular  area  directly  by  means  of  altered 
blood. 

B.  A  decrease  of  the  blood-pressure  may  be  produced  : — 

(1.)   By  stimulation  of  the  vaso-motor  centre  in  the  medulla,  either 
(a)   Directly,  as  by  oxygenated  or  aerated  blood. 
(/3)  Indirectly,     by     impressions    descending    from    the    cere- 
brum— e.g.,  in  blushing. 
(7)  Reflexly,  by  stimulation  of  the   depressor  nerve,  and  con- 
sequent dilatation  of  vessels  of  splanchnic  area,  and  pro- 
ducing inhibition  of  the  centre  by  stimulation  of  other 
sensory  nerves. 
(3.)  By  stimulation  of  the  centres  in  spinal  cord.     Possibly  directly, 

indirectly,  or  reflexly. 
(3.)  By  stimulation  of  each  vascular  area  directly,  e.g.,  by  means  of 
altered  blood,  or  by  heat. 

Besides  the  regulation  of  the  heart  beat  and  of  the  peripheral  resist- 
ance, it  must  be  recollected  that  other  circumstances  may  affect  the  blood 
pressure,  of  which  changes  in  the  blood  are  the  chief.  First  of  all — 
a.  As  regards  quantity.  At  first  sight  it  would  appear  probable  that 
one  of  the  easiest  ways  to  diminish  the  blood-pressure  would  be  to  re- 
move blood  from  the  vessels  by  bleeding.  It  has  been  found  by  experi- 
ment, however,  although  the  blood-pressure  sinks  while  large  abstractions 
of  blood  are  taking  place,  that  as  soon  as  the  bleeding  ceases  it  rises 
rapidly,  and  speedily  becomes  normal;  that  is  to  say,  unless  so  large  an 
amount  of  blood  has  been  taken  as  to  be  positively  dangerous  to  life. 


THE    CIRCULATIOX    OF   THE    BLOOD.  237 

abstraction  of  blood  has  little  effect  upon  the  blood-pressure.  The  rapid 
return  to  the  normal  pressure  is  due  not  so  much  to  the  withdrawal  of 
lymph  and  other  fluids  from  the  body  into  the  blood,  as  was  formerly 
supposed,  as  to  the  regulation  of  the  peripheral  resistance  by  the  vaso- 
motor nerves;  in  other  words,  the  small  arteries  contract,  and  in  so  do- 
ing maintain  pressure  on  the  blood  and  favor  its  accumulation  in  the 
arterial  system.  This  is  due  to  the  stimulation  of  the  vaso-motor  cen- 
tre from  diminution  of  the  supply  of  blood,  and  therefore  of  oxygen.. 
The  failure  of  the  blood-pressure  to  return  to  normal  in  the  too  great 
abstraction  must  be  taken  to  indicate  a  condition  of  exhaustion  of  the 
centre,  and  consequently  of  want  of  regulation  of  the  peripheral  resist- 
ance. In  the  same  way  it  might  be  thought  that  injection  of  blood  into 
the  already  full  vessels  would  be  at  once  followed  by  rise  in  the  blood- 
pressure,  and  this  is  indeed  the  case  up  to  a  certain  point — the  pressure 
does  rise,  but  there  is  a  limit  to  the  rise.  Until  the  amount  of  blood 
injected  equals  about  2  to  3  per  cent  of  the  body- weight,  the  pressure 
continues  to  rise  gradually;  but  if  the  amount  exceed  this  proportion, 
the  rise  does  not  continue.  In  this  case,  therefore,  as  in  the  opposite 
when  blood  is  abstracted,  the  vaso-motor  apparatus  must  counter- 
act the  great  increase  of  pressure,  but  now  by  dilating  the  small  ves- 
sels, and  so  diminishing  the  peripheral  resistance,  for  after  each  rise 
there  is  a  partial  fall  of  pressure;  and  after  the  limit  is  reached  the 
whole  of  the  injected  blood  displaces,  as  it  were,  an  equal  quantity  which 
passes  into  the  small  veins,  and  remains  within  them.  It  should  be  re- 
membered that  the  veins  are  capable  of  holding  the  whole  of  the  blood 
of  the  body. 

Further,  as  we  have  seen,  the  amount  of  blood  supplied  to  the  heart, 
both  to  its  substance  and  to  its  chambers,  has  a  marked  effect  upon  the 
blood-pressure. 

b.  As  regards  quality.  The  quality  of  the  blood  supplied  to  the 
heart  has  a  distinct  effect  upon  its  contraction,  as  too  watery  or  too 
little  oxygenated  blood  must  interfere  with  its  action.  Thus  it  appears 
that  blood  containing  certain  substances  affects  the  peripheral  resistance 
by  acting  upon  the  muscular  fibres  of  the  arterioles,  and  so  directly  alter- 
ing the  calibre  of  the  vessels. 

Proofs  of  the  Circulation  of  the  Blood. 

It  seems  hardly  necessary  at  the  present  time  to  bring  forward  the 
proofs  that  during  life  the  blood  circulates  within  the  body;  they  are 
so  well  Jcnown.  It  is  interesting,  however,  to  recount  the  main  argu- 
ments by  which  Harvey  in  the  first  instance  established  the  fact  of  the 
circulation;  they  were  as  follows: — 

1.  That  the  heart  in  half  an  hour  propels  more  blood  than  the  whole 
mass  of  blood  in  the  body; 


238  HANDBOOK    OF    PHYSIOLOGY. 

3.  That  the  blood  spurts  with  great  force  and  in  a  jerky  manner 
from  an  opened  artery,  such  as  the  carotid,  with  every  beat  of  the 
heart ; 

3.  That  if  true,  the  normal  course  of  the  circulation  would  explain 
why  after  death  the  arteries  are  commonly  found  empty  and  the  veins 
full; 

4.  That  if  the  large  veins  near  the  heart  be  tied  in  a  fish  or  snake, 
the  heart  becomes  pale,  flaccid,  and  bloodless;  and  that  on  moving  the 
ligature,  the  blood  again  flows  into  the  heart.  If  the  artery  is  tied,  the 
heart  becomes  distended,  the  distention  lasting  until  the  ligature  is 
removed ; 

5.  That  if  a  ligature  round  a  limb  be  drawn  very  tight,  no  blood  can 
enter  the  limb,  and  it  becomes  pale  and  cold.  If  the  ligature  be  some- 
what relaxed,  blood  can  enter  but  cannot  leave  the  limb;  hence  it  be- 
comes swollen  and  congested.  If  the  ligature  be  removed,  the  limb 
soon  regains  its  natural  appearance; 

6.  That  the  valves  in  the  veins  only  permit  the  blood  to  flow  toward 
the  heart; 

7.  That  there  is  general  constitutional  disturbance  resulting  from 
the  introduction  of  a  poison  at  a  single  point,  e.g.,  snake  poison; 

To  these  may  now  be  added  many  further  proofs  which  have  accu- 
mulated since  the  time  of  Harvey,  e.g. : — 

8.  That  in  wounds  of  arteries  and  veins;  in  the  former  case  hemor- 
rhage may  be  almost  stopped  by  pressure  between  the  heart  and  the 
wound,  in  the  latter  by  pressure  beyond  the  seat  of  injury; 

9.  That  the  passage  of  blood-corpuscles  from  small  arteries  through 
capillaries  into  veins  in  all  transparent  vascular  parts,  as  the  mesentery, 
tongue,  or  web  of  the  frog,  the  tail  or  gills  of  a  tadpole,  etc.,  may  actu- 
ally be  observed  under  the  microscope. 

Further,  it  is  obvious  that  the  mere  fact  of  the  existence  of  a  hollow 
muscular  organ  (the  heart)  with  valves  so  arranged  as  to  permit  the 
blood  to  pass  only  in  one  direction,  of  itself  suggests  the  course  of  the 
circulation.  The  only  part  of  the  circulation  which  Harvey  could  not 
follow  was  that  through  the  capillaries,  for  the  simple  reason  that  he 
had  no  lenses  sufficiently  powerful  to  enable  him  to  see  it.  Malpighi 
(1661)  and  Leeuwenhoek  (16C8)  demonstrated  this  in  the  tail  of  the  tad- 
pole and  lung  of  the  frog. 


CHAPTER  YII. 

RESPIRATION. 

The  maintenance  of  animal  life  necessitates  the  continual  absorption 
of  oxygen  and  excretion  of  carbonic  acid;  the  blood  being,  in  all  ani- 
mals which  possess  a  well-developed  blood-vascular  system,  the  medium 
by  which  these  gases  are  carried.  By  the  blood,  oxygen  is  absorbed 
from  without  and  conveyed  to  all  parts  of  the  organism;  and,  by  the 
blood,  carbonic  acid,  which  comes  from  within,  is  carried  to  those  parts 
bv  which  it  may  escape  from  the  body.  The  two  processes, — absorption 
of  oxygen  and  excretion  of  carbonic  acid,  are  complementary,  and  their 
sum  is  termed  the  process  of  Respiration. 

In  all  Vertebrata,  and  in  a  large  number  of  Invertebrata,  certain  parts, 
either  lungs  or  gills,  qxq  specially  constructed  for  bringing  the  blood 
into  proximity  with  the  aerating  medium  (atmospheric  air,  or  water  con- 
taining air  in  solution).  In  some  of  the  lower  Vertebrata  (frogs  and 
other  naked  Amphibia)  the  skin  is  important  as  a  respiratory  organ, 
and  is  capable  of  supplementing,  to  some  extent,  the  functions  of  the 
proper  breathing  apparatus;  but  in  all  the  higher  animals,  including 
man,  the  respiratory  capacity  of  the  skin  is  so  infinitesimal  that  it  may 
be  practically  disregarded. 

Essentially  a  lung  or  gill  is  constructed  of  a  fine  transparent  mem- 
brane, one  surface  of  which  is  exposed  to  the  air  or  water,  as  the  case 
may  be,  while,  on  the  other,  is  a  network  of  blood-vessels, — the  only  sep- 
aration between  the  blood  and  aerating  medium  being  the  thin  wall  of 
the  blood-vessels,  and  the  fine  membrane  on  one  side  of  which  vessels 
are  distributed.  The  difference  between  the  simplest  and  the  most 
complicated  respiratory  membrane  is  one  of  degree  only. 

The  various  complexity  of  the  respiratory  membrane,  and  the  kind 
of  aerating  medium,  are  not,  however,  the  only  conditions  which  cause 
a  difference  in  the  respiratory  capacity  of  different  animals.  The  num- 
ber and  size  of  the  red  blood-corpuscles,  the  mechanism  of  the  breathing 
apparatus,  the  presence  or  absence  of  a  pulmonary  heart,  physiologically 
distinct  from  the  systemic,  are,  all  of  them,  conditions  scarcely  second 
in  importance. 

It  may  be  as  well  to  state  here  that  the  lungs  are  only  the  medium 
for  the  exchange,  on  the  part  of  the  blood,  of  carbonic  acid  for  oxygen. 
They  are  not  the  seat,  in  any  special  manner,  of  those  combustion-pro- 

289 


240 


HAXDBOOK    OF    PHYSIOLOGY. 


cesses  of  which  the  production  of  carbonic  acid  is  the  final  result. 
These  processes  occur  in  all  parts  of  the  body  in  the  substance  of  the 
tissues. 

Of  the  Respiratory   Apparatus. 

The  object  of  respiration  being  the  interchange  of  gases  in  the  lungs, 
it  is  necessary  that  the  atmospheric  air  shall  pass  into  them  and  that 
the  changed  air  should  be  expelled  from  them.  The  lungs  are  contained 
in  the  chest  or  thorax,  which  is  a  closed  cavity  having  no  communica- 


Fig.  202. 


Fig.  203. 


Fig.  203.— Outline  showing  the  general  form  of  the  larj-nx,  trachea,  and  bronchi,  as  seen  from 
before,  h,  Tlie  great  cornu  of  the  hyoid  bone;  e,  epiglottis;  t,  superior,  and  t',  inferior  coruu  of  tl.e 
thyroid  cartilage;  c.  middle  of  the  cricoid  cartilage  ;  tr,  the  trachea,  sliowing  sixteen  cartilaginous 
rings;  b,  the  right,  and  b',  the  left  bronchus.     (Allen  Thomson.)     x  i4- 

Fig.  203. — Outline  showing  the  general  form  of  the  larynx,  trachea,  and  bronchi,  as  seen  from 
behind,  h,  Gi-eat  cornu  of  the  hyoid  bone;  f,  superior,  and  t'.  the  inferior  cornu  of  the  thyroid 
cartilage;  e,  epiglottis;  a,  points  to  the  back  of  both  the  arytenoid  cartilages,  which  are  sur- 
mounted by  the  cornicula  ;  c,  the  middle  ridge  on  the  back  of  the  cricoid  cartilage;  tr,  the  pos- 
terior membranous  part  of  the  trachea;  6,  6',  right  and  left  bronchi.    (Allen  Thomson.^     x  i^. 


RESPIRATION.  241 

tion  with  the  outside,  except  by  means  of  the  respiratory  passages.  The 
air  enters  these  passages  through  the  nostrils  or  through  the  mouth, 
thence  it  passes  through  tlie  hirynx  into  the  trachea  or  windpipe,  which 
about  the  middle  of  the  chest  divides  into  two  tubes,  bronchi,  one  to 
each  (right  and  left)  lung. 

The  Larynx  is  the  upper  part  of  the  passage  which  leads  exclusively 
to  the  lung;  it  is  formed  by  the  thyroid,  cricoid,  and  arytenoid  cartilages 
(fig.  202),  and  contains  the  vocal  cords,  by  the  vibration  of  which  the 
voice  is  chiefly  produced.  These  vocal  cords  are  ligamentous  bands 
attached  to  certain  cartilages  capable  of  movement  by  muscles.  By 
their  approximation  the  cords  can  entirely  close  the  entrance  into  the 
larynx;  but  under  ordinary  conditions,  the  entrance  of  the  larynx  is 
formed  by  a  more  or  less  triangular  chink  between  them,  called  the 
rima  glottidis.  Projecting  at  an  acute  angle  between  the  base  of  the 
tongue  and  the  larynx,  to  which  it  is  attached,  is  a  leaf-shaped  cartilage, 
with  its  larger  extremity  free,  called  the  ejnglottis  (fig.  203,  e).  The 
whole  of  the  larynx  is  lined  by  mucous  membrane,  which,  however,  is 
extremely  thin  over  the  vocal  cords.  At  its  lower  extremity  the  larynx 
joins  the  trachea.*  With  the  exception  of  the  epiglottis  and  the  so- 
called  cornicnla  laryngis,  the  cartilages  of  the  larynx  are  of  the  hyalin 
variety. 

The  Epiglottis. — The  supporting  cartilage  of  the  ejjiglottis  is  com- 
posed of  yellow  elastic  cartilage,  inclosed  in  a  fibrous  sheath  (perichon- 
drium), and  covered  on  both  sides  with  mucous  membrane.  The  ante- 
rior surface,  which  looks  toward  the  back  of  the  tongue,  is  covered  with 
mucous  membrane,  the  basis  of  which  is  fibrous  tissue,  elevated  toward 
both  surfaces  in  the  form  of  rudimentary  papillfe,  and  covered  with 
several  layers  of  squamous  epithelium.  In  it  ramify  capillary  blood- 
vessels, and  in  its  meshes  are  a  large  number  of  lymphatic  channels. 
Under  the  mucous  membrane,  in  the  less  dense  fibrous  tissue  of  which 
it  is  composed,  is  a  number  of  tubular  glands.  The  posterior  or  laryn- 
geal surface  of  the  epiglottis  is  covered  by  a  mucous  membrane,  similar 
in  structure  to  that  on  the  other  surface,  but  its  epithelial  coat  is  thin- 
ner, the  number  of  strata  of  cells  is  less,  and  the  papillae  few  and  less 
distinct.  The  fibrous  tissue  which  constitutes  the  mucous  membrane  is 
in  great  j^art  of  the  adenoid  variety,  and  is  here  and  there  collected  into 
distinct  masses  or  follicles.  The  glands  of  the  posterior  surface  are 
smaller  but  more  numerous  than  those  of  the  other  surface.  In  many 
places  the  glands  which  are  situated  nearest  to  the  perichondrium  are 
directly  continuous  through  apertures  in  the  cartilage  with  those  on  the 
other  side,  and  often  the  ducts  of  the  glands  from  one  side  of  the  carti- 

*  A  detailed  account  of  the  structure  and  function  of  the  Larynx  will  be 
found  ill  a  later  chapter. 
i6 


242  HANDBOOK    OF    PHYSIOLOGY. 

lage  pass  tnrough  and  open  upon  the  mucous  surface  of  the  other  side. 
Taste  goblets  have  been  found  in  the  epithelium  of  the  posterior  surface 
of  the  epiglottis,  and  in  several  other  situations  in  the  laryngeal  mucous 
membrane. 

The  Trachea  and  Bronchi. — The  trachea  extends  from  the  cricoid 
cartilage,  which  is  on  a  level  with  the  fifth  cervical  vertebra,  to  a  point 
opposite  the  third  dorsal  vertebra,  where  it  divides  into  the  two  bronchi. 


^-^7  3^'< 


Fig  204.— Section  of  the  trachea,  o,  Columnar  ciliated  epithelium;  h  and  c,  proper  structure  of 
the  mucous  membrane,  containing  elastic  fibres  cut  across  transversely;  d,  submucuous  tissue 
containing  mucous  glands,  e,  separated  from  the  hyaline  cartilage,  g,  by  a  fine  fibrous  tissue,  /;  /i, 
external  investment  of  fine  fibrous  tissue.    (S.  K.  Alcock . ) 

one  for  each  lung  (fig.  203).  It  measures,  on  an  average,  four  or  four- 
and-a-half  inches  in  length,  and  from  three-quarters  of  an  inch  to  an 
inch  in  diameter,  and  is  essentially  a  tube  of  fibro-elastic  membrane, 
within  the  layers  of  which  are  enclosed  a  series  of  cartilaginous  rings, 
from  sixteen  to  twenty  in  number.  These  rings  extend  only  around 
the  front  and  sides  of  the  trachea  (about  two-thirds  of  its  circumfer- 
ence), and  are  deficient  behind;  the  interval  between  their  posterior 
extremities  being  bridged  over  by  a  continuation  of  the  fibrous  mem- 


KESPIRATION".  243 

brane  in  which  they  are  closed  (fig.  204).  The  cartilages  of  the  trachea 
and  bronchial  tubes  are  of  the  hyaline  variety. 

Immediately  within  this  tube,  at  the  back,  is  a  layer  of  unstriped 
muscular  fibres,  which  extends,  transversely,  between  the  ends  of  the 
cartilaginous  rings  to  which  they  are  attached,  and  opposite  the  inter- 
vals between  them,  also;  their  evident  function  being  to  diminish,  when 
required,  the  calibre  of  the  trachea  by  approximating  the  ends  of  the 
cartilages.  Outside  there  are  a  few  longitudinal  bundles  of  muscular 
tissue,  which,  like  the  preceding,  are  attached  both  to  the  fibrous  and 
cartilaginous  framework. 

The  mucous  membrane  consists  to  a  great  extent  of  adenoid  tissue, 
separated  from  the  stratified  columnar  epithelium  which  lines  it  by  a 
homogeneous  basement  membrane.  This  is  penetrated  here  and  there 
by  channels  which  connect  the  adenoid  tissue  of  the  mucosa  with  the 
intercellular  substance  of  the  epithelium.  The  stratified  columnar 
epithelium  is  formed  of  several  layers,  of  which  the  most  superficial  layer 
is  ciliated,  and  is  often  branched  downward  to  join  connective  tissue 
corpuscles;  while  between  these  branched  cells  are  smaller  elongated 
cells  prolonged  up  toward  the  surface  and  down  to  the  basement  mem- 
brane. Beneath  these  are  one  or  more  layers  of  more  irregularly-shaped 
cells.  Many  of  the  superficial  cells  are  of  the  goblet  variety.  In  the 
deeper  part  of  the  mucosa  are  many  elastic  fibres  between  which  lie 
connective-tissue  corpuscles  and  capillary  blood-vessels. 

Numerous  mucous  glands  are  situated  on  the  exterior  and  in  the 
substance  of  the  fibrous  framework  of  the  trachea;  their  ducts  perforat- 
ing the  various  structures  which  form  the  wall  of  the  trachea,  and  open- 
ing through  the  mucous  membrane  into  the  interior. 

The  two  bronchi  into  which  the  trachea  divides,  of  which  the  right 
is  shorter,  broader,  and  more  horizontal  than  the  left  (fig.  202),  resem- 
ble the  trachea  exactly  in  structure,  with  the  difference  that  in  them 
there  is  a  distinct  layer  of  unstriped  muscle  arranged  circularly  beneath 
the  mucous  membrane,  forming  the  mnscularis  mucosm.  On  entering 
the  substance  of  the  lungs  the  cartilaginous  rings,  although  they  still 
form  only  larger  or  smaller  segments  of  a  circle,  are  no  longer  confined 
to  the  front  and  sides  of  the  tubes,  but  are  distributed  impartially  to  all 
parts  of  their  circumference. 

The  bronchi  divide  and  subdivide,  in  the  substance  of  the  lungs, 
into  a  number  of  smaller  and  smaller  branches,  which  penetrate  into 
every  part  of  the  organ,  until  at  length  they  end  in  the  smaller  sub- 
divisions of  the  lungs,  called  lobvles. 

All  the  lai-ger  branches  have  walls  formed  of  tough  membrane,  con- 
taining portions  of  cartilaginous  rings,  by  which  they  are  held  open,  and 
unstriped  muscular  fibres,  as  well  as  longitudinal  bundles  of  elastic  tis- 
sue.    They  are  lined  by  mucous  membrane,  the  surface  of  which,  like 


244  HANDBOOK    OF    PHYSIOLOGY. 

that  of  the  larynx  and  trachea,  is  covered  with  ciliated  epithelium,  but 
the  several  layers  become  less  and  less  distinct  until  the  lining  consists 
of  a  single  layer  of  more  or  less  cubical  cells  covered  with  cilia  (fig.  205). 
The  mucous  membrane  is  abundantly  provided  with  mucous  glands. 

As  the  bronchi  become  smaller  and  smaller,  and  their  walls  tliinner, 
the  cartilaginous  rings  become  scarcer  and  more  irregular,  until,  in  the 
smaller  bronchial  tubes,  they  are  represented  only  by  minute  and  scat- 
tered cartilaginous  flakes.  And  when  the  bronchi,  by  successive  branches 
are  reduced  to  about  j^  of  an  inch  (.6  mm.)  in  diameter,  they  lose  their 
cartilaginous  element  altogether,  and  their  walls  are  formed  only  of  a 
tough  fibrous  elastic  membrane,  with  circular  muscular  fibres;  they  are 
still  lined,  however,  by  a  thin  mucous  membrane,  with  ciliated  epithe- 
lium, the  length  of  the  cells  bearing  the  cilia  having  become  so  far 
diminished  that  the  cells  are  now  almost  cubical.     In  the  smaller  bron- 


<5^o  ^i 


Fig.  205.— Transverse  section  of  a  bronchus,  about  i^  inch  in  diameter,  e.  Epithelium  (ciliated) ; 
immediately  beneath  it  is  the  mucous  membrane  or  internal  fibrous  layer,  of  varying:  thickness:  m, 
muscular  layer  ;  s.  m,  submucous  tissue;  /,  fibrous  tissue  ;  c,  cartilage  enclosed  within  the  layers 
of  fibrous  tissue  ;  g,  mucous  gland.     (F.  E.  Schulze.) 

chi  the  circular  muscular  fibres  are  relatively  more  abundant  than  in 
the  larger  bronchi,  and  form  a  distinct  circular  coat. 

The  Lungs  and  PlenrcB. — The  Lungs  occupy  the  greater  portion  of 
the  thorax.  They  are  of  a  spongy  elastic  texture,  and  on  section  appear 
to  the  naked  eye  as  if  they  were  in  great  part  solid  organs,  except  here 
and  there,  at  certain  points,  where  branches  of  the  bronchi  or  air-tubes 
may  have  been  cut  across,  and  show,  on  the  surface  of  the  section,  their 
tubular  structure.  In  fact,  however,  the  lungs  are  hollow  organs,  each 
of  which  communicates  by  a  separate  orifice  with  a  common  air-tube, 
the  trachea. 

Each  lung  is  enveloped  by  a  serous  membrane — the  pleura,  one  layer 
of  which  adheres  closely  to  its  surface,  and  provides  it  with  its  smooth 
and  slippery  covering,  while  the  other  adheres  to  the  inner  surface  of 
the  chest-wall.  The  continuity  of  the  two  layers,  which  form  a  closed 
sac,  as  in  the  case  of  other  serous  membranes,  will  be  best  understood 
by  reference  to  fig.  206.     The  appearance  of  a  space,  however,  between 


RESPIEATION". 


245 


the  pleura  which  covers  the  king  {visceral  layer),  and  that  which  lines 
the  inner  surface  of  the  chest  ( parietal  layer),  is  inserted  in  the  draw- 
ing only  for  the  sake  of  distinctness.  These  layers  are,  in  health,  every- 
wJiere  in  contact,  one  with  the  other;  and  between  them  is  only  just  so 
much  fluid  as  will  insure  gliding  easily,  in  their  expansion  and  contrac- 
tion, on  the  inner  surface  of  the  parietal  layer,  which  lines  the  chest- 
wall.  While  considering  the  subject  of  normal  respiration,  we  may 
discard  altogether  the  notion  of  the  existence  of  any  space  or  cavity 
between  the  lungs  and  the  wall  of  the  chest. 

If,  however,  an  opening  be  made  so  as  to  permit  air  or  fluid  to  enter 
the  pleural  sac,  the  lung,  in  virtue  of  its  elasticity,  recoils,  and  a  consid- 
erable space  is  left  between  it  and  the  chest-wall.  In  other  words,  the 
natural  elasticity  of  the  lungs  would  cause  them  at  all  times  to  contract 


Fig.  206.— Transverse  section  of  the  chest. 


away  from  the  ribs  were  it  not  that  the  contraction  is  resisted  by  atmos- 
pheric pressure  which  bears  only  on  the  inner  surface  of  the  air-tubes 
and  air-cells.  On  the  admission  of  air  into  the  pleural  sac,  atmospheric 
pressure  bears  alike  on  the  inner  and  outer  surfaces  of  the  lung,  and 
their  elastic  recoil  is  thus  no  longer  prevented. 

The  pulmonary  pleura  consists  of  an  outer  or  denser  layer  and  an 
inner  looser  tissue.  The  former  or  pleura  proper  consists  of  dense 
fibrous  tissue  with  elastic  fibres,  covered  by  endothelium,  the  cells  of 
which  are  large,  flat,  hyaline,  and  transparent  when  the  lung  is  ex- 
panded, but  become  smaller,  thicker,  and  granular  when  the  lung  col- 
lapses. In  the  pleura  is  a  lymph-canalicular  system;  and  connective 
tissue  corpuscles  are  found  in  the  fibrous  tissue  which  forms  its  ground- 
work. The  inner,  looser,  or  sub-pleural  tissue  contains  lamellae  of  fibrous 
connective  tissue  and  connective-tissue  corpuscles  between  them.  Nu- 
merous lymphatics  are  to  be  met  with,  which  form  a  dense  plexus  of 
vessels,  many  of  which  contain  valves.     They  are  simple  endothelial 


246 


HANDBOOK    OF    PHYSIOLOGY. 


tubes,  and  take  origin  in  the  lymph-canalicular  system  of  the  pleura, 
proper.  Scattered  bundles  of  unstriped  muscular  fibre  occur  in  the 
pulmonary  pleura.  They  are  especially  strongly  developed  on  the  an- 
terior and  internal  surfaces  of  the  lungs,  the  parts  which  move  most 


Fig.  207.— Ciliary  epithelium  of  the  human  trachea,  a.  Layer  of  longitudinally  arranged  elastic 
fibres  ;  b,  basement  membrane  ;  c,  deepest  cells,  circular  in  form  ;  d,  intermediate  elongated  cells  ; 
e,  outermost  layer  of  cells  fully  developed  and  bearing  cilia.     X  350.    (Kolliker.) 

freely  in  respiration :  their  function  is  doubtless  to  aid  in  expiration. 
The  structure  of  the  parietal  portion  of  the  pleura  is  very  similar  to 
that  of  the  visceral  layer. 

Each  lung  is  partially  subdivided  into  separate  portions  called  lobes; 
the  right  lung  into  three  lobes,  and  the  left  into  two.  Each  of  these 
lobes,  again,  is  composed  of  a  large  number  of  minute  parts,  called  lob- 


Fig.  208. 


i-  ig.  209. 


Fig.  208.— Terminal  orauch  of  a  bronchial  tube,  with  its  infundibula  and  air-cells,  from  the  mar- 
gin of  the  lung  of  a  monkey,  in jected  with  quicksilver,  a.  Terminal  bronchial  twig;  bb,  infundibula 
and  air-cells.     X  10.    (F.  E.  Schulze.) 

Fig.  209.— Two  small  infundibula  or  groups  of  air-cells,  a  o,  with  air-cells,  b  b.  and  the  ultimate 
bronchial  tubes,  c  c,  with  which  the  air-cells  communicate.    From  a  new-born  child.     (Kolliker.) 

ules.  Each  pulmonary  lobule  may  be  considered  to  be  a  lung  in  minia- 
ture, consisting,  as  it  does,  of  a  branch  of  the  bronchial  tube,  of  air-cells, 
blood-vessels,  nerves,  and  lymphatics,  with  a  sparing  amount  of  areolar 
tissue. 


RESPIRATIOTvT. 


247 


On  entering  a  lobule,  the  small  bronchial  tube,  the  structure  of 
which  has  been  just  described  {a,  fig.  208),  divides  and  subdivides;  its 
walls  at  the  same  time  becoming  thinner  and  thinner,  until  at  length 
they  are  formed  only  of  a  thin  membrane  of  areolar  and  elastic  tissue, 
lined  by  a  layer  of  squamous  epithelium,  not  provided  with  cilia.  At 
the  same  time,  they  are  altered  in  shape;  each  of  the  minute  terminal 
branches  widening  out  funnel-wise,  and  its  walls  being  pouched  out 
irregularly  into  small  saccular  dilatations,  called  air-cells  (fig.  208,  b). 
Such  a  funnel-shaped  terminal  branch  of  the  bronchial  tube,  with  its 


Fig.  210. — From  a  section  of  the  lung  of  a  cat  stained  with  sih  c  i  mti  ite  A.  D  Alveolar  duct  or 
intercellular  passage.  S.  Alveolar  septa.  N.  Alveoli  oi  air-celk  lined  w  ith  laige  flat  nucleated  cells, 
with  some  smaller  polyhedral  nucleated  cells.  M.  Unstriped  musculai  fibres.  L  ii  cidar  muscular 
fibres  are  seen  surrounding  the  interior  of  the  alveolar  duct,  and  at  one  part  is  seen  a  group  of  small 
polyhedral  cells  continued  from  the  bronchus.     (Klein  and  Noble  Smith.) 


group  of  pouches  or  air-cells,  has  been  called  an  infundihulum  (figs.  208, 
209),  and  the  irregular  oblong  space  in  its  centre,  with  which  the  air- 
cells  communicate,  an  intercellular  passage. 

The  air-cells,  or  air-vesicles,  may  be  placed  singly,  like  recesses  from 
the  intercellular  passage,  but  more  often  they  are  arranged  in  groups  or 
even  in  rows,  like  minute  sacculated  tubes;  so  that  a  short  series  of  ves- 
icles, all  communicating  with  one  another,  open  by  a  common  orifice 
into  the  tube.  The  vesicles  are  of  various  forms,  according  to  the 
mutual  pressure  to  which  they  are  subject;  their  walls  are  nearly  in 
contact,  and  they  vary  from  -^  to  ^^y  of  an  inch  (.5  to  .3  mm.)  in  diam- 
eter.    Their  walls  are  formed  of  fine  membrane,  similar  to  that  of  the 


248 


HANDBOOK    OF    PIIYSTOLOOY. 


intercellular  passages,  and  continuous  with  it,  which  membrane  is  folded 
on  itself  so  as  to  form  a  sharp-edged  border  at  each  circular  orifice  of 
communication  between  contiguous  air-vesicles,  or  between  the  vesicles 
and  the  bronchial  passages.  ISiumerous  fibres  of  elastic  tissue  are  spread 
out  between  contiguous  air-cells,  and  many  of  these  are  attached  to  the 
outer  surface  of  the  fine  membrane  of  which  each  cell  is  composed,  im- 
parting to  it  additional  strength,  and  the  power  of  recoil  after  disten- 
tion. The  cells  are  lined  by  a  layer  of  epithelium  (fig.  210),  not  pro- 
vided with  cilia.  Outside  the  cells,  a  network  of  pulmonary  capillaries 
is  spread  out  so  densely  (fig.  311)  that  the  interspaces  or  meshes  are 
even  narrower  than  the  vessels,  which  are,  on  an  average,  -joVo  ^^  ^^ 
inch  (8//)  in  diameter.  Between  the  atmospheric  air  in  the  cells  and 
the  blood  in  these  vessela,  nothing  intervenes  but  the  thin  walls  of  the 


Fig.  211.— Capillary  network  of  the  pulmonary  blood-vessels  in  the  human  lung.  X  60,  (Kolliker.) 

cells  and  capillaries;  and  the  exposure  of  the  blood  to  the  air  is  the 
more  complete,  because  the  folds  of  membrane  between  contiguous 
cells,  and  often  the  spaces  between  the  walls  of  the  same,  contain  only  a 
single  layer  of  capillaries,  both  sides  of  which  are  thus  at  once  exposed 
to  the  air. 

The  air-vesicles  situated  nearest  to  the  centre  of  the  lung  are  smaller 
and  their  networks  of  capillaries  are  closer  than  those  nearer  to  the  cir- 
cumference. The  vesicles  of  adjacent  lobules  do  not  communicate;  and 
those  of  the  same  lobule  or  proceeding  from  the  same  intercellular  pas- 
sage, do  so  as  a  general  rule  only  near  angles  of  bifurcation;  so  that, 
when  any  bronchial  tube  is  closed  or  obstructed,  the  supply  of  air  is  lost 
for  all  the  cells  opening  into  it  or  its  branches. 

Blood-siqJijJy. — The  lungs  receive  blood  from  two  sources,  {a)  the 
pulmonary  artery,  [h]  the  bronchial  arteries.  The  former  conveys  venous 
blood  to  the  lungs  for  its  arterialization,  and  this  blood  takes  no  share 


RESPIRATION".  249 

in  the  nutrition  of  the  pulmonary  tissues  througli  which  it  passes,  (b) 
The  branches  of  the  bronchial  arteries  ramify  for  nutrition's  sake  in  the 
walls  of  the  bronchi,  of  the  larger  pulmonary  vessels,  in  tlie  interlobular 
connective  tissue,  etc. ;  the  blood  of  the  bronchial  vessels  being  returned 
chiefly  through  the  bronchial  and  partly  through  the  pulmonary  veins. 

Lymphatics. — The  lymphatics  are  arranged  in  three  sets: — 1.  Irreg- 
ular lacuna  in  the  walls  of  the  alveoli  or  air-cells.  The  lymphatic 
vessels  which  lead  from  these  accompany  the  pulmonary  vessels  toward 
the  root  of  the  lung.  2.  Irregular  anastomosing  spaces  in  the  walls  of 
the  bronchi.  3.  Lymph-spaces  in  the  pulmonary  pleura.  The  lym- 
phatic vessels  from  all  these  irregular  sinuses  pass  in  toward  the  root 
of  the  lung  to  reach  the  bronchial  glands. 

Nerves. — The  nerves  of  the  lung  are  to  be  traced  from  the  anterior 
and  posterior  pulmonary  plexuses,  which  are  formed  by  branches  of  the 
vagus  and  sympathetic.  The  nerves  follow  the  course  of  the  vessels  and 
bronchi,  and  in  the  walls  of  the  latter  many  small  ganglia  are  situated. 

The  Respiratory  Mechanism. 

Eespiration  consists  of  the  alternate  expansion  and  contraction  of 
the  thorax,  by  means  of  which  air  is  drawn  into  or  expelled  from  the 
lungs.     These  acts  are  called  Inspiration  and  Expiration  respectively. 

For  the  inspiration  of  air  into  the  lungs  it  is  evident  that  all  that  is 
necessary  is  such  a  movement  of  the  side- walls  or  floor  of  the  chest,  or 
of  both,  that  the  capacity  of  the  interior  shall  be  enlarged.  By  such 
increase  of  capacity  there  will  be  of  course  a  diminution  of  the  pressure 
of  the  air  in  the  lungs,  and  a  fresh  quantity  will  enter  through  the 
larynx  and  trachea  to  equalize  the  pressure  on  the  inside  and  outside 
of  the  chest. 

For  the  expiration  of  air,  on  the  other  hand,  it  is  also  evident  that, 
by  an  opposite  movement  which  shall  diminish  the  capacity  of  the  chest, 
the  pressure  in  the  interior  will  be  increased,  and  air  will  be  expelled, 
until  the  pressure  within  and  without  the  chest  are  again  equal.  In  both 
cases  the  air  passes  through  the  trachea  and  larynx,  whether  in  entering 
or  leaving  the  lungs,  there  being  no  other  communication  with  the  ex- 
terior of  the  body;  and  the  lung,  for  the  same  reason,  remains  under  all 
the  circumstances  described  closely  in  contact  with  the  walls  and  floor 
of  the  chest.  To  speak  of  expansion  of  the  chest,  is  to  speak  also  of  ex- 
pansion of  the  lung. 

We  have  now  to  consider  the  means  by  which  the  respiratory  move- 
ments are  effected. 

Inspiration. — The  enlargement  of  the  cnest  in  inspiration  is  a 
muscular  act;  the  effect  of  the  action  of  the  inspiratory  muscles  being 
an  increase  in  the  size  of  the  chest-cavity  {a)  in  the  vertical,  and   {b) 


250 


HANDBOOK    OF    PHYSIOLOGY. 


in  the  lateral  and  antero-posterior  diameters.  The  muscles  engaged  in 
ordinary  inspiration  are  the  diaphragm;  the  external  intercostals;  parts 
of  the  internal  intercostals;  the  levatores  costarum;  and  serratus  pos- 
ticus superior. 

(a.)  The  vertical  diameter  of  the  chest  is  increased  by  the  contraction 
and  consequent  descent  of  the  diaphragm — the  sides  of  the  muscle  de- 
scending most,  and  the  central  tendon  remaining  comparatively  unmoved 
while  the  intercostal  and  other  muscles,  by  acting  at  the  same  time,  pre- 
vent the  diaphragm,  during  its  contraction,  from  drawing  in  the  sides 
of  the  chest. 

(i.)  The  increase  in  the  lateral  and  antero-posterior  diameters  of  the= 


Fig.  212 —Diagram  of  axes  of  movement  of  ribs. 

chest  is  effected  by  the  raising  of  the  ribs,  the  greater  number  of  which 
are  attached  very  obliquely  to  the  spine  and  sternum. 

The  elevation  of  the  ribs  takes  place  both  in  front  and  at  the  sides 
— the  hinder  ends  being  prevented  from  performing  any  upward  move- 
ment by  their  attachment  to  the  spine.  The  movement  of  the  front 
extremities  of  the  ribs  is  of  necessity  accompanied  by  an  upward  and 
forward  movement  of  the  sternum  to  which  they  are  attached,  the  move- 
ment being  greater  at  the  lower  end  than  at  the  upper  end  of  the  latter 
bone. 

The  axes  of  rotation  in  these  movements  are  two;  one  corresponding 
with  a  line  drawn  through  the  two  articulations  which  the  rib  forms 
with  the  spine  {a,  b,  fig.  212) ;  and  the  other  with  a  line  drawn  from  one 
of  these  (head  of  rib)  to  the  sternum  (A  B,  fig.  212);  the  motion  of  the 
rib  around  the  latter  axis  being  somewhat  after  the  fashion  of  raising 
the  handle  of  a  bucket. 


RESPIRATION.  251 

The  elevation  of  the  ribs  is  accompauied  by  a  slight  opening  out  of 
the  angle  which  the  bony  part  forms  with  its  cartilage  (fig.  213,  A); 
and  thus  an  additional  means  is  provided  for  increasing  the  antero- 
posterior diameter  of  the  chest. 

The  muscles  by  which  the  ribs  are  raised,  in  ordinary  quiet  inspira- 
tion, are  external  intercostals,  and  that  portion  of  the  internal  intercostals 
which  is  situate  between  the  costal  cartilages;  and  these  are  assisted 
by  the  levator es  costarum,  and  the  serratus  postic7ts  superior.  The  ac- 
tion of  the  levatores  and  the  serratus  is  very  simple.  Their  fibres,  aris- 
ing from  the  spine  as  a  fixed  point,  pass  obliquely  downward  and  for- 
ward to  the  ribs,  and  necessarily  raise  the  latter  when  they  contract. 
The  action  of  the  intercostal  muscles  is  not  quite  so  simple,  inasmuch 
as,  passing  merely  from  rib  to  rib,  they  seem  at  first  sight  to  have  no 


Fig.  213. — Diagram  of  movement  of  a  rib  in  inspiration. 

fixed  point  toward  which  they  can  pull  the  bones  to  which  they  are 
attached. 

In  tranquil  breathing,  the  expansive  movements  of  the  lower  part  of 
the  chest  are  greater  than  those  of  the  upper.  In  forced  inspiration, 
on  the  other  hand,  the  greatest  extent  of  movement  appears  to  be  in 
the  upper  antero-posterior  diameter. 

In  extraordinary  or  forced  inspiration,  as  in  violent  exercise,  or  in 
cases  in  which  there  is  some  interference  with  the  due  entrance  of  air 
into  the  chest,  and  in  which,  therefore,  strong  efforts  are  necessary,  other 
muscles  than  those  just  enumerated,  are  pressed  into  the  service.  It  is 
very  difficult  or  impossible  to  separate  by  a  hard  and  fast  line  the  so- 
called  muscles  of  ordinary  from  those  of  extraorditiary  ms^imtiow,  but 
there  is  no  doubt  that  the  following  are  but  little  used  as  respiratory 
agents,  except  in  cases  in  which  unusual  efforts  are  required — the  scaleni 
muscles,  the  sternomastoid,  the  serratus  magnus,  the  pector ales,  and  the 
trapezius. 


252  HAISTDBOOK    OF    PHYSIOLOGY. 

The  expansion  of  the  chest  in  inspiration  presents  some  peculiarities 
in  different  persons.  In  young  children,  it  is  effected  chiefly  by  the 
diaphragm,  which  being  highly  arched  in  expiration,  becomes  flatter  as 
it  contracts,  and,  descending,  presses  on  the  abdominal  viscera,  and 
pushes  forward  the  front  walls  of  the  abdomen.  The  movement  of  the 
abdominal  walls  being  here  more  manifest  than  that  of  any  other  part, 
it  is  usual  to  call  this  the  ahdormnal  type  of  respiration.  In  men,  to- 
gether with  the  descent  of  the  diaphragm,  and  the  jmshing  forward  of 
the  front  wall  of  the  abdomen,  the  chest  and  the  sternum  are  subject  to 
a  wide  movement  in  inspiration  {i)iferior  costal  type).  In  women,  the 
movement  appears  less  extensive  in  the  lower,  and  more  so  in  the  upper, 
part  of  the  chest  {superioi'  costal  type). 

Expiration. — From  the  enlargement  produced  in  inspiration,  the 
chest  and  lungs  return  in  ordinary  tranquil  exj^iration,  by  their  elastic- 
ity; the  force  employed  by  the  inspiratory  muscles  in  distending  the 
chest  and  overcoming  the  elastic  resistance  of  the  lungs  and  chest-walls, 
being  returned  as  an  expiratory  effort  when  the  muscles  are  relaxed. 
This  elastic  recoil  of  the  chest  and  lungs  is  sufficient,  in  ordinary  quiet 
breathing,  to  expel  air  from  the  lungs  in  the  intervals  of  inspiration, 
and  no  muscular  power  is  required.  In  all  voluntary  expiratory  efforts, 
however,  as  in  speaking,  singing,  blowing,  and  the  like,  and  in  many  in- 
voluntary actions  also,  as  sneezing,  coughing,  etc.,  something  more  than 
merely  passive  elastic  power  is  necessary,  and  the  proper  expiratory 
muscles  are  brought  into  action.  By  far  the  chief  of  these  are  the  ab- 
dominal muscles,  which,  by  pressing  on  the  viscera  of  the  abdomen,  jDush 
up  the  floor  of  the  chest  formed  by  the  diaphragm,  and  by  thus  making 
pressure  on  the  lungs,  exi^el  air  from  them  through  the  trachea  and 
larynx.  All  muscles,  however,  which  depress  the  ribs,  must  act  also  as 
muscles  of  expiration,  and  therefore  we  must  conclude  that  the  abdom- 
inal muscles  are  assisted  in  their  action  by  the  greater  part  of  the  inter- 
nal intercostals,  the  triangularis  sterni,  the  serratus  posticus  inferior 
and  quadratus  lumhorum.  When  by  the  efforts  of  the  expiratory  mus- 
cles, the  chest  has  been  squeezed  to  less  than  its  average  diameter,  it 
again,  on  relaxation  of  the  muscles,  returns  to  the  normal  dimensions 
by  virtue  of  its  elasticity.  The  construction  of  the  chest-walls,  there- 
fore, admirably  adapts  them  for  recoiling  against  and  resisting  as  well 
undue  contraction  as  undue  dilatation. 

In  the  natural  condition  of  the  parts  the  lungs  can  never  contract 
to  the  utmost,  but  are  always  more  or  less  "  on  the  stretch,"  being  kept 
closely  in  contact  with  the  inner  surface  of  the  walls  of  the  chest  by 
cohesion  as  well  as  by  atmospheric  pressure,  and  can  contract  away  from 
these  only  when,  by  some  means  or  other,  as  by  making  an  opening  into 
the  pleural  cavity,  or  by  the  effusion  of  fluid  there,  the  pressure  on  the 
exterior  and  interior  of  the  lungs  becomes  equal.     Thus,  under  ordinary 


EESPIRATIOX. 


253 


circumstances,  the  degree  of  contraction  or  dilatation  of  the  lungs  is 
dependent  on  that  of  the  boundary  walls  of  the  chest,  the  outer  surface 
of  the  one  being  in  close  contact  with  the  inner  surface  of  the  other, 
and  obliged  to  follow  it  in  all  its  movements. 

Methods  of  recording  Respiratory  Movements. 

The  movements  of  respiration  may  be  recorded  graphically  in  several  ways. 
The  ordinary  method  is  to  introduce  a  tube  into  the  trachea  of  an  animal,  and 
to  connect  this  tube  by  some  gutta-iiercha  tubing  with  a  T  piece  introduced 
into  the  cork  of  a  large- sized  bottle,  the  other  end  of  the  T  having  attached  to 
it  a  second  piece  of  tubing,  which  can  remain  open  or  can  be  partially  or 
completely  closed  by  means  of  a  screw'  clamp.  Into  the  cork  is  inserted  a  sec- 
ond piece  of  glass  tubing  connected  with  a  Marey's  tambour  by  suitable  tubing. 
This  second  tube  communicates  any  alteration  of  the  pressure   in  the  bottle  of 


Fig.  214.— Stethograph  or  Pneumograph,  h,  tambour  fixed  at  right  angles  to  plate  of  steel/; 
c  and  d.  arms  by  which  Instrument  is  attached  to  chest  by  belt  e.  When  the  chest  expands,  the 
arms  are  pulled  asunder,  which  bends  the  steel  plate,  and  the  tambour  is  affected  by  the  pressure 
of  b  which  is  attacheii  to  it  on  the  one  hand,  and  to  the  upright  in  connection  with  horizontal  screw 
g.    (^Modilied  from  Jlarey"s  instrument.) 


the  tambour,  and  this  may  be  made  to  write  on  a  recording  surface  (fig. 
173).  If  the  tube  attached  to  the  T  piece  be  closed  the  movements  of  inspira- 
tion and  expiration  are  larger  than  if  it  were  closed.  The  alteration  of  the 
pressure  within  the  lungs  on  inspiration  and  expiration  is  shown  by  the  move- 
ment of  the  column  of  air  in  the  trachea.  By  these  means  a  record  of  the 
respiratory  movements  may  be  obtained. 

Various  instruments  for  recording  the  movements  of  the  chest  by  applica- 
tion of  apparatus  to  the  exterior.  Such  is  the  stethometer  of  Burton  Sander- 
son. This  consists  of  a  frame  formed  of  two  parallel  steel  bars  joined  by  a 
third  at  one  end.  At  the  free  end  of  the  bars  is  attached  a  leather  strap,  by 
means  of  which  the  apparatus  may  be  suspended  from  the  neck.  Attached  to 
the  inner  end  of  one  bar  is  a  tambour  and  ivory  button,  to  the  end  of  the 
other  an  ivory  button.  When  in  use,  the  apparatus  is  suspended  with  the 
transverse  bar  posteriori}^,  the  button  of  the  tambour  is  placed  on  the  part  of 
the  chest  the  movement  of  which  it  is  desired  to  record,  and  the  other  button 


254 


HANDBOOK    OF    PHYSIOLOGY. 


is  made  to  press  upon  the  corresponding  side  of  the  chest,  so  that  the  chest  is, 
as  it  were,  held  between  a  pair  of  calipers.  The  tambour  is  connected  by 
tubing  and  a  T  piece  with  a  recording  tambour  of  Marey's,  and  with  a  ball, 
by  means  of  which  air  can  be  squeezed  into  the  cavity  of  the  tympanum. 
When  in  work  the  tube  connected  with  the  air  ball  is  shut  off  by  means  of  a 
screw  clamp.  The  movement  of  the  chest  is  thus  communicated  to  the  recording 
tambour. 

A  simpler  form  of  this  apparatus,  called  a  pneumograph  or  stethograph, 
consisting  of  a  thick  India-rubber  bag  of  elliptical  shape  about  three  inches 
long,  to  one  end  of  whicli  a  rigid  gutta-percha  tube  is  attached.  This  bag 
may  be  fixed  at  any  required  place  on  the  chest  by  means  of  a  strap  and  buckle. 
By  means  of  the  gutta-percha  tube  the  variations  of  the  presssure  of  air  in  the 


Tamboiir. 
Ivory  button. 


Tube  to  commu- 
nicate with  re- 
cording tam- 
bour. 


Ball  to  fill  appa-  _ 
ratufl  -with  air. 


Fig.  215.— Stethometer.    (Burdon  Sanderson.) 


bag  produced  by  the  movements  of  the  chest  are  communicated  to  a  recording 
tambour.  This  apparatus  is  a  simplified  form  of  Marey's  pneumograph  (fig. 
214). 

The  variations  of  intrapleural  pressure  may  be  recorded  by  the  introducton 
of  a  canula  into  the  pleural  or  pericardial  cavity,  which  is  connected  with  a 
mercurial  manometer. 

Finally,  it  has  been  found  possible  in  various  ways  to  record  the  dia- 
phragmatic movements  by  the  insertion  of  an  elastic  bar  connected  with  a 
tambour  into  the  abdomen  below  it  (phrenograph) ,  by  the  insertion  of  needles 
into  different  parts  of  its  structure,  or  by  recording  the  contraction  of  isolated 
strips  of  the  diaphragm. 

The  acts  of  expansion  and  contraction  of  the  chest  take  up  under 
ordinary  circumstances  a  nearly  equal  time.     The  act  of  inspiring  air. 


RESPIRATION. 


355 


however,  especially  in  women  and  children,  is  a  little  shorter  than  that 
of  expelling  it,  and  there  is  commonly  a  very  slight  pause  between  the 
end  of  expiration  and  the  beginning  of  the  next  inspiration.  The  res- 
piratory rhythm  may  be  thus  expressed : — 


Inspiration 
Expiration 


6 

7  or  8 


A  very  slight  pause. 


If  the  ear  be  placed  in  contact  with  the  wall  of  the  chest,  or  be  sep- 
arated from  it  only  by  a  good  conductor  of  sound  or  stethoscope,  a  faint 
respiratory  rnurmtcr  is  heard  during  inspiration.     This  sound  varies 


Fig.  216.— Tracing  of  the  normal  diaphragm  respirations  of  rabbit,  a,  with  quick  movement  of 
drum.  b.  with  slow  movement,  j,  inspiration,  e,  expu-ation.  To  be  read  from  left  to  right. 
(Marckwald.) 

somewhat  in  different  parts — being  loudest  or  coarsest  in  the  neighbor- 
hood of  the  trachea  and  large  bronchi  (tracheal  and  bronchial  breathing), 
and  fading  oft'  into  a  faint  sighing  as  the  ear  is  placed  at  a  distance  from 
these  (vesicular  breathing).  It  is  best  heard  in  children,  and  in  them 
a  faint  murmur  is  heard  in  expiration  also.  The  cause  of  the  vesicular 
murmur  has  received  various  explanations.  Most  observers  hold  that 
the  sound  is  produced  by  the  friction  of  the  air  against  the  walls  of  the 
alveoli  of  the  lungs  when  they  are  undergoing  distention  (Laennec, 
Skoda),  others  that  it  is  due  to  an  oscillation  of  the  current  of  air  as  it 
enters  the  alveoli  (Chauveau),  while  others  believe  that  the  sound  is 
produced  in  the  glottis,  but  that  it  is  modified  in  its  passage  to  the 
pulmonary  alveoli  (Beau,  Gee). 

Respiratory  movements  of  the  JVostrils  atid  of  the  Glottis. — During 


256  HANDBOOK    OF    PHYSIOLOGY. 

the  action  of  the  muscles  which  directly  draw  air  into  the  chest,  those 
which  guard  the  opening  through  which  it  enters  are  not  passive.  In 
hurried  breathing  the  instinctive  dilatation  of  the  nostrils  is  well  seen, 
although  under  ordinary  conditions  it  may  not  be  noticeable.  The 
opening  at  the  upper  part  of  the  larynx,  however,  or  rima  glottidis,  is 
dilated  at  each  inspiration  for  the  more  ready  passage  of  air,  and  be- 
comes smaller  at  each  expiration;  its  condition,  therefore,  corresponding 
during  respiration  with  that  of  the  walls  of  the  chest.  There  is  a  fur- 
ther likeness  between  the  two  acts  in  that,  under  ordinary  circumstan- 
ces, the  dilatation  of  the  rima  glottidis  is  a  muscular  act  and  its  contrac- 
tion chiefly  an  elastic  recoil;  although,  under  various  conditions  to  be 
hereafter  mentioned,  there  may  be  in  the  latter  considerable  muscular 
power  exercised. 

Terms  used  to  express  Quantity  of  Air  breathed. — a.  Breath- 
ing or  tidal  air,  is  the  quantity  of  air  which  is  habitually  and  almost 
uniformly  changed  in  each  act  of  breathing.  In  a  healthy  adult  man 
it  is  about  30  cubic  inches,  or  about  500  ccm.,  or  half  a  litre. 

b.  Comphmental  air,  is  the  quantity  over  and  above  this  which  can 
be  drawn  into  the  lungs  in  the  deepest  inspiration;  its  amount  varies,, 
but  may  be  reckonded  as  100  cubic  inches,  or  about  1,600  ccm. 

c.  Reserve  air. — After  ordinary  expiration,  such  as  that  which  expels 
the  breathing  or  tidal  air,  a  certain  quantity  of  air,  about  100  cubic 
inches  (1,600  ccm.)  remains  in  the  lungs,  which  may  be  expelled  by  a 
forcible  and  deeper  expiration.  This  is  termed  reserve  or  supplemental 
air. 

d.  Residual  air  is  the  quantity  which  still  remains  in  the  lungs  after 
the  most  violent  expiratory  effort.  Its  amount  depends  in  great  meas- 
ure on  the  absolute  size  of  the  chest,  but  may  be  estimated  at  about  100 
cubic  inches,  or  about  1,600  ccm.  to  2,000  ccm. 

The  total  quantity  of  air  which  passes  into  and  out  of  the  lungs  of 
an  adult,  at  rest,  in  24  hours,  is  about  686,000  cubic  inches.  This  quan- 
tity, however,  is  largely  increased  by  exertion;  the  average  amount  for 
a  hard-working  laborer  in  the  same  time  being  1,568,390  cubic  inches. 

e.  Respirator y  Capacity. — The  greatest  respiratory  capacity  of  the 
chest  is  indicated  by  the  quantity  of  air  which  a  person  can  exijel  from 
his  lungs  by  a  forcible  expiration  after  the  deepest  inspiration  possible; 
it  expresses  the  power  which  a  person  has  of  breathing  in  the  emergen- 
cies of  active  exercise,  violence,  and  disease.  The  average  capacity  of 
an  adult,  at  15.4°  C.  (60°  F.),  is  about  225  to  250  cubic  inches,  or  3,500 
to  4,000  ccm. 

The  respiratory  capacity,  or  as  John  Hutchinson  called  it,  vital  capacity, 
is  usually  measured  by  a  modified  gasometer  or  spirometer,  into  which  the 
experimenter  breathes, — making  the  most  prolonged  expiration  possible  after 
the  deepest  possible  inspiration.     The  quantity  of  air  which  is  thus  expelled 


•    RESPIRATION^.  257 

from  the  lungs  is  indicated  by  tlie  lieight  to  which  the  air  chamber  of  the 
spirometer  rises  ;  and  by  means  of  a  scale  placed  in  connection  with  this,  the 
number  of  cubic  inclies  is  read  off. 

In  healthy  men,  the  respiratory  capacity  varies  chiefly  with  the 
stature,  weight,  and  age. 

It  was  found  by  Hutchinson,  from  whom  most  of  our  information 
on  this  subject  is  derived,  that  at  a  temperature  of  15.4°  C.  (60°  F.), 
225  cubic  inches  is  the  average  vital  or  respiratory  capacity  of  a  healthy 
person,  five  feet  seven  inches  in  height. 

Circumstances  affecting  the  amount  of  respiratory  capacity. — For  every  inch 
of  height  above  this  standard  the  capacity  is  increased,  on  an  average,  by  eight 
inches ;  and  for  every  inch  below,  it  is  diminished  by  the  same  amount. 

The  influence  of  weight  on  the  capacity  of  respiration  is  less  manifest  and 
considerable  than  that  of  height :  and  it  is  difficult  to  arrive  at  any  definite 
conclusions  on  this  point,  because  the  natural  average  weight  of  a  healthy 
man  in  relation  to  stature  ha«  not  yet  been  determined.  As  a  general  state- 
ment, however,  it  may  be  said  that  the  capacity  of  respiration  is  not  affected 
by  weights  under  161  pounds,  or  IH  stones;  but  that,  above  this  point,  it  is 
diminished  at  the  rate  of  one  cubic  inch  for  every  additional  pound  up  to  196 
pounds  or  14  stones. 

By  age,  the  capacity  appears  to  be  increased  from  abovit  the  fifteenth  to  the 
thirty-fifth  year,  at  tlie  rate  of  five  cubic  inches  per  year ;  from  thirty-five  to 
sixty-five  it  diminishes  at  the  rate  of  about  one  and  a  half  cubic  inch  per  year  ; 
so  that  the  capacity  of  respiration  of  a  man  of  sixty  years  old  would  be  about 
30  cubic  inches  less  than  that  of  a  man  of  forty  years  old,  of  the  same  height 
and  weight.      (John  Hutchinson.) 

The  number  of  respirations  in  a  healthy  adult  person  usually  ranges 
from  14  to  18  per  minute.  It  is  greater  in  infancy  and  childhood.  It 
varies  also  much  according  to  different  circumstances,  such  as  exercise 
or  rest,  health,  or  disease,  etc.  Variations  in  the  number  of  respirations 
correspond  ordinarily  with  similar  variations  in  the  pulsations  of  the 
heart.  In  health  the  proportion  is  about  1  to  4,  or  1  to  5,  and  when  the 
rapidity  of  the  heart's  action  is  increased,  that  of  the  chest  movement  is 
commonly  increased  also;  but  not  in  every  case  in  equal  proportion.  It 
happens  occasionally  in  disease,  especially  of  the  lungs  or  air-passages, 
that  the  number  of  resjnrafor>/  acts  increases  in  quicker  proportion  than 
the  beats  of  the  pulse;  and,  in  other  affections,  much  more  commonly, 
that  the  number  of  the  pulses  is  greater  in  proportion  than  that  of  the 
respirations. 

The  Force  of  Inspiratory  and  Expiratory  Muscles. — The  force  witb 
which  the  inspiratory  muscles  are  capable  of  acting  is  greatest  in  iiuli- 
viduals  of  the  height  of  from  five  feet  seven  inches  to  five  feet  eight 
inches,  and  will  elevate  a  column  of  three  inches  of  mercury.  Above 
this  height  the  force  decreases  as  the  stature  increases;  so  that  the  aver- 
age of  men  of  six  feet  can  elevate  only  about  two  and  a  half  inches  of 
t7 


25S  HANDBOOK    OF    PHYSIOLOGY. 

mercury.  The  force  manifested  in  the  strongest  expiratory  acts  is,  on 
the  average,  one-third  greater  than  that  exercised  in  inspiration.  But 
this  difference  is  in  great  measure  due  to  the  power  exerted  by  the 
ehistic  reaction  of  the  walls  of  the  chest;  and  it  is  also  much  influenced 
by  the  disproportionate  strength  which  the  expiratory  muscles  attain, 
from  their  being  called  into  use  for  other  purposes  than  that  of  simple 
expiration.  The  force  of  the  inspiratory  act  is,  therefore,  better  adapted 
than  that  of  the  expiratory  for  testing  the  muscular  strength  of  the 
body.     (John  Hutchinson.) 

The  instrument  used  by  Hutchinson  to  gauge  the  inspiratory  and  expiratory 
power  was  a  mercurial  manometer,  to  which  was  attached  a  tube  fitting  the 
nostrils,  and  through  which  the  inspiratory  or  expiratory  effort  was  made. 
The  following  table  represents  the  results  of  numerous  experiments : 

Power  of  Power  of 

Inspiratory  Muscles.  Expiratory  Muscles. 

1.5  in Weak  .         .         .         .     2.0  in. 

2.0  "  .         .  .         .          Ordinary          .  .         .          2.0  " 

2.5   "         .  .         .         .     Strong           .         .         .         .     3.5  " 

3. 5   "   .         .  .         .          Very  strong     .  .         .          4. 5  " 

4.5   "         .  .         .         .     Remarkable          .          .         .     7.0  " 

5. 5   "  .         .  .         .           Very  remarkable  .          .          5.8  " 

6. 0   "         .  .         .         .     Extraordinary      .         .         .     8. 5  " 

7.0   "   .         .  .         .          Very  extraordinary          .        10.0  " 

The  greater  part  of  the  force  exerted  in  deep  inspiration  is  employed 
in  overcoming  the  resistance  offered  by  the  elasticity  of  the  lungs. 

The  amount  of  this  elastic  resistance  was  estimated  by  observing  the  ele\a- 
tion  of  a  column  of  mercury  raised  by  the  return  of  air  forced,  after  deaih, 
into  the  lungs,  in  quantity  equal  to  the  known  capacity  of  respiration  during 
life  ;  and  Hutchinson  calculated,  according  to  the  well-known  hydrostatic  law 
of  equality  of  pressures  (as  shown  in  the  Bramah  press),  that  the  total  force  to 
be  overcome  by  the  muscles  in  the  act  of  inspiring  200  cubic  inches  of  air  is 
more  than  450  lbs. 

The  elastic  force  overcome  in  ordinary  inspiration  is,  according  to  the  same 
authority,  equal  to  about  170  lbs. 

Douglas  Powell  has  shown  that  within  the  limits  of  ordinary  tran- 
quil respiration  the  elastic  resilience  of  the  walls  of  the  chest  favors  in- 
spiration; and  that  it  is  only  in  deep  inspiration  that  the  ribs  and  rib- 
cartilages  offer  an  opposing  force  to  their  dilatation.  In  other  words, 
the  elastic  resilience  of  the  lungs,  at  the  end  of  an  act  of  ordinary 
breathing,  has  drawn  the  chest-walls  within  the  limits  of  their  normal 
degree  of  expansion.  Under  all  circumstances,  of  course,  the  elastic 
tissue  of  the  lungs  opposes  inspiration  and  favors  expiration. 

It  is  possible  that  the  contractile  power  which  the  bronchial  tubes 
and  air-vesicles  possess,  by  means  of  their  muscular  fibres  may  (1)  assist 
in  expiration ;  but  it  is  more  likely  that  its  chief  purpose  is  (2)  to  regu- 
late and  adapt,  in  some  measure,  the  quantity  of  air  admitted  to  1  he 


RESPIKATION.  "2,59 

lungs,  and  to  each  part  of  them,  according  to  the  supply  of  blood;  (3) 
the  muscular  tissue  contracts  upon  and  gradually  expels  collections  of 
mucus,  which  may  have  accumulated  within  the  tubes,  and  which  cannot 
be  ejected  by  forced  expiratory  efforts,  owing  to  collapse  or  other  mor- 
bid conditions  of  the  portion  of  lung  connected  with  the  obstructed 
tubes  (Gairdner).  (4)  Apart  from  any  of  the  before-mentioned  func- 
tions, the  presence  of  muscular  fibre  in  the  walls  of  a  hollow  viscus, 
such  as  a  lung,  is  only  what  might  be  expected  from  analogy  with  other 
organs.  Subject  as  the  lungs  are  to  such  great  variation  in  size,  it 
might  be  anticipated  that  the  elastic  tissue,  which  enters  so  largely  into 
their  composition,  would  be  supplemented  by  the  presence  of  much 
muscular  fibre  also. 

Respiratory  Changes  in  the  Air  Breathed. 

Composition  of  the  Atmosphere. — The  atmosphere  we  breathe  has,  in 
every  situation  in  which  it  has  been  examined  in  its  natural  state,  a 
nearly  uniform  composition.  It  is  a  mixture  of  oxygen,  nitrogen,  car- 
bon dioxide,  and  watery  vapor,  with,  commonly,  traces  of  other  gases, 
as  ammonia,  sulphuretted  hydrogen,  etc.  Of  every  100  volumes  of  pure 
atmospheric  air,  79  volumes  (on  an  average)  consist  of  nitrogen,  the  re- 
maining 21  of  oxygen.  By  weight  the  proportion  is  N.  77,  0.  23.  The 
proportion  of  carbon  dioxide  is  extremely  small;  10,000  volumes  of 
atmospheric  air  contain  only  about  4  or  5  of  that  gas. 

The  quantity  of  watery  vapor  varies  greatly  according  to  the  temper- 
ature and  other  circumstances,  but  the  atmosphere  is  never  without 
some.  In  this  country,  the  average  quantity  of  watery  vapor  in  the  at- 
mosphere is  1.40  per  cent. 

Compiosition  of  Air  wliicli  has  been  breathed. — The  changes  effected 
by  respiration  in  the  atmospheric  air  are:  1,  an  increase  of  temperature; 
2,  an  increase  in  the  quantity  of  carbonic  acid;  3,  a  diminution  in  the 
quantity  of  oxygen;  4,  a  diminution  of  volume;  5,  an  increase  in  the 
amount  of  watery  vapor;  6,  the  addition  of  a  minute  amount  of  organic 
matter  and  of  free  ammonia. 

1.  The  expired  air,  heated  by  its  contact  with  the  interior  of  the 
lungs,  is  (at  least  in  most  climates)  hotter  than  the  inspired  air.  Its 
temperature  varies  bet«^een  36°— 37.5°  C.  (97°  and  99.5°  F.),  the  lower 
temperature  being  observed  when  the  air  has  remained  but  a  short  time 
in  the  lungs.  Whatever  may  be  the  temperature  of  the  air  when  in- 
haled, it  acquires  nearly  that  of  the  blood  before  it  is  expelled  from  the 
chest. 

2.  The  Carbonic  dioxide  is  increased;  but  the  quantity  exhaled  in  a 
given  time  is  subject  to  change  from  various  circumstances.  From 
every  volume  of  air  inspired,  about  4.8  per  cent  of  oxygen  is  abstracted; 


260  HAXDBOOK    OF    PHYSIOLOCi  V 

while  a  rather  smaller  quantity,  4.3  of  carbon  dioxide  is  added  in  \\<, 
place:  the  expired  air  will  contain,  therefore,  434  vols,  of  carbon  dioxide 
in  10,000.  The  quantity  of  carbon  dioxide  exhaled  into  the  air  breathed 
by  a  healthy  adult  man,  calculating  that  22  com.  of  the  500  ccra.  of  the 
air  breathed  out  at  each  expiration  consists  of  carbon  dioxide,  and  that 
the  rate  of  respiration  is  on  an  average  16,  the  total  amount  would  be 
about  506  litres  in  the  24  hours.  From  actual  experiment  this  amount 
seems  to  be  too  high,  since  from  the  average  of  many  investigations  the 
total  amount  of  carbon  dioxide  excreted  per  diem  has  been  found  to  be 
about  400  litres,  weighing  800  grms.,  consisting  of  218  grms.  of  C,  and 
582  grms.  of  0.  From  this  has  to  be  deducted  about  10  grms.  excreted  in 
any  other  way  than  by  the  lungs,  it  leaves  about  215  grms.  as  the  amount 
of  C.  excreted  by  the  average  healthy  man  by  respiration  each  day  and 
night,  that  is  about  7  oz.,  about  half  a  pound.  These  quantities  must 
be  considered  approximate  only,  inasmuch  as  various  circumstances,  even 
in  health,  influence  the  amount  of  carbon  dioxide  excreted,  and,  correla- 
tively,  the  amount  of  oxygen  absorbed. 

Circumstances  influencing  the  amount  of  carbon  dioxide  excreted. — a.  Age 
and  Sex. — The  quantity  of  carbon  dioxide  exhaled  into  the  air  breatlied  by- 
males,  regularly  inci-eases  from  8  to  30  years  of  age  ;  from  30  to  50  the  quantity, 
after  remaining  stationary  for  a  while,  gradually  diminishes,  and  from  50  to 
extreme  age  it  goes  on  diminishing,  till  it  scarcely  exceeds  the  quantity  ex- 
haled at  ten  years  old.  In  females  (in  whom  the  quantity  exhaled  is  always 
less  than  in  males  of  the  same  age)  the  same  regular  increase  in  quantity  goes 
on  from  the  8th  year  to  the  age  of  puberty,  when  the  quantity  abruptlj^  ceases 
to  increase,  and  remains  stationary  so  long  as  they  continue  to  menstruate. 
When  menstruation  has  ceased,  it  soon  deci-eases  at  the  same  rate  as  it  does  in 
old  men. 

b.  Respiratory  Movements. — The  quicker  the  respirations,  the  smaller  is  the 
proportionate  quantity  of  carbon  dioxide  contained  in  each  volume  of  the  expired 
air.  Although  the  proportionate  quantity  of  carbon  dioxide  is  thus  diminished, 
the  absolute  amount  exhaled  within  a  given  time  is  increased  thereby,  owing  to 
the  larger  quantity  of  air  which  is  breathed  in  the  time.  The  last  half  of  a  vol- 
ume of  expired  air  contains  more  carbonic  acid  than  the  half  first  expired  ;  a 
circumstance  which  is  explained  by  the  one  portion  of  air  coming  from  the 
remote  part  of  the  lungs,  where  it  has  been  in  more  immediate  and  prolonged 
contact  with  the  blood  than  the  other  has,  which  comes  chiefly  from  the  larger 
bronchial  tubes. 

c.  External  temperature. — The  observation  made  by  Vierordt  at  various 
temperatures  between  3.4° — 23.8°  C.  (38°  F.  and  75°  F.)  show,  for  warm-blooded 
animals,  that  within  this  range,  every  rise  equal  to  5.5°  C.  (10°  F. )  causes  a 
diminution  of  about  33  ccm.  (2  cubic  inches)  in  the  quantity  of  carbonic  acid 
exhaled  per  minute. 

d.  Season  of  the  Year.  — The  season  of  the  year,  independently  of  tempera- 
ture, materially  influences  the  respiratory  phenomena ;  spring  being  the  season 
of  the  greatest,  and  autumn  of  the  least  activity  of  the  respiratory  and  other 
functions. 

e.  Purity  of  the  Respired   Air. — The  average  quantity    of  carbon  dioxide 


KESPIKATIOX.  261 

given  out  by  the  lungs  constitutes  about  4. 3  per  cent,  of  the  expired  air ;  but 
if  the  air  which  is  breathed  be  previously  impregnated  with  carbon  dioxide 
(as  is  the  case  when  the  same  air  is  frequently  respired) ,  then  the  quantity  of 
carbon  dioxide  exhaled  becomes  relatively  much  less. 

/.  Hygrometric  State  of  Atmosphere. — The  amount  of  carbon  dioxide  exhaled 
is  considerably  influenced  by  the  degree  of  moisture  of  the  atmosphere,  much 
more  being  given  off  when  the  air  is  moist  than  when  it  is  dry. 

g.  Period  of  the  Day. — During  the  day-time  more  carbon  dioxide  is  exhaled 
than  corresponds  to  the  oxygen  absorbed  ;  while,  on  the  other  hand,  at  night 
very  much  more  oxygen  is  absorbed  than  is  exhaled  in  carbon  dioxide.  There  is, 
thus,  a  reserve  fund  of  oxygen  absorbed  by  night  to  meet  the  requirements  of  the 
day.  If  the  total  quantity  of  carbon  dioxide  exhaled  in  24  hours  be  repre- 
sented by  100,  52  parts  are  exhaled  during  the  day,  and  48  at  night.  While 
similarly.  33  j^arts  of  the  oxygen  are  absorbed  during  the  day,  and  the  remain- 
ing 67  by  night. 

h.  Food  and  Drink. — By  the  use  of  food  the  quantity  is  increased,  while 
by  fasting  it  is  diminished ;  it  is  greater  when  animals  are  fed  on  farinaceous 
food  than  when  fed  on  meat.  The  effects  produced  by  spirituous  drinks  de- 
pend much  on  the  kind  of  drink  taken.  Pure  alcohol  tends  rather  to  increase 
than  to  lessen  respiratory  changes,  and  the  amount  therefore  of  carbon  dioxide 
expired ;  rum,  ale,  and  porter,  also  sherry,  have  very  similar  effects.  On  the 
other  hand,  brandy,  whiskey,  and  gin,  particularly  the  latter,  almost  always 
lessened  the  respiratory  changes,  and  consequently  the  amount  of  the  gas 
exhaled. 

i.  Exercise. — Bodily  exercise,  in  moderation,  increases  the  quantity  to  about 
i-  more  than  it  is  during  rest :  and  for  about  an  hour  after  exercise  the  volume 
of  the  air  expired  in  the  minute  is  increased  nearly  2,000  ccm.,  or  118  cubic 
inches  :  and  the  quantity  of  carbon  dioxide  about  125  ccm.,  or  7.8  cubic  inches 
per  minute.  Violent  exercise,  such  as  full  labor  on  the  tread-wheel,  still  fur- 
ther increases  the  amount  of  the  acid  exhaled. 

A  larger  quantity  is  exhaled  when  the  barometer  is  low  than  when  it  is 
high. 

3.  The  oxygen  is  diminished,  and  its  diminution  is  generally  propor- 
tionate to  the  increase  of  the  carbon  dioxide.  For  every  volume  of  car- 
bon dioxide  exhaled  into  the  air,  1.17421  volumes  of  oxygen  are  absorbed 
from  it,  from  the  result  of  the  experiments  to  estimate  the  carbon  diox- 
ide exhaled  and  the  oxygen  absorbed,  it  was  found  that  while  about  575 
grms.  of  oxygen  appeared  in  the  CO2  exhaled,  700  grms.  disappeared 
froTu  the  inspired  air. 

4.  Tlie  volume  of  air  is  diviinished  (allowance  being  made  for  the  ex- 
pansion in  being  heated),  the  loss  being  due  to  a  portion  of  oxygen  ab- 
sorbed and  not  returned  in  the  exhaled  carbonic  acid,  all  observers  agree, 
though  as  to  the  actual  quantity  of  oxygen  so  absorbed,  they  differ  even 
widely.  The  amount  of  oxygen  absorbed  is  on  an  average  4.8  per  cent, 
so  that  the  expired  air  contains  G.2  volumes  per  cent  of  that  gas.  The 
quantity  of  oxygen  that  does  not  combine  Avith  the  carbon  given  off  in 
carbonic  acid  from  the  lungs  is  probably  disposed  of  in  forming  some 
of  the  carbonic  acid  and  water  given  off  from  the  skin,  and  in  combining 


20:^  HANDBOOK    OF    PHYSIOLOGY. 

with  sulphur  and  phospliorus  to  form  part  of  the  acids  of  the  sulpliates 
and  phosphates  excreted  in  the  urine,  and  probably  also,  with  the  nitro- 
gen of  the  decomposing  nitrogenous  tissues. 

The  quantity  of  oxygen  in  the  atmosphere  surrounding  animals,  ap- 
pears to  have  very  little  influence  on  the  amount  of  this  gas  absorbed  by 
them,  for  the  quantity  consumed  is  not  greater  even  though  an  excess 
of  oxygen  be  added  to  the  atmosphere  experimented  with. 

It  has  often  been  discussed  whether  Nitrogen  is  absorbed  by  or  ex- 
haled from  the  lungs  during  respiration.  At  present,  all  that  can  be 
said  on  the  subject  is  that,  under  most  circumstances,  animals  appear 
to  expire  a  very  small  quantity  above  that  which  exists  in  the  inspired 
air.  During  prolonged  fasting,  on  the  contrary,  a  small  quantity  appears 
to  be  absorbed. 

5.  Tlie  watery  vapor  is  increased. — The  quantity  emitted  is,  as  a 
general  rule,  sufficient  to  saturate  the  expired  air,  or  very  nearly  so. 
Its  absolute  amount  is,  therefore,  influenced  by  the  following  circum- 
stances, (1),  by  the  quantity  of  air  respired;  for  the  greater  this  is,  the 
greater  also  will  be  the  quantity  of  moisture  exhaled;  (2),  by  the  quan- 
tity of  watery  vapor  contained  in  the  air  j)revious  to  its  being  inspired ; 
because  the  greater  this  is,  the  less  will  be  the  amount  to  comjilete  the 
saturation  of  the  air;  (3),  by  the  temperature  of  the  expired  air;  for 
the  higher  this  is,  the  greater  will  be  the  quantity  of  watery  vapor  re- 
quired to  saturate  the  air;  (4),  by  the  length  of  time  which  each  volume 
of  inspired  air  is  allowed  to  remain  in  the  lungs;  for  although,  during 
ordinary  respiration,  the  expired  air  is  always  saturated  with  watery 
vapor,  yet  when  resi^iration  is  performed  very  rapidly  the  air  has  scarcely 
time  to  be  raised  to  the  highest  temperature,  or  be  fully  charged  with 
moisture  ere  it  is  expelled. 

The  quantity  of  water  exhaled  from  the  lungs  in  twenty-four  hours 
ranges  (according  to  the  various  modifying  circumstances  already  men- 
tioned) from  about  6  to  27  ounces,  the  ordinary  quantity  being  about  9 
or  10  ounces.  Some  of  this  is  probably  formed  by  the  chemical  com- 
bination of  oxygen  with  hydrogen  in  the  system;  but  the  far  larger 
proportion  of  it  is  water  which  has  been  absorbed,  as  such,  into  the 
blood  from  the  alimentary  canal,  and  which  is  exhaled  from  the  surface 
of  the  air-passages  and  cells,  as  it  is  from  the  free  surfaces  of  all  moist 
animal  membranes,  particularly  at  the  high  temiperature  of  warm-blooded 
animals. 

6.  A  small  quantity  of  ammonia  is  added  to  the  ordinary  constitu- 
ents of  expired  air.  It  seems  probable,  however,  both  from  the  fact  that 
this  substance  cannot  be  always  detected,  and  from  its  minute  amount 
when  present,  that  the  whole  of  it  may  be  derived  from  decomposing 
particles  of  food  left  in  the  mouth,  or  from  carious  teeth  or  the  like; 
and  that  it  is,  therefore,  only  an  accidental  constituent  of  expired  air. 


EESPIKATIO]Sr.  363 

T.  The  quantity  of  organic  matter  in  the  breath  is  increased.  It  is 
due  to  the  presence  of  this  organic  matter  that  air  containing  the  prod- 
ucts of  respiration  is  more  injurious  than  it  might  be  expected  to  be 
from  the  amount  of  CO2  it  contains.  The  condensed  aqueous  vapor  is 
found  soon  to  decompose  and  to  contain  substances  which  are  of  a 
poisonous  nature. 

Method  of  Experiment. — The  following  represents  the  kind  of  experiment  by 
which  the  foregoing  facts  regarding  the  excretion  of  carbonic  acid,  water,  and 
organic  matter,  have  been  established. 

A  bird  or  mouse  is  placed  in  a  large  bottle,  through  the  stopper  of  which 
two  tubes  pass,  one  to  supply  fresh  air,  and  the  other  to  carry  off  that  which 
has  been  expired.  Before  entering  the  bottle,  the  air  is  made  to  bubble  through 
a  strong  solution  of  caustic  potash,  which  absorbs  the  carbonic  acid,  and  then 
through  lime-water,  which,  by  remaining  limpid,  proves  the  absence  of  car- 
bonic acid.  The  air  which  has  been  breathed  by  the  animal  is  luade  to  bubble 
thi-ougli  lime-water,  which  at  once  becomes  turbid  and  soon  quite  milky  from 
the  precipitation  of  calcium  carbonate ;  and  it  finally  passes  through  strong 
sulphuric  acid,  which,  b}'  tiuning  brown,  indicates  the  presence  of  organic 
matter.  The  watery  rapor  in  the  expired  air  will  condense  inside  the  bottle  if 
the  surface  be  kept  cool.  By  means  of  an  apparatus  sufficiently  large  and  well- 
constructed,  experiments  of  the  kind  have  been  made  extensively  on  man. 

How  the  Changes  in  the  Air  are  effected. — The  method  by  which 
fresh  air  is  inhaled  and  expelled  from  the  lungs  has  been  explained. 
It  remains  to  consider  how  it  is  that  the  blood  absorbs  oxygen  from, 
and  gives  u]^  carbonic  acid  to,  the  air  of  the  alveoli.  In  the  first  place, 
it  must  be  remembered  that  the  tidal  air  only  amounts  to  about  25 — 30 
cubic  inches  (about  .500  ccm.)  at  each  inspiration,  and  that  this  is  of 
course  insufficient  to  fill  the  lungs,  but  it  mixes  with  the  stationary  air 
by  diffusion,  and  so  supplies  to  it  new  oxygen.  The  amount  of  oxygen 
in  expired  air,  which  may  be  taken  as  the  average  composition  of  the 
mixed  air  in  the  lungs,  is  about  16  to  17  per  cent;  in  the  pulmonary 
alveoli  it  may  be  rather  less  than  this.  From  this  air  the  venous  blood 
has  to  take  up  oxygen  in  the  proportion  of  8  to  12  vols,  per  cent  of 
blood,  as  the  difference  between  the  amount  of  oxygen  in  arterial  and 
venous  blood  is  no  less.  It  seems  therefore  somewhat  difficult  to  under- 
stand hov/  this  can  be  accomplished  at  the  low  partial  pressure  of  oxygen 
in  the  pulmonary  air.  But  as  Avas  pointed  out  in  a  previous  Chapter 
(IV.),  the  oxygen  is  not  simply  dissolved  in  the  blood,  but  is  to  a  great 
extent  chemically  combrned  with  the  haemoglobin  of  the  red  corpuscles; 
and  when  a  fluid  contains  a  body  which  enters  into  loose  chemical  com- 
bination in  this  way  with  a  gas,  the  tension  of  the  gas  in  the  fluid  is 
not  directly  proportional  to  the  total  quantity  of  the  gas  taken  up  by 
the  fluid,  but  to  the  excess  above  the  total  quantity  which  the  substance 
dissolved  in  the  fluid  is  capable  of  taking  up  (a  known  quantity  in  the 
case  of  heemoglobin,  viz.,   1.59  cm.  for  1  grm.  haemoglobin).     On  the 


264  HANDBOOK    OF    PHYSIOLO(iY. 

other  hand,  if  the  substance  be  not  saturated,  i.e.,  if  it  be  not  combined 
with  as  niucli  of  the  gas  as  it  is  capable  of  taking  up,  further  combina- 
tion leads  to  no  increase  of  its  tension.  However,  there  is  a  point  at 
which  the  haemoglobin  gives  up  its  oxygen  when  it  is  exposed  to  a 
low  partial  pressure  of  oxygen,  and  there  is  also  a  point  at  which  it 
neither  takes  up  nor  gives  out  oxygen;  in  the  case  of  arterial  blood  of 
the  dog,  this  is  found  to  be  when  the  oxygen  tension  of  the  atmosphere 
is  equal  to  3.9  per  cent  (or  29.6  mm.  of  mercury),  which  is  equivalent 
to  saying  that  the  oxygen  tension  of  arterial  blood  is  3.9  per  cent;  venous 
blood,  in  a  similar  manner,  has  been  found  to  have  an  oxygen  tension  of 
2.8  per  cent.  At  a  higher  temperature,  the  tension  is  raised,  as  there  is 
a  greater  tendency  at  a  high  temjDcrature  for  the  chemical  compound  to 
undergo  dissociation.  It  is  therefore  easy  to  see  that  the  oxygen  tension 
of  the  air  of  the  pulmonary  alveoli  is  quite  sufficient,  even  supposing  it 
much  less  than  that  of  the  expired  air,  to  enable  the  venous  blood  to 
take  up  oxygen,  and  what  is  more,  it  will  take  it  up  until  the  ha?mo- 
globin  is  very  nearly  saturated  with  the  gas. 

As  regards  the  elimination  of  carbon  dioxide  from  the  blood,  there 
is  evidence  to  show  that  it  is  given  up  by  a  process  of  simple  diffusion, 
the  only  condition  necessary  for  tlie  process  being  that  the  tension  of 
the  carbonic  acid  of  the  air  in  the  pulmonary  alveoli  should  be  less  than 
the  tension  of  the  carbonic  acid  in  venous  blood.  The  carbonic  acid 
tension  of  the  alveolar  air  probably  does  not  exceed  (in  the  dog)  3  or  4 
per  cent,  while  that  of  the  venous  blood  is  5.4  per  cent,  or  equal  to  41 
mm.  of  mercury. 

Respiratory  Changes  in  the  Blood. 

Circnlation  of  Blood  in  the  Besjnratory  Organs. — To  be  exposed  to 
the  air  thus  alternately  moved  into  and  out  of  the  air-cells  and  minute 
bronchial  tubes,  the  blood  is  propelled  from  the  right  ventricle  through 
the  pulmonary  capillaries  in  steady  streams,  and  slowly  enough  to  per- 
mit every  minute  portion  of  it  to  be  for  a  few  seconds  exposed  to  the 
air,  with  only  the  thin  walls  of  the  capillary  vessels  and  the  air-cells 
intervening.  The  pulmonary  circulation  is  of  the  simi^lest  kind:  for 
the  pulmonary  artery  branches  regularly;  its  successive  branches  run  in 
straight  lines,  and  do  not  anastomose:  the  capillary  plexus  is  uniformly 
spread  over  the  air-cells  and  intercellular  passtiges;  and  the  veins  de- 
rived from  it  proceed  in  a  course  as  simple  and  uniform  as  that  of  the 
arteries,  their  branches  converging  but  not  anastomosing.  The  veins 
have  no  valves,  or  only  small  imperfect  ones  prolonged  from  their  angles 
of  junction,  and  incapable  of  closing  the  orifice  of  either  of  the  veins 
between  which  they  are  placed.  The  pulmonary  circulation  also  is  un- 
affected by  changes  of  atmospheric  pressure,  and  is  not  exposed  to  the 


RESPIRATION.  265 

influence  of  the  j)ressure  of  muscles:  the  force  by  which  it  is  accom- 
plished, and  the  course  of  the  blood  are  alike  simple. 

Changes  in  the  Blood. — The  most  obvious  change  which  the  blood  of 
the  pulmonary  artery  undergoes  in  its  passage  through  the  lungs  is  1st, 
that  of  color,  the  dark  crimson  of  venous  blood  being  exchanged  for  the 
bright  scarlet  of  arterial  blood.  The  cause  of  this  has  been  already 
shown  to  be  that  the  arterial  blood  contains  a  greater  quantity  of  scarlet 
or  oxyhaemoglobin;  2d,  and  in  connection  with  the  preceding  change  it 
gains  oxygen  ;  3f7,  it  loses  carbon  dioxide.  It  w^as  incidentally  mentioned 
in  the  Chapter  on  the  Blood  that  the  carbon  dioxide  which  is  carried 
by  the  blood  to  be  eliminated  by  the  lungs  is  not  simply  dissolved  in 
the  plasma.  It  is  combined  with  some  substance  in  the  blood,  and 
when  it  is  carried  to  the  lungs  this  substance  must  undergo  decomposi- 
tion. What  is  the  nature  of  the  compound  it  forms  is  not  known,  but 
it  appears  most  likely  that  the  gas  is  combined  in  the  plasma  with  the 
sodium  carbonate  which  it  contains.  It  has  also  been  suggested  that  as 
the  carbon  dioxide  of  the  entire  blood  is  more  easily  given  up  to  the 
vacuum  of  a  mercurial  air-pump  than  is  the  gas  of  the  serum  correspond- 
ing to  the  blood  taken,  that  the  corpuscles  of  the  blood  exercise  some 
power  in  promoting  the  decomposition  of  the  substance  with  which  the 
gas  is  combined  in  the  plasma.  The  plasma  or  serum  will  not  give  up 
the  whole  of  its  carbon  dioxide  until  the  addition  of  an  acid,  when  the 
last  portion,  2  to  5  per  cent,  comes  off,  the  entire  blood  gives  up  the 
whole  of  its  carbon  dioxide  to  the  action  of  the  mercurial  pump,  and 
does  not  require  the  action  of  an  acid.     It  may  be  mentioned  that,  ae- 

■  cording  to  some,  the  carbon  dioxide  is  combined  with  proteid,  either  in 
the  plasma  or  in  the  red  blood-corpuscles;  4/*/?,  it  becomes  slightly 
cooler;  oth,  it  coagulates  sooner  and  more  firmly,  apparently  containing 
more  fibrin.  The  oxygen  absorbed  into  the  blood  from  the  atmospheric 
air  in  the  lungs  is  combined  cliemically  with  the  haemoglobin  of  the 
red  blood-corpuscles.  In  this  condition  it  is  carried  in  the  arterial  blood 
to  the  various  parts  of  the  body,  and  brought  into  near  relation  or  con- 
tact with  the  tissues.  In  these  tissues,  a  certain  portion  of  the  oxygen, 
which  the  arterial  blood  contains,  disappears,  and  a  proportionate  quan- 
tity of  carbon  dioxide  and  water  is  formed.  The  venous  blood,  contain- 
ing the  new-formed  carbon  dioxide,  returns  to  the  lungs,  where  a  portion 
of  the  carbon  dioxide  is  exhaled,  and  a  fresh  supply  of  oxygen  is  taken  in. 

In  what  way  these  changes  are  brought  about  will  be  next  discussed. 

Respiratory  Changes  in  the  Tissues. 

The  changes  which  occur  in  the  composition  of  the  blood  during  its 

■  circulation  are  believed  to  take  place  in  the  tissues,  and  particularly  in 
the  muscles.     The  changes  are,  as  we  have  just  mentioned,  chiefly  the 


266  HANDBOOK    OF    PHYSIOLOGY. 

removal  of  oxygen  from  and  the  addition  of  carbon  dioxide  to  tlie  blood. 
These  changes  are  sometimes  spoken  of  as  internal  res2Diration.  The- 
oxygen  carried  by  the  corpuscles  of  the  blood  in  the  form  of  oxyhgemo- 
globin  is  given  ujd  to  the  tissues,  as  the  tension  of  the  gas  within  them 
is  very  small.  The  gas  thus  set  free  is  apparently  seized  upon  by  the 
protoplasm  of  the  tissues  and  built  up  into  its  molecule,  and  thus  assists 
in  the  process  of  anabolism,  possibly  uniting  with  some  compound 
somewhat  in  the  same  manner  but  more  firmly  than  it  does  with  hemo- 
globin. The  low  oxygen  pressure  of  the  tissues  thus  allows  a  constant 
abstraction  of  the  gas  from  the  blood.  The  process  of  katabolism,  or 
breaking  down,  is  always  associated  with  the  evolution  of  carbon  diox- 
ide, so  that  as  the  blood  passes  through  the  tissues  containing  little  of 
this  gas,  the  high  tension  of  the  gas  in  the  tissues  permits  of  its  passage 
into  the  blood.  It  has  been  proved  that  the  process  of  the  evolution  of 
carbon  dioxide  from  living  muscle  will  go  on  for  a  time  in  the  absence 
of  a  supply  of  free  oxygen,  and  so  it  is  clear  that  the  former  gas  is  not 
derived  directly  from  the  combustion  of  the  carbon  in  the  presence  of 
the  latter  gas.  It  was  at  one  time  believed  that  the  carbon  dioxide  of 
venous  blood  resulted  from  the  oxidation  of  substances  in  the  blood 
itself.  It  has,  however,  been  shown  that  the  blood  itself  has  very  slight 
oxidizing  powers,  and  that  in  the  frog  the  whole  of  the  blood  may  be 
replaced  by  saline  solution  without  producing  any  marked  effect  upon 
the  metabolism  of  the  body.  It  is  obviously  nnlikely  that  any  but  very 
slight  oxidation  could  go  on  in  such  a  medium.  It  has  moreover  been 
demonstrated  that  the  tension  of  carbon  dioxide  in  the  tissues  is  con- 
siderably greater  in  the  tissues  than  it  is  in  the  venous  blood. 

Special  Respiratory  Acts. 

It  will  be  well  here,  perhaps,  to  explain  certain  special  respiratory 
acts,  which  appear  at  first  sight  somewhat  complicated,  but  cease  to  be 
so  when  the  mechanism  by  which  they  are  performed  is  clearly  under- 
stood. The  diagram  (fig.  219)  shows  that  the  cavity  of  the  chest  is  sep- 
arated from  that  of  the  abdomen  by  the  diaphragm,  which,  when  acting, 
will  lessen  its  curve,  and  thus  descending,  will  push  dowmvard  and 
forward  the  abdominal  viscera;  while  the  abdominal  muscles  have  the 
opposite  effect,  and  in  acting  will  jiush  the  viscera  upward  and  back- 
ward, and  with  them  the  diaphragm,  supposing  its  ascent  to  be  not 
from  any  cause  interfered  with.  It  will  also  be  seen  that  the  lungs 
communicate  with  the  exterior  of  the  body  through  the  trachea  and 
larynx,  and  further  on  through  the  mouth  and  nostrils — through  either 
of  them  separately,  or  through  both  at  the  same  time,  according  to  the 
position  of  the  soft  palate.  The  stomach  communicates  with  the  ex- 
terior of  the  body  through  the  oesophagus,  pharynx,  and  mouth;  while 


RESPIRATIOX.  267 

below  the  rectum  opens  at  the  anus,  and  the  bladder  through  the  ure- 
thra. All  these  openings,  through  which  the  hollow  viscera  communi- 
cate with  the  exterior  of  the  body,  are  guarded  by  muscles,  called 
sphincters,  which  can  act  independently  of  each  other. 

Sighiny. — In  sighing  there  is  a  somewhat  prolonged  inspiration;  the 
air  almost  noiselessly  joassiug  in  through  the  glottis,  and  by  the  elastic 
recoil  of  the  lungs  and  chest- walls,  and  probably  also  of  the  abdominal 
walls,  being  suddenly  expelled. 

In  the  first,  or  inspirafonj  part  of  this  act,  the  descent  of  the  dia- 
phragm presses  the  abdominal  viscera  downward,  and  of  course  this 
pressure  tends  to  evacuate  the  contents  of  such  of  them  as  communicate 
with  the  exterior  of  the  body.  Inasmuch,  however,  as  their  various 
openings  are  guarded  by  sphincters,  in  a  state  of  constant  tonic  contrac- 
tion, there  is  no  escape  of  their  contents,  and  the  air  simjily  enters  the 
lungs.  In  the  second,  or  expiratory  part  of  the  act,  pressure  is  also 
made  on  the  abdominal  viscera  in  the  opposite  direction,  by  the  recoil 
of  the  abdominal  Avails;  but  the  pressure  is  relieved  by  the  escape  of  air 
through  the  open  glottis,  and  the  relaxed  diaphragm  is  pushed  up  again 
into  its  original  position.  The  sphincters  of  the  stomach,  rectum,  and 
bladder,  act  in  the  same  manner  as  before. 

Hiccovgh  resembles  sighing  in  that  it  is  an  inspiratory  act:  but  tlie 
inspiration  is  sudden  instead  of  gradual,  the  diaphragm  acting  suddenly 
and  spasmodically;  and  the  air,  suddenly  rushing  through  the  unpre- 
pared rima  glottidis,  causes  vibration  of  the  vocal  cords  and  the  jDecu'iar 
sound. 

Coughinfi. — In  the  act  of  coughing  there  is  most  often  first  of  all  a 
deep  inspiration,  followed  by  an  expiration;  but  the  latter,  instead  of 
being  easy  and  uninterrupted,  as  in  normal  breathing,  is  obstructed,  the 
glottis  being  momentarily  closed  by  the  approximation  of  the  vocal 
cords.  The  abdominal  muscles,  then  strongly  acting,  push  up  the 
viscera  against  the  diaphragm,  and  thus  make  pressure  on  the  air  in  the 
lungs  until  its  tension  is  sufficient  to  noisily  open  the  vocal  cords  which 
oppose  its  outward  passage.  In  this  way  considerable  force  is  exercised, 
and  mucus  or  any  other  matter  that  may  need  expulsion  from  the  air- 
passages  is  quickly  and  sharply  expelled  by  the  outstreaming  current  of 
air.  It  will  be  evident  on  reference  to  fig.  217,  that  pressure  exercised 
by  the  abdominal  muscles  in  the  act  of  coughing,  acts  lis  forcibly  on  the 
abdominal  viscera  as  on  the  lungs,  inasmuch  as  the  viscera  form  the 
medium  by  which  the  upward  pressure  on  the  diaphragm  is  made,  and 
there  is  of  necessity  quite  as  great  a  tendency  to  the  expulsion  of  their 
contents  as  of  the  air  in  the  lungs.  The  instinctive  and  if  necessary 
voluntarily  increased  contraction  of  the  sphincters,  however,  prevents 
any  escape  at  the  openings  guarded  by  them,  and  the  pressure  is  effec- 
tive at  one  part  only,  at  the  rima  glottidis. 


268 


HANDBOOK    OF   PHYSIOLOGT, 


Sneezing. — The  same  remarks  that  apply  to  coughing,  are  almost 
exactly  applicable  to  the  act  of  sneezing;  but  in  this  instance  the  blast 
of  air,  on  escaping  from  the  lungs,  is  directed,  by  an  instinctive  contrac- 
tion of  the  pillars  of  the  fauces,  and  descent  of  the  soft  palate,  chiefly 
through  the  nose,  and  any  offending  matter  is  thence  expelled. 

Speaking. — In  speaking,  there  is  a  voluntary  expulsion  of  air  through 
the  glottis  bv  means  of  the  expiratory  muscles.     The  vocal  cords,  by  the 


Fig.  217. 

muscles  of  the  larynx,  are  put  in  a  jDroper  position  and  state  of  tension 
for  vibrating  as  the  air  jDasses  over  them,  and  sound  is  produced.  The 
sound  is  moulded  into  articulate  speech  by  the  tongue,  teeth,  lips,  etc. 
— the  vocal  cords  producing  the  sound  only,  and  having  nothing  to  do 
with  articulation. 

Singing. — Singing  resembles  speaking  in  the  manner  of  its  produc- 
tion; the  laryngeal  muscles,  by  variously  altering  the  position  and  de- 
gree of  tension  of  the  vocal  cords,  producing  the  different  notes.  Words 
used  in  the  act  of  singing  are  of  course  framed,  as  in  speaking,  by  the 
tongue,  teeth,  lips,  etc. 

Sniffing. — Snifhng  is  produced  by  a  rapidly  repeated  but  incomplete 


RESPIRATIOX.  269 

action  of  the  diaphragm  and  other  inspiratory  muscles.  The  mouth  is 
closed,  and  the  whole  stream  of  air  is  made  to  enter  the  air-passages 
through  the  nostrils.  The  alse  nasi  are  commonly  at  the  same  time 
instinctively  dilated. 

Sobbing. — Sobbing  consists  of  a  series  of  convulsive  inspirations,  at 
the  moment  of  which  the  glottis  is  usually  more  or  less  closed. 

Laughing. — Laughing  is  made  up  of  a  series  of  short  and  rapid  expi- 
rations. 

Yaivning. — Yawning  is  an  act  of  inspiration  but  is  unlike  most  of 
the  preceding  actions  as  it  is  always  more  or  less  involuntary.  It  is 
attended  by  a  stretching  of  various  muscles  about  the  palate  and  lower 
jaw,  which  is  probably  analogous  to  the  stretching  of  the  muscles  of  the 
limbs  in  which  a  weary  man  finds  relief,  as  a  voluntary  act,  when  they 
have  been  some  time  out  of  action.  The  involuntary  and  reflex  charac- 
ter of  yawning  probably  depends  on  the  fact  that  the  muscles  concerned 
are  themselves  at  all  times  more  or  less  used  involuntarily,  and  require, 
therefore,  something  beyond  the  exercise  of  the  will  to  set  them  in 
action.  For  the  same  reason,  yawning,  like  sneezing,  cannot  be  well 
performed  voluntarily. 

Sucking. — Sucking  is  not  properly  a  respiratory  act,  but  it  may  be 
most  conveniently  considered  in  this  place.  It  is  caused  chiefly  by  the 
depressor  muscles  of  the  os  hyoides.  These,  by  drawing  downward  and 
backward  the  tongue  and  floor  of  the  mouth,  produce  a  partial  vacuum 
in  the  latter:  and  the  weight  of  the  atmosjihere  then  acting  on  all  sides 
tends  to  produce  equilibrium  on  the  inside  and  outside  of  the  mouth  as 
best  it  may.  The  communication  between  the  mouth  and  pharynx  is 
completely  shut  off  by  the  contraction  of  the  pillars  of  the  soft  palate 
and  descent  of  the  latter  so  as  to  touch  the  back  of  the  tongue;  and  the 
e(iuilibrium,  therefore,  can  be  restored  only  by  the  entrance  of  some- 
thing through  the  mouth.  The  action,  indeed,  of  the  tongue  and  floor 
of  the  mouth  in  sucking  may  be  compared  to  that  of  the  piston  in  a 
syringe,  and  the  muscles  which  pull  down  the  os  hyoides  and  tongue,  to 
the  power  which  draws  the  handle. 

The  Nervous  Apparatus  of  Respiration. 

Like  all  other  functions  of  the  body,  the  discharge  of  which  is  nec- 
essary to  life,  respiration  is  essentially  an  involuntary  act.  Unless  these 
were  the  case,  life  would  be  in  constant  danger,  and  Avould  cease  on  the 
loss  of  consciousness  for  a  few  moments,  as  in  sleep.  It  is,  however, 
also  necessary  that  respiration  should  be  to  some  extent  under  the  con- 
trol of  tho  will.  For  were  it  not  so,  it  would  be  impossible  to  j^erform 
those  respiratory  acts  which  have  been  just  discussed,  such  as  speaking,, 
singing,  and  the  like. 


270  HANDBOOK    OF    PHYSIOLOGY. 

It  has  been  known  for  centuries  that  there  exists  a  district  of  the. 
central  nervous  system  on  the  destruction  of  which  both  respiration 
and  life  cease.  All  attempts  to  localize  this  district,  however,  before 
those  of  Flourens  were  unsuccessful.  Flourens,  after  many  series  of 
experiments  as  to  the  exact  position  of  what  he  called  the  "knot  of 
life"  (noeud  vital),  placed  it  in  the  fourth  ventricle,  at  the  point  of  the 
V  in  the  gray  matter  at  the  lower  end  of  the  calamus  scriptorius;  a  dis- 
trict of  considerable  size,  viz.,  5  mm.,  on  both  sides  of  the  middle  line. 
Observers  subsequent  to  Flourens  have  attempted  to  show  that  the  chief 
respiratory  centre  on  the  one  hand  is  situated  higher  up  in  the  nervous 
system,  e.g.,  in  the  floor  of  the  third  ventricle  (Christian!),  or  in  the 
corpora  quadrigemina  (Martin  and  Booker,  Christiani,  and  Stanier),  or 
on  the  other  hand,  lower  down  in  the  spinal  cord,  and  that  the  medullary 
centres,  if  they  exist,  are  either  accessory  or  subservient  to  such  centres. 
The  balance  of  experimental  evidence,  however,  is  to  prove  that  the  sole 
centres  for  respiration  is  a  limited  district  in  the  medulla  oblongata  in 
close  connection  with  the  vagus  nucleus  on  each  side,  with  which  they 
are  probably  identical.  The  destruction  of  this  district  stops  respira- 
tion forever;  whereas,  if  it  be  left  in  connection  with  the  muscles  of 
respiration  by  their  nerves,  although  the  remainder  of  the  central  nervous 
system  be  separated  from  it,  respiration  continues.  It  may  be  considered 
;ilmost  certain  that  the  medullary  centre  is  the  only  true  respiratory 
centre,  and  that  the  observations  of  Langendorif,  that  in  newly-born 
animals  in  which  the  medulla  has  been  cut  immediately  or  a  few  milli- 
metres below  the  point  of  the  calamus  scriptorius  respiration  continues 
for  some  time  as  in  normal  animals  cannot  be  received.  We  are  indebted 
to  Marckwald  for  much  information  on  this  subject,  and  he  has  come  to 
the  conclusion  that  normal  respiration  does  not  occur  after  division  of 
the  bulb  from  the  cord,  and  that  the  so-called  respiratory  movements 
noticed  by  Langendorff  are  merely  tetanic  contractions  of  the  respira- 
tory muscles  with  which  often  enough  other  muscles  take  part. 

The  action  of  the  medullary  centre  is  to  send  out  impulses  during 
inspiration,  which  cause  respiratory  movements  of  the  muscles — («)  of 
the  nostrils,  and  jaws  through  the  facial  and  inferior  division  of  the 
fifth  nerves;  {h)  of  the  glottis,  chiefly  through  the  inferior  laryngeal 
branches  of  the  vagi;  {c)  of  the  intercostal  and  other  muscles  which 
produce  raising  of  the  ribs,  chiefly  through  the  intercostal  nerves,  and 
{(1)  of  the  diaphragm  through  the  phrenic  nerves. 

If  any  one  of  these  sets  of  .nerves  be  divided,  respiratory  movements 
of  the  corresponding  part  cease. 

Similarly  it  may  be  supposed  that  the  centre  sends  out  impulses  dur- 
ing expiration  to  certain  other  muscles.  It  has  been  suggested,  however, 
that  the  centre  consists  of  two  parts,  or  is  double,  and  that  it  is  made 
up  of  an  inspiratory  centre,  which  is  constantly  in  action,  and  of  an  ex- 


RESPIKATION".  27  H 

piratory  centre,  which  acts  less  generally,  inasmuch  as  ordinary  tranquil 
expiration  is  seldom  more  than  an  elastic  recoil,  and  not  a  muscular  act 
to  any  marked  degree. 

Assuming  this  view  of  the  double  centres  to  be  correct,  of  their  ex- 
act mode  of  action  there  is  some  difference  of  opinion;  it  is  now  generally 
thought  that  they  act  automatically,  but  are  influenced  by  afferent  im- 
pulses from  the  j)eriphery,  as  well  as  by  impulses  passing  down  from 
the  cerebrum.  The  centre  is,  in  other  words,  both  automatic  and  re- 
flex.    It  will  be  simplest  to  discuss  its  reflex  function  first  of  all. 

Action  of  Afferent  Stimuli. — {a)  Action  of  the  vagi. — If  both  vagi 
be  divided  in  the  neck,  the  respirations  become  much  slower  and  deeper; 
this  may  be  the  case,  but  to  a  less  marked  degree,  if  one  of  the  nerves 
is  divided  instead  of  both.  If  the  central  end  of  the  divided  nerve  be 
stimulated  with  a  weak  interrupted  current,  the  most  constant  effect  is 
that  the  respirations  are  quickened,  and  if  the  stimuli  are  properly  reg- 
ulated, the  normal  rhythm  of  respiration  may  be  resumed.  If  the  stimuli 
be  repeated  with  sufficient  quickness,  after  a  while  the  breathing  is 
brought  to  a  stand-still  at  the  height  of  inspiration  by  tetanus  of  the 
diaphragm.  Sometimes,  however,  stimulation  of  the  central  end  of  the 
divided  vagi  produces  still  greater  slowing  than  that  which  follows 
the  division,  so  that  if  it  be  continued,  the  respirations  cease,  with  the 
diaphragm  in  a  condition  of  complete  relaxation.  Marckwald  considers 
that  the  differences  in  the  effects  of  vagus  stimulation  are  due  to  the 
stimulus  being  applied  to  the  nerve  at  different  periods  in  the  respira- 
tory cycle,  and  that  the  action  of  the  vagus  may  be  to  call  forth  either 
inspiration  or  expiration — the  impulses  passing  up  the  vagi  being  neces- 
sary to  the  production  of  the  normal  respiratory  rhythm.  The  fibres 
of  the  vagus  are  used  under  the  following  circumstances,  those  fibres 
which  tend  to  inhibit  expiration  and  to  stimulate  inspiration  are  stim- 
ulated at  their  distribution  in  the  lung  when  the  lung  is  empty  and  in 
a  condition  of  expiration,  and  the  fibres  which  tend  to  inhibit  inspira- 
tion and  to  promote  expiration  are  stimulated  when  the  lung  is  fully  ex- 
panded. The  afferent  impulses  are  the  results  of  mere  mechanical 
stimulation,  and  do  not  depend  upon  the  chemical  nature  of  the  gases 
within  the  pulmonary  alveoli.  The  vagus  always  acts  upon  the  centres 
as  a  stimulator  of  discharge,  or  exciter  of  catabolism. 

{b)  Action  of  the  superior  laryngeal  nerves.— If  the  superior 
laryngeal  branch  of  the  vagus  be  divided,  which  usually  produces  no 
apparent  effect,  and  the  central  end  be  stimulated,  the  effect  is  very 
constant,  respirations  are  slowed,  but  there  is  a  tendency  toward  expi- 
ration, as  is  shown  by  the  contraction  of  the  abdominal  muscles.  Thus 
if  the  vagus  fibres  contain  fibres  which  stimulate  inspiration  and  inhibit 
expiration,  as  well  as  other  fibres  which  have  the  reverse  effect,  the  su- 
perior laryngeal  fibres  inhibit  inspiration  and  stimulate  expiration. 


272  HANDBOOK    OF    PHYSIOLOGY. 

The  superior  laryngeal  nerves  are  true  expiratory  nerves,  and  may 
be  set  in  action  when  the  mucous  membrane  of  the  larynx  is  irritated. 
They  are  not  constantly  in  action  like  the  vagi. 

(c)  Action  of  the  glosso-pharyngeal  nerves. — It  has  been  as- 
certained, chiefly  by  the  researches  of  Marckwald,  that  while  division  of 
the  glosso-pharyngeal  nerves  produces  no  effect  upon  respiration,  stim- 
ulation of  them  causes  inhibition  of  inspiration  for  a  short  period.  This 
action  accounts  for  the  very  necessary  cessation  of  breathing  during 
swallowing.  The  effect  of  the  stimulation  is  only  temporary,  and  is 
followed  by  normal  breathing  movements. 

{d)  Action  of  other  sensory  nerves. — The  respiratory  centres 
are  as  a  rule  stimulated  to  produce  respiration  by  impressions  conveyed 
by  sensory  nerves,  e.g.,  the  nerves  of  the  skin;  cold  water  applied  to 
the  sui-face  is  almost  invariably  followed  by  a  deep  inspiration.  Stimu- 
lation of  the  splanchnics  and  of  the  abdominal  branches  of  the  vagi 
produce  expiration.  The  fifth  nerves,  as  well  as  the  glosso-pharyngeal 
and  the  superior  laryngeal,  inhibit  inspiration,  but  they  tend  to  produce 
a  gradual  slowing  and  not  an  absolute  inhibition,  as  do  the  glosso- 
pharyngeal. 

It  must  be  remembered  that  although  many  sensory  nerves  may  on 
stimulation  be  made  to  produce  an  effect  upon  the  respiratory  centres, 
there  is  no  evidence  to  show  that  any  one  of  them,  except  the  vagi,  is 
constantly  in  action.  The  vagi  indeed  are,  as  far  as  we  know,  the  only 
normal  regulators  of  respiration. 

Automatic  Action  of  the  Respiratory  Centres. — Although  it  has  been 
very  definitely  proved  that  the  respiratory  centres  may  be  affected  by 
afferent  stimuli,  and  particularly  by  those  reaching  them  through  the 
vagi,  there  is  reason  for  believing  that  the  centres  are  capable  of  sending 
out  efferent  impulses  to  the  respiratory  muscles  without  the  action  of 
any  afferent  stimuli.  Thus,  if  the  brain  be  removed  above  the  bulb, 
respiration  continues.  If  the  spinal  cord  be  divided  below  the  bulb,  the 
facial  and  laryngeal  respiratory  movements  continue,  although  no  affer- 
ent impulses  can  reach  the  centres  except  through  the  cranial  sensory 
nerves,  and  tliese,  as  we  have  seen,  are  not  always  in  action,  and  indeed 
may  be  divided  without  producing  any  effect,  when  the  bulb  and  cord 
are  intact.  As  has  been  shown,  too,  respiration  continues  when  the  vagi 
are  divided.  All  of  these  experiments  render  it  highly  probable  that 
afferent  impulses  are  not  required  in  order  that  the  respiratory  centres 
should  send  out  efferent  impulses  of  some  kind  to  the  respiratory  mus- 
cles; these  centres,  then,  are  automatic.  How  they  act  in  the  absence 
of  afferent  stimuli  has  been  demonstrated  by  Marckwald.  He  has  shown 
—  (rt)  firstly,  that  if  the  bulb  be  separated  from  the  brain,  and  the  vagi 
be  then  cut,  there  is  first  of  all  inspiratory  spasm  followed  by  irregular 
spasm  of  muscles  both  of  inspiration  and  expiration,  and  death;  {h) 


RESPIRATIOX.  273 

secondly,  that  if  the  vagi  are  divided,  the  respirations,  although  altered 
in  character,  are  regular,  but  that  if  then  the  brain  is  separated  from 
the  medulla,  the  same  respiratory  spasms  occur.  From  these  experiments 
it  is  concluded  that  the  automatic  action  of  the  centres  consists  in  the 
liberation  of  respiratory  spasms  only,  and  not  of  regular  rhythmic  move- 
ments; but  that  impressions  reaching  the  centres  either  from  the  cere- 
brum or  through  the  vagi,  prevent  the  gathering  tension  in  the  centres 
from  becoming  too  great,  and  convert  the  spasms  which  would  other- 
wise arise  into  regular  movements.  The  chief  ditference  between  the 
action  of  the  vagi  and  of  the  cerebral  tracts,  is  that  the  former  are  always 
in  action,  whilst  the  latter  are  not.  When  the  vagi  are  in  action  and  the 
higher  centres  are  not,  periodic  respiration  takes  place,  that  is  to  say, 
respirations  occurring  in  groups,  each  such  group  being  followed  by  a 
pause;  a  type  of  respiration  known  as  Cheyne- Stokes  breathing,  to  which. 
we  shall  return  presently.  It  will  be  thus  seen  that  even  the  ordinary 
action  of  the  respiratory  centres  is  to  a  large  extent  reflex,  and  depend- 
ent upon  vagus  or  cerebral  stimulation. 

Method  of  Stiniulation  of  the  Respiratory  Centres. — Apart  then  from 
afferent  impulses,  the  respiratory  centres  are  capable  of  working  auto- 
matically, and  this  fact  has  been  explained  by  the  supposition  that  they 
are  stimulated  to  action  by  the  condition  of  the  blood  circulating  through 
them,  since  when  the  blood  becomes  more  and  more  venous  the  action 
of  the  centres  becomes  more  and  more  energetic,  and  if  the  air  is  pre- 
vented from  entering  the  chest,  the  respiration  in  a  short  time  becomes 
very  labored.  Any  obstruction  to  the  entrance  of  air  indeed,  whether 
partial  or  complete,  is  followed  by  an  abnormal  rapidity  of  the  inspira- 
tory acts.  The  condition  caused  by  any  incerference  with  the  free  ex- 
change of  gases  in  the  lungs,  or  by  any  circumstance  in  consequence  of 
which  the  oxygen  of  the  blood  is  used  up  in  an  abnormally  quick  man- 
ner, is  known  as  dyspncea.  If  the  aeration  of  the  blood  is  much  inter- 
fered with,  not  only  are  the  ordinary  respiratory  muscles  employed,  but 
also  those  muscles  of  extraordinary  inspiration  and  expiration  which 
have  been  previously  enumerated.  Thus  as  the  blood  becomes  more  and 
more  venous,  the  action  of  the  medullary  centres  becomes  more  and 
more  active.  The  question  has  been  much  debated  as  to  what  quality 
of  the  venous  blood  it  is  which  causes  this  increased  activity;  whether 
it  is  its  deficiency  of  oxygen  or  its  excess  of  carbonic  acid.  It  has  been 
answered  to  some  extent  by  the  experiments,  which  show  on  the  one 
hand  that  dyspnoea  occurs  when  there  is  no  obstruction  to  the  exit  of 
carbonic  acid  as  when  an  animal  is  placed  in  an  atmosphere  of  nitrogen, 
and  that  it  cannot  therefore  be  due  to  the  accumulation  of  carbonic 
acid;  and  on  the  other,  that  if  plenty  of  oxygen  is  supplied,  true  dyspnoea 
does  not  occur,  although  the  carbonic  acid  of  the  blood  is  in  excess.  It 
is  highly  probable,  therefore,  that  the  respiratory  centres  may  be  stimu- 


274  HANDBOOK    OF    PHYSIOLOGY. 

lated  to  action  by  the  absence  of  sufficient  oxygen  in  the  blood  circulat- 
ing in  it,  and  not  by  the  presence  of  an  excess  of  carbonic  acid. 

But  this  is  not  all,  since  it  has  been  j^i'oved  by  Marckwald  that  the 
medullary  centres  are  capable  of  acting  for  some  time  in  the  absence 
of  any  circulation,  and  after  excessive  bleeding.  The  view  taken  by 
this  author  with  regard  to  the  action  of  the  centres  is  as  follows :  the 
respiratory  centres  are  set  to  act  by  the  condition  of  their  metabolism, 
much  in  the  same  way  as  the  heart  is  set  to  beat  rliythmically.  When 
anabolism  is  completed,  catabolism  or  discharge  occurs,  and  this  alter- 
nate but  crude  and  spasmodic  action  will  occur  Avithout  a  definite  blood- 
supply,  as  long  as  the  centres  are  proj^erly  nourished  and  stimulated  by 
their  own  intercellular  fluid.  The  afferent  impulses  brought  by  the  vagi, 
in  consequence  of  the  stimulation  of  their  terminal  fibres  in  the  lungs, 
have  a  tendency  to  bring  about  catabolism,  and  to  convert  crude  respi- 
ratory spasms  into  regular  and  rhythmic  discharges.  In  the  absence  of 
the  vagus  stimulation,  the  impulses  from  the  cerebrum  may  be  effectual 
for  the  same  purpose. 

It  is  unreasonable  to  think,  however,  that  the  respiratory  centres  are 
independent  of  the  character  of  the  blood-supply  either  as  regards  quan- 
tity or  quality.  This  must  have  a  great  influence  ujoon  their  irritability; 
it  is  certain,  for  example,  that  venous  blood  greatly  increases  the  respi- 
ratory movements,  first  of  all  both  of  inspiration  and  of  expiration,  and 
then  of  the  latter  to  a  greater  degree.  It  may  be  that  the  diminution 
of  oxygen  in  the  blood  acts  as  a  stimulator  of  catabolism,  in  both  in- 
spiratory and  expiratory  centres,  but  j^'ii'ticularly  in  the  latter,  in  a 
manner  similar  to  but  not  identical  with,  that  of  the  vagus.  It  has  also 
been  shown  that  the  presence  of  the  products  of  great  muscular  metabo- 
lism in  the  blood  will  greatly  increase  the  irritability  of  the  respiratory 
centres,  even  if  the  blood  itself  be  not  particularly  venous  in  character. 

It  appears  that  the  inspiratory  and  expiratory  respiratory  centres  are 
bilateral,  and  that  each  pair  may  act  independently,  since  the  bulb  may 
be  divided  longitudinally,  and  then  if  one  vagus  be  divided,  the  respi- 
ratory rhythm  on  the  two  sides  of  the  body  becomes  unequal,  the  move- 
ments of  the  side  upon  which  the  vagus  is  divided  being  slower  than  on 
the  other  side,  while  stimulation  of  the  divided  nerve  acts  only  upon 
the  movements  of  its  own  side. 

Apncea. — When  we  take  several  deep  inspirations  in  rapid  succes- 
sion by  voluntary  effort,  we  find  that  we  can  do  without  breathing  for  a 
much  longer  time  than  usual;  in  other  words,  several  rapid  respirations 
seem  to  inhibit  for  a  time  normal  respiratory  movements.  It  was 
thought  that  the  reason  for  this  partial  cessation  of  respiration,  which 
was  called  apnma,  is  that  by  taking  several  deep  breaths  we  overcharge 
our  blood  with  oxygen,  and  that  as  the  respiratory  centre  can  only  be 
stimulated  by  blood  in  which  the  standard  of  oxygen  is  below  a  certain 


RESPIRATION.  275 

level,  no  respiratory  impulses  can  occur  until  the  oxygen  tension  of  the 
blood  reach  that  level.  This  idea  must  now  be  modified,  if  not  given  up, 
in  face  of  the  experiments,  e.g.,  those  of  Hering,  on  cats'  blood  during 
apnoea,  which  have  shown  that  animals  in  a  condition  of  apnoea  may 
have  less  and  not  more  oxygen  in  their  blood  than  in  a  normal  state, 
although  the  carbonic  anhydride  is  less.  One  view  now  taken  of  the 
cause  of  apnoea  is  that  by  rapid  inflations  of  the  lungs  impulses  pass  up 
by  the  vagi,  by  means  of  which  inspiration  is  after  a  while  inhibited; 
<inother  view  is  that  by  the  repeated  stimulation  of  the  centre  by  vagus 
impulses  which  result  in  rapid  respiratory  movements,  anabolism  is  at 
last  arrested.  Apnoea  is  with  difficulty  produced,  if  at  all,  when  the 
Tagi  are  divided. 

Effects  of  Vitiated  Air. — Ventilation.— As  the  air  expired  from 
the  lungs  contains  a  large  proportion  of  carbon  dioxide  and  a  minute 
amount  of  organic  putrescible  matter,  it  is  obvious  that  if  the  same  air 
be  breathed  again  and  again,  the  proportion  of  carbonic  dioxide  and 
organic  matter  in  it  will  constantly  increase  till  it  becomes  unfit  to 
breathe;  long  before  this  point  is  reached  however,  uneasy  sensations 
occur,  such  as  headache,  languor,  and  a  sense  of  oppression.  It  is  a  re- 
markable fact,  however,  that  the  organism  after  a  time  adapts  itself  to 
a  very  vitiated  atmosphere,  and  that  a  person  soon  comes  to  breathe, 
without  sensible  inconvenience,  an  atmosphere  which,  when  he  first  en- 
ters it,  feels  intolerable.  Such  an  adaptation,  however  can  only  take 
place  at  the  expense  of  a  depression  of  all  the  vital  functions,  which 
must  be  injurious  if  long  continued  or  often  rej^eated. 

This  power  of  adaptation  is  well  illustrated  by  the  experiments  of 
Claude  Bernard.  A  sparrow  is  placed  under  a  bell-glass  of  such  a  size 
that  it  will  live  for  three  hours.  If  now  at  the  end  of  the  second  hour 
(when  it  could  have  survived  another  hour)  it  be  taken  out  and  a  fresh 
healthy  sparrow  introduced,  the  latter  will  perish  instantly. 

It  must  be  evident  that  provision  for  a  constant  and  plentiful  supply 
of  fresh  air,  and  the  removal  of  that  which  is  vitiated,  is  of  far  greater 
importance  than  the  actual  cubic  space  per  head  of  occupants.  Xot 
less  than  2,000  cubic  feet  per  head  should  be  allowed  in  sleeping  apart- 
ments (barracks,  hospitals,  etc.),  and  with  this  allowance  the  air  can  only 
be  maintained  at  the  proper  standard  of  purity  by  such  a  system  of  ven- 
tilation as  provides  for  the  supply  of  1,500  to  2,000  cubic  feet  of  fresh 
.air  per  head  per  hour.     (Parkes.) 

The  Effect  of  Respiration  on  the  Circulation, 

As  the  heart,  the  aorta,  and  pulmonary  vessels  are  situated  in  the 
air-tight  thorax,  they  are  exposed  to  a  certain  alteration  of  pressure 
when  the  capacity  of  the  latter  is  increased  in  inspiration;  for  although 
the  expansion  of  the  lungs  tends  to  counter-balance  this  increase  of  area, 


270 


HANDBOOK    OF    PHYSIOLOGY. 


it  never  does  so  entirely,  since  part  of  the  pressure  of  the  air  which  is 
drawn  into  the  lungs  through  the  trachea  is  expended  in  overcoming 
their  elasticity.  The  amount  thus  used  up  increases  as  the  lungs 
become  more  and  more  expanded,  so  that  the  pressure  inside  the  thorax 
during  inspiration,  as  far  as  the  heart  and  great  vessels  are  concerned, 
never  quite  equals  that  outside,  and  at  the  conclusion  of  inspiration  is 
considerably  less  than  the  atmospheric  pressure.  It  has  been  ascertained 
that  the  amount  of  the  pressure  used  up  in  tlie  way  above  described, 
varies  from  5  or  7  mm.  of  mercury  during  tlie  pause,  to  30  mm.  of 
mercury  when  the  lungs  are  expanded  at  the  end  of  a  deep  inspiration, 
so  that  it  will  be  understood  that  the  pressure  to  which  ther  heart  and 
great  vessels  are  subjected  diminishes  as  inspiration  progresses,  and  at 


Fig.  218.— Diagram  of  an  apparatus  illustranng  me  effect  of  iDspiration  upon  the  heart  and 
great  vessels  within  tlie  thorax.  I,  tlie  thorax  at  res  ;  II,  lUiring  inspiration  ;  d,  represents  the 
diaphragm  when  relaxed  ;  d',  when  ooiitraeted  (it  must  be  i  emembered  that  this  position  is  a  mere 
diagram),  i.e.,  when  the  capacity  of  the  thora''  is  eula.ged  ;  h,  the  heart;  v,  the  veins  entering  it, 
and  A,  the  aorta  ;  nl,  l/,  the  right  and  left  lung  ;  t,  th  trachea;  m,  mercurial  manometer  in  con- 
nection with  pleura.  The  increase  in  the  capacity  of  the  box  representing  the  thorax  is  seen  to 
dilate  the  heart  as  well  as  the  lungs,  and  so  to  pump  in  blood  through  v,  whereas  the  valve  prevents 
reflex  through  a.  The  position  of  the  mercury  in  m  shows  also  the  suction  which  is  taking  place. 
(Landois.) 


its  minimum  is  less  by  30  mm.,  than  the  normal  pressure,  760  mm.  of 
mercury.  It  will  be  understood  from  the  accompanying  diagram  how, 
that  if  there  were  no  lungs  in  the  chest,  if  its  capacity  were  increased, 
the  effect  of  the  increase  would  be  expended  in  pumping  blood  into  the 
heart  from  the  veins.  With  the  lungs  placed  as  they  are,  during  in- 
spiration the  pressure  outside  the  heart  and  great  vessels  is  diminished, 
and  they  have  therefore  a  tendency  to  expand  and  to  diminish  the  intra- 
vascular pressure.  The  diminution  of  pressure  within  the  veins  passing 
to  the  right  auricle  and  within  the  right  auricle  itself,  will  draw  the 
blood  into  the  thorax,  and  so  assist  the  circulation.  This  suction  action 
is  independent  of  the  suction  power  of  the  diastole  of  the  auricle  about 
which  we  have  previously  spoken.     The  effect  of  sucking  more  blood 


RESPIRATION.  277 

into  the  right  auricle  will,  aeferis  paribus,  increase  the  amount  passing 
through  the  right  ventricle,  which  also  exerts  a  similar  suction  action, 
and  through  the  lungs  into  the  left  auricle  and  ventricle,  and  thus  into 
the  aorta.  This  all  tends  to  increase  the  blood-pressure.  The  effect  of 
the  diminished  j'l'cssure  upon  the  pulmonary  vessels  will  also  help 
toward  the  same  end,  i.e.,  an  increased  flow  through  the  lungs,  so  that, 
as  far  as  the  heart  and  its  veins  are  concerned,  inspiration  increases  the 
blood-pressure  in  the  arteries.  The  effect  of  inspiration  upon  the  aorta 
and  its  branches  vvithin  the  thorax  would  be,  however,  contrary;  for  as 
the  pressure  outside  is  diminished  the  vessels  would  tend  to  expand,  and 
thus  to  diminish  the  tension  of  the  blood  within  them,  but  inasmuch  as 
the  large  arteries  are  capable  of  little  expansion  beyond  their  natural 
calibre,  the  diminution   of  the  arterial  tension   caused  by  this  means 


Fig.  219.— Comparison  of  blood-pressure  curve  with  curve  of  intra-thoracic  pressure.  (To  be  read 
from  left  to  right.)  a  is  the  curve  of  blood-pressure  with  irs  respiratory  undulations,  the  slower 
beats  on  the  descent  being  very  marked;  b  is  the  curve  of  intra-thoracic  pressure  obtained  by  con- 
necting one  limb  of  a  manometer  with  the  plural  cavity.  Inspiration  begins  at  i  mul  expiration  at 
€.  The  intra-thoracic  pressure  rises  very  rapidly  after  the  cessation  of  the  inspiratory  effort,  and 
then  slowly  falls  as  the  air  issues  from  the  chest;  at  the  beginning  of  the  inspiratory  effort  the  fall 
becomes  more  rajjid.     (M.  Foster.) 

would  be  insufficient  to  counteract  the  increase  of  blood-jiressure  pro- 
duced by  the  effect  of  inspiration  upon  the  veins  of  the  chest,  and  the 
balance  of  the  whole  action  would  be  in  favor  of  an  increase  of  blood- 
pressure  during  the  inspiratory  period.  But  if  a  blood-pressure  tracing 
be  taken  at  the  same  time  that  the  respiratory  movements  are  being 
recorded,  it  will  be  found  that,  although  speaking  generally,  the  arterial 
tension  is  increased  during  inspiration,  the  maximum  of  arterial  tension 
does  not  correspond  with  the  acme  of  inspiration  (fig.  219).  In  fact,  at 
the  beginning  of  inspiration  the  pressure  continues  to  fall,  then  gradually 
rises  until  the  end  of  inspiration,  and  continues  to  do  so  for  some  time 
after  expiration  has  commenced. 

As  regards  the  effect  of  expiration,  the  capacity  of  the  chest  is 
diminished,  and  the  intra-thoracic  pressure  returns  to  the  normal,  which 
is  not  exactly  equal  to  the  atmospheric  pressure.     The  effect  of  this  on 


278  HANDBOOK    OF    PHYSIOLOGY. 

the  veins  is  to  increase  their  extra-vascnlar  and  so  their  intra-vascular 
pressure,  and  to  diminish  the  flow  of  blood  into  the  left  side  of  the 
heart,  and  with  it  the  general  blood-pressure,  but  this  is  almost  exactly 
balanced  by  the  necessary  increase  of  arterial  tension  caused  by  the 
increase  of  the  extra- vascular  pressure  of  the  aorta  and  large  arteries,  sO' 
that  the  arterial  tension  is  not  much  affected  during  expiration  either 
way.  Thus,  ordinary  expiration  does  not  produce  a  distinct  obstruction 
to  the  circulation,  as  even  when  the  expiration  is  at  an  end  the  intra- 
thoracic pressure  is  less  than  the  extra-thoracic. 

The  effect  of  violent  expiratory  efforts,  however,  has  a  distinct  action 
in  obstructing  the  current  of  blood  through  the  lungs,  as  seen  in  the 
blueness  -of  the  face  from  congestion  in  straining,  this  condition  being- 
produced  by  pressure  on  the  small  pulmonary  vessels. 

We  may  summarize  this  mechanical  effect  of  respiration  on  the  blood- 
pressure  therefore,  and  say  that  inspiration  aids  the  circulation  and  so 
increases  the  arterial  tension,  and  ihat  although  ex2:)iration  does  not 
materially  aid  the  circulation,  yet  under  ordinary  conditions  neither  does, 
it  obstruct  it.  Under  extraordinary  conditions,  however,  as  in  violent 
expiration,  the  circulation  is  decidedly  obstructed. 

We  have  seen,  however,  that  there  is  no  exact  correspondence  between 
the  point  of  highest  blood-pressure  and  the  end  of  inspiration,  and  we 
must  suppose  that  there  are  other  mechanical  factors,  such,  for  example,, 
as  the  effect  of  the  abdominal  movements,  both  in  insj^iration  and  in 
expiration,  upon  the  arteries  and  veins  within  the  abdomen  and  of  the 
lower  extremities,  and  the  influence  of  the  varying  intrathoracic  pres- 
sure upon  the  pulmonary  vessels,  both  of  which  ought  to  be  taken  into 
consideration.  As  regards  the  first  of  these,  the  effect  during  insjiira- 
tion — as  the  cavity  of  the  abdomen  is  diminished  by  the  descent  of  the 
diaphragm — should  be  two-fold:  on  the  one  hand,  blood  would  be  sent 
upward  into  the  chest  by  compression  of  the  vena  cava  inferior;  on  the 
other  hand,  the  passage  of  blood  downward  from  the  chest  in  the 
abdominal  aorta,  and  upward  in  the  veins  of  the  lower  extremity,  would 
be  to  a  certain  extent  obstructed.  In  ordinary  expiration  all  this  would 
be  reversed,  but  if  the  abdominal  muscles  are  violently  contracted,  as  in 
extraordinary  expiration,  the  same  effect  would  be  produced  as  by  in- 
spiration. The  effect  of  the  varying  intrathoracic  pressure,  which  occurs- 
during  inspiration  upon  the  pulmonary  vessels  is  to  produce  an  initial 
dilatation  of  both  artery  and  veins,  and  this  delays  for  a  short  time  the 
passage  of  blood  toward  the  left  side  of  the  heart,  and  the  arterial 
pressure  falls,  but  the  fall  of  blood-pressure  is  soon  followed  by  a  steady 
rise,  since  the  flow  is  increased  by  the  initial  dilatation  of  the  vessels: 
the  converse  is  the  case  with  expiration.  As,  however,  the  pulmonary 
veins  are  more  easily  dilatable  than  the  pulmonary  artery,  their  greater 
distensibility  increases  the  flow  of   blood  as  inspiration  proceeds,  while 


RESPIKATIOX. 


279 


during  expiration,  except  at  its  beginning,  this  property  of  theirs  acts  in 
the  o^jposite  direction,  and  diminishes  the  flow.  Thus,  at  the  beginning 
of  inspiration  the  diminution  of  blood-pressure,  which  commenced  during 
expiration,  is  continued,  but  after  a  time  the  diminution  is  succeeded  by 
a  steady  rise;  the  reverse  is  the  case  with  expiration — at  first  a  rise  and 
then  a  fall. 

The  effect  of  the  nervous  system  in  producing  rhythmical  altera- 
tions quite  independent  of  the  mechanically  caused  undulations  of  the 


Fig.  220.— Traube-Herin^'s  curves.  (To  be  read  from  left  to  right.)  The  curves  1.  2,  3,  4,  and  5 
are  portions  selected  from  one  continuous  tracing  forming  the  record  of  a  prolonged  observation, 
so  that  the  several  curves  represent  successive  stages  of  the  same  experiment.  Each  curve  is  placed 
in  its  proper  position  relative  to  the  base  line,  which  is  omitted  ;  the  blood-pressure  rises  in  stages 
from  1  to  2,  3,  and  4,  but  falls  again  in  stage  5.  Curve  1  is  taken  from  a  period  when  artificial  res- 
piration was  being  kept  up,  but  the  vagi  having  been  divided,  the  pulsations  on  tlie  ascent  and  de- 
scent of  the  undulations  do  not  differ;  when  artificial  respiration  ceased  these  undulations  for  a 
while  disappeared,  and  the  blood-pressure  rose  .'Steadily  while  the  heart-heats  became  slower.  Soon, 
as  at  2,  new  undulations  appeared  :  a  little  later,  th^  blood-pressure  was  still  rising,  the  heart  beats 
still  slower,  but  the  undulations  still  more  obvious  (3);  still  later  (4),  the  pressure  was  still  higher, 
but  the  heart-beats  were  quicker,  and  the  midulatii  >ns  flatter,  the  pressure  then  began  to  fallrapidly 
(5),  and  continued  to  fall  un,.il  some  time  after  artificial  respiration  was  resumed.    CM.  Foster.) 

blood-pressure  is  two-fold.  In  the  first  place  the  cardio-inliihitory  centre 
is  stimulated  during  the  fall  of  blood-pressure,  and  produces  a  slower 
rate  of  heart-beat,  which  will  be  noticed  in  the  tracing  (fig.  220).  The 
undulations  during  the  decline  of  blood-pressure  are  therefore  longer 
but  less  frequent.  This  effect  disappears  when,  by  section  of  the  vagi, 
the  effect  of  the  centre  is  cut  off  from  the  heart.  In  the  second  place, 
the  vaso-motor  centre  sends  out  rhythmical  impulses,  by  which  undula- 
tions of  blood-pressure  are  produced,  quite  independent  of  the  so-called 


280  HANDBOOK    OF    PHYSIOLOGY. 

respiratory  unduliitions.  The  action  of  this  centre  in  producing  such 
unduhitions  is  thus  demonstrated.  In  an  animal  under  the  influence 
of  urari,  a  record  of  whose  blood-pressure  is  being  taken,  and  where 
artificial  respiration  has  been  stopped,  and  both  vagi  cut,  the  blood- 
pressure  curve  rises  at  first  almost  in  a  straight  line,  but  after  a  time 
rhythmical  undulations  occur  (called  Traube's  or  Traube-Herinxfs 
curves);  there  may  be  upward  of  ten  of  the  respiratory  undulations  in 
one  Traube-Hering  curve.  They  continue  as  long  as  the  blood-pressure 
continues  to  rise,  and  only  cease  when  the  vaso-motor  centie  and  the 
heart  are  exhausted,  when  the  pressure  falls.  The  undulations  cannot 
depend  upon  anything  but  the  vaso-motor  centre,  as  the  mechanical 
effects  of  respiration  have  been  eliminated  by  the  urari  and  by  the 
cessation  of  artificial  respiration,  and  the  effect  of  the  cardio-inhibitory 
centre  has  been  removed,  by  the  division  of  the  vagi.  The  rhythmic 
rise  of  blood-pressure  is  most  likely  due  to  a  rhythmic  constriction  of 
the  arterioles  followed  by  a  rhythmic  fall  of  pressure  and  relaxation, 
both  being  due  to  the  action  of  the  vaso-motor  centre.  The  vaso-motor 
centre,  therefore,  as  well  as  the  cardio-inhibitory,  is  capable  of  produc- 
ing rhythmical  undulations  of  blood-pressure. 

Cheyne-Stokes'  hreathing  is  a  rhythmical  irregularity  in  respirations 
which  has  been  observed  in  various  diseases,  and  is  especially  connected 
with  fatty  degeneration  of  the  heart.  Eespirations  occur  in  groups,  at 
the  beginning  of  each  group  the  inspirations  are  very  shallow,  but  each 
successive  breath  is  deeper  than  the  preceding,  until  a  climax  is  reached, 
after  which  the  inspirations  become  less  and  less  deep,  until  they  cease 
after  a  slight  pause  altogether.  This  phenomenon  appears  to  be  due  to 
the  want  of  action  of  some  of  the  usual  cerebral  influences  which  pass 
down  to  and  regulate  the  discharges  of  the  respiratory  centres. 

Whatever  is  the  exact  quality  of  the  venous  blood  which  excites  the 
respiratory  centre  to  produce  normal  respirations,  there  can  be  no  doubt 
that  as  the  blood  becomes  more  and  more  venous  from  obstruction  to 
the  entrance  of  air  into  the  lung,  or  from  the  blood  not  taking  up  from 
the  air  its  usual  supply  of  oxygen,  the  respiratory  centre  becomes  more 
active  and  excitable,  and  a  condition  ensues,  which  passes  rapidly  from 
Hyijerjiuoea  (excessive  breathing)  to  the  state  of  Dyspnrea  (difficult 
breathing),  and  afterward  to  ^isphi/xia  ;  and  the  latter,  unless  relieved, 
quickly  ends  in  death. 

The  ways  by  which  this  condition  of  asphyxia  may  be  produced  are 
very  numerous: — As,  for  example,  by  the  j^revention  of  the  due  entry 
of  oxygen  into  the  blood,  either  by  direct  obstruction  of  the  trachea  or 
other  part  of  the  respiratory  passages,  or  by  introducing  instead  of 
ordinary  air  a  gas  devoid  of  oxygen,  or,  by  interference  with  the  due  in- 
terchange of  gases  between  the  air  and  the  blood. 

The  symptoms  of  asphyxia  may  be  divided  into  three  groups,  which 


EESPIRATION".  281 

correspond  with  the  stages  of  the  condition  which  are  usually  recog- 
nized, these  are  (1),  the  stage  of  exaggerated  breathing;  (2),  the  stage 
of  convulsions;  (3),  the  stage  of  exhaustion. 

In  the  first  stage  the  breathing  becomes  more  rapid  and  at  the  same 
time  more  deep  than  usual,  the  inspirations  at  first  being  especially  ex- 
aggerated and  prolonged.  The  muscles  of  extraordinary  inspiration  are 
called  into  action,  and  the  effort  to  respire  is  labored  and  painful.  This 
is  soon  followed  by  a  similar  increase  in  the  expiratory  efforts,  which 
become  excessively  prolonged,  being  aided  by  all  the  muscles  of  extra- 
ordinary expiration.  During  this  stage,  which  lasts  a  varying  time, 
from  a  minute  upward,  according  as  the  deprivation  of  oxygen  is  sudden 
ov  gradual,  the  lips  become  blue,  the  eyes  are  prominent,  and  the  ex- 
pression intensely  anxious.  The  prolonged  respirations  are  accompanied 
by  a  distinctly  audible  sound;  the  muscles  attached  to  the  chest  stand 
out  as  distinct  cords.  This  stage  includes  the  two  conditions  hyperpnoea 
and  dyspnoea  already  spoken  of.  It  is  due  to  the  increasingly  powerful 
stimulation  of  the  respiratory  centres  by  the  increasingly  venous  blood. 

In  the  second  stage,  which  is  not  marked  out  by  any  distinct  line  of 
demarcation  from  the  first,  the  violent  expiratory  efforts  become  con- 
Tulsive,  and  then  give  way,  in  men  and  other  warm-blooded  animals  at 
any  rate,  to  general  convulsions,  which  arise  from  the  further  stimula- 
tion of  the  centres.  The  spasms  of  the  muscles  of  the  body  in  general 
occur,  and  not  of  the  respiratory  muscles  only.  The  convulsive  stage 
is  a  short  one,  and  lasts  far  less  than  a  minute. 

The  t/iird  stage  or  stage  of  e.rltanstion.  In  it,  the  respirations  all  but 
•cease,  the  spasms  give  way  to  flaccidity  of  the  muscles,  there  is  insensi- 
bility^ the  conjunctivae  are  insensitive  and  the  pupils  are  widely  dilated. 
JEvery  now  and  then  a  prolonged  sighing  inspiration  takes  place,  at 
longer  and  longer  intervals  until  they  cease  altogether,  and  death  en- 
sues. During  this  stage  the  pulse  is  scarcely  to  be  felt,  but  the  lieart 
may  beat  for  some  seconds  after  respirations  have  quite  ceased.  The 
condition  is  due  to  the  gradual  paralysis  of  the  respiratory  centre  by 
the  prolonged  action  of  the  increasingly  venous  blood. 

As  with  the  first  stage,  the  duration  of  the  second  and  third  stages 
■depends  whether  the  manner  of  the  deprivation  of  oxygen  is  sudden  or 
gradual.  The  convulsive  stage  is  short,  lasting,  it  may  be,  only  one 
minute.     The  third  stage  may  last  three  minutes  and  U2:)ward. 

The  conditions  of  the  vascular  system  in  asphyxia  are: — (1)  More  or 
less  interference  with  the  passage  of  the  blood  through  the  pulmonary 
blood-vessels;  (2)  Accumulation  of  blood  in  the  right  side  of  the  heart 
and  in  the  systemic  veins;  (o)  Circulation  of  impure  (non-aerated) 
blood  in  all  parts  of  the  body. 

After  death  from  asphyxia  it  is  found  in  the  great  majority  of  cases 
that  the  right  side  of  the  heart,  the  pulmonary  arteries,  and  the  systemic 


282  HANDBOOK    OF    PHYSIOLOGY. 

veins  are  gorged  with  dark,  almost  black  blood,  and  the  left  side  of  the 
lieart,  the  pulmonary  veins,  and  the  arteries  are  empty.  The  explana- 
tion of  these  appearances  maybe  thus  summarized:  when  respiration 
is  stopped,  venous  blood  at  first  passes  freely  through  the  lungs  to  the 
left  heart,  and  so  to  the  great  arteries.  When  it  reaches  the  arterioles 
either  by  its  direct  action  upon  their  muscular  tissue,  or  more  probably 
through  the  medium  of  the  vaso-motor  centres,  the  arterioles  contract, 
particularly  those  of  the  splanchnic  area,  the  blood-pressure  rises  and 
the  left  side  of  the  heart  becomes  distended.  This  latter  effect  may  be 
from  the  extra  action  of  the  right  heart,  but  is  more  probably  due  to 
the  increased  peripheral  resistance,  and  its  slower  beat.  Although  the 
arterioles  are  contracted,  a  little  blood  is  allowed  to  j^ass  through  them, 
and  this  highly  venous  bluod,  favored  by  the  labored  respiratory  move- 
ments, arrives  at  the  right  side  of  the  heart.  When  it  reaches  the  pul- 
monary arterioles  it  gives  rise  to  the  same  contraction  in  them  as  it  did 
in  the  systemic  vessels.  This  obstruction  to  the  circulation  through 
the  lungs  causes  a  distended  condition  of  the  right  heart  and  the  pul- 
monary artery,  and  on  the  other  hand,  produces  a  greatly  diminished 
blood-flow  through  the  pulmonary  veins  and  to  the  left  side  of  the  heart, 
resulting  after  a  time  in  practical  emptiness.  So  that  in  the  third  stage 
of  asphyxia  it  is  stated  by  some  observers  that  the  left  heart  gets  into 
the  condition  in  which  it  is  found  after  death.  Others  think  that  the 
empty  condition  of  the  left  heart  is  a  post-mortem  phenomenon.  In 
the  first  and  second  stages  of  tiie  condition  the  blood-pressure  continu- 
ously rises  until  it  reaches  a  point  far  above  the  normal.  The  veins  are 
greatly  engorged,  so  that  when  pricked  they  act  as  arteries,  inasmuch  as 
they  eject  the  blood  for  some  distance.  Both  sides  of  the  heart  and  the 
pulmonary  vessels  are  engorged  with  blood,  at  any  rate  during  the 
greater  portion  of  these  stages,  and  at  the  third  stage  blood-j^ressure 
falls  rapidly. 

Cause  of  death. — The  causes  of  these  conditions  and  the  manner  in 
which  they  act,  so  as  to  be  incompatible  with  life,  may  be  here  briefly 
considered. 

(1)  The  obstruction  to  the  passage  of  blood  through  the  lungs  occurs 
chiefly  in  the  later  stages  of  asphyxia,  the  obstruction  being  chiefly  in 
the  arterioles,  which  contract  under  the  influence  of  the  vaso-motor 
centre,  or  possibly  of  a  special  part  of  it,  which  governs  the  action  of 
the  pulmonary  blood-vessels. 

(2)  Accumulation  of  blood,  with  consequent  distention  of  the  right 
side  of  the  heart  and  of  the  systemic  veins,  is  the  direct  result,  at  least 
in  part,  of  the  obstruction  to  the  pulmonary  circulation  just  referred  to. 
Other  causes,  however,  are  in  operation,  {a)  The  vaso-motor  centres 
stimulated  by  blood  deficient  in  oxygen,  cause  contraction  of  all  the 
small  arteries  with  increase  of  arterial  tension,  and  as  an  immediato 


RESPIKATIOlSr.  283 

consequence  the  filling  of  the  systemic  veins,  (b)  The  increased  arterial 
tension  is  followed  by  inhibition  of  the  action  of  the  heart,  and  the 
heart,  contracting  less  frequently,  and  also  gradually  enfeebled  by  defi- 
cient supply  of  oxygen,  becomes  over-distended  with  blood  which  it 
cannot  expel.  At  this  stage  the  left  as  well  as  the  right  cavities  are 
over-distended. 

The  ill  effects  of  these  conditions  are  to  be  looked  for  partly  in  the 
heart,  the  muscular  fibi-es  of  which,  like  those  of  the  urinary  bladder  or 
any  other  hollow  muscular  organ,  may  be  paralyzed  by  over-stretching; 
and  partly  in  the  venous  congestion,  and  consequent  interference  with 
the  function  of  the  higher  nerve-centres,  especially  the  medulla  ob- 
longata. 

(3)  The  passage  of  non-aerated  blood  through  the  lungs  and  its  dis- 
tribution over  the  body  are  events  incompatible  with  life  in  one  of  the 
higher  animals  for  more  than  a  few  minutes;  the  rapidity  with  which 
death  ensues  in  asphyxia  being  due,  more  particularly,  to  the  effect  of 
non-oxygenized  blood  on  the  medulla  oblongata,  and,  through  the 
coronary  arteries,  on  the  muscular  substance  of  the  heart.  The  excita- 
bility of  both  nervous  and  muscular  tissue  is  dependent  on  a  constant 
and  large  supply  of  oxygen,  and,  Avheu  this  is  interfered  with,  excita- 
bility is  rapidly  lost. 

Effects  of  hreatiting  gases  other  fJuoi  the  atmosphere. — The  diminu- 
tion of  oxygen  has  a  more  direct  influence  in  the  production  of  the  usual 
symptoms  of  asphyxia  than  the  increased  amount  of  carbon  dioxide. 
Indeed,  the  fatal  effect  of  a  gradual  accumulation  of  carbon  dioxide 
in  the  blood,  when  a  due  supply  of  os3'gen  is  maintained,  resembles- 
rather  the  action  of  a  narcotic  poison  than  it  does  asphyxia. 

Then  again  we  must  carefully  distinguish  the  asphyxiating  effect  of 
an  insufficient  supply  of  oxygen  from  the  directly  poisonous  action  of 
such  gases  as  carbonic  oxide,  which  is  contained  to  a  considerable 
amount  in  common  coal-gas.  The  fatal  effects  often  produced  by  this 
gas  (as  in  accidents  from  burning  charcoal  stoves  in  small,  close  rooms) 
are  due  to  its  entering  into  combination  with  the  hsemoglobin  of  the 
blood-corpuscles  and  thus  expelling  the  oxygen.  The  partial  pressure 
of  oxygen  in  the  atmosphere  may  be  considerably  increased  without 
much  effect.  Hydrogen  may  take  the  place  of  nitrogen  if  the  oxygen 
is  in  the  usual  proportion  with  no  marked  ill  effect.  Sulphuretted 
hydrogen  interferes  with  the  oxygenation  of  blood.  Nitrous  oxide 
acts  directly  on  the  nervous  system  as  a  narcotic.  Certain  gases,  such 
as  carbon  dioxide  in  more  than  a  certain  proportion;  sulphurous 
and  other  acid  gases,  ammonia,  and  chlorine  produce  spasmodic 
closure  of  the  glottis,  and  are  irrespirable. 

As  conditions  causing  asphyxia  in  addition  to  the  obstruction  to  the 
trachea  or  elsewhere,  and  the  prevention  of  the  meeting  of  the  blood 


284  HANDBOOK    OP    PHYSIOLOGY. 

and  the  air  in  the  lung  tissue  by  the  blocking  of  one  or  more  branches 
of  the  pulmonary  artery,  may  be  mentioned  the  following: 

Alteration  in  the  atmospheric  jjressure. — The  normal  condition  of 
breathing  is  that  the  oxygen  of  the  air  breathed  should  be  at  the  pres- 
sure of  \  of  the  atmosphere,  viz.,  |  of  760  mm.  of  mercury,  or  152  mm., 
but  it  is  found  that  life  may  be  carried  on  by  gradual  diminution  of 
the  oyxgen  pressure  to  considerably  less  than  one  half  of  this,  viz.,  to 
76  mm,,  or  -^^  partial  pressure,  which  is  reached  at  an  altitude  above 
15,000  feet.*  Any  pressure  less  than  this  may  begin  to  produce  altera- 
tions in  the  relations  of  the  gases  in  the  blood,  and  if  an  animal  is  sub- 
jected suddenly  to  a  marked  decrease  of  barometric  pressure,  and  so  of 
oxygen  pressure  (below  ?  per  cent),  it  is  thrown  into  convulsions,  and  it 
is  found  that  the  gases  are  set  free  in  the  blood-vessels,  no  doubt  carbon 
dioxide  and  oyxgen  as  well  as  nitrogen,  although  the  latter  is  the  only 
one  of  the  three  gases  the  jjresence  of  which  in  the  vessels  in  death 
from  this  condition  of  affairs  has  been  proved;  the  others  are  said  to 
be  reabsorbed.  Other  derangements  may  precede  this,  e.g.,  bleeding 
from  the  nose,  dyspncea,  and  vascular  derangement.  On  the  other  hand, 
the  oygxen  may  be  gradually  increased  to  a  considerable  extent  without 
marked  effect,  even  to  the  extent  of  8  or  10  atmospheres,  but  when  the 
oxygen  pressure  is  increased  up  to  20  atmospheres  the  animals  experi- 
mented upon  by  Paul  Bert  died  with  severe  tetanic  convulsions.  The 
alteration  of  pressure  above  or  below  a  certain  average  affects  primarily 
the  gaseous  interchange  in  the  lungs,  jyul  then  that  in  the  tissues  gene- 
rally, but  signs  of  dyspnoea  may  be  produced  as  well  either  by  cutting 
off  the  sup2)ly  of  blood  to  the  medullary  centres,  or  by  warming  the  hlood 
of  the  carotid  arteries  which  supply  them.  The  cause  in  the  former 
case  being  the  deprivation  of  oxygen  and  the  accumulation  of  the  car- 
bon dioxide,  and  of  the  latter,  the  increased  metabolism  of  the  centre 
set  up  by  the  warmed  blood. 

*  For  an  interesting  account  of  the  symptoms  produced  by  diminished  atmos- 
pheric pressure  in  those  mounting  to  very  high  altitudes,  Whymper's  "Travels 
amongst  the  Andes  of  the  Equator"  may  be  consulted. 


CHAPTEE  YIII. 

FOOD  AND   DIGESTION. 

The  object  of  digestion  is  to  bring  the  materials  of  the  food  into 
such  a  condition  that  they  may  be  taken  up  by  the  blood  and  lymphatic 
vessels,  and  so  rendered  available  for  the  wants  of  the  system.  Very 
few  of  these  materials  are  fit  for  this  purpose  when  taken  into  the  body, 
and  the  majority  would  therefore  be  to  all  intents  and  purposes  quite 
useless  unless  digested. 

It  is  unnecessary  to  mention  all  the  various  substances  which  may 
have  been  used  as  food  at  some  time  or  another,  and  we  shall  confine  our 
attention,  therefore,  to  the  chief  and  most  familiar  articles  of  diet. 

We  find,  then,  that  foods  may  be  divided  into  classes  corresponding 
closely  to  those  employed  to  describe  the  chief  substances  of  which  the 
animal  body  consists.  This  classification  may  be  recapitulated  as  fol- 
lows : — 

ORGANIC. 

I.   Foods  primarily  containing  Nitrogenous  substances,  consisting  of  Pro- 
teids,  e. (/., albumen,  casein,  myosin,  gluten,  legumin  and  their  allies; 
and   Gelatins,  e.g.,  gelatin,  elastin,  and  chondrin. 
II.  Food  primarily  containing  Non-Nitrogenous  substances,  comprising : 
(1.)  Amyloid  or  saccharine   bodies,   chemically  known   as  carbo-hydrates; 

e.  g. ,  starches  and  sugars. 
(2.)   Oils  and  fats. — These  substances  contain  carbon,  hydrogen,  and  oxy- 
gen, but  the  oxygen  is  less  in  amount  than   in  the  amyloids  and 
saccharine  bodies. 

INORGANIC. 

I.  Foods  which  supply  Mineral  and  saline  matter. 
II.   Liquid  food  containing  chiefly  Water. 

Man  requires  that  the  chief  part  of  his  food  should  be  cooked,  Yerj 
few  organic  substances  can  be  properly  digested  without  previous  ex- 
posure to  heat  and  to  other  manipulations  which  constitute  the  process 
of  cooking. 

Organic  nitrogenous  foods. 

a. — The  Flesh  of  Animals,  e.g.,  of  the  ox  (beef,  veal),  sheep  (mutton^ 
lamb),  pig  (pork,  bacon,  ham). 

Of  these,  beef  is  richest  in  nitrogenous  matters,  containing  about  20- 
per  cent,  whereas  mutton  contains  about   18  per  cent,  veal  1G.5,  and 

285 


286  HANDBOOK    OF    PHYSIOLOGY. 

pork,  10;  beef  is  also  firmer,  more  satisfying,  and  is  supjjosed  to  be 
more  strengthening  than  mutton,  whereas  the  latter  is  more  digestible. 
The  flesh  of  young  animals,  such  as  lamb  and  veal,  is  less  digestible  and 
less  nutritious.  Pork  is  comparatively  indigestible,  and  contains  a 
large  amount  of  fat. 

Flesh  contains: — (1)  Nitrogenous  bodies;  chiefly  myosin,  and  one  or 
more  glohulins;  serwn-albumin,  gelatin  (from  the  interstitial  fibrous 
connective  tissue);  elastin  (from  the  elastic  tissue),  as  well  as  lumio- 
globin.  (3)  Fatty  matters,  including  lecithin  and  cholesterin.  (3)  Ex- 
tractive matters,  some  of  which  are  agreeable  to  the  palate,  e.g.  osmazome, 
and  others,  which  are  weakly  stimulating,  e.g.,  creatin.  Besides,  there 
are  sarcolactic  and  inositic  acids,  taurin,  xanthin,  and  others.  (4)  Salts, 
chiefly  of  potassium,  calcium,  and  magnesium.  (5)  Water,  the  amount 
of  which  varies  from  15  per  cent  in  dried  bacon  to  39  in  pork,  51  to  53 
in  fat  beef  and  mutton,  to  72  per  cent  in  lean  beef  and  mutton.  (6)  A 
certain  amount  of  carbo-hydrate  material  is  found  in  the  flesh  of  some 
animals,  in  the  form  of  inosite,  dextrin,  grape  sugar,  and  (in  young 
animals)  ghjcogen. 


Beef. — Lean    . 

Fat   . 
Mutton. — Lean 

Fat      .        .        . 
Veal         .... 
Pork.— Fat 

Together  with  the  flesh  of  the  above-mentioned  animals,  that  of  the 
deer,  hare,  rabbit,  and  birds,  constituting  venison,  game,  and  poultry, 
should  be  added  as  taking  j)art  in  the  supply  of  nitrogenous  substances, 
and  n\^o  fish — salmon,  eels,  etc.,  and  shell-fish,  e.g.,  lobster,  crab,  mussels, 
oysters,  shrimps,  scollops,  cockles,  etc. 

Table  of  Percentage  Composition  of  Poultry  and  Fish.  —  (Letheby.) 

W^ater.       Albumen.         Fats.  Salts. 

Poultry 74  21  3.8  1.2 

'    (Singularly  devoid  of  fat,  and  is  therefore  generally  eaten  with  bacon 
or  pork.) 


Beef, 

iBY  ) 

Mutton, 

Pork, 

AND  Veal. 

>a  1  .  } 

ater. 

Albumen. 

Fats. 

Salts. 

72 

19.3 

3.6 

5.1 

51 

14.8 

29.8 

44 

72 

18.3 

4.9 

4.8 

53 

12.4 

31.1 

3.5 

63 

16.5 

15.8 

4.7 

39 

9.8 

48.9 

2.3 

Water.       Albumen. 

Fats. 

Salts. 

White  Fish 

78              18.1 

2.9 

1. 

Salmon        .         .         .         . 

77             16.1 

5.5 

1.4 

Eels  (very  rich  in  fat)    . 

75              9.9 

13.8 

1.3 

Oysters        .         .         .         . 

75.74       11.72 

2.42 

2.73 

(7.39  consist  of  non-nitrogenous  matter  and  loss.)     (Payen.) 
Even  now  the  list  of  fleshy  foods  is  not  complete,  as  the  flesh   of 
nearly  all  animals  has  been  occasionally  eaten,  and  we  may  presume 


FOOD    AND    DIGESTION.  28? 

that   except  for  difference  of  flavor,  etc.,  the  average    composition    is 
nearly  the  same  in  every  case. 

b.  Milk* — -Is  intended  as  the  entire  food  of  young  animals,  and  as 
such  contains,  when  pure,  all  the  elements  of  a  typical  diet.  (1)  Albu- 
minous substances  in  the  form  of  caseinogen,  and  serum  or  lact-albiimin. 
(2)  Fats  in  the  cream.  (3)  Carbo-hydrates  in  the  form  of  lactose  or  milk 
sugar.  (4)  '^•aXi^,  chie^j  calcium i^hosphate ;  and  (5)  Water.  From  it  we 
obtain  {a)  clieese,  which  is  the  clotted  caseinogen  or  casein  precipitated 
Avith  more  or  less  of  fat  according  as  the  cheese  is  made  of  skim  milk 
{skim  cheese),  of  fresh  milk  with  its  cream  (Cheddar  and  Cheshire),  or  of 
fresh  milk  plus  cream  (Stilton  and  double  Gloucester).  The  precipi- 
tated casein  is  allowed  to  ripen,  by  which  process  some  of  the  al- 
bumin is  further  split  up,  with  formation  of  fat.  (,5)  Cream,  consists  of 
the  fatty  globules  encased  in  caseinogen  and  serum-albumin,  and  which 
being  of  low  specific  gravity  float  to  the  surface,  {y)  Butter,  or  the 
fatty  matter  deprived  of  its  proteid  envelope  by  the  process  of  churning. 
{(i)  Buttermilk,  or  the  fluid  obtained  from  cream  after  butter  has  been 
formed;  very  rich  therefore  in  nitrogen.  (;)  HV/py,  or  the  fluid  which 
remains  after  the  precipitation  of  casein;  it  contains  sugar,  salt,  and  a 
small  quantity  of  albumen. 

Table  of  Composition  of  Milk,  Butter- milk,  Cream,  and  Cheese. — (Letheby 

AND  Pa  yen.  ) 

Nitrogenous  mattei-s.  Fats.  Lactose.  Salts.  Water. 
Milk  {Cow)         ....           4. 1            3. 9            5. 3            . 8        86 
Buttermilk      ....               4.1               .7             6.4             .8         88 

Cream         .         .         .         .  .  2.7  26.7  2.8  1.8         66 

Cheese.— Skim.      ...  44.8  6.3  —  4.9        44 

Cheese.— Cheddar    .         .         .  28.4  81.1  —  4.5        36 

Non-nitrogenous 
matter  and  loss. 

Cheese.— Neufchatel  (Fresh).  8.  40.71        36.58  .51       36.58 

c.  Eggs. — The  yolk  and  albumen  of  eggs  are  in  the  same  relation  as 
food  for  the  embryos  of  oviparous  animals  that  milk  is  to  the  young  of 
mammalia,  and  afford  another  example  of  the  natural  admixture  of 
the  various  alimentary  principles.  The  proteids  of  eggs  are  egg-albumin 
and  globulins,  of  which  the  vitelUn  of  the  yolk  is  most  important; 
nuclein  in  combination  with  iron  is  also  found.  In  addition  to  the 
three  common  fats  there  is  a  yellow  fat,  lutein  (lipoehome),  a  small 
quantity  of  grape  sugar;  lecitliin,  and  cliolesterin  and  inorganic  salts, 
chiefly  potassium  chloride  and  phosphates. 


Table  op  the  Percentage  Composition  of  Fowls'  Eggs. 


White 
Yolk 


itrogenous  substances. 

Fats. 

Salts. 

Water. 

20.4 



1.6 

78 

16. 

30.7 

1.3 

53 

*The  details  of  the  comijosition  of  milk  will  be  discussed  in  the  Chapter  on 
Secretion. 


288  UANDBOOK    OF    PHYSIOLOGY. 

d.  Legumi)ious  friiifs  are  used  by  vegetarians,  as  the  chief  source  of 
the  nitrogen  of  the  food.  Those  chiefly  used  are  j'jea*,  beans,  lentils, 
etc.,  they  contain  a  nitrogenous  substance  called  legumin,  allied  to 
albumen.  They  contain  about  25.30  per  cent  of  this  nitrogenous  body, 
and  twice  as  much  nitrogen  as  wheat. 

Organic  non-nitrogenous  foods. 

1.  Carbo-Tiych'ates. — a.  Bread,  made  from  the  ground  grain  obtained 
from  various  so-called  cereals,  viz.,  wheat,  rye,  maize,  barley,  rice,  oats, 
etc.,  is  the  direct  form  in  which  the  carbo-hydrate  is  supplied  in  an 
ordinary  diet.  It  contains  starch,  dextrin,  and  a  little  sugar.  It  also, 
besides  these,  contains  gluten,  composed  of  several  vegetable  proteids, 
and  a  small  amount  of  fat. 

Table  of  Percentage  Composition  of  Bread  and  Flour. 


Nitrogenous 
matters. 

Carbo- 

hydrates. 

Fats. 

Salts. 

Water. 

8.1 

51. 

1.6 

2.^ 

37 

10.8 

70.85 

o 

1.7 

15 

Bread 

Flour  .... 

Various  articles  of  course  besides  bread  are  made  from  flour,  e.g., 
sago,  macaroni,  biscuits,  etc.  There  is  dextrine  and  a  small  amount  of 
dextrose  in  bread,  particularly  in  the  crust. 

h.  Vegetables,  especially  potatoes.  They  contain  starch  and  sugar. 
In  cabbage,  turnips,  etc.,  the  salts  of  potassium  are  abundant. 

c.  Fruits  contain  sugar,  and  organic  acids,  tartaric,  malic,  citric, 
and  others. 

d.  Sugar,  chiefly  saccharose,  used  pure  or  in  various  sweetmeats. 

//.  Oils  and  fats. — The  substances  supplying  the  oils  and  fats  of  the 
food  are  chiefly  butter,  bacon  and  lard  (pig's  fat),  suet  (beef  and  mutton 
fat),  and  vegetable  oils.  These  contain  olein,  stearin,  and  palmitin. 
Butter  contains  others  in  addition,  while  vegetable  oils,  as  a  rule,  con- 
tain no  stearin. 

Mineral  or  Inorganic  Foods. 

The  salts  of  the  food. — Nearly  all  the  foregoing  substances  in  the 
preceding  classes,  contain  a  greater  or  less  amount  of  the  salts  required 
in  food,  but  green  vegetables  and  fruit  supply  certain  salts,  chiefly 
potassium,  without  which  the  normal  health  of  the  body  cannot  be 
maintained. 

Sodium  chloride  is  an  essential  food;  it  is  contained  in  nearly  all 
solids,  but  so  much  is  required  that  it  has  also  to  be  taken  as  a  condi- 
ment. Potassium  salts  are  supplied  in  muscle,  nerve,  in  meats  generally, 
and  in  potatoes.  Calcium  salts  are  supplied  in  eggs,  blood  of  meat,  wheat 
and  vegetables.     Iron  is  contained  in  haemoglobin,  in  milk,  eggs,  and 


FOOD    AND    DIGESTION.  289 

vegetables.  It  is  derived  in  all  cases,  so  it  is  supposed,  by  organic 
compounds,  into  which  it  is  built  up  during  plant  life,  or  during  the  life 
of  other  animals  (haBmatogens). 

Liquid  Foods. 

Water  is  consumed  alone,  or  together  with  certain  other  substances 
used  to  flavor  it,  e.g.,  tea,  coffee,  etc.  Tea  in  moderation  is  a  stimulant, 
and  contains  an  aromatic  oil  to  which  it  owes  its  peculiar  aroma,  an 
astringent  of  the  nature  of  tannin,  and  an  alkaloid,  theine.  The  composi- 
tion of  coffee  is  very  nearly  similar  to  that  of  tea.  Cocoa,  in  addition 
to  similar  substances  contained  in  tea  and  coffee,  contains  fat,  albumin- 
ous matter  and  starch,  and  must  be  looked  upon  more  as  a  food. 

Beer,  in  various  forms,  is  an  infusion  of  malt  (barley  which  has 
sprouted,  and  in  which  its  starch  is  converted  in  great  part  into  sugar), 
boiled  with  hops  and  allowed  to  ferment.  Beer  contains  from  1.2  to  8.8 
per  cent  of  alcohol. 

Cider  and  Perry,  the  fermented  juice  of  the  apple  and  pear. 

Wine,  the  fermented  juice  of  the  grape,  contains  from  6  or  7  (Ehine 
wines,  and  white  and  red  Bordeaux)  to  24-25  (ports  and  sherries)  per 
cent  of  alcohol. 

Spirits,  obtained  from  the  distillation  of  fermented  liquors.  They 
contain  upward  of  40-70  per  cent  of  absolute  alcohol. 

The  effect  of  cooking. — In  general  terms  this  may  be  said  to  make 
the  food  more  easily  digestible;  this  usually  implies  two  alterations, — 
food  is  made  more  agreeable  to  the  palate  and  also  more  pleasing  to  the 
eye.  Cooking  consists  in  exposing  the  food  to  various  degrees  of  heat, 
either  to  the  direct  heat  of  the  fire,  as  in  roasting,  or  to  the  indirect 
heat  of  the  fire,  as  iii  broiling,  baking,  or  frying,  or  to  hot  water,  as  in 
boiling  or  stewing.  The  effect  of  heat  upon  {a)  flesh  is  to  coagulate  the 
albumen  and  coloring  matter,  to  solidify  fibrin,  and  to  gelatinize  ten- 
dons and  fibrous  connective  tissue.  Previous  beating  or  bruising  (as 
with  steaks  and  chops)  or  keeping  (as  in  the  case  of  game),  renders  the 
meat  more  tender.  Prolonged  exposure  to  heat  also  develops  on  the  sur- 
face certain  erapyreumatic  bodies,  which  are  agreeable  both  to  the  taste 
and  smell.  By  placing  meat  in  hot  water,  the  external  coating  of  albu- 
men is  coagulated,  and  very  little,  if  any,  of  the  constituents  of  the 
meat  are  lost  afterward  if  boiling  be  prolonged;  but  if  the  constituents 
of  the  meat  are  to  be  extracted,  it  should  be  exposed  to  prolonged  sim- 
mering at  a  much  lower  temperature, and  the  "troth"  will  then  contain 
the  gelatin  and  extractive  matters  of  the  meat,  as  well  as  a  certain 
amount  of  albumen.     The  addition  of  salt  will  help  to  extract  myosin. 

The  effect  of  boiling  {b)  an  Qg^  is  to  coagulate  the  albumen,  which 
helps  to  render  it  more  easily  digestible.  Upon  (c)  milk,  the  effect  of 
19 


290  HANDBOOK    OF    PHYSIOLOGY, 

heat  is  to  produce  a  scum  composed  of  albumen  and  ii  little  caseinogeu 
(the  greater  part  of  the  caseinogen  being  uucoagulated)  with  some  fat. 
Upon  (tl)  vegetables,  the  cooking  j)roduces  the  necessary  effect  of  ren- 
dering them  softer,  so  that  they  can  be  more  readily  broken  up  in  the 
mouth;  it  also  causes  the  starch  grains  to  swell  up  and  burst,  and  so 
aids  the  digestive  fluids  in  penetrating  into  their  substance.  The  albu- 
minous matters  are  coagulated,  and  the  gummy,  saccharine  and  saline 
matters  are  removed.  The  conversion  of  flour  into  dough  is  effected  by 
mixing  it  with  water,  and  adding  a  little  salt  and  a  certain  amount  of 
yeast.  Yeast  consists  of  the  cells  of  an  organized  ferment  {Torula 
cerevism),  and  it  is  by  the  growth  of  this  plant,  changing  by  ferment 
action  the  sugar  produced  from  the  starch  of  the  flour,  that  a  quantity 
of  carbonic  acid  gas  and  alcohol  is  formed.  By  means  of  the  former 
the  dough  rises.  Another  method  of  making  dough  consists  in  mixing 
the  flour  with  water  containing  a  large  quantity  of  carbonic  acid  gas  in 
solution. 

By  the  action  of  heat  during  baking  [d)  the  dough  continues  to  ex- 
pand, and  the  gluten  being  coagulated,  the  bread  sets  as  a  permanently 
vesiculated  mass. 

The  food  is  first  of  all  received  into  the  mmith,  and  is  subjected  to 
the  action  of  the  teeth  and  tongue,  being  at  the  same  time  mixed  with 
the  first  of  the  digestive  juices — the  saliva.  It  is  then  swallowed,  and, 
passing  through  the  phanjnx  and  cesophagus  into  the  stomach,  is  sub- 
jected to  the  action  of  the  gastric  juice — the  second  digestive  juice. 
Thence  it  passes  into  the  intestines,  where  it  meets  with  the  hile,  the 
pancreatic  juice,  and  the  intestinal  juices,  all  of  which  exercise  an  in- 
fluence u23on  the  portion  of  the  food  not  already  absorbed  from  the 
stomach.  By  this  time  most  of  the  food  is  digested,  and  the  residue  of 
undigested  matter  leaves  the  body  in  the  form  of  forces  by  the  external 
opening  of  the  bowel. 

The  Mouth  is  the  cavity  contained  between  the  jaws  and  inclosed 
by  the  cheeks  laterally,  the  lips  anteriorly;  behind,  it  opens  into  the 
pharynx  by  the  fauces,  and  is  separated  from  the  nasal  cavity  above, 
by  the  hard  palate  in  front,  and  the  soft  palate  behind,  which  forms  its 
roof.  The  tongue  forms  the  lower  part  or  floor.  In  the  jaws  are  con- 
tained the  teeth,  and  when  the  mouth  is  closed  these  form  its  anterior 
boundaries.  The  whole  of  the  cavity  of  the  mouth  is  lined  with  strati- 
fied epithelium,  of  which  the  superficial  layers  are  squamous.  This 
epithelium  is  continuous  at  the  lips  with  that  of  the  skin  anteriorly, 
and  posteriorly  with  that  of  the  pharynx.  The  mucous  membrane 
itself,  varying  in  thickness  in  various  parts,  and  consisting  of  a  fine 
areolar  connective,  in  which  is  found  ade^ioid  tissue  in  considerable 
amount,  is  provided  with  numerous  small  t^ibular  glands  lined   with 


FOOD    AND    DIGESTION.  291 

columuar  epithelium,  and  resembling  in  structure  the  mucous  salivary 
glands,  to  be  presently  described.  Into  the  buccal  cavity  open  the 
ducts  of  the  salivary  glands,  which  are  three  in  number  on  either  side. 

In  the  mouth,  then,  the  food  is  subjected  to  the  action  of  the  teeth, 
or  is  masticated,  and  is  mixed  with  saliva.  These  processes  of  mastica- 
tion and  in  salivation  must  be  considered  more  in  detail. 

Mastication. — The  act  of  chewing,  or  mastication,  is  performed  by 
the  biting  and  grinding  movement  of  the  lower  range  of  teeth  against 
the  upper.  The  simultaneous  movements  of  the  tongue  and  cheeks 
assist  partly  by  crushing  the  softer  portions  of  the  food  against  the 
hard  palate  and  gums,  and  thus  supplementing  the  action  of  the  teeth, 
and  partly  by  returning  the  morsels  of  food  to  the  action  of  the  teeth, 
again  and  again,  as  they  are  squeezd  out  from  between  them,  until  the 
have  been  sufficiently  chewed 

Muscles. — The  simple  up  and  down,  or  biting  movements  of  the 
lower  jaw,  are  performed  by  the  temporal,  masseter,  and  internal  ptery- 
goid muscles,  the  action  of  which  in  closing  the  jaws  alternates  with  that 
of  the  digastric  and  other  muscles  passing  from  the  os  hyoides  to  the 
lower  jaw,  which  open  them.  The  grinding  or  side  to  side  movements 
of  the  lower  jaw  are  performed  mainly  by  the  external  pterygoid  mus- 
cles, the  muscle  of  one  side  acting  alternately  with  the  other.  When 
both  external  pterygoids  act  together,  the  lower  jaw  is  pulled  directly 
forward,  so  that  the  lower  incisor  teeth  are  brought  in  front  of  the  level 
of  the  upper. 

Temporo-maxillary  Fibro- Cartilage.  —  The  function  of  the  inter- 
articulo-fibro-cartilage  of  the  temjioro -maxillary  joint  in  mastication  is 
to  serve : — (1)  As  an  elastic  pad  to  distribute  the  pressure  caused  by 
the  exceedingly  powerful  action  of  the  masticatory  muscles.  (2)  As  a 
joint  surface  or  socket  for  the  condyle  of  the  lower  jaw  when  the  latter 
has  been  partially  drawn  forward  out  of  the  glenoid  cavity  of  the  tem- 
poral bone  by  the  external  pterygoid  muscle,  some  of  the  fibres  of  the 
latter  being  attached  to  its  front  surface,  and  consequently  drawing  it 
forward  with  the  condyle  which  moves  on  it. 

Nervous  Mechanism. — The  act  of  mastication  is  partly  voluntary  and 
partly  reflex  and  involuntary.  The  consideration  of  such  nervous 
actions  will  come  hereafter.  It  will  suffice  here  to  state  that  the  affer 
ent  nerves  chiefly  concerned  are  the  sensory  branches  of  the  fifth  and 
the  tenth  or  glosso-pharyngeal,  and  the  efferent  are  the  motor  branches 
of  the  fifth  and  the  twelfth  (hypoglossal)  cerebral  nerves.  The  nerve- 
centre  through  which  the  reflex  action  occurs,  and  by  which  the  move- 
ments of  the  various  muscles  are  harmonized,  is  situated  in  the  medulla 
oblongata.  In  so  far  as  mastication  is  voluntary  or  mentally  perceived, 
it  is  under  the  influence  of  the  cerebral  hemispheres. 

Insalivation. — The  act  of  mastication  is  much  assisted  by  the  saliva 


292 


HANDBOOK    OF    PHYSIOLOGY. 


which  is  secreted  by  the  salivary  glands  in  largely  increased  amount 
during  the  process,  and  the  intimate  incorporation  of  which  with  the 
food,  as  it  is  being  chewed,  is  termed  iiisalivation. 


The  Salivary  Glands. 

The  glands  which  secrete  the  saliva  in  the  human  subject  are  the 
salivary  glands  proper,  viz.,  the  parotid,  the  sub-maxillary,  and  the 
sub-lingual,  and  numerous  smaller  bodies  of  similar  structure,  and  with 
separate  ducts,  which  are  scattered  thickly  beneath  the  mucous  mem- 
brane of  the  lips,  cheeks,  soft  palate,  and  root  of  the  tongue. 

Structure. — The  salivary  glands  are  compound  tubular  or  tubulo- 
racemose  glands.  They  are  made  up  of  lobules.  Eacli  lobule  consists 
of  the  branchings  of  a  subdivision  of  the  main  duct  of  the  gland,  which 


Fig.  221.— Section  of  sub-maxillary  gland  of  dog.    Showing  gland  cells,  h.  and  a  duct,  a,  in  section. 

(Kolliker.) 

is  generally  more  or  less  convoluted  toward  its  extremities,  and  some- 
times, according  to  some  observers,  sacculated  or  pouched.  The  con- 
vluted  or  pouched  portions  form  the  alveoli,  or  proper  secreting  parts 
of  the  gland.  The  alveoli  are  composed  of  a  basement  membrane  of 
flattened  cells  joined  together  by  processes  to  produce  a  fenestrated 
membrane,  the  spaces  of  which  are  occupied  by  a  homogenous  ground- 
substance.  Within,  upon  this  membrane,  which  forms  the  tube,  the 
nucleated  salivary  secreting  cells,  of  cubical  or  columnar  form,  are  ar- 
ranged parallel  to  one  another  enclosing  a  central  canal.  The  granular 
appearance  frequently  seen  in  the  salivary  cells  is  due  to  the  very  dense 
network  of  fibrils  which  they  contain.  When  isolated,  the  cells  not  in- 
frequently are  found  to  be  branched.  Connecting  the  alveoli  into  lobules 
is  a  considerable  amount  of  fibrous  connective  tissue,  which  contains 
both  flattened  and  granular  protoplasmic  cells,  lymph  corpuscles,  and 
in  some  cases  fat  cells.  The  lobules  are  connected  to  form  larger  lobules 
(lobes),  in  a  similar  manner.  The  alveoli  pass  into  the  intralobular 
ducts  by  a  narrowed  portion  (intercalary),  lined  with  flattened  epithe- 


FOOD    AND    DIGESTION. 


293 


lium  with  elongated  nuclei.  The  intercalary  ducts  pass  into  the  intra- 
lobular ducts  by  a  narrowed  neck,  lined  with  cubical  cells  with  small 
nuclei.  The  intralobular  duct  is  larger  in  size,  and  is  lined  with  large 
columnar  nucleated  cells,  the  parts  of  which,  toward  the  lumen  of  the 
tube,  present  a  fine  longitudinal  striation,  due  to  the  arrangement  of 
the  cell  network.  It  is  most  marked  in  the  submaxillary  gland.  The 
intralobular  ducts  pass  into  the  larger  ducts,  and  these  into  the  main 
duct  of  the  gland.  As  these  ducts  become  larger  they  acquire  an  out- 
side coating  of  connective  tissue,  and  later  on  some  unstriped  muscular 
fibres.  The  lining  of  the  larger  ducts  consists  of  one  or  more  layers  of 
columnar  epithelium,  the  cells  of  which  contain  an  intracellular  net- 
work of  fibres  arranged  longitudinally. 

Varieties. — Certain   differences    in  the  structure  of  salivary  glands 
may  be  observed  according  as  the  glands  secrete  pure  saliva,  or  saliva 


Fig.  223.— From  a  section  through  a  true  salivary  gland,    a,  The  gland  alveoli,  lined  with  albuminous 
•'  salivary  cells  ;  "  b.  intralobular  duct  cut  transversely.     (Klein  and  Noble  Smith.) 

mixed  with  mucus,  or  pure  mucus,  and  therefore  the  glands  have  been 
-classified  as: — 

(1)  True  salivary  (jlamU  (called  most  unfortunately  by  some,  serous 
glands),  e.g.,  the  parotid  of  man  and  other  animals,  and  the  submaxil- 
lary of  the  rabbit  and  guinea-pig  (fig.  222).  In  this  kind  the  alveolar 
lumen  is  small,  and  the  cells  lining  the  tubule  are  short  granular  colum- 
nar cells,  with  nuclei  presenting  the  intranuclear  network.  During  rest 
the  cells  become  larger,  highly  granular,  with  obscured  nuclei,  and  the 
lumen  becomes  smaller.  During  activity,  and  after  stimulation  of  the 
sympathetic,  the  cells  become  smaller  and  their  contents  more  opaque; 
the  granules  first  of  all  disappearing  from  the  outer  j)art  of  the  cells, 
and  then  being  found  only  at  the  extreme  inner  part  and  contiguous 
border  of  the  cell.     The  nuclei  reappear,  as  does  also  the  lumen. 

(2)  In  the  true  mucus-secreting  glands, -as,  the  sublingual  of  man  and 
other  animals,  and  in  the  submaxillary  of  the  dog,  the  tubes  are  larger, 
contain  a  larger  lumen,  and  also  have  larger  cells  lining  them.  The 
cells  are  of  two  kinds,  {a)  mucous  or  central  cells,  which  are  transparent 


294 


HANDBOOK    OF    PHYSIOLOGY. 


columnar  cells  with  irregular  or  flattened  nuclei  near  the  basement  mem- 
brane. The  cell  substance  is  made  up  of  a  fine  network,  which  in  the 
resting  state  contains  a  transparent  substance  called  mucigen,  during 
which  the  cell  does  not  stain  well  with  logwood  (fig.  223).  When  the 
gland  is  secreting,  as  well  as  on  stimulation  of  the  nerve,  mucigen  is  con- 
verted into  mucin,  and  the  cells  swell  up,  appear  more  transparent,  and 
stain  deeply  in  logwood  (fig.  224).  After  stimulation,  the  cells  become 
smaller,  more  granular,  and  more  easily  stained,  from  having  discharged 
their  contents.  The  nuclei  appear  more  distinct,  {h)  Crescent.^  of  Gla- 
nuzzi,  sometimes  called  the  Semihmes  of  Ihidenliain  (fig.  223),  which 
are  crescentic  masses  of  granular  parietal  cells  found  here  and  there  be- 
tween the  basement  membrane  and  the  central  cells.  The  cells  com- 
posing the  mass  are  small,  and  have  a  very  dense  reticulum,  the  nuclei 


Fig.  233. 


Fig.  234. 


Fig.  22.3. — From  a  section  through  a  mucous  gland  in  a  quiescent  state.  The  alveoli  are  lined 
with  transparent  mucous  cells,  and  outside  these  are  the  semilunes.  The  cells  should  have  been 
represented  as  more  or  less  granular.     (Heidenhain.) 

Fig.  224. — A  part  of  a  section  through  a  mucous  gland  after  prolonged  electrical  stimulation. 
The  alveoli  are  lined  with  small  granular  cells.    (Lavdovs^  i.) 

are  spherical,  and  increase  in  size  during  secretion.  In  the  mucous 
gland  there  are  some  large  tubes,  lined  with  large  transparent  central 
cells,  and  having  besides  a  few  granular  parietal  cells;  other  small  tubes 
are  lined  with  small  granular  parietal  cells  alone;  and  a  third  variety 
are  lined  equally  with  each  kind  of  cell. 

(3)  In  the  muco-salivary  or  mixed  glands,  as  the  human  submaxillary 
gland,  part  of  the  gland  presents  the  structure  of  the  mucous  gland, 
while  the  remainder  has  that  of  the  salivary  glands  proper. 

Nerves  and  blood-vessels. — Nerves  of  large  size  are  found  in  the  sali- 
vary glands ;  they  are  principally  contained  in  the  connective  tissue  of 
the  alveoli,  and  in  certain  glands,  especially  in  the  dog,  are  provided 
with  ganglia.  Some  nerves  have  special  endings  in  Pacinian  corpuscles, 
some  supply  the  blood-vessels,  and  others,  according  to  Pfliiger,  pene- 
trate the  basement  membrane  of  the  alveoli  and  enter  the  salivary  cells. 

The  blood-vessels  form  a  dense  capillary  network  around  the  ducts 


FOOD   AXD    DIGESTION.  295 

of  tiie  iilveoli,  being  carried  iu  by  the  fibrous  trabeciilas  between  the 
alveoli,  in  which  also  begin  the  lymphatics  by  lacunar  spaces. 

The  so-called  mucous  glands  of  the  mouth  and  tongue  present  in 
some  cases  the  structures  of  mucous,  in  others  of  serous  glands. 

Saliva. 

Saliva,  as  it  commonly  flows  from  the  mouth,  is  the  mixed  secretion 
of  the  salivary  glands  proper  and  of  the  glands  of  the  buccal  mucous 
membrane  and  tongue;  it  is  often  mixed  with  air,  which,  being  retained 
by  its  viscidity,  makes  it  frothy.  When  obtained  from  the  parotid 
ducts,  and  free  from  mucus,  saliva  is  a  transparent  watery  fluid,  the 
specific  gravity  of  which  varies  from  1004  to  1008,  and  in  which,  when 
examined  with  the  microscope,  are  found  floating  a  number  of  minute 
particles,  derived  from  the  secreting  ducts  and  vesicles  of  the  glands. 
In  the  impure  or  mixed  saliva  are  found,  besides  these  particles,  numer- 
ous epithelial  scales  separated  from  the  surface  of  the  mucous  mem- 
brane of  the  mouth  and  tongue,  and  the  so-called  salivary  corjjuscles, 
discharged  probably  from  the  mucous  glands  of  the  mouth  and  the 
tonsils,  which,  when  the  saliva  is  collected  in  a  deep  vessel,  and  left  at 
rest,  subside  in  the  form  of  a  white  opaque  matter,  leaviijg  the  super- 
natant salivary  fluid  transparent  and  colorless,  or  with  a  pale  bluish- 
gray  tint.  It  also  contains  various  kinds  of  micro-organisms  (bacteria). 
In  reaction,  the  saliva,  when  first  secreted,  appears  to  be  always  alka- 
ine..  During  fasting,  the  saliva,  although  secreted  alkaline,  shortly 
becomes  neutral;  especially  when  it  is  secreted  slowly  and  is  allowed  to 
mix  with  the  acid  mucus  of  the  mouth,  by  which  its  alkaline  reaction  is 
reutralized. 

Chemical  Composition  of  Mixed  Saliva  (Frerichs). 

Water 994.10 

Solids  : — 

Ptyalin .  1.41  ' 

Fat 0.07  ' 

Epithelium  and  Proteids  (including  Serum- 
Albumin,  Globulin,  Mucin,  etc.)  ,  2.13 

Salts  :— 

Potassium  Sulpho-Cyanate 

Sodium  Phosphate     ..... 

Calcium  Phosphate       .... 

Magnesium  Phosphate      ... 

Sodium  Chloride  .... 

PotassiuUi  Chloride  ..... 


2.29 


5.9 

1000 

The  mucin  is  the  largest  representative  of  the  organic  nitrogenous 
class  of  bodies  in  the  saliva;  it  may  be  thrown  down  by  addition  of 
acetic  acid,  if  sodium  chloride  be  absent.     It  gives  the  three  chief  pro- 


29G  HANDBOOK    OF    PHYSIOLOGY. 

teid  reactions,  and  may  easily  be  sjDlit  up  by  the  action  of  a  dilute  min- 
eral acid  into  a  proteid,  and  a  substance  which  will  reduce  copper  sul- 
phate solutions,  but  which  is  not  exactly  a  sugar. 

The  presence  of  potassium  sulphoci/at/die  (or  tJiiocyanate]  (CNKS) 
in  saliva,  may  be  shown  by  the  blood-red  coloration  which  the  fluid 
gives  with  a  solution  of  ferric  chloride  (FeaCle),  and  which  is  bleached 
on  the  addition  of  a  solution  of  mercuric  chloride  (HgCla),  but  not  by 
hydrochloric  acid. 

Rate  of  Secretio7i  and  Quantity. — The  rate  at  which  saliva  is  secreted 
is  subject  to  considerable  variation.  When  the  tongue  and  muscles 
concerned  in  mastication  are  at  rest,  and  the  nerves  of  the  mouth  are 
subject  to  no  unusual  stimulus,  the  quantity  secreted  is  not  more  than 
sufficient,  with  the  mucus,  to  keep  the  mouth  moist.  During  actual 
secretion  the  flow  is  much  accelerated. 

The  quantity  secreted  in  twenty-four  hours  varies:  its  average 
amount  is  j^robably  from  1  to  3  joints  (^  to  1^  litres). 

Uses  of  Saliva. — The  purposes  served  by  saliva  are  {a)  mechanical 
and  {b)  chemical. 

a.  Mechanical. — (1)  It  keeps  the  mouth  in  a  due  condition  of  moist- 
ure, facilitating  the  movements  of  the  tongue  in  speaking,  and  the 
mastication  of  food.  (2)  It  serves  also  in  dissolving  sapid  substances' 
and  rendering  them  capable  of  exciting  tlie  nerves  of  taste.  But  the 
principal  mechanical  purpose  of  the  saliva  is,  (3)  that  by  mixing  with 
the  food  during  mastication,  it  makes  it  a  soft  pulpy  mass,  such  as  may 
be  easily  swallov/ed.  To  this  purpose  the  saliva  is  adapted  both  by 
quantity  and  quality.  For,  speaking  generally,  the  quantity  secreted 
during  feeding  is  in  direct  j)roportion  to  the  dryness  and  hardness  of 
the  food.  The  quality  of  saliva  is  equally  adapted  to  this  end.  It  is 
easy  to  see  how  much  more  readily  it  mixes  with  most  kinds  of  food  than 
water  alone  does;  and  the  saliva  from  the  parotid,  labial,  and  other 
small  glands,  being  more  aqueous  than  the  rest,  is  that  which  is  chiefly 
braided  and  mixed  with  the  food  in  mastication ;  while  the  more  viscid 
mucous  secretion  of  the  submaxillary,  palatine,  and  tonsillitic  glands 
is  spread  over  the  surface  of  the  softened  mass,  to  enable  it  to  slide 
more  easily  through  the  fauces  and  oesojihagus. 

(b)  Chemical. — The  chemical  action  which  the  saliva  exerts  upon  the 
food  in  the  mouth  is  to  convert  the  starchy  materials  which  it  contains 
into  sugar.  This  power  the  saliva  owes  to  one  of  its  constituents  ^^^//rt- 
lin,  which  is  a  nitrogenous  body  of  uncertain  composition.  It  is  classed 
among  the  unorganized  ferments,  which  are  substances  capable  of  pro- 
ducing changes  in  the  composition  of  other  bodies  with  which  they  come 
into  contact,  without  themselves  undergoing  change  or  suffering  dimin- 
ution. The  conversion  of  the  starch  under  the  influence  of  the  ferment 
into  sugar  takes  place  in  several  stages,  and  in  order  to  understand  it. 


FOOD    AND    DIGESTION.  297 

a  knowledge  of  the  structure  and  composition  of  starch  granules  is  nec- 
essary. A  starch  granule  consists  of  two  parts :  an  envelope  of  cellulose, 
which  does  not  give  a  blue  color  with  iodine  except  on  addition  of  sul- 
phuric acid,  and  of  gramdose,  which  is  contained  within,  and  which 
gives  a  blue  with  iodine  alone.  Briicke  states  that  a  third  body  is  con- 
tained in  the  granule,  which  gives  a  red  with  iodine,  viz.,  erythro- 
granulose.  On  boiling,  the  granulose  swells  up,  bursts  the  envelope, 
and  the  whole  granule  is  more  or  less  completely  converted  into  a  paste 
or  gruel,  which  is  called  gelatinous  starch. 

When  ptyalin  or  other  amylolytic  ferment  is  added  to  boiled  starch, 
sugar  almost  at  once  makes  its  appearance  in  small  quantities,  but  in 
addition  there  is  another  body,  intermediate  between  starch  and  sugar, 
called  ei-ytliro-dextrin,  which  gives  a  reddish-brown  coloration  with 
iodine.  As  the  sugar  increases  in  amount,  the  erythro-dextrin  disap- 
pears, but  its  place  is  taken  in  part  by  another  dextrin,  achroo-dextrin, 
which  gives  no  color  with  iodine,  but  may  be  thrown  down  with  alcohol. 
However  long  the  reaction  goes  on,  it  is  unlikely  that  all  the  dextrin 
becomes  sugar. 

Next  with  regard  to  the  kind  of  sugar  formed,  it  is  not  glucose  but 
maltose,  the  formula  for  which  is  C12H02O11.  Maltose  is  allied  to  sac- 
charose or  cane-sugar  more  nearly  than  to  glucose;  it  is  crystalline;  its 
solution  has  the  property  of  polarizing  light  to  the  right  to  a  greater 
degree  than  solutions  of  glucose  (3  to  1) ;  it  is  not  so  sweet,  and  reduces 
copper  sulphate  less  easily.  It  can  be  converted  into  glucose  by  boiling 
with  dilute  acids. 

According  to  Brown  and  Heron  the  reactions  may  be  represented  thus  : — 
One  molecule  of  gelatinous  starcli  is  converted  by  the  action  of  an  amylolytic 

ferment  into  n  molecules  of  soluble  starch. 
One  molecule  of  soluble  starch  =  10  (Cr2H2oO,o)  +  8  (H2O),  which  is  further  con- 
verted by  the  ferment  into 

1.  Ervthro-dextrin  (giving  red  with  iodine)  -|-  Maltose. 

9  (Ci.H^oOu,)  (C:2H.,20„) 

then  into  2.   Ervthro-dextrin  (giving  yellow  with  iodine)    -|-     Maltose. 

'  8  (C,.,H.,oO,„)  2  (C,2Ho.,0x,) 

next  into  3.  Achi-oo-dextrin        -{-        Maltose. 

7  (CioH^oOio)  3  (C,2H.,20n) 

And  so  on  ;  the  resultant  being  : — 

10  (Ci^H^oOio)  +  8  (H2O)  =  8  (C^H^^On)  +  2  (Ci^H^oO.o) 
Soluble  starch        Water  Maltose  Achroo-dextrin. 

Test  for  Sugar. — In  such  an  experiment  the  presence  of  sugar  is  at 
once  discovered  by  the  application  of  Trommer's  test,  which  consists  in 
the  addition  of  a  drop  or  two  of  a  solution  of  copper  sulphate,  followed 
by  a  larger  quantity  of  caustic  potash.  When  the  liquid  is  boiled,  an 
orange-red  precipitate  of  copper  suboxide  indicates  the  presence  of 
sugar. 

The  action  of  saliva  o?i  starch  is  facilitated  by :  {a)  Moderate  heat, 
about  37.8°  C.  (100°  F.).     (b)  A  slightly  alkaline  medium,     (c)  Removal 


298  HANDBOOK    OF    PHYSIOLOGY. 

of  the  changed  material  from  time  to  time.  Its  action  is  retarded  hi/  : 
(a)  Cold;  a  temperature  of  0°  C.  (32°  ¥.)  sto]3s  it  for  a  time,  but  does 
not  destroy  it,  whereas  a  high  temperature  above  760°C.  (140°  F.)  de- 
stroys it.  {b)  Acids  or  strong  alkalies  either  delay  or  stop  the  action 
altogether,  (c)  Presence  of  too  much  of  the  changed  material.  Ptyalin, 
in  that  it  converts  starch  into  sugar,  is  an  amylolytic  or  diastasic  ferment. 

Starch  appears  to  be  the  only  principle  of  food  upon  which  saliva 
acts  chemically :  the  secretion  has  no  apparent  influence  on  any  of  the 
other  ternary  principles,  such  as  sugar,  gum,  cellulose,  or  on  fat,  and 
seems  to  be  equally  destitute  of  power  over  albuminous  and  gelatinous 
substances. 

Saliva  from  the  parotid  is  less  viscid;  less  alkaline,  the  first  few 
drops  discharged  in  secretion  being  even  acid  in  reaction;  clearer,  al- 
though it  may  become  cloudy  on  standing  from  the  precipitation  of 
calcium  carbonate  from  escape  of  carbon  dioxide;  and  more  watery  than 
that  from  the  submaxillary.  It  has  moreover  a  less  powerful  action  on 
starch.  Sublingual  saliva  is  the  most  viscid,  and  contains  more  solids 
than  either  of  the  other  two,  but  has  little  diastasic  action. 

The  salivary  glands  of  children  do  not  become  functionally  active 
till  the  age  of  4  to  6  months,  and  hence  the  bad  effect  of  feeding  them 
before  this  age  on  starchy  food,  corn-flour,  etc.,  which  they  are  unable 
to  render  soluble  and  capable  of  absorption.  The  salivas  of  the  dog, 
cat,  bear,  and  pig  are  almost  inactive,  whereas  that  of  monkeys,  rabbits, 
mice,  squirrels,  and  guinea-pigs,  are  strongly  diastasic. 

The  Nervous  Mechanism  of  the  Secretion  of  Saliva. 

The  secretion  of  saliva  is  under  the  control  of  the  nervous  system. 
It  is  a  reflex  action.  Under  ordinary  conditions  it  is  excited  by  the 
stimulation  of  the  peripheral  branches  of  two  nerves,  viz.,  the  gustatory 
or  lingual  branch  of  the  inferior  maxillary  division  of  the  fifth  nerve, 
and  the  glosso-pltaryngeal  part  of  the  eighth  pair  of  nerves,  which  are 
distributed  to  the  mucous  membrane  of  the  tongue  and  pharynx  con- 
jointly. The  stimulation  occurs  on  the  introduction  of  sapid  substances 
into  the  mouth,  and  the  secretion  is  brought  about  in  the  follwing  w;iy. 
From  the  terminations  of  the  above-mentioned  sensory  nerves  distrib- 
uted in  the  mucous  membrane  an  impression  is  conveyed  upward 
(afferent)  to  the  special  nerve  centre  situated  in  the  medulla-oblongata 
which  controls  the  process,  and  by  it  is  reflected  to  certain  nerves  sup- 
plied to  the  salivary  glands,  which  will  be  presently  indicated.  In  other 
words,  the  centre,  stimulated  to  action  by  the  sensory  impressions  car- 
ried to  it,  sends  out  impulses  along  efferent  or  secretory  nerves  siipplied 
to  the  salivary  glands,  which  cause  the  saliva  to  be  secreted  by  and  dis- 
charged from  the  gland  cells.     Other  stimuli,  however,  besides  that  of 


FOOD    AND    DIGESTION".  299 

the  food,  and  other  sensory  nerves  besides  those  mentioned,  may  j^ro- 
duce  reflexly  the  same  effects.  For  example,  saliva  may  be  caused  to 
flow  by  irritation  of  the  mucous  membrane  of  the  mouth  with  mechani- 
cal, chemical,  electrical,  or  thermal  stimuli,  also  by  the  irritation  of  the 
mucous  membrane  of  the  stomach  in  some  way,  as  in  nausea,  which 
precedes  vomiting,  when  some  of  the  peripheral  fibres  of  the  vagi  are 
irritated.  Stimulation  of  the  olfactory  nerves  by  smell  of  food,  of  the 
ojytic  nerves  by  the  sight  of  it,  and  of  the  auditory  nerves  by  the  sounds 
which  are  known  by  experience  to  accompany  the  preparation  of  a  meal, 
may  also,  in  the  hungry,  stimulate  the  nerve  centre  to  action.  In  addi- 
tion to  these,  as  a  secretion  of  saliva  follows  the  movement  of  the  mus- 
cles of  mastication,  it  may  be  assumed  that  this  movement  stimulates  the 
secreting  nerve  fibres  of  the  gland,  direct  or  reflexly.  From  the  fact 
that  the  flow  of  saliva  may  be  increased  or  diminished  by  mental  emo- 
tions, it  is  evident  that  impressions  from  the  cerebrum  also  are  capable 
of  stimulating  the  centre  to  action  or  of  inhibiting  its  action. 

Salivary  secretion  may  also  be  excited  by  direct  stimulation  of  the 
centre  in  the  medulla. 

On  the  Submaxillary  Gland. — The  subm^axillary  gland  has  been  the 
gland  chiefly  employed  for  the  purpose  of  exj)erimentally  demonstrating 
the  influence  of  the  nervous  system  upon  the  secretion  of  saliva,  because 
of  the  comparative  facility  with  which,  with  its  blood-vessels  and  nerves, 
it  may  be  exposed  to  view  in  the  dog,  rabbit,  and  other  animals.  The 
chief  nerves  supplied  to  the  gland  are  (1)  the  chorda  tympani,  a  branch 
given  off  from  the /acta/  [ov  portio  dura  of  the  seventh  pair  of  nerves), 
in  the  canal  through  which  it  passes  in  the  temporal  bone,  in  its  passiige 
from  the  interior  of  the  skull  to  the  face;  and  (2)  branches  of  the  sym- 
pathetic nerve  from,  the  plexus  around  the  facial  artery  and  its  branches 
to  the  gland.  The  chorda  (fig.  225,  eh.  /.),  after  quitting  the  temporal 
bone,  passes  downward  and  forward,  under  cover  of  the  external  ptery- 
goid muscle,  and  joins  at  an  acute  angle  the  lingual  or  gustatory  nerve, 
proceeds  with  it  for  a  short  distance,  and  then  passes  along  the  submax- 
illary gland  duct  (fig.  225,  sm.  d.),  to  which  it  is  distributed,  giving 
branches  to  the  submaxillary  ganglion  (fig.  225, sm.  r//.),and  sending  others 
to  terminate  in  the  superficial  muscles  of  the  tongue.  It  consists  of  fine 
medullated  fibres  which  lose  their  medulla  in  the  gland.  If  this  nerve 
be  exposed  and  divided  anywhere  in  its  course  from  its  exit  from  the  skull 
to  the  gland,  the  secretion,  if  the  gland  be  in  action,  is  arrested,  and  no 
stimulation  either  of  the  lingual  or  of  the  glosso-pharyngeal  will  produce  a 
flow  of  saliva.  But  if  the  peripheral  end  of  the  divided  nerve  be  stimu- 
lated, an  abundant  secretion  of  saliva  ensues,  and  the  blood  supply  is 
enormously  increased,  the  arteries  being  dilated.  The  veins  even  pul- 
sate, and  the  blood  contained  within  them  is  more  arteriarthan  venous 
in  character. 


300  HANDBOOK    OF    PHYSIOLOGY. 

When,  on  the  other  hand,  the  stimulus  is  applied  to  the  sympathetic 
filaments  (mere  division  producing  no  apparent  effect),  the  arteries  con- 
tract, and  the  blood  stream  is  in  consequence  much  diminished;  and 
from  the  veins,  when  opened,  there  escapes  only  a  sluggish  stream  of 
dark  blood.  The  saliva,  instead  of  being  abundant  and  watery,  becomes 
scanty  and  tenacious.  If  both  chorda  tympani  and  sympathetic  branches 
be  divided,  the  gland,  released  from  nervous  control,  may  secrete  con- 
tinuously and  abundantly  ( imralytic  secretion). 

The  abundant  secretion  of  saliva,  which  follows  stimulation  of  the 
chorda  tympani,  is  not  merely  the  result  of  a  filtration  of  fluid  from 


Fig.  225.— Diagrammatic  representation  of  the  sub-maxillary  gland  of  the  dog  with  its  nerves  and 
blood-vessels.  (This  is  not  intended  to  illustrate  the  exact  anatomical  relations  of  the  several  struc- 
tures.) sm.  gld.,  the  submaxillary  gland  into  the  duct  (sm.  d.~)  of  which  a  canula  has  been  tied. 
The  subungual  g-land  and  duct  are  not  shown,  n.  I.,  71.  I'.,  the  lingual  or  gustatory  nerve  ;  ch.  t., 
ch.  t'.,  the  chorda  tympani  proceeding  from  the  facial  nerve,  becoming  conjoined  with  the  lingual 
at  ii.  ?'.,  and  afterward  diverging  nnd  passing  to  the  gland  along  the  duet ;  S7n.  gl.,  sub-maxillary 
ganglion  with  its  roots;  n,  ?.,  the  lingualnerve  proceeding  to  the  tongue  ;  a.  car.,  the  carotid  artery, 
two  branches  of  which,  ct.  sm.  a.  and  r.  sin.  p.,  pas';  to  the  anterior  and  posterior  parts  of  the  gland  ; 
V.  sm.,  the  anterior  and  posterior  veins  from  the  gland  ending  in  v.j..  the  jugular  vein  ;  v.  sym.,  the 
conjoined  vagus  and  sympathetic  trunks  ;  gl.  cer.s..  the  superior-cervical  ganglion,  two  branches 
of  which  forming  a  plexus,  a.f.,  over  the  facial  artery  are  distributed  (n.  sym.  sm.}  along  the  two 
glandular  arteries  to  the  anterior  and  posterior  portion  of  the  gland.  The  arrows  indicate  the 
direction  taken  by  the  nervous  impulses  ;  during  reflex  stimulations  of  the  gland  theyascend  to  the 
brain  by  the  lingual  and  descend  by  the  chorda  tympani.     ( M.  Foster.) 

the  blood-vessels,  in  consequence  of  the  largely  increased  circulation 
through  them.  This  is  proved  by  the  fact  that,  when  the  main  duct  is 
obstructed,  the  pressure  within  may  considerably  exceed  the  blood-pres- 
sure in  the  arteries,  and  also  that  when  into  the  veins  of  the  animal 
experimented  upon  some  atrojnn  has  been  previously  injected,  stimula- 
tion of  the  peripheral  end  of  the  divided  chorda  produces  all  the  vascu- 
lar effects  as  before,  without  any  secretion  of  saliva  accompanying  them. 
Again,  if  an  animal's  head  be  cut  off,  and  the  chorda  be  rapidly  exposed 
and  stimulated  with  an  interrupted  current,  a  secretion  of  saliva  ensues  for 
a  short  time,  although  the  blood  supply  is  necessarily  absent.     These 


FOOD   AND    DIGESTION.  301 

experiments  serve  to  prove  that  the  chorda  contains  two  sets  of  nerve 
fibres,  one  set  {vaso-dilator)  M^hich,  when  stimuhited,  act  upon  a  local 
vaso-motor  centre  for  regulating  the  blood  supply,  inhibiting  its  action, 
and  causing  the  vessels  to  dilate,  and  so  producing  an  increased  supply  of 
"blood  to  the  gland;  while  another  set,  which  are  paralyzed  by  injection 
of  atropiu,  directly  stimulate  the  cells  themselves  to  activity,  whereby 
they  secrete  and  discharge  the  constituents  of  the  saliva  which  they 
produce.  These  latter  fibres  very  possibly  terminate  in  the  salivary  cells 
themselves.  If,  on  the  other  hand,  the  sympathetic  fibres  be  divided, 
stimulation  of  the  tongue  by  sapid  substances,  or  of  the  trunk  of  the 
lingual,  or  of  the  glosso-pharyngeal,  continues  to  produce  a  flow  of  saliva. 
From  these  experiments  it  is  evident  that  the  chorda  tympani  nerve  is 
the  principal  nerve  through  which  efferent  impulses  proceed  from  the 
centre  to  excite  the  secretion  of  this  gland. 

The  sympathetic  fibres  appear  to  act  principally  as  a  vaso-constrictor 
nerve,  and  to  exalt  the  action  of  the  local  vaso-motor  centres.  The 
sympathetic  is  more  powerful  in  this  direction  than  the  chorda.  There 
is  not  sufficient  evidence  in  favor  of  the  belief  that  the  submaxillary 
ganglion  is  ever  the  nerve  centre  which  controls  the  secretion  of  the 
submaxillary  gland. 

On  the  Parotid  Gland. — The  nerves  which  influence  secretion  in  the 
parotid  gland  are  branches  of  the  facial  (lesser  superflcial  petrosal)  and 
of  the  sympathetic.  The  former  nerve,  after  passing  througli  the  optic 
ganglion,  joins  the  auriculo-temporal  branch  of  the  fifth  cerebral  nerve, 
and,  with  it,  is  distributed  to  the  gland.  The  nerves  by  which  the 
stimulus  ordinarily  exciting  secretion  is  conveyed  to  the  medulla  ob- 
longata, are,  as  in  the  case  of  the  submaxillary  gland,  the  fifth,  and  the 
glosso-pharyngeal.  The  pneumogastric  nerves  convey  a  further  stimu- 
lus to  the  secretion  of  saliva,  when  food  has  entered  the  stomach;  the 
nerve  centre  is  the  same  as  in  the  case  of  the  submaxillary  gland. 

Changes  in  tlie  Gland  Cells. — The  method  by  which  the  salivary  cells 
produce  the  secretion  of  saliva  appears  to  be  divided  into  two  stages, 
which  differ  somewhat  according  to  the  class  to  which  the  gland  belongs, 
viz.,  whether  to  (1)  the  true  salivary,  or  (2)  to  the  mucous  type.  In  the 
former  case,  it  has  been  noticed,  as  has  been  already  described,  that 
during  the  rest  which  follows  an  active  secretion  the  lumeii  of  the  alveo- 
lus becomes  smaller,  the  gland  cells  larger  and  very  granular.  During 
secretion  the  alveoli  and  their  cells  become  smaller,  and  the  granular 
appearance  in  the  latter  to  a  considerable  extent  disappears,  and  at  the 
end  of  secretion  the  granules  are  confined  to  the  inner  part  of  the  cell 
nearest  to  the  lumen,  which  is  now  quite  distinct  (fig.  226).' 

It  is  supposed  from  these  appearances  that  the  first  stage  in  the  act. 
of  secretion  consists  in  the  protoplasm  of  the  salivary  cell  taking  up 
from  the  lymph  certain  materials  from  which  it  manufactures  the  ele- 


302 


HANDBOOK    OF    PHYSIOLOGY. 


ments  of  its  own  secretion,  and  which  are  stored  up  in  the  form  of 
granules  in  the  cell  during  rest,  the  second  stage  consisting  of  the  actual 
discharge  of  these  granules,  with  or  without  previous  change.  The 
granules  are  taken  to  represent  the  chief  substance  of  the  salivary  secre- 
tion, i.e.,  the  ferment  ptyalin.  In  the  case  of  the  submaxillary  gland  of 
the  dog,  at  any  rate,  the  sympathetic  nerve-fibres  appear  to  have  to  do 
with  the  first  stage  of  tlie  process,  and  when  stimulated  the  protoplasm  is 
extremely  active  in  manufacturing  the  granules,  whereas  the  chorda 
tympani  is  concerned  in  the  production  of  the  second  act,  the  actual  dis- 
charge of  the  materials  of  secretion,  together  with  a  considerable  amount 
of  fluid,  the  latter  being  an  actual  secretion  by  the  protoplasm,  as  it 
ceases  to  occur  when  atropin  has  been  subcutaneously  injected. 

In  the  mucus-secreting  gland,  the  changes  in  the  cells  dkring  secre- 
tion have  been  already  spoken  of.     They  consist  in  the  gradual  secre- 


rig,  226.— Alveoli  of  true  salivary  gland.    A,  at  rest;  B,  in  the  first  stage  of  secretion  ;  C,  after  pro- 
longed secretion.     (Langley.) 


tion  by  the  protoplasm  of  the  cell  of  a  substance  called  imicigen,  which 
is  converted  into  mucin,  and  discharged  on  secretion  into  the  canal  of 
the  alveoli.  The  mucigen  is,  for  the  most  part,  collected  into  the  inner 
part  of  the  cells  during  rest,  pressing  the  nucleus  and  the  small  portion 
of  the  protoplasm  which  remains,  against  the  limiting  membrane  of  the 
alveoli. 

The  process  of  secretion  in  the  salivary  glands  is  identical  with  that 
of  glands  in  general;  the  cells  which  line  the  ultimate  branches  of  the 
ducts  being  the  agents  by  which  the  special  constituents  of  the  saliva 
are  formed.  The  materials  which  they  have  incorporated  with  them- 
selves are  almost  at  once  given  up  again,  in  the  form  of  a  fluid  (secre- 
tion), which  escapes  from  the  ducts  of  the  gland;  and  the  cells,  them- 
selves, undergo  disintegration— again  to  be  renewed,  in  the  intervals  of 
the  active  exercise  of  the  functions.  The  source  whence  the  cells  obtain 
the  materials  of  their  secretion  is  the  blood,  or,  to  speak  more  accu- 
rately, the  plasma,  which  is  filtered  off  from  the  circulating  blood  into 
the  interstices  of  the  glands  as  of  all  living  textures. 


FOOD   AXD   DIGESTION". 


303 


The  Tongue. 

Structure. — The  tongue  is  a  muscular  organ  covered  by  mucous 
membrane.  The  muscles,  which  form  the  greater  part  of  the  substance 
of  the  tongue  {intrinsic  muscles)  are  termed  Unguales;  and  by  these. 


Fig.  227. — Papillar  surface  of  the  tongue,  with  the  fauces  and  tonsils.  1,  1,  circumvallate  pa- 
pillae, in  front  of  2,  the  foramen  csecum;  3,  fungiform  papilla?  ;  4.  filiform  and  conical  papillae ;  5, 
transverse  and  oblique  rugae  ;  6,  mucous  glands  at  the  base  of  the  tongue  and  in  the  fauces;  7.  tonsils; 
8,  part  of  the  epiglottis  ;  9,  median  glosso-epiglottidean  fold  (fraenimi  epiglottidis).  (From  Sappey.) 


which  are  attached  to  the  mucous  membrane  chiefly,  its  smaller  and 
more  delicate  movements  are  chiefly  performed. 

By  other  muscles  {extrinsic  muscles),  as  the  genio-hyoglossus,  the 
styloglossus,  etc.,  the  tongue  is  fixed  to  surrounding  parts,  and  by  this 
group  of  muscles  its  larger  movements  are  performed. 

The  mucous  membrane  of  the  tongue  resembles  other  mucous  mem- 


304 


HANDBOOK    OF    PHYSIOLOGY. 


branes  in  essential  points  of  structure,  but  contains  yainllui,  more  or 
less  peculiar  to  itself;  peculiar,  however,  in  details  of  structure  and  ar- 
rangement, not  in  their  nature.  The  tongue  is  beset  with  numerous 
mucous  follicles  and  glands. 

The  larger  i)ai)ill(B  of  the  tongue  are  thickly  set  over  the  anterior 
two-thirds  of  its  upper  surface,  or  dorsum  (fig.  227),  and  give  to  it  its 
characteristic  roughness.  In  carnivorous  animals,  especially  those  of 
the  cat  tribe,  the  papillae  attain  a  large  size,  and  are  developed  into 

sharp  recurved  horny  spines.  Such  papillae 
cannot  be  regarded  as  sensitive,  but  they  en- 
able the  tongue  to  play  the  part  of  a  most 
efficient  rasp,  as  in  scraping  bones,  or  of  a 
comb  in  cleaning  fur.  Their  greater  prom- 
inence than  those  of  the  skin  is  due  to  their 
interspaces  not  being  filled  up  with  epithe- 
lium, as  the  interspaces  of  the  papilla  of 
the  skin  are.  The  papilla3  of  the  tongue 
present    several    diversities    of    form;    but 


Fig.  228. 


Fig.  229. 


Fig.  228.— Section  of  a  mucous  gland  from  the  tongue.  A,  opening  of  the  duct  on  the  free  sur- 
face; C,  Ijasement  membrane  with  nuclei;  B,  flattened  epithelial  cells  lining  duct  The  duct  divides 
into  several  branches,  which  are  convoluted  and  end  blindly,  being  lined  throughout  by  columnar 
epithelium.     D,  lumen  of  one  of  the  tubuli  of  the  gland,     x  90.     (Klein  and  Noble  Smith.) 

Fig.  229. — Vertical  section  of  a  circumvallate  iiapilla  of  the  calf  1  and  3,  epithehal  layers 
covering  it ;  2,  taste  goblets  ;  4  and  4',  duet  of  serous  gland  opening  out  into  the  pit  in  which  papilla 
is  situated;  5  and  6,  nerves  ramifying  within  the  papilla.     CEngeluiann.) 


three  principal  varieties,  differing  both  in  seat  and  general  characters, 
may  usually  be  distinguished,  namely,  the  (1)  circumvallate,  the  (2) 
fungiform,  and  the  (3)  filiform  papillae.  Essentially  these  have  all  of 
them  the  same  structure,  that  is  to  say,  they  are  all  formed  by  a  projec- 
tion of  the  mucous  membrane,  and  contain  special  branches  of  blood- 
vessels and  nerves.  In  details  of  structure,  however,  they  differ  consid- 
erably one  from  another. 

The  surface  of  each  kind  is  studded  by  minute  conical  processes  of 
mucous  membrane,  which  thus  form  secondary  papillae. 

(1.)  Circumvallate. — These  papillae  (fig.  229),  eight  or  ten  in  num- 


FOOD    AND    DIGESTION. 


305 


Iser,  are  situate  in  two  V-shaped  lines  at  the  base  of  the  tongue  (1,  1, 
fig.  227).  They  are  circular  elevations  from  oVth  to  ya^h  of  an  inch 
wide,  (1  to  2  mm.),  each  with  a  central  depression,  and  surrounded  by 
a  circular  fissure,  at  the  outside  of  which  again  is  a  slightly  elevated 
ring,  both  the  central  elevation  and  the  ring  being  formed  of  close-set 
simple  papilla. 

(2.)  Fungiform. — The  fungiform  papillse  (3,  fig.  227)  are  scattered 
chiefly  over  the  sides  and  tip,  and  sparingly  over  the  middle  of  the  dor- 
sum, of  the  tongue;  their  name  is  derived  from  their  being  usually  nar- 
rower at  their  base  than  at  their  summit.  They  also  consist  of  groups 
of  simple  papillse  (A.  fig.  200),  each  of  which  contains  in  its  interior  a 
loop  of  capillary  blood-vessels  (B.),  and  a  nerve-fibre. 

(3.)  Conical  or  Filiform. — These,  which  are  the  most  abundant  pa- 
pillae, are  scattered  over  the  whole  surface  of  the  tongue,  but  especially 


Fig.  230.— Surface  a.nd  section  of  the  fungiform  papillae.  A,  the  surface  of  a  fungiform  papilla, 
partially  denuded  of  Its  epithelium;  jJ,  secondary  papillae:  e,  epithelium.  B,  section  of  a  fungiform 
papilla  with  the  blood-vessels  injected  :  a,  artery  :  i\  vein;  c.  capillary  loops  of  similar  papillae  in 
the  neighboring  structure  of  the  tongue;  d,  capillary  loops  of  the  secondary  papillae;  e,  epithelium. 
(From  Kiilliker,  after  Todd  and  Bowman.) 


over  the  middle  of  the  dorsum.  They  vary  in  shape  somewhat,  but  for 
the  most  part  are  conical  or  filiform,  and  covered  by  a  thick  layer  of 
epidermis,  which  is  arranged  over  them,  either  in  an  imbricated  manner, 
or  is  prolonged  from  their  surface  in  the  form  of  fine  stiff  projections, 
hair-like  in  appearance,  and  in  some  instances  in  structure  also  (fig. 
231).  From  their  peculiar  structure,  it  seems  likely  that  these  papillae 
have  a  mechanical  function,  or  one  allied  to  that  of  touch  rather  than 
of  taste ;  the  latter  sense  being  probably  seated  especially  in  the  other 
two  varieties  of  papillte,  the  circumvallate  and  the  fungiform. 

The  epitlielium  of  the  tongue  is  stratified  with  the  upper  layers  of 
the  squamous  kind.  It  covers  every  part  of  the  surface;  but  over  the 
fungiform  papillte  forms  a  thinner  layer  than  elsewhere.  The  epithelium 
covering  the  filiform  papillae  is  extremely  dense  and  thick,  and,  as  befoi-e 
mentioned,  projects  from  their  sides  and  summits  in  the  form  of  long, 
stilf,  hair-like  processes  (fig.  231).  Many  of  these  processes  bear  a  close 
resemblance  to  hairs.     Blood-vessels  and  nerves  are  supplied  freely  to 

20 


306  HANDBOOK    OF    PHYSIOLOGY. 

the  papillae.  The  nerves  in  the  fungiform  and  circumvallate  papillae 
form  a  kind  of  plexus,  spreading  out  brushwise  (fig.  231),  but  the  exact 
mode  of  termination  of  the  nerve-filaments  is  not  certainly  known. 

In  the  circumvallate  papillse  of  the  tongue  of  man  peculiar  struc- 
tures known  as  gustatory  buds  or  taste  goblets,  have  been  discovered. 
They  are  of  an  oval  shape,  and  consist  of  a  number  of  closely  packed, 

very  narrow  and  fusiform,  cells 
{gustatory  cells).  This  central 
core  of  gustatory  cells  is  in- 
closed in  a  single  layer  of 
broader  fusiform  cells  {incas- 
ing cells).  The  gustatory  cells 
terminate  in  fine  spikes  not 
unlike  cilia,  which  project  on 
the  free  surface  (fig.  232  a). 

These  bodies  also  occur  side 
bv  side  in  considerable   num- 


Fig.  231.  Fig.  332. 

Fig.  231  .—Two  filiform  papillas,  one  with  epithelium,  the  other  without,  ^.—d,  the  substance  of 
the  papillae  dividing  at  their  upper  extremities  into  secondary  papilte  :  a.  artery,  and  v.  vein. 
dividing  into  capillary  loops  ;  e.  epithelial  covering,  laminated  between  the  papillae,  but  extended 
into  hair-like  processes.  /.  from  the  extremities  of  the  secondary  papillae.  (From  KoUiker,  after 
Todd  and  Bowman.)  ,        ,  ,     ,  .    ,      .    ., 

Fig.  232.— Taste-goblet  from  dog's  epiglottis  Gaiyngeal  surface  near  the  base),  precisely  similar 
in  structure  to  those  foimd  in  the  tongue,  a.  depression  in  epithelium  over  goblet;  below  the  letter 
are  seen  the  fine  hair-like  processes  in  which  the  cells  terminate  :  c.  two  nuclei  of  the  axial  (gusta- 
torv;  cells.  The  more  superficial  nuclei  belong  to  the  superficial  (incasing)  cells  ;  the  converging 
lines  indicate  the  fusiform  shape  of  the  incasing  cells.     X  400.     (Schofield.) 

hers  in  the  epithelium  of  the  papilla  foliata,  which  is  situated  near  the 
root  of  the  tongue  in  the  rabbit,  and  also  in  man.  Similar  taste-goblets 
have  been  observed  on  the  posterior  (laryngeal)  surface  of  the  epiglottis. 

The  Pharyxx. 

The  portion  of  the  alimentary  canal  which  intervenes  between  the 
mouth  and  the  oesophagus  is  termed  the  Pharynx.  It  will  suffice  here 
to  mention  that  it  is  constructed  of  a  series  of  three  muscles  with  stri- 


FOOD   AND    DIGESTION".  307 

ated  fibres  {constnctors),  which  are  covered  by  a  thin  fascia  externally, 
and  are  lined  internally  by  a  strong  fascia  (pharyngeal  aponeurosis),  on 
the  inner  aspect  of  which  is  areolar  (submucous)  tissue  and  mucous 
membrane,  continuous  with  that  of  the  mouth,  and,  as  regards  the  part 
concerned  in  swallowing,  is  identical  with  it  in  general  structure.  The 
epithelium  of  this  part  of  the  pharynx,  like  that  of  the  mouth,  is  strati- 
fied and  squamous. 

The  pharynx  is  well  supplied  with  mucous  glands  (fig.  228). 

Between  the  anterior  and  posterior  arches  of  the  soft  palate  are  sit- 
uated the  Tonsils,  one  on  each  side.  A  tonsil  consists  of  an  elevation 
of  the  mucous  membrane  representing  32  to  15  orifices,  which  lead  into 


Fig.  233,  Fig.  234. 

Fig.  2.33.— Lingual  follicle  or  crypt,  a,  involution  of  mucous  membrane  with  its  papillae;  6, 
lymphoid  tissues,  with  several  lymphoid  sacs.    CFrey.^ 

Fie.  234.— Vertical  section  through  a  crypt  of  the  human  tonsil.  1,  entrance  to  the  crypt ;  2  and 
3,  the  framework  or  adenoid  tissue;  4,  the  inclosing  fibrous  tissue  ;  a  and  b,  lymphatic  follicles;  5 
and  6,  blood-vessels.     (Stohr.) 

crypts  or  recesses,  in  the  walls  of  which  are  placed  nodules  of  adenoid 
or  lymphoid  tissue  (fig.  234).  These  nodules  are  enveloped  in  a  less 
dense  adenoid  tissue  which  reaches  the  mucous  surface.  The  surface 
is  covered  with  stratified  squamous  epithelium,  and  the  subepithelial  or 
mucous  membrane  proper  may  present  rudimentary  papillae  formed  of 
adenoid  tissue.  The  tonsil  is  bounded  by  a  fibrous  capsule  (fig.  234,  4). 
Into  the  crypts  open  the  ducts  of  numerous  mucous  glands. 

The  viscid  secretion  which  exudes  from  the  tonsils  serves  to  lubri- 
cate the  bolus  of  food  as  it  passes  them  in  the  second  part  of  the  act  of 
deglutition. 


308  HANDBOOK    OF    PHYSIOLOGY. 


The  CEsophagus  or  Gullet. 


The  Esophagus  or  Gullet,  the  narrowest  portion  of  the  alimentary 
canal,  is  a  muscular  and  mucous  tube,  nine  or  ten  inches  in  length,  which 
extends  from  the  lower  end  of  the  pharynx  to  the  cardiac  orifice  of  the 
stomach. 

Structure. — The  oesophagus  is  made  up  of  three  coats — viz.,  the 
outer,  muscular;  the  middle,  suJmiucous ;  and  the  inner,  mucous.  The 
muscular  coat  is  covered  externally  by  a  varying  amount  of  loose  fibrous 


~^~  -x-^r  X-'''      .^ 

Fig  235.— Section  of  the  mucous  membrane  of  the  oesophagus. 

tissue.  It  is  composed  of  two  layers  of  fibres,  the  outer  being  arranged 
longitudinally,  and  the  inner  circularly.  At  the  upper  part  of  the  (esoph- 
agus this  coat  is  made  up  principally  of  striated  muscle  fibres,  as  they 
are  continuous  with  the  constrictor  muscles  of  the  pharynx;  but  lower 
down  the  unstriated  fibres  become  m.oreand  more  numerous,  and  toward 
the  end  of  the  tube  form  the  entire  coat.  The  muscular  coat  is  con- 
nected with  the  mucous  coat  by  a  more  or  less  developed  layer  of  areolar 
tissue,  which  forms  the  submucous  coat  (fig.  335, /),  in  which  is  con- 
tained in  the  lower  half  or  third  of  the  tube  many  mucous  glands,  the 
ducts  of  which,  passing  through  the  mucous  membrane,  open  on  its  sur- 
face.    Separating  this  coat  from  the  mucous  membrane  proper  is  a  well- 


FOOD   AKD    DIGESTION.  309 

developed  layer  of  longitudinal,  unstriated  muscle,  called  the  muscularis 
mucosie.  The  mucous  membrane  is  composed  of  a  closely  felted  mesh- 
work  of  fine  connective  tissue,  which,  toward  the  surface,  is  elevated  into 
rudimentary  papilla?.  It  is  covered  with  a  stratified  epithelium,  of 
which  the  most  superficial  layers  are  squamous.  The  epithelium  is  ar- 
ranged upon  a  basement  membrane. 

In  newly-born  children  the  mucous  membrane  exhibits,  in  many 
parts,  the  structure  of  lymphoid  tissue  (Klein). 

Blood-  and  lymph-vessels,  and  nerves,  are  distributed  in  the  walls  of 
the  oesophagus.  Between  the  outer  and  inner  layers  of  the  muscular 
coat,  nerve-ganglia  of  Auerbach  are  also  found  (fig.  241). 

Deglutition. 

When  properly  masticated,  the  food  is  transmitted  in  successive  por- 
tions to  the  stomach  by  the  act  of  deglutition  or  swallowing.  This,  for 
the  purpose  of  description,  may  be  divided  into  three  acts.  In  the  first, 
particles  of  food  collected  to  a  morsel  are  made  to  glide  between  the  sur- 
face of  the  tongue  and  the  palatine  arch,  till  they  have  passed  the  ante- 
rior arch  of  the  fauces;  in  the  second,  the  morsel  is  carried  through  the 
pharynx;  and  in  the  third,  it  reaches  the  stomach  through  the  oesopha- 
gus. These  three  acts  follow  each  other  rapidly.  (1.)  The  first  act  may 
be  voluntary,  although  it  is  usually  performed  unconsciously;  the  mor- 
sel of  food,  when  sufficiently  masticated,  being  pressed  between  the 
tongue  and  palate,  by  the  agency  of  the  muscles  of  the  former,  in  such 
a  manner  as  to  force  it  back  to  the  entrance  of  the  pharynx.  (2.)  The 
second  act  is  the  most  complicated,  because  the  food  must  pass  by  the 
posterior  orifice  of  the  nose  and  the  upper  oj^ening  of  the  larynx  with- 
out touching  them.  When  it  has  been  brought,  by  the  first  act,  between 
the  anterior  arches  of  the  palate,  it  is  moved  onward  by  the  movement 
of  the  tongue  backward,  and  by  the  muscles  of  the  anterior  arches  con- 
tracting on  it  and  then  behind  it.  The  root  of  the  tongue  being  re- 
tracted, and  the  larynx  being  raised  with  the  pharynx  and  carried  for- 
ward under  the  base  of  the  tongue,  the  epiglottis  is  pressed  over  the 
upper  opening  of  the  larynx,  and  the  morsel  glides  past  it;  the  closure 
of  the  glottis  being  additionally  secured  by  the  simultaneous  contraction 
of  its  own  muscles:  so  that,  even  when  the  epiglottis  is  destroyed,  there 
is  little  danger  of  food  or  drink  passing  into  the  larynx  so  long  as  its 
muscles  can  act  freely.  At  the  same  time,  the  raising  of  the  soft  palate, 
so  that  its  posterior  edge  touches  the  back  part  of  the  pharynx,  and  the 
approximation  of  the  sides  of  the  posterior  palatine  arch,  which  move 
quickly  inward  like  side  curtains,  close  the  passage  into  the  upper  part 
of  the  pharynx  and  the  posterior  nares,  and  form  an  inclined  plane, 
along  the  under  surface  of  which  the  morsel  descends;  then  the  pharynx. 


310  HANDBOOK    OF    PHYSIOLOGY. 

raised  up  to  receive  it,  in  its  turn  contracts,  and  forces  it  onward  into 
the  oesophagus.  The  passage  of  the  bolus  of  food  through  the  constric- 
tors of  the  pharynx  is  counted  by  some  as  a  distinct  stage.  (3.)  In 
the  third  act,  in  whicli  the  food  passes  through  the  oesophagus,  every 
part  of  that  tube,  as  it  receives  the  morsel  and  is  dilated  by  it,  is  stim- 
ulated to  contract:  hence  an  undulatory  contraction  of  the  oesophagus, 
which  is  easily  observable  in  horses  while  drinking,  joroceeds  rapidly 
along  the  tube.  It  is  only  when  the  morsels  swallowed  are  large,  or 
taken  too  quickly  in  succession,  that  the  progressive  contraction  of  the 
oesophagus  is  slow,  and  attended  with  pain.  Division  of  both  pneumo- 
gastric  nerves  paralyzes  the  contractile  power  of  the  oesophagus  and  food 
accordingly  accumulates  in  the  tube.  The  second  and  third  parts  of 
the  act  of  deglutition  are  involuntary. 

Nervous  Meclianism. — The  nerves  engaged  in  the  reflex  act  of  deglu- 
tition are : — sensory,  branches  of  the  fifth  cerebral  sujiplying  the  soft  pal- 
ate; glosso-pharyngeal,  supplying  the  tongue  and  pharynx;  the  superior 
laryngeal  branch  of  the  vagus,  supplying  the  epiglottis  and  the  glottis; 
while  the  motor  fibres  concerned  are : — branches  of  the  fifth,  sujoplying 
part  of  the  digastric  and  mylo-hyoid  muscles,  and  the  muscles  of  masti- 
cation; the  facial,  supplying  the  levator  palati;  the  glosso-pharyngeal, 
supplying  the  muscles  of  the  pharynx;  the  vagus,  supplying  the  muscles 
of  the  larynx  through  the  inferior  laryngeal  branch,  and  the  hypoglos- 
sal, the  muscles  of  the  tongue.  The  nerve-centre  by  which  the  muscles 
are  harmonized  in  their  action,  is  situate  in  the  medulla  oblongata.  In 
the  movements  of  the  oesophagus,  the  ganglia  contained  in  its  walls, 
with  the  pneumo-gastrics,  are  the  nerve-structures  chiefly  concerned. 

It  is  important  to  note  that  the  swallowing  both  of  food  and  drink  is 
a  muscular  act,  and  can,  therefore,  take  place  in  opposition  to  the  force 
of  gravity.  Thus,  horses  and  many  other  animals  habitually  drink  up- 
hill, and  the  same  feat  can  be  performed  by  jugglers. 

The  Stomach. 

In  man  and  those  Mammalia  which  are  provided  with  a  single  stom- 
ach, it  consists  of  a  dilatation  of  the  alimentary  canal  placed  between 
and  continuous  with  the  oesophagus,  which  enters  its  larger  or  cardiac 
end  on  the  one  hand,  and  the  small  intestine,  which  commences  at  its 
narrowed  end  or  pylorus,  on  the  other.  It  varies  in  shape  and  size  ac- 
cording to  its  state  of  distention. 

Structure. — The  stomach  is  composed  of  four  coats,  called  respectively 
—(1)  an  external  or  peritoneal,  (2)  muscular,  (3)  submucous,  and  (4) 
mucous  coat;  with  blood-vessels,  lymphatics',  and  nerves  distributed  in 
and  between  them. 

(1)  The  peritoneal  coat  has  the  structure  of  serous  membranes  in 


FOOD    AXD    DIGESTION. 


311 


general,  to  be  presently  described.  (2)  The  mtiscular  coat  consists  of 
three  separate  layers  or  sets  of  fibre,  which,  according  to  their  several 
directions,  are  named  the  longitudinal,  circular,  and  oblique.  The  lon- 
gitudinal set  are  the  most  superficial:  they  are  continuous  with  tlie 
longitudinal  fibres  of  the  oesophagus 
and  spread  out  in  a  diverging  man- 
ner over  the  cardiac  end  and  sides 
of  the  stomach.  They  extend  as 
far  as  the  pylorus,  being  especially 
distinct  at  the  lesser  or  upper  curva- 
ture of  the  stomach,  along  which 
they  pass  in  several  strong  bands. 
The  next  set  are  the  circiila?'  or 
transverse  fibres,  which  more  or  less 
completely  encircle  all  parts  of  the 
stomach ;  they  are  most  abundant  at 
the  middle  and  in  the  p3^1oric  por- 
tion of  the  organ,  and  form  the  chief 
part  of  the  thick  projecting  ring  of 
the  pylorus.  These  fibres  are  not 
simple  circles,  but  form  double  or 
figure-of-8  loops,  the  fibres  intersect- 
ing very  obliquely.  The  next,  and 
consequently  deepest  set  of  fibres, 
are  the  oblique,  continuous  with  the 
circular  muscular  fibres  of  the 
oesophagus,  and  having  the  same 
double-looped  arrangement  that 
prevails  in  the  preceding  layer :  they 
are  comparatively  few  in  number, 
and  are  placed  only  at  the  cardiac 
orifice  and  portion  of  the  stomach, 
over  both  surfaces  of  which  they  are 
spread,  some  passing  obliquely  from 
left  to  right,  others  from  right  to 
left,  around  the  cardiac  orifice,  to 
which,  by  their  interlacing,  they 
form  a  kind  of  sphincter,  continuous 
with  that  around  the  lower  end  of 
the  oesophagus.  The  muscular  fibres  of  the  stomach  and  of  the  in- 
testinal canal  are  unstriated,  being  composed  of  elongated,  spindle- 
shaped  fibre-cells. 

(3)  and  (4)  The  mucous  membrane  of  the  stomach,  which  rests  upon 
a  layer  of   loose  cellular  membrane,   or  submucous   tissue,  is  smooth, 


Fig.  236.— From  a  vertical  section  through 
the  mucous  membrane  of  the  cardiac  end  of 
stomach.  Two  peptic  glands  are  shown  with  a 
duct  common  to  both,  one  gland  only  in  part. 
a,  duct  with  columnar  epithelium  becoming 
shorter  as  the  cells  are  traced  downward;  ii, 
neck  of  gland  tubes,  with  central  and  parietal 
or  so-called  peptic  cells;  6,  fundus  with  curved 
csecal  extremity— the  parietal  cells  are  not  so 
numerous  here.  X  400.  (Klein  and  Noble 
Smith.) 


312  HANDBOOK    OF   PHYSIOLOGY. 

level,  soft,  and  velvety;  of  a  pale  pink  color  during  life,  and  in  the  con- 
tracted state  thrown  into  numerous,  chiefly  longitudinal,  folds  or  rugge, 
which  disappear  when  the  organ  is  distended. 

The  basis  of  the  mucous  membrane  is  a  fine  connective  tissue,  which 
approaches  closely  in  structure  to  adenoid  tissue;  this  tissue  supports 
the  tubular  glands  of  which  the  superficial  and  chief  joart  of  the  mucous 
membrane  is  composed,  and  passing  up  between  them  assists  in  binding 
them  together.  Here  and  there  are  to  be  found  in  this  coat,  immedi- 
ately underneath  the  glands,  masses  of  adenoid  tissue  sufficiently 
marked  to  be  termed  by  some  lymphoid  follicles.  The  glands  are  sepa- 
rated from  the  rest  of  the  mucous  membrane  by  a  very  fine  homogene- 
ous basement  membrane. 

At  the  deepest  part  of  the  mucous  membrane  are  two  layers  (circu- 
lar and  longitudinal)  of  unstriped  muscular  fibres,  called  the  miiscularis 
7nucosce,  which  separate  the  mucous  membrane  from  the  Gcanty  sub- 
mucous tissue. 


Fig.  237.— Transverse  section  through  lower  part  of  peptic  glands  of  a  cat.    a,  peptic  cells;  b,  small 
spheroidal  or  cubical  cells;  c,  transverse  section  of  capillaries.     (Frey.) 

When  examined  with  a  lens,  the  internal  or  free  surface  of  the  stom- 
ach presents  a  peculiar  honeycomb  appearance,  produced  by  shallow 
polygonal  depressions,  the  diameter  of  which  varies  generally  from  -oTToth 
to  ^^th  of  an  inch  (about  125/^)  ;  but  near  the  pylorus  is  as  much  as 
yio^th  of  an  inch  (250/ji).  They  are  separated  by  slightly  elevated 
ridges,  which  sometimes,  especially  in  certain  morbid  states  of  the  stom- 
ach, bear  minute,  narrow  vascular  processes,  which  look  like  villi,  and 
have  given  rise  to  the  erroneous  supposition  that  the  stomach  has 
absorbing  villi,  like  those  of  the  small  intestines.  In  the  bottom  of 
these  little  pits,  and  to  some  extent  between  them,  minute  openings  are 
visible,  which  are  the  orifices  of  the  ducts  of  perpendicularly  arranged 
tubular  glands  (fig.  236),  imbedded  side  by  side  in  sets  or  bundles,  on 
the  surface  of  the  mucous  membrane,  and  composing  nearly  the  whole 
structure. 

The  glands  of  the  mucous  membrane  are  of  two  varieties,  (a)  Peptic, 
(b)  Pyloric  or  Mucous. 

{a)  Peptic  glands  are  found  throughout  the  whole  of  the  stomach 
except  at  the  pylorus.     They  are  arranged  in   groups  of  four  or  five. 


FOOD    A?s"D    DIGESTION".  313 

which  are  separated  by  a  fine  connective  tissue.  Two  or  three  tubes 
often  open  into  one  duct,  which  forms  about  a  third  of  the  wliole  length 
of  the  tube  and  opens  on  the  surface.  The  ducts  are  lined  with  co- 
lumnar epithelium.  Of  the  gland  tube  proper,  i.e.,  the  part  of  the  gland 
below  the  duct,  the  upper  third  is  the  nec/c  and  the  rest  the  bodi/.  The 
neck  is  narrower  than  the  body,  and  is  lined  with  granular  cubical  cells 
which  are  continuous  with  the  columnar  cells  of  the  duct.  Between 
these  cells  and  the  membraua  propria  of  the  tubes,  are  large  oval  or 
spherical  cells,  opaque  or  granular  in  appearance,  with  clear  oval  nuclei, 
bulging  out  the  membrana  propria;  these  cells  are  called  peptic  or  jJa- 

rietal  cells.  They  do  not  form  a  continuous 
layer.  The  body,  which  is  broader  than 
the  neck  and  terminates  in  a  blind  ex- 
tremity ov  fundus  near  the  muscularis  mu- 


Fig.  238,  Fig.  239. 

Fig.  2.38.— Section  showing  the  pyloric  glands,  s,  free  surface;  d,  ducts  of  pyloric  glands;  n, 
neck  of  same;  m,  the  gland  alveoli;  mm,  muscularis  mucosae.    (Klein  and  Noble  Smith.) 

Fig.  2:W.— Plan  of  the  blood-vessels  of  the  stomach,  as  they  would  be  seen  in  a  vertical  section. 
a,  arteries,  passing  up  from  the  vessels  of  submucous  coat;  6,  capillaries  branching  between  and 
around  the  tubes;  c,  superficial  plexus  of  capillaries occupyingtheridgesof  the  mucousmembrane; 
d,  vein  formed  liy  t!ie  imion  of  veins  v.'hicli,  having  collected  the  blood  of  the  superficial  capillary 
plexus,  are  seen  passing  down  between  the  tubes.    (Brinton.) 

cos£e,  is  lined  by  cells  continuous  with  the  cubical  or  central  cells  of 
the  neck,  but  longer,  more  columnar  and  more  transparent.  In  this 
part  are  a  few  parietal  cells  of  the  same  kind  as  in  the  neck  (fig. 
236). 

As  the  pylorus  is  approached  the  gland  ducts  become  longer  and 
the  tube  proper  becomes  shorter,  and  occasionally  branched  at  the 
fundus. 

{h)  Pyloric  Glands. — These  glands  (fig.  238)  have  much  longer  ducts 
than  the  peptic  glands.  Into  each  duct  two  or  three  tubes  open  by 
very  short  and  narrow  necks,  and  the  body  of  each  tube  is  branched. 


314  HANDBOOK    OF    PHYSIOLOGY. 

wavy,  and  convoluted.  The  lumen  is  very  large  The  duots  are  lined 
with  columnar  epithelium,  and  the  neck  and  body  with  shorter  and 
more  granular  cubical  cells,  which  corres^jond  with  the  central  cells  oi' 
the  peptic  glands.  During  secretion  the  cells  become,  as  in  the  case  of 
the  peptic  glands,  larger  and  the  granules  restricted  to  the  inner  zone 
of  the  cell.  As  they  approach  the  duodenum  the  pyloric  glands  become 
larger,  more  convoluted  and  more  deeply  situated.  They  are  directly 
continuous  with  Brunner's  glands  in  the  duodenum,     (Watney.) 

Changes  in  the  gland  cells  during  secretion. — The  chief  or  cubical 
cells  of  the  peptic  glands,  and  the  corresponding  cells  of  the  pyloric 
glands  during  the  early  stage  of  digestion,  if  hardened  in  alcohol,  appear 
swollen  and  granular,  and  stain  readily.  At  a  later  stage  the  cells  be- 
come smaller,  but  more  granular  and  stain  even  more  readily.  The 
parietal  cells  swell  up,  but  are  otherwise  not  altered  during  digestion. 
The  granules,  however,  in  the  alcohol-hardened  specimen,  are  believed 
not  to  exist  in  the  living  cells,  but  to  have  been  2irecipitated  by  the 
hardening  reagent;  for  if  examined  during  life  they  appear  to  be  con- 
fined to  the  inner  zone  of  the  cells,  and  the  outer  zone  is  free  from 
granules,  whereas  during  rest  the  cell  is  granular  throughout.  These 
granules  are  thought  to  be  pepsin,  or  the  substance  from  which  jDcpsin 
in  formed,  pepsinogen,  which  is  during  rest  stored  chiefly  in  the  inner 
zone  of  the  cells  and  discharged  into  the  lumen  of  the  tube  during 
secretion.     (Langley.) 

Lymphatics. — Lymphatic  vessels  surround  the  gland  tubes  to  a 
greater  or  less  extent.  Toward  the  fundus  of  the  peptic  glands  are 
found  masses  of  lymphoid  tissue  which  may  appear  as  distinct  follicles, 
somewhat  like  the  solitary  glands  of  the  small  intestine. 

Blood-vessels. — The  blood-vessels  of  the  stomach,  which  first  break 
up  in  the  sub-mucous  tissue,  send  branches  upward  between  the  closely 
packed  glandular  tubes,  anastomosing  around  them  by  means  of  a  fine 
capillary  network,  with  oblong  meshes.  Continuous  with  this  deeper 
plexus,  or  prolonged  upward  from  it,  so  to  speak,  is  a  more  superficial 
network  of  larger  capillaries,  which  branch  densely  around  the  orifices 
of  the  tubes,  and  form  the  framework  on  which  are  moulded  the  small 
elevated  ridges  of  mucous  membrane  bounding  the  minute,  polygonal 
pits  before  referred  to.  From  this  superficial  network  the  veins  chiefly 
take  their  origin.  Thence  passing  down  between  the  tubes,  with  no 
very  free  connection  with  the  deeper  infer-tubular  capillary  plexus, 
they  open  finally  into  the  venous  network  in  the  submucous  tissue. 

Nerves. — The  nerves  of  the  stomach  are  derived  from  the  pneumo- 
gastric  and  sympathetic,  and  form  a  plexus  in  the  sub-mucous  and  mus- 
cular coats  containing  many  ganglia  (Remak,  Meissner). 


FOOD   AND    DIGESTION.  315 


Gastric  Juice. 

The  functions  of  the  stomach  are  (a)  to  secrete  a  digestive  fluid,  the 
gastric  juice,  to  the  action  of  which  the  food  is  subjected  after  it  lias 
entered  the  cavity  of  the  stomacli  from  the  oesopliagus;  (b)  to  thor- 
oughly incorporate  the  fluid  with  the  food  by  means  of  its  muscular 
movements;  and  (c)  to  absorb  such  substances  as  are  ready  for  absorp- 
tion. While  the  stomach  contains  no  food,  and  is  inactive,  no  gastric 
fluid  is  secreted;  and  mucus,  which  is  either  neutral  or  slightly  alkaline, 
covers  its  surface.  But  immediately  on  the  introduction  of  food  or  other 
substance,  the  mucous  membrane,  previously  quite  pale,  becomes  slightly 
turgid  and  reddened  with  the  influx  of  a  larger  quantity  of  blood;  the 
gastric  glands  commence  secreting  actively,  and  an  acid  fluid  is  poured 
out  in  minute  drops,  which  gradually  run  together  and  flow  down  the 
walls  of  the  stomach,  or  soak  into  the  substances  within  it. 

Chemical  Composition. — The  first  accurate  analysis  of  gastric  juice 
was  made  by  Prout :  but  it  does  not  appear  to  have  been  collected  in 
any  large  quantity,  or  pure  and  separate  from  food,  until  the  time  when 
Beaumont  was  enabled,  by  a  fortunate  circumstance,  to  obtain  it  from 
the  stomach  of  a  man  named  St.  Martin,  in  whom  there  existed,  as  the 
result  of  a  gunshot  wound,  an  opening  leading  directly  into  the  stomach, 
near  the  upper  extremity  of  the  great  curvature,  and  three  inches  from 
the  cardiac  orifice.  The  introduction  of  any  mechanical  irritant,  such 
as  the  bulb  of  a  thermometer,  into  the  stomach,  through  this  artificial 
opening,  excited  at  once  the  secretion  of  gastric  fluid.  This  was  drawn 
off,  and  was  often  obtained  to  the  extent  of  nearly  an  ounce.  The  in- 
troduction of  alimentary  substances  caused  a  much  more  rapid  and 
abundant  secretion  than  did  other  mechanical  irritants.  Xo  increase  of 
temperature  could  be  detected  during  the  most  active  secretion;  the 
thermometer  introduced  into  the  stomach  always  stood  at  37.8°  C.  (100° 
F.)  except  during  muscular  exertion,  when  the  temperature  of  the  stom- 
ach, like  that  of  other  parts  of  the  body,  rose  one  or  two  degrees  higher. 

The  chemical  composition  of  human  gastric  juice  has  been  also  in- 
vestigated by  Schmidt.  The  fluid  in  this  case  was  obtained  by  means 
of  an  accidental  gastric  fistula,  which  existed  for  several  years  below 
the  left  mammary  region  of  a  patient  between  the  cartilages  of  the  ninth 
and  tenth  ribs.  The  mucous  membrane  was  excited  to  action  by  the 
introduction  of  some  hard  matter,  such  as  dry  peas,  and  the  secretion 
was  removed  by  means  of  an  elastic  tube.  The  fluid  thus  obtained  was 
found  to  be  acid,  limpid,  odorless,  with  a  mawkish  taste — with  a  specific 
gravity  of  1002  to  1010.  It  contained  a  few  cells,  seen  with  the  micro- 
scope, and  some  fine  granular  matter.  The  analysis  of  the  fiuid  obtained 
in  this  way  is  given  below.     The  gastric  juice  of  dogs  and  other  animals 


31G  HANDBOOK    OF    PHYSIOLOGY. 

obtained  by  the  introduction  into  the  stomach  of  a  clean  sponge  tlirough 
an  artificially  made  gastric  fistula,  shows  a  decided  difference  in  comjao- 
sition,  but  possibly  this  is  due,  at  least  in  part,  to  admixture  with  food. 

CHEMICAL  COMPOSITION  OP  GASTRIC  JUICE. 


Dogs. 

Human. 

Water 

971.17 

994.4 

Solids 

28.82 

5.39 

Solids- 

Ferment — Pepsin 

17.5 

3.19 

Hydrochloric  acid  (free) 

2.7 

.2 

Salts- 

Calcium,  sodium,  and  potassium,  chlorides  ;  and 

calcium,  magnesium,  and  iron,  phosphates 

8.57 

2.18 

The  quayitity  of  gastric  juice  secreted  daily  has  been  variously  esti- 
mated; but  the  average  for  a  healthy  adult  may  be  assumed  to  range 
from  ten  to  twenty  pints  in  the  twenty-four  hours.  The  acidity  of  the 
fluid  is  due  to  frefe  hydrochloi'ic  acid,  although  other  acids,  e.g,  lactic, 
acetic,  butyric,  are  not  infrequently  to  be  found  therein  as  products  of 
gastric  digestion  or  abnormal  fermentation.  The  amount  of  hydro- 
chloric acid  varies  from  2  to  .2  per  1000  parts.  In  healthy  gastric 
juice  the  amount  of  free  acid  may  be  as  much  as  .3  per  cent. 

There  is  but  little  doubt  that  hydrochloric  acid  is  the  proper  acid  of 
healthy  gastric  juice,  and  various  tests  have  been  used  to  prove  this; 
most  of  these  depend  upon  changes  produced  in  aniline  colors  by  the 
action  of  hydrochloric  acid,  even  in  minute  traces,  whereas  lactic  and 
other  organic  acids  have  no  such  action.  Of  these  tests  the  following 
may  be  mentioned. 

An  aqueous  alkaline  solution  of  00  tropceolin,  a  bright  yellow  dye, 
is  turned  red  on  the  addition  of  a  minute  trace  of  hydrochloric  acid;  and 
aqueous  solutions  of  methyl  violet  and  gentian  violet  are  turned  blue 
under  the  same  circumstances.  The  lactic  acid  sometimes  present  in 
the  contents  of  the  stomach  is  derived  partly  from  the  sarcolactic  acid 
of  muscle,  and  partly  from  lactic  acid  fermentation  of  carbohydrates. 
Lactic  acid  (CsHeOa),  if  jiresent,  gives  the  following  test.  A  solution  of 
10  cc.  of  a  4  per  cent  aqueous  solution  of  carbolic  acid,  20  cc.  of  water, 
and  one  drop  of  liquor  ferri  perchloride  is  made,  forming  a  blue-colored 
mixture;  a  mere  trace  of  free  lactic  acid  added  to  such  a  solution  causes 
it  to  become  yellow,  whereas  hydrochloric  acid  even  in  large  amount 
only  bleaches  it. 

As  regards  the  formation  of  pepsin  and  acid,  the  former  is  produced 
by  the  central  or  chief  cells  of  the  peptic  glands,  and  also  most  likely  by 
t?ie  similar  cells  in  the  pyloric  glands:  the  acid  is  chiefly  found  at  the 
surface  of  the  mucous  membrane,  but  is  in  all  probability  formed  by  the 


FOOD   AND    DIGESTION.  317 

parietal  cells  of  the  peptic  glands,  hence  called  oxyntic,  as  no  acid  is 
formed  by  the  pyloric  glands  in  which  this  variety  of  cell  is  absent. 

The  ferment  Pepsin  can  be  procured  by  digesting  jjortions  of  the  mucous 
membrane  of  the  stomach  in  cold  water,  after  they  have  been  macerated  for 
some  time  in  water  at  a  temperature  37° — 37.8°  C.  (80° — 100°  F.).  The  warm 
water  dissolves  various  substances  as  well  as  some  of  the  pepsin,  but  the  cold 
water  takes  up  little  else  than  pepsin,  which  is  contained  in  a  grajash-brown 
viscid  fluid,  on  evaporating  the  cold  solution.  The  addition  of  alcohol  throws 
down  the  i5ei:)sin  in  grayish-white  flocculi.  Glycerine  also  has  the  property  of 
dissolving  out  the  ferment ;  and  if  the  mucous  membrane  be  finely  minced. 
and  the  moisture  removed  by  absolute  alcohol,  a  powerful  extract  may  be 
obtained  by  throwing  into  glycerine. 

Functions. — {a)  The  chief  digestive  power  of  the  gastric  juice  de- 
pends on  the  j)epsin  and  acid  contained  in  it,  both  of  which  are,  under 
ordinary  circumstances,  necessary  for  the  process. 

The  general  effect  of  digestion  in  the  stomach  is  the  conversion  of 
the  food  into  chyme,  a  substance  of  varying  composition  according  to 
the  nature  of  the  food,  yet  always  presenting  a  characteristic  thick, 
pultaceous,  grumous  consistence,  with  the  undigested  portions  of  the 
food  mixed  in  a  more  fluid  substance,  and  a  strong,  disagreeable  acid 
odor  and  taste. 

The  chief  function  of  the  gastric  juice  is  to  convert  proteids.  into 
jicptones.  This  action  may  be  shown  by  adding  a  little  gastric  juice 
(natural  or  artificial)  to  some  diluted  egg-albumin,  and  keeping  the  mix- 
ture at  a  temperature  of  about  37.8°  C.  (100°  F.) ;  it  is  soon  found  that  the 
albumin  cannot  be  precipitated  on  boiling,  but  that  if  the  solution  be 
neutralized  with  an  alkali,  a  precipitate  of  acid-albumin  is  thrown  down. 
After  a  while  the  acid-albumin  disappears,  so  that  no  precipitate  results 
on  neutralization,  and  finally  it  is  found  that  all  the  albumin  has  been 
changed  into  another  proteid  substance  which  is  not  precipitated  on 
boiling  or  on  neutralization.  This  is  0,2^^^  peptone,  but  in  the  conver- 
sion of  the  albumin  into  peptone  there  are  various  intermediate  prod- 
ucts called  proteoses.  Of  these  there  are  two  chief  forms,  viz., /;ro/o- 
albumose  and  deutero-albumose. 

Characteristics  of  Peptones. — Peptones  have  a  certain  characteristic 
which  distinguishes  them,  from  other  proteids.  They  are  diffusible,  i.e., 
they  possess  the  property  of  passing  through  animal  membranes. 

In  their  diflusibility  peptones  differ  remarkably  from  egg-albumin, 
and  on  this  ditfusibiliiy  depends  one  of  their  chief  uses.  Egg-albumin 
as  such,  even  in  a  state  of  solution,  would  be  of  little  service  as  food, 
inasmuch  as  its  indiffusibility  would  effectually  prevent  its  passing  by 
absorption  into  the  blood-vessels  of  the  stomach  and  intestinal  canal. 
AVhen  completely  changed  by  the  action  of  the  gastric  juice  into  pep- 
tones, albuminous  matters  diffuse  readily,  and  are  thus  quickly  absorbed. 


318  HANDBOOK    OF    PHYSIOLOGY, 

After  entering  the  blood  the  peptones  are  very  soon  again  modified, 
so  as  to  reassunie  the  chemical  characters  of  albumin,  a  change  as  nec- 
essary for  preventing  their  diffusing  out  of  the  blood-vessels,  as  the 
previous  change  was  for  enabling  them  to  pass  in.  This  is  effected, 
probably,  in  great  part  by  their  passage  through  the  vascular  walls. 

Products  of  Gastric  Digestion. — The  chief  product  of  gastric  diges- 
tion is  undoubtedly  peptone.  It  should  be  stated,  however,  that  the 
conversion  of  native  albumin  into  acid-albumin  may  be  effected  by  the 
hydrochloric  acid  alone,  the  further  action  is  undoubtedly  due  to  the 
ferment  and  the  acid  acting  together,  as  although  under  high  pressure 
any  acid  solution  may,  it  is  said,  if  strong  enough,  produce  the  entire 
conversion  into  peptone,  under  the  condition  of  digestion  in  the  stomach 
this  would  be  quite  impossible;  and,  on  the  other  hand,  pepsin  will  not 
act  without  the  j^resence  of  acid.  The  production  of  the  two  forms  of 
peptone  above  mentioned  is  usually  recognized.  Their  differences  in 
chemical  properties  have  not  yet  been  made  out,  but  they  are  distin- 
guished by  this  remarkable  fact,  that  the  pancreatic  juice,  while  pos- 
sessing no  action  over  the  anti-peptone,  is  able  to  convert  the  hemi- 
peptone  into  two  nitrogenous  crystallizable  bodies,  leucin  and  tyrosin. 
Pepsin  acts  the  part  of  a  hydrolytic  ferment  (proteolytic),  and  appears 
to  cause  hydration  of  albumen,  peptone  being  a  highly  hydrated  form 
of  albumin. 

According  to  recent  observatio7is  a  molecule  of  albumen  may  be 
considered  to  be  made  up  of  two  parts,  a  hemi-albumin  moiety  and  an 
anti-albumin  moiety,  and  the  conversion  of  these  parts  by  the  action 
of  gastric  juice  has  been  drawn  up  into  the  following  table  by  Halliburton 
from  the  researches  of  Neumeister. 

Albumin. 


Hemi-Albumin.  Anti-Albumin. 

I  1 


Proto-Albumose.  Hetero-Albumose.                   Anti-Albuminate. 

I  I                                                    I 

Hemi-deutero  Ampho-deutero                        Anti-Albumid. 

Albumose.  Albumose.                                             | 

I  I  Anti-deutero  Albumose. 

Hemi-Peptone.  Ampho-Peptone.  Anti-Peptone. 

Proto-albumose,  the  first  product,  is  soluble  in  either  hot  or  cold 
water,  as  well  as  in  hot  or  cold  saline  solution,  but  is  precipitated  by 
saturation  with  solid  sodium  chloride  or  magnesium  sulphate,  as  well  as 
with  solid  ammonium  sulphate.  On  the  addition  of  copper  sulphate 
it  is  precipitated,  and  the  precipitate  is  redissolved  on  addition  of  caustic 
potash  forming  a  rose  red  solution  (biuret  test). 

Hetero-alhumose  differs  from  proto-albumose  in  being  insoluble  in  hot 
or  cold  water;  it  is  soluble  in  hot  or  cold  saline  solutions,  but  is  precip- 


FOOD    AND    DIGESTION.  319 

itated,  not  coagulated,  at  a  temperature  of  65°  0.  In  all  other  respects 
it  resembles  proto-albumose. 

Deutero-albumose  is  soluble  in  hot  or  cold  water,  as  well  as  in  hot  or 
cold  saline  solution.  It  is  not  precipitated  by  saturation  with  solid 
sodium  chloride  or  magnesium  sulphate,  but  m  all  other  respects  re- 
sembles the  other  albumoses. 

Peptone  reacts  to  the  same  test  as  deutero-albumose,  but  is  not  pre- 
cipitated on  saturation  with  ammonium  sulphate. 

In  the  above  table  then  the  ultimate  result  is  seen  to  be  peptone; 
hemi-albumin  yielding  proto-albumose  and  hetero-albumose  in  the  first 
instance;  then  hemi-deutero-albumose,  then  hemi-peptone;  anti-albumin 
yielding  first  hetero-albumose  and  anti-albuminate  (or  acid-albumin), 
then  anti-deutero-albumose;  anti-albumid,  an  insoluble  product,  slowly 
yielding  anti-deutero-albumose,  and  finally  anti-peptone.  The  term 
ampho-deutero-albumose,  and  ampho-pejDtone  indicating  a  mixture  of 
the  hemi  and  anti  products  respectively. 

Circumstances  favoring  Gastric  Digestion. — 1.  A  temperature  of 
about  37.8°  C.  (100°  F.) ;  at  0°  C.  (32°  F.)  it  is  delayed,  and  by  boiling  is 
altogether  stopped.  2.  An  acid  medium  is  necessary.  Hydrochloric  is 
the  best  acid  for  the  purpose.  Excess  of  acid  or  neutralization  stops  the 
process.  3.  The  removal  of  the  products  of  digestion.  Excess  of  peptone 
delays  the  action. 

a.  Fibrin  is  first  dissolved,  forming  a  solution  of  globulins.  The 
intermediate  products  of  the  digestion  of  globulins  are  called  globuloses; 
of  vitellin,  vitelloses;  of  casein,  caseinoses;  of  myosin,  myosinoses. 
These  are  practically  the  same  as  albumoses,  and  are  included  under 
the  term  proteoses. 

b.  Proteids. — All  proteids  are  converted  by  the  gastric  juice  into 
peptones,  and,  therefore,  whether  they  be  taken  into  the  body  in  meat, 
eggs,  milk,  bread,  or  other  foods,  peptone  is  still  the  resultant. 

c.  Milk  is  curdled,  the  casein  being  precipitated,  and  theu  dissolved. 
The  curdling  is  due  to  a  special  ferment  of  the  gastric  juice,  and  is  not 
due  to  the  action  of  the  free  acid  only.  The  effect  of  rennet,  which  is 
a  decoction  of  the  fourth  stomach  of  a  calf  in  brine  (rennet),  has  long 
been  known,  as  it  is  used  extensively  to  cause  precipitation  of  casein  in 
cheese  manufacture.  The  ferment  which  produces  this  curdling  action 
is  distinct  from  pepsin,  and  is  called  rennin. 

d.  Gelatin  is  dissolved  and  changed  into  peptone,  as  are  also  chondrin 
and  elastin;  but  mncin,  and  the  horny  tissues,  which  contain  keratin 
generally  are  unaffected. 

e.  On  the  amylaceous  articles  of  food,  and  upon  pure  oUnginous  prin- 
ciples the  gastric  juice  has  no  action.  In  the  case  of  adipose  tissue,  its 
effect  is  to  dissolve  the  areolar  tissue,  albuminous  cell-walls,  etc.,  which 


320  HANDBOOK    OF    PHYSIOLOGY. 

enter  into  its  composition,  by  which  means  the  fat  is  able  to  mingle 
more  uniformly  with  the  other  constituents  of  the  chyme. 

The  gastric  fluid  acts  as  a  general  solvent  for  some  of  the  saline 
constituents  of  the  food,  as,  for  example,  particles  of  common  salt,  which 
may  happen  to  have  escaped  solution  in  the  saliva;  while  its  acid  may 
enable  it  to  dissolve  some  other  salts  which  are  insoluble  in  the  latter 
or  in  water. 

/.  It  also  dissolves  cane  sugar,  and  by  the  aid  of  its  mucus  (which 
may  contain  an  inverting  ferment)  causes  its  conversion  in  part  into 
grape  sugar. 

g.  The  action  of  the  gastric  juice  in  preventing  and  checking  putre- 
faction has  been  often  directly  demonstrated.  Indeed,  that  the  secre- 
tions which  the  food  meets  with  in  the  alimentary  canal  are  antiseptic  in 
their  action,  is  what  might  be  anticipated,  not  only  from  the  proneness 
to  decomposition  of  organic  matters,  such  as  those  used  as  food, 
especially  under  the  influence  of  warmth  and  moisture,  but  also  from 
the  well-known  fact  that  decomposing  flesh  {e.g.,  high  game)  may  be 
eaten  with  impunity,  while  it  would  certainly  cause  disease  were  it 
allowed  to  enter  the  blood  by  any  other  route  than  that  formed  by  the 
organs  of  digestion. 

Time  occupied  in  Gastric  Digestion. — Under  ordinary  conditions, 
from  three  to  four  hours  may  be  taken  as  the  average  time  occupied  by 
the  digestion  of  a  meal  in  the  stomach.  But  many  circumstances  will 
modify  the  rate  of  gastric  digestion.  The  chief  are:  the  nature  of  the 
food  taken  and  its  quantity  (the  stomach  should  be  fairly  filled — not 
distended) ;  the  time  that  has  elapsed  since  the  last  meal,  which  should 
be  at  least  enough  for  the  stomach  to  be  quite  clear  of  food;  the  amount 
of  exercise  previous  and  subsequent  to  a  meal  (gentle  exercise  being  fa- 
vorable, over-exertion  injurious  to  digestion) ;  the  state  of  mind  (tran- 
quillity of  temper  being  essential,  in  most  cases,  to  a  quick  and  due  di- 
gestion), and  the  bodily  health. 

Movements  of  the  Stomach. — The  gastric  fluid  is  assisted  in  accom- 
plishing its  share  in  digestion  by  the  movements  of  the  stomach.  In 
granivorous  birds,  for  example,  the  contraction  of  the  strong  muscular 
gizzard  affords  a  necessary  aid  to  digestion,  by  grinding  and  triturating 
the  hard  seeds  which  constitute  part  of  the  food.  But  in  the  stomachs 
of  man  and  other  Mammalia  the  movements  of  the  muscular  coat  are 
too  feeble  to  exercise  any  such  mechanical  force  on  the  food;  neither 
are  they  needed,  for  mastication  has  already  done  the  mechanical  work 
of  a  gizzard;  and  experiments  have  demonstrated  that  substances  are 
digested  even  inclosed  in  perforated  tubes,  and  consequently  protected 
from  mechanical  influence. 

The  normal  actions  of  the  muscular  fibres  of  the  human  stomach 
appear  to  have  a  three-fold  purpose:   (1)  to  adapt  the  stomach  to  the 


FOOD   AND    DIGESTIOlSr.  321 

quantity  of  food  in  it,  so  that  its  walls  may  be  in  contact  with  the  food 
on  all  sides,  and,  at  the  same  time,  may  exercise  a  certain  amount  of 
compression  upon  it ;  (2)  to  keep  the  orifices  of  the  stomach  closed  until 
the  food  is  digested;  and  (3)  to  perform  certain  peristaltic  movements, 
whereby  the  food,  as  it  becomes  chymified,  is  gradually  propelled  toward, 
and  ultimately  through,  the  pylorus.  In  accomplishing  this  latter  end, 
the  movements  without  doubt  materially  contribute  toward  effecting  a 
thorough  intermingling  of  the  food  and  the  gastric  fluid. 

"When  digestion  is  not  going  on,  the  stomach  is  uniformly  contracted, 
its  orifices  not  more  firmly  than  the  rest  of  its  walls;  but,  if  examined 
shortly  after  the  introduction  of  food,  it  is  found  closely  encircling  its 
contents,  and  its  orifices  are  firmly  closed  like  sphincters.  The  cardiac 
orifice,  every  time  food  is  swallowed,  opens  to  admit  its  passage  to  the 
stomach,  and  immediately  again  closes.  The  pyloric  orifice,  during  the 
first  part  of  gastric  digestion,  is  usually  so  completely  closed,  that  even 
when  the  stomach  is  separated  from  the  intestines,  none  of  its  contents 
escape.  But  toward  the  termination  of  the  digestive  process,  the  pylorus 
seems  to  offer  less  resistance  to  the  passage  of  substances  from  the  stom- 
ach; first  it  yields  to  allow  the  successively  digested  portions  go  through 
it;  and  then  it  allows  the  transit  of  even  undigested  substances.  It  ap- 
pears that  food,  so  soon  as  it  enters  the  stomach,  is  subjected  to  a  kind 
of  peristaltic  action  of  the  muscular  coat,  whereby  the  digested  portions 
are  gradually  moved  toward  the  pylorus.  The  movements  were  observed 
to  increase  in  rapidity  as  the  process  of  chymification  advanced,  and  were 
continued  until  it  was  completed. 

The  contraction  of  the  fibres  situated  toward  the  pyloric  end  of  the 
stomach  seems  to  be  more  energetic  and  more  decidedly  peristaltic  than 
those  of  the  cardiac  portion.  Thus,  it  was  found  in  the  case  of  St.  Mar- 
tin, that  when  the  bulb  of  the  thermometer  was  placed  about  three  inches 
from  the  pylorus,  through  the  gastric  fistula,  it  was  tightly  embraced 
from  time  to  time,  and  drawn  toward  the  pyloric  orifice  for  a  distance  of 
three  or  four  inches.  The  object  of  this  movement  appears  to  be,  as 
just  said,  to  carry  the  food  toward  the  pylorus  as  fast  as  it  is  formed  into 
chyme,  and  to  propel  the  chyme  into  the  duodenum;  the  undigested 
portions  of  food  being  kept  back  until  they  are  also  reduced  into  chyme, 
or  until  all  that  is  digestible  has  passed  out.  The  action  of  these  fibres 
is  often  seen  in  the  contracted  state  of  the  pyloric  portion  of  the  stom- 
ach after  death,  when  it  alone  is  contracted  and  firm,  while  the  cardiac 
portion  forms  a  dilated  sac.  Sometimes,  by  a  predominant  action  of 
strong  circular  fibres  placed  between  the  cardia  and  pylorus,  the  two  por- 
tions, or  ends  as  they  are  called,  of  the  stomach,  are  partially  separated 
from  each  other  by  a  kind  of  hour-glass  contraction.  By  means  of  the 
peristaltic  action  of  the  muscular  coats  of  the  stomach,  not  merely  is 
chymified  food  gradually  propelled  through  the  pylorus,  but  a  kind  of 


322 


HANDBOOK    OF    PHY.SIOLOGT. 


double  current  is  continually  kept  up  among  the  contents  of  the  stomach, 
the  circumferential  parts  of  the  mass  being  gradually  moved  onward 
toward  the  pylorus  by  the  contraction  of  the  muscular  fibres,  while  the 
central  portions  are  propelled  in  the  opposite  direction,  namely  toward 
the  cardiac  orifice;  in  this  way  is  kept  up  a  constant  circulation  of  the 
contents  of  the  viscus,  highly  conducive  to  their  free  mixture  with  the 
gastric  fluid  and  to  their  ready  digestion. 

Influence  of  the  Nervous  System. — The  normal  movements  of 
the  stomach  during  gastric  digestion  do  not  appear  to  be  so  closelv  con- 


Fig.  240.— Very  diagrammatic  representation  of  the  nerves  of  the  alimentary  canal.  Oe  to  Ret, 
the  various  parts  of  the  alimentary  canal  from  oesophagus  to  rectum;  L.  V,  left  vagus,  ending  on 
front  of  stomach;  rl,  recurrent  laryngeal  nerve,  supplying  upper  part  of  oesophagus;  R.V,  right 
vagus,  joining  left  vagus  in  oesophageal  plexus;  ce.pl,  supplying  the  posterior  part  of  stomach,  and 
continues  as  R'V  to  join  the  solar  plexus,  here  represented  by  a  single  ganglion,  and  connected  with 
the  inferior  mesenteric  ganglion  m.gl.;  a,  branches  from  the  solar  plexus  to  stomach  and  small 
intestine,  and  from  the  mesenteric  ganglia  to  the  large  intestine;  Spl.inaj.,  large  splanchnic  nerve, 
arising  from  the  thoracic  ganglia  and  rami  communicantes;  r.c,  belonging  to  dorsal  nerves  from 
the  tith  to  the  9th  (or  10th);  Spl.min.,  small  splanchnic  nerve  similarly  from  the  10th  and  11th  dorsal 
nerves.  These  both  join  the  solar  plexus,  and  thence  make  their  way  to  the  alimentary  canal;  c.r., 
nerves  from  the  ganglia,  etc..  belonging  to  11th  and  12th  dorsal  and  1st  and  3d  lumbar  nerves, 
proceeding  to  the  inferior  mesenteric  ganglia  (or  plexus),  m.gl.,  and  thence  by  the  hypogastric 
nerve,  n.hyp.,  and  the  hypogastric  nerve,  n.hyp.,  and  the  hypogastric  plexus,  pi. hyp.,  to  the  circular 
muscles  of  the  rectum  ;  l.r.,  ner%-es  from  the  2d  and  3d  sacral  nerves,  S.2,  S.3  (nervi  erigentes) 
proceeding  by  the  hypogastric  plexus  to  the  longitudinal  muscles  of  the  rectmn.    (M.  Foster.) 

nected  with  the  plexuses  of  nerves  and  ganglia  contained  in  its  walls  as 
was  formerly  supposed.  The  action,  however,  appears  to  be  set  up  by 
the  presence  of  food  within  it.  The  stomach  is,  moreover,  directly  con- 
nected with  the  higher  nerve-centres  by  means  of  branches  of  the  vagi 
and  of  the  splanchnic  nerves  through  the  solar  plexus. 

The  exact  function  of  the  vagi  in  connection  with  the  movements 
is  not  certainly  known.  Irritation  of  the  vagi  produces  contraction  of 
the  stomach,  if  digestion  is  proceeding;  and  on  the  other  hand,  peristaltic 
action  is  retarded,  although  it  is  not  stopped,  when  these  nerves  are  di- 


FOOD   AND    DIGESTION.  323 

vided.  On  the  other  hand,  there  are  other  nerve-fibres,  which  reach  tlie 
stomach  and  intestines  through  the  solar  plexus.  These  fibres  pass  from 
the  spinal  cord  in  the  anterior  roots  of  the  nerves  from  the  sixth  to  the 
twelfth  dorsal  process  in  the  splanchnic  nerves  to  the  solar  plexus,  and 
thence  to  the  stomach.  Stimulation  of  the  splanchnics  causes  stoppage 
of  the  muscular  movements  as  well  as  constriction  of  the  blood-vessels. 
Thus  it  seems  2)robable  that  automatic  peristaltic  contraction  is  inher- 
ent in  the  muscular  coat  of  the  stomach,  and  that  the  central  nervous 
system  is  only  employed  to  regulate  it  by  impulses  passing  down  by  tlie 
vagi  or  splanchnic  nerves. 

Bernard,  watching  the  act  of  gastric  digestion  in  dogs  which  had 
fistulous  openings  into  their  stomachs,  saw  that  immediately  on  the  di- 
vision of  their  vagi  nerves,  the  process  of  digestion  was  stopped,  and  the 
mucous  membrane  of  the  stomach,  previously  turgid  with  blood,  became 
pale,  and  ceased  to  secrete;  but  although  division  of  both  vagi  always 
temporarily  suspends  the  secretion  of  gastric  fluid,  and  so  arrests  the 
process  of  digestion,  being  occasionally  followed  by  death  from  inani- 
tion; yet  the  digestive  powers  of  the  stomach  may  be  completely  restored 
after  the  operation,  and  the  formation  of  chyme  and  the  nutrition  of  the 
animal  may  be  carried  on  almost  as  perfectly  as  in  health. 

Bernard  further  found  that  stimulation  of  the  vagi  excited  an  active 
secretion  of  the  fluid  and  that  stimulation  of  the  splanchnics  caused  a 
diminution  and  even  a  complete  arrest  of  the  secretion. 

Stimulation  of  the  vagi  at  any  rate  produces  an  effect,  besides  peris- 
talsis of  the  stomach,  it  causes  dilatation  of  the  blood-vessels  of  the  or- 
gan, in  other  words  acts  as  a  vaso-dilator  nerve. 

The  influence  of  the  higher  nerve-centres  on  gastric  digestion,  as  in 
the  case  of  mental  emotion,  is  too  well  known  to  need  more  than  a  ref- 
erence. 

Digestion  of  the  Stomach  after  Death. — If  an  animal  die  during  the  pro- 
cess of  gastric  digestion,  and  when,  therefore,  a  quantity  of  gastric  juice 
is  present  in  the  interior  of  the  stomach,  the  walls  of  this  organ  itself  are 
frequently  themselves  acted  on  by  their  own  secretion,  and  to  such  an 
extent,  that  a  perforation  of  considerable  size  may  be  produced,  and  the 
contents  of  the  stomach  may  in  part  escape  into  the  cavity  of  the  abdo- 
men. This  phenomenon  is  not  infrequently  observed  in  post-mortem  ex- 
aminations of  the  human  body.  If  a  rabbit  be  killed  during  a  period 
of  digestion,  and  afterward  exposed  to  artificial  warmth  to  prevent  its 
temperature  from  falling,  not  only  the  stomach,  but  many  of  the  sur- 
rounding parts  will  be  found  to  have  been  dissolved  (Pavy). 

From  these  facts,  it  becomes  an  interesting  question  why,  during 
life,  the  stomach  is  free  from  liability  to  injury  from  a  secretion,  which, 
after  death,  is  capable  of  such  destructive  effects. 

It  is  only  necessary  to  refer  to  the  idea  of  Bernard,  that  the  living 


324 


HANDBOOK    OF    PHYSIOLOGY. 


stomach  finds  protection  from  its  secretion  in  the  presence  of  epithelium 
and  mucus,  which  are  constantly  renewed  in  the  same  degree  that  they 
are  constantly  dissolved,  in  order  to  remark  that  although  the  gastric 
mucus  is  probably  protective,  this  theory,  so  far  as  the  epithelium  is 
concerned,  has  been  disproved  by  experiments  of  Pavy's,  in  which  the 
mucous  membrane  of  the  stomachs  of  dogs  was  dissected  off  for  a  small 
space,  and,  on  killing  the  animals  some  days  afterward,  no  sign  of  diges- 
tion of  the  stomach  was  visible.  "  Upon  one  occasion,  after  removing 
the  mucous  membrane,  and  exposing  the  muscular  fibres  over  a  space 
of  about  an  inch  and  a  half  in  diameter,  the  animal  was  allowed  to  live 


Fig  341.— Auerbach's  nerve-plexus  in  small  intestine.  The  plexus  consists  of  flbrillated  sub- 
stance, and  is  made  up  of  trabeculae  of  various  thicl<nesses.  Nucleus-like  elements  and  panglion- 
cells  are  imbedded  in  the  plexus,  the  whole  of  which  is  inclosed  in  a  nucleated  sheath.     (Klein.) 


for  ten  days.  It  ate  food  every  day,  and  seemed  scarcely  affected  by 
the  operation.  Life  was  destroyed  while  digestion  was  being  carried  on, 
and  the  lesion  in  the  stomach  was  found  very  nearly  repaired;  new  mat- 
ter had  been  deposited  in  the  place  of  what  had  been  removed,  and  the 
denuded  spot  had  contracted  to  much  less  than  its  original  dimensions." 
Pavy  believes  that  the  natural  alkalinity  of  the  blood,  which  circu- 
lates so  freely  during  life  in  the  walls  of  the  stomach,  is  sufficient  to 
neutralize  the  acidity  of  the  gastric  juice;  and  as  may  be  gathered  from 
what  has  been  previously  said,  the  neutralization  of  the  acidity  of  the 
gastric  secretion  is  quite  sufficient  to  destroy  its  digestive  powers;  but 
the  experiments  adduced  in  favor  of  this  theory  are  open  to  many  objec- 
tions, and  afford  only  a  negative  support  to  the  conclusions  they  are  in- 
tended to  prove.  Again,  the  pancreatic  secretion  acts  best  on  proteids 
in  an  alkaline  medium;  but  it  has  no  digestive  action  on  the  living  in- 


FOOD   AXD    DIGESTION.  325 

testine.     No  satisfactory  theory  of  the  reason  vvhy  the  stomach  does  not 
digest  itself  has  yet  been  suggested. 

VOMITI^TG. 

The  expulsion  of  the  contents  of  the  stomach  in  vomiting,  like  that 
of  mucus  or  other  matter  from  the  lungs  in  cougliing,  is  preceded  by 
an  inspiration;  the  glottis  is  then  closed,  and  immediately  afterward  the 
abdominal  muscles  strongly  act;  but  here  occurs  the  difference  in  the 
two  actions.  Instead  of  the  vocal  cords  yielding  to  the  action  of  the  ab- 
dominal muscles,  they  remain  tightly  closed.  Thus  the  diaphragm  being 
unable  to  go  up,  forms  an  unyielding  surface  against  which  the  stomach 
can  be  pressed.  In  this  way,  as  well  as  by  its  own  contraction,  the  dia- 
phragm \^  fixed,  to  use  a  technical  phrase.  At  the  same  time  the  cardiac 
sphincter-muscle  being  relaxed,  and  the  orifice  which  it  naturally  guards 
being  actively  dilated,  while  the  pylorus  is  closed,  and  the  stomach  itself 
also  contracting,  the  action  of  the  abdominal  muscles,  by  these  means 
assisted,  expels  the  contents  of  the  organ  through  the  oesophagus, 
pharynx,  and  mouth.  The  reversed  peristaltic  action  of  the  oesophagus 
probably  increases  the  effect. 

It  has  been  frequently  stated  that  the  stomach  itself  is  quite  jjassive 
during  vomiting,  and  that  the  expulsion  of  its  contents  is  effected  solely 
by  the  pressure  exerted  upon  it  Avhen  the  capacity  of  the  abdomen  is  di- 
minished by  the  contraction  of  the  diaphragm,  and  subsequently  of  the 
abdominal  muscles.  The  experiments  and  observations,  however,  which 
are  supposed  to  confirm  this  statement,  only  show  that  the  contraction 
of  the  abdominal  muscles  alone  is  sufficient  to  expel  matters  from  an 
unresisting  bag  through  the  oesophagus;  and  that,  under  very  abnormal 
circumstances,  the  stomach,  by  itself,  cannot  expel  its  contents.  They 
by  no  means  show  that  in  ordinary  vomiting  the  stomach  is  passive; 
and,  on  the  other  hand,  there  are  good  reasons  for  believing  the  contrary. 

It  is  true  that  facts  are  wanting  to  demonstrate  witli  certainty  this 
action  of  the  stomach  in  vomiting;  but  some  of  the  cases  of  fistulous 
opening  into  the  organ  appear  to  support  the  belief  that  it  does  take 
place;  and  the  analogy  of  the  case  of  the  stomach  with  that  of  the  other 
hollow  viscera,  as  the  rectum  and  bladder,  may  be  also  cited  in  confir- 
mation. 

The  muscles  concerned  in  the  act  of  vomiting,  are  chiefly  and  pri- 
marily those  of  tJie  abdomen;  the  diapliragm  also  acts,  but  usually  not  as 
the  muscles  of  the  abdominal  walls  do.  They  contract  and  compress 
the  stomach  more  and  more  toward  the  diaphragm;  and  the  diaphragm 
(which  is  usually  drawn  down  in  the  deep  inspiration  that  precedes  each 
act  of  vomiting)  is  fixed,  and  presents  an  unyielding  surface  against 
which  the  stomach  may  be  pressed.     The  diaphragm  is,  therefore,  as  a 


326  HANDBOOK    OF    PHYSIOLOGY. 

rule  passive,  during  tlie  actual  expulsion  of  the  contents  of  the  stonuich. 
But  there  are  grounds  for  believing  that  sometimes  this  muscle  actively 
contracts,  so  that  the  stomach  is,  so  to  sj)eak,  squeezed  between  the  de- 
scending diaphragm  and  the  retracting  abdominal  walls. 

Some  persons  possess  the  power  of  vomiting  at  will,  without  applying 
any  undue  irritation  to  the  stomach,  but  simply  by  a  voluntary  effort. 
It  seems  also,  that  this  power  may  be  acquired  by  those  who  do  not  nat- 
urally possess  it,  and  by  continual  practice  may  become  a  habit.  There 
are  cases  also  of  rare  occurrence  in  which  persons  habitually  swallow 
their  food  hastily,  and  nearly  unmasticated,  and  then  at  their  leisure  re- 
gurgitate it,  piece  by  i^iece,  into  their  mouth,  remasticate,  and  again 
swallow  it,  like  members  of  the  ruminant  order  of  Mammalia. 

The  various  nerve-actions  concerned  in  vomiting  are  governed  by  a 
nerve-centre  situated  in  the  medulla  oblongata. 

The  sensory  nerves  are  the  fifth,  glosso-pharyngeal  and  vagus  prin- 
cipally; but,  as  well,  vomiting  may  occur  from  stimulation  of  sensory 
nerves  from  many  organs,  e.g.,  kidney,  testicle,  etc.  The  centre  may 
also  be  stimulated  by  impressions  from  the  cerebrum  and  cerebellum, 
so-called  central  vomiting  occurring  in  disease  of  those  parts.  The 
efferent  impulses  are  carried  by  the  phrenics  and  other  spinal  nerves. 

The  Intestixes. 

The  Intestinal  canal  is  divided  into  tAVO  chief  portions,  named  from 
their  differences  in  diameter,  the  small  and  large  intestine  (fig.  217). 
These  are  continuous  with  each  other,  and  communicate  by  means  of 
an  opening  guarded  by  a  valve,  the  ileoccecal  valve,  which  allows  the 
passage  of  the  products  of  digestion  from  the  small  into  the  large  bowel, 
but  not,  under  ordinary  circumstances,  in  the  opposite  direction. 

The  Small  Intestine. — The  Small  Intestine,  the  average  length 
of  which  in  an  adult  is  about  twenty  feet,  has  been  divided,  for  conven- 
ience of  description,  into  three  portions,  viz.,  the  duodenum,  which  ex- 
tends for  eight  or  ten  inches  beyond  the  pylorus;  the  jejunum,  which 
forms  two-fifths,  and  the  ileum,  which  forms  three-fifths  of  the  rest  of 
the  canal. 

Structure. — The  small  intestine,  like  the  stomach,  is  constructed  of 
four  principal  coats,  viz.,  the  serous,  muscular,  sub-mucous,  and  mucous. 

(1.)  The  serous  coat  is  formed  by  the  visceral  layer  of  the  jjerito- 
neum,  and  has  the  structure  of  serous  membranes  in  general. 

(2.)  The  muscidar  coats  consist  of  an  internal  circular  and  an  ex- 
ternal longitudinal  layer:  the  former  is  usually  considerably  the  thicker. 
Both  alike  consist  of  bundles  of  unstriped  muscle  supported  by  con- 
nective tissue.  They  are  well  provided  with  lymphatic  vessels,  which 
form  a  set  distinct  from  those  of  the  mucous  membrane. 


FOOD    AXD    DIGESTION. 


327 


Between  the  two  muscular  coats  is  a  nerve  plexus  (Auerbacli's 
plexus)  (fig.  241),  similar  in  structure  to  Meissner's  (in  the  submucous 
tissue),  but  with  more  numerous  ganglia. 

(3.)  Between  the  mucous  and  muscular  coats,  is  the  submucous  coat, 
which  consists  of  connective  tissue,  in  which  numerous  blood-vessels 
and  lymphatics  ramify.  A  fine  plexus,  consisting  mainly  of  non-medul- 
lated  nerve-fibres,  Meissner's  plexus,  with  ganglion  cells  at  its  nodes, 
occurs  in  the  submucous  tissue  from  the  stomach  to  the  anus. 

(4.)  The  mucous  membrane  is  the  most  important  coat  in  relation  to 
the  function  of  digestion.  The  following  structures,  which  enter  into 
its  composition,  may  now  be  successively  described: — the  valvulre  conni- 
ventes  /  the  villi ;  and  the  glands.     The  general  structure  of  the  mucous 


^%- 


"^/•,qS\ 


'J/' 

Fig.  242. 


Fig.  343. 


Fig.  242.— Horizontal  section  of  a  small  fragment  of  the  mucous  membrane,  including  one 
entire  crypt  of  Liebcrkiihn  and  parts  of  several  others. 

Fig.  243.— Piece  of  small  intestine  (previously  distended  and  hardened  by  alcohol),  laid  open  to 
show  the  normal  position  of  the  valvulae  conniventes. 


membrane  of  the  intestines  resembles  that  of  the  stomach  (p.  338),  and, 
like  it,  is  lined  on  its  inner  surface  by  columnar  epithelium.  Adenoid 
tissue  (fig.  242)  enters  largely  into  its  construction;  and  on  its  deep 
surface  is  the  muscularis  mucosm  {mm,  fig.  247),  the  fibres  of  which  are 
arranged  in  two  layers :  the  outer  longitudinal  and  the  inner  circular. 

Valvules  Conniventes. — The  valvule  conniventes  (fig.  243)  commence 
in  the  duodenum,  about  one  or  two  inches  beyond  the  pylorus,  and 
becoming  larger  and  more  numerous  immediately  beyond  the  entrance 
of  the  bile  duct,  continue  thickly  arranged  and  well  developed  through- 
out the  jejunum;  then,  gradually  diminishing  in  size  and  number,  they 
cease  near  the  middle  of  the  ileum.  They  are  formed  by  a  doubling 
inward  of  the  mucous  membrane;  the  crescentic,  nearly  circular,  folds 
thus  formed  being  arranged  transversely  to  the  axis  of  the  intestine,  and 
each  individual  fold  seldom  extending  around  more  than  ^  or  f  of  the 


328 


HANDBOOK    OF    PHYSI0L0f4Y. 


bowel's  circumference.  Unlike  the  rugse  in  the  oesopnagus  and  stom- 
ach, they  do  not  disappear  on  distention  of  the  canal.  Only  an  imper- 
fect notion  of  their  natural  position  and  function  can  be  obtained  by 
looking  at  them  after  the  intestine  has  been  laid  open  in  the  usual 
manner.  To  understand  them  aright,  a  piece  of  gut  should  be  distended 
either  with  air  or  alcohol,  and  not  opened  until  the  tissues  have  become 
hardened.  On  then  making  a  section  it  will  be  seen  that,  instead  of 
disappearing,  they  stand  out  at  right  angles  to  the  general  surface  of 
the  mucous  membrane  (fig.  243).  Their  functions  are  (1)  to  afford  a 
largely  increased  surface  for  secretion  and  absorption,  and  (2)  to  prevent 
the  too  rapid  passage  of  the  very  liquid  products  of  gastric  digestion, 
immediately  after  their  escape  from  the  stomach,  and  (3)  to  assist  in 
the  more  perfect  mingling  of  the  latter  with  the  secretions  poured  out 


Fig.  244. 


Fig.  245. 


Fig.  244.— Transverse  section  through  four  crypts  of  Lieberkiihn  from  the  large  intestine  of  the 
pig.  They  are  lined  by  columnar  epithelial  cells,  the  nuclei  being  placed  in  the  outer  part  of  the 
cells.  The  divisions  between  the  cells  are  seen  as  lines  radiating  from  l,  the  lumen  of  the  crypt;  g, 
epithelial  cells,  which  have  become  transformed  into  goblet  cells,     x  350.     (Klein  and  Noble  Smith.) 

Fig.  245.— A  gland  of  Lieberkiihn  in  longitudinal  section.     (Brinton.) 

to  act  on  them,  by  their  projection,  and  consequent  interference  with 
an  uniform  and  untroubled  current  of  the  intestinal  contents. 

Glands. — The  glands  are  of  three  principal  kinds: — viz.,  those  of  (1) 
Lieberkiihn,  (2)  Brunner,  and  (3)  Peyer. 

(1.)  The  glands  or  crypts  of  Lieherkiihn  are  simple  tubular  depres- 
sions of  the  intestinal  mucous  membrane,  thickly  distributed  over  the 
whole  surface  both  of  the  large  and  small  intestines.  In  the  small  in- 
testine they  are  visible  only  with  the  aid  of  a  lens;  and  their  orifices 
appear  as  minute  dots  scattered  between  the  villi.  They  are  larger  in 
the  large  intestine,  and  increase  in  size  the  nearer  they  approach  the 
anal  end  of  the  intestinal  tube;  and  in  the  rectum  their  orifices  may  be 
visible  to  the  naked  eye.  In  length  they  vary  from  y^  to  -^  of  an 
inch.  Each  tubule  (fig.  245)  is  constructed  of  the  same  essential  part  as 
the  intestinal  mucous  membrane,  viz.,  of  a  fine  memhrana  propria,  or 


FOOD   AXD    DIGESTION". 


329 


basement  membrane,  a  layer  of  columnar  epithelium  lining  it,  many  of 
which  are  goblet  cells,  and  capillary  blood-vessels  covering  its  exterior, 
the  free  surface  of  the  columnar  cells  presenting  a  striated  appearance. 

(2.) — Brunners  glands  (fig.  247)  are  confined  to  the  duodenum;  they 
are  most  abundant  and  thickly  set  at  its  commencement,  diminish  grad- 
ually as  the  duodenum  advances.  They  are  situated  beneath  the  mus- 
cularis  mucosa?,  imbedded  in  the  submucous  tissue;  each  gland  is  a 
branched  and  convoluted  tube,  lined  with  columnar  epithelium.  A 
before  said,  in  structure  they  are  very  similar  to  the  pyloric  glands  of 
the  stomach,  and  their  epithelium  undergoes  a  similar  change  during 
secretion;  but  they  are  more  branched  and  convoluted  and  their  ducts 


^' 


!»1  (N  V- 


Fig.  246.— Transverse  section  of  injected  Peyer's  glands  (from  Kolliker).  The  drawing  was 
taken  from  a  preparation  made  by  Frey:  it  represents  the  fine  capillary-looped  network  spreading 
from  the  surrounding  blood-vessels  into  the  interior  of  three  of  Peyer's  capsules  from  the  intest  ine 
of  the  rabbit. 


are  longer.  (Watney.)  The  duct  of  each  gland  passes  through  the 
muscularis  mucosae,  and  opens  on  the  surface  of  the  mucous  membrane. 
(3.)  The  glands  of  Peyer  occur  chiefly  but  not  exclusively  in  the 
small  intestine.  They  are  found  in  greatest  abundance  in  the  lower 
part  of  the  ileum  near  to  the  ileo-cascal  valve.  They  are  met  with  in 
two  conditions,  viz.,  either  scattered  singly,  in  which  case  they  are 
termed  glandules  solitaries,  or  aggregated  in  groups  varying  from  one  to 
three  inches  in  length,  and  about  half-an-inch  in  width,  chiefly  of  an 
oval  form,  their  long  axis  parallel  with  that  of  the  intestine.  In  this 
state,  they  are  named  glandnlm  agminalw,  the  groups  being  commonly 
called  Peyer's  patches  (fig.  248),  and  almost  always  placed  opposite  the 
attachment  of  the  mesentery.     In  structure,  and  in  function,  there  is 


330 


HANDBOOK    OF   PHYSIOLOGY. 


no  essential  diiference  between  the  solitary  glands  and  the  individual 
bodies  of  which  each  group  or  patch  is  made  up.  They  are  really  single 
or  aggregated  masses  of  adenoid  tissue  forming  lymph-follicles.  In  the 
condition  in  which  they  have  been  most  commonly  examined,  each 
gland  appears  as  a  circular  opaque-white  rounded  body,  from  -^^  to  ^ 
inch  (1  to  2  mm.)  in  diameter,  according  to  the  degree  in  which  it  is 
developed.   'They  are  principally  contained  in  the  submucous  coat,  but 


^m^^    ?i^, 


sometimes  project  through  the  muscularis 
mucosm  into  the  mucous  membrane.  In 
the  agminate  glands,  each  follicle  reaches 
the  free  surface  of  the  intestine,  and  is 
covered  with  columnar  epithelium.  Each 
gland  is  surrounded  by  the  openings  of 
Lieberkiihn's  follicles. 

The  adjacent  glands  of  a  Peyer's  patch 
are  connected  together  by  areolar  tissue. 
Sometimes  the  lymphoid  tissue  reaches  the 
free  surface,  replacing  the  epithelium,  as  is 
also  the  case  with  some  of  the  lymphoid 
follicles  of  the  tonsil. 

Peyer's  glands  are  surrounded  by  lym- 
phatic sinuses  which  do  not  penetrate  into 
their  interior;  the  interior  is,  however, 
traversed  by  a  very  rich  blood  capillary 
plexus.  If  the  vermiform  appendix  of  a 
rabbit,  which  consists  largely  of  Peyer's 
glands,  be  injected  with  blue  by  pressing 
the  point  of  a  fine  syringe  into  one  of  the 
lymphatic  sinuses,  the  Peyer's  glands  will 
appear  as  grayish  white  spaces  surrounded 
by  blue;  if  now  the  arteries  of  the  same  be 
injected  with  red,  the  grayish  patches  will 
change  to  red,  thus  proving  that  they  are 
surrounded  by  lymphatic-  spaces  but  pene- 
trated by  blood-vessels.  The  lacteals  passing  out  of  the  villi  communi- 
cate with  the  lymph  sinuses  round  Peyer's  glands.  It  is  to  be  noted 
that  Peyer's  patches  are  largest  and  most  prominent  in  children  and 
young  persons. 

Villi.— Th.Q  Villi  (figs.  247,  249,  and  250),  are  confined  exclusively  to 
the  mucous  membrane  of  the  small  intestine.  They  are  minute  vascu- 
lar processes,  from  a  line  Jg  to  i  of  an  inch  (.5  to  3  mm.)  in  length, 
covering  the  surface  of  the  mucous  membrane,  and  giving  it  a  peculiar 
velvety,  fleecy  appearance.  Krause  estimates  them  at  fifty  to  ninety 
in  number  in  a  square  line  at  the  upper  part  of  the  small  intestine,  and 


Fig.  247. — Vertical  section  of  du- 
odenum, showing  a,  villi;  6,  crypts 
of    Lieberkiihn,  and  c,   Brunner's 

f  lands  in  the  submucosa  s,  with 
ucts,  d  ;  muscularis  mucosae,  m; 
and  circular  muscular  coat  /. 
(Schofleld.) 


FOOD    AXD    DIGESTIOX. 


331 


at  forty  to  seventy  in  the  same  area  at  the  lower  part.  They  vary  in 
form  even  in  the  same  animal,  and  differ  according  as  the  lymphatic 
vessels  or  lacteals  which  they  contain  are  empty  or  full;  being  usually, 
in  the  former  case,  flat  and  pointed  at  their  summits,  in  the  latter  cylin- 
drical or  clavate. 

Each  villus  consists  of  a  small  projection  of  mucous  membrane;  its 
interior  is  supported  throughout  by  fine  adenoid  tissue,'which  forms 
the  framework  or  stroma  in  Avhich  the  other  constituents  are  contained. 

The  surface  of  the  villus  is  clothed  by  columnar  epithelium,  which 
rests  on  a  fine  basement  membrane;  while  within  this  are  found,  reck- 
oning from  without  inward,  blood-vessels,  fibres  of  the  muscularis  mu- 
coscp,  and  a  single  lymphatic  or  lacteal  vessel  rarely  looped  or  branched 
(fig.  250). 

The  epithelium  is  continuous  with  that  lining  the  other  parts  of  the 


Fig.  248. — Agnninate  follicles,  or  Peyer's  patch,  iu  the  state  of  distention,     x  5.     CBoehm.) 


mucous  membrane.  The  cells  are  arranged  with  their  long  axis  radiat- 
ing from  the  surface  of  the  villus  (fig.  247),  and  their  smaller  bends 
resting  on  the  basement  membrane.  The  free  surface  of  the  epithelial 
cells  of  the  villi,  like  that  of  the  cells  which  cover  the  general  surface 
of  the  mucous  membrane,  is  covered  by  a  fine  border  which  exhibits  very 
delicate  striations  whence  it  derives  its  name,  striated  basilar  border. 

Beneath  the  basement  or  limiting  membrane  there  is  a  rich  supply  of 
blood-vessels.  Two  or  more  minute  arteries  are  distributed  within  each 
villus;  and  from  their  capillaries,  which  form  a  dense  network,  proceed 
one  or  two  small  veins,  which  pass  out  at  the  base  of  the  villus. 

The  layer  of  the  mnscidaris  mucosm  in  the  villus  forms  a  kind  of 
thin  hollow  cone  immediately  around  the  central  lacteal,  and  is,  there- 
fore, situated  beneath  the  blood-vessels.  It  is  without  doubt  instru- 
mental in  the  propulsion  of  chyle  along  the  lacteal. 

The  lacteal  vessel  in  each  villus  is  the  form  of  commencement  of  the 


332  HANDBOOK    OF    PHYSIOLOGY. 

lymphatic  system  of  vessels  *  in  the  intestines.  It  begins  almost  at  the 
tip  of  the  villus  commonly  by  a  dilated  extremity.  In  the  larger  villi 
there  may  be  two  small  lacteal  vessels  which  join  on  (fig.  250),  or  the 
lacteals  may  form  a  kind  of  network  in  the  villus.  The  last  method 
is  rarely  or  never  seen  in  the  human  subject,  although  common  in  some 
of  the  lower  animals  (a,  fig.  250). 

The  Large  Intestine. — The  Large  Intestine,  which  in  an  adult 
is  from  about  4  to  6  feet  long,  is  subdivided  for  descriptive  purposes 
into  three  portions,  viz. : — the  ccBcum,  a  short  wide  pouch,  communi- 
cating with  the  lower  end  of  the  small  intestine  through  an  opening, 
guarded  by  the  ileo-cwcal  valve;  the  colon,  continuous  with  the  caecum, 
which  forms  the  principal  part  of  the  large  intestine,  and  is  divided 
into  ascending,  transverse,  and  descending  portions;  and  the  rtctum, 
which,  after  dilating   at  its  lower  part,  again  contracts,   and  immedi- 


Fig.  249. — Vertical  section  of  a  villus  of  the  small  intestine  of  a  cat.  a,  striated  basUar  border 
of  the  epithelium ;  6,  columnar  epithelium;  c,  goblet  cells;  d,  central  lymph-vessel;  e,  smooth  mus- 
cular fibres;  /,  adenoid  stroma  of  the  villus  in  which  lymph  corpuscles  he.     (Klein.) 

ately  afterward  opens  externally  tiirough  the  anus.     Attached  to  the 
caecum  is  the  small  appendix  vermiformis. 

Structure. — Like  the  small  intestine,  the  large  intestine  is  con- 
structed of  four  principal  coats,  viz.,  the  serous,  muscular,  sub-mucous 
and  mucous.  The  serous  coat  need  not  be  here  particularly  described. 
Connected  with  it  are  the  small  jirocesses  of  peritoneum  containing 
fat,  called  appendices  epij)loic(S.  The  fibres  of  the  muscular  coat,  like  those 
of  the  small  intestine,  are  arranged  in  two  layers — the  outer  longitudinal, 
the  inner  circular.  In  the  caecum  and  colon,  the  longitudinal  fibres,  be- 
sides being,  as  in  the  small  intestine,  thinly  disposed  in  all  jiarts  of  the  wall 
of  the  bowel,  are  collected,  for  the  most  part,  into  three  strong  bands, 
which,  being  shorter,  from  end  to  end,  than  the  other  coats  of  the  in- 
testine, hold  the  canal  in  folds,  bounding  intermediate  sacculi.  On  the 
division  of  these  bands,  the  intestine  can  be  drawn  out  to  its  full  length. 

For  an  account  of  the  Lymphatic  System,  see  Chapter  IX. 


FOOD    AXD    DIGESTION". 


333 


and  it  then  assumes,  of  course,  an  uniformly  cylindrical  form.  In  the 
rectum,  the  fasciculi  of  these  longitudinal  bands  spread  out  and  mingle 
with  the  other  longitudinal  fibres,  forming  Avith  them  a  thicker  layer  of 
fibres  than  exists  on  any  other  part  of  the  intestinal  canal.  The  circu- 
lar muscular  fibres  are  spread  over  the  whole  surface  of  the  bowel,  but 
are  somewhat  more  marked  in  the  intervals  between  the  sacculi. 
Toward  the  lower  end  of  the  rectum  they  become  more  numerous,  and 
at  the  anus  they  form  a  strong  band  called  the  internal  sjjhincter  muscle. 
The  tnncous  membrane  of  the  large,  like  that  of  the  small  intestine, 


Fig.  350.— A.  Villus  of  sheej}.    B.  Villi  of  man.     (Slightly  altered  frotn  Teichmann.) 

is  lined  throughout  by  columnar  epithelium,  but,  unlike  it,  is  quite  des- 
titute of  villi,  and  is  not  projected  in  the  form  of  valvulce  conniventes. 
Its  general  microscopic  structure  resembles  that  of  the  small  intestine* 
and  it  is  bounded  below  by  the   muscularis  mucosa). 

The  general  arrangement  of  ganglia  and  nerve-fibres  in  the  large 
intestine  resembles  that  in  the  small. 

Glands. — The  glands  with  which  the  large  intestine  is  provided  are 
of  two  kinds,  (1)  the  tubular  and  (2)  the  lymphoid. 

(1.)  The  tubular  glands,  or  glands  of  Lieberkiihn,  resemble  those 
of  the  small  intestine,  but  are  somewhat  larger  and  more  numerous. 
They  are  also  more  uniformly  distributed. 


334  HANDBOOK    OF    I'H YSIOI>OGY. 

(2.)  Follicles  of  adenoid  or  lymplioid  tissue  are  most  numerous  in 
the  caecum  and  vermiform  appendix.  They  resemble  in  shape  and 
structure,  almost  exactly,  the  solitary  glands  of  the  small  intestine. 
Peyer's  patches  are  not  found  in  the  large  intestine. 

lleo-cmcal  Valve. — The  ileo-C£ecal  valve  is  situate  at  the  place  of 
junction  of  the  small  with  the  large  intestine,  and  guards  against  any 
reflux  of  the  contents  of  the  latter  into  the  ileum.  It  is  composed  of 
two  semilunar  folds  of  mucous  membrane.  Each  fold  is  formed  by  a 
doubling  inward  of  the  mucous  membrane,  and  is  strengthened  on  the 
outside  by  some  of  the  circular  muscular  fibres  of  the  intestine,  which 
are  contained  between  the  outer  surfaces  of  the  two  layers  of  which  each 
fold  is  composed.  While  the  circular  muscular  fibres,  however,  of  the 
bowel  at  the  junction  of  the  ileum  with  the  csecum  are  contained  be- 
tween the  outer  opposed  surfaces  of  the  folds  of  mucous  membrane 
which  form  the  valve,  the  longitudinal  muscular  fibres  and  the  peri- 
toneum of  the  small  and  large  intestine  respectively  are  continuous 
with  each  other,  without  dipping  in  to  follow  the  circular  fibres  and  the 
mucous  membrane.  In  this  manner,  therefore,  the  folding  inward  of 
these  two  last-named  structures  is  preserved,  while  on  the  other  hand, 
by  dividing  the  longitudinal  muscular  fibres  and  the  peritoneum,  the 
valve  can  be  made  to  disappear,  just  as  the  constrictions  between  the 
sacculi  of  the  large  intestine  can  be  made  to  disappear  by  performing  a 
similar  operation.  The  inner  surface  of  the  folds  is  smooth;  the 
mucous  membrane  of  the  ileum  being  continuous  with  that  of  the  caecum. 
That  surface  of  each  fold  which  looks  toward  the  small  intestine  is 
covered  with  villi,  while  that  which  looks  to  the  caecum  has  none. 
When  the  caecum  is  distended,  the  margin  of  the  folds  are  stretched, 
and  thus  are  brought  into  firm  apposition  one  with  the  other. 

Digestion  in  the  Intestines. 

After  the  food  has  been  duly  acted  upon  by  the  gastric  juice,  such  of 
it  as  has  not  been  absorbed  passes  into  the  duodenum,  and  is  there 
subjected  to  the  action  of  the  secretions  of  the  pancreas  and  liver  which 
enter  that  portion  of  the  small  intestine,  as  well  as  to  the  secretion 
(succus  entericus)  which  is  poured  out  into  the  intestines  from  the  glands 
lining  them. 

The  Pancreas,  and  its  Secretion. 

The  Pancreas  is  situated  within  the  curve  formed  by  the  duo- 
denum; and  its  main  duct  opens  into  that  part  of  the  small  intestine, 
through  a  small  opening,  or  through  a  duct  common  to  it  and  to  the 
liver,  about  two  and  a  half  inches  from  the  pylorus. 

Structure. — In  structure  the  pancreas  bears  some  resemblance  to  the 


FOOD    AND    DIGESTION".  335 

salivary  glands.  Its  capsule  and  septa,  as  well  as  the  blood-vessels  and 
lymphatics,  are  similarly  distributed.  It  is,  however,  looser  and  softer, 
the  lobes  and  lobules  being  less  compactly  arranged.  The  main  duct 
divides  into  branches  (lobar  ducts),  one  for  each  lobe,  and  these  branches 
subdivide  into  intra-lobular  ducts,  and  these  again  by  their  division 
and  branching  form  the  gland  tissue  proper.  The  intralobar  ducts 
correspond  to  a  lobule,  while  between  them  and  the  secreting  tubes  or 
alveoli  are  longer  or  shorter  intermediary  ducts.  The  larger  ducts 
possess  a  very  distinct  lumen  and  a  membrana  propria  lined  with 
columnar  epithelium,  the  cells  of  which  are  longitudinally  striated,  but 
are  shorter  than  those  found  in  the  ducts  of  the  salivary  glands.  In  the 
intralobular  ducts  the  epithelium  is  short  and  the  lumen  is  smaller. 
The  intermediary  ducts  opening  into  the  alveoli  possess  a  distinct  lumen, 

f^   - 

i 


Si2^s^ 


Fig  251.— Section  of  the  pancrea-s  of  a  dog  during  digestion,  a,  alveoli  lined  with  cells,  the 
outer  zone  of  which  is  well  stained  with  hasmatoxylin ;  d,  intermediary  duct  lined  with  squamous 
epithebnm.     x  350.     (Klein  and  Noble  Smith.) 

with  a  membrana  propria  lined  with  a  single  layer  of  flattened  elongated 
cells.  The  alveoli  are  branched  and  convoluted  tubes,  with  a  membrana 
propria  lined  with  a  single  layer  of  columnar  cells.  They  have  no 
distinct  lumen,  the  centre  portion  of  the  tube  being  occupied  by  fusi- 
form or  branched  cells.  Heidenhain  has  observed  that  the  alveolar 
cells  in  the  pancreas  of  a  fasting  dog  consist  of  two  zones,  an  inner  or 
central  zone  which  is  finely  granular,  and  which  stains  feebly,  and  a 
smaller  parietal  zone  of  finely  striated  protoplasm  which  stains  easily. 
The  nucleus  is  partly  in  one,  partly  in  the  other  zone.^  During  digestion, 
it  is  found  that  the  outer  zone  increases  in  size,  and  the  central  zone 
diminishes;  the  cell  itself  becoming  smaller  from  the  discharge  of  the 
secretion.  At  the  end  of  digestion  the  first  condition  again  appears,  the 
inner  zone  enlarging  at  the  expense  of  the  outer.  It  appears  that  the 
granules  are  formed  by  and  stored  up  in  the  protoplasm  of  the  cells,  from 


336  HANDBOOK    OF    PHYSIOLOGY. 

the  material  supplied  to  it  by  the  blood.  The  granules  are  thought  to 
consist  of  material  from  which,  under  certain  conditions,  the  ferments 
of  the  gland  are  developed,  and  which  is  therefore  called  Zymogen.  In 
addition  to  the  ordinary  alveoli  of  the  pancreas  there  are  found  distri- 
buted irregularly  in  the  gland  other  collections  of  cells  of  a  different 
character.  They  are  considerably  smaller,  their  protoplasm  is  more 
granular,  and  is  less  easily  stained  with  haematoxylin,  and  their  nuclei 
are  small  and  deeply  staining,  being  situated  also  more  toward  the 
centre  of  the  cells.  The  collections  of  cells  vary  in  size  and  shape,  and 
sometimes  seem  to  be  mere  masses  of  protoplasm  witli  nuclei  undifferen- 
tiated into  cells.  These  nests  of  cells  are  sometimes  seen  to  consist  of 
distinct  columns  of  cells.  No  distinct  basement  membrane,  however, 
can  be  made  out  as  bounding  these  columns.  The  special  form  of  nerve 
terminations,  called  Paciiiian  corpuscles,  are  often  found  in  the  pancreas. 


Fig.  252.— Section  of  the  pancreas  of  armadillo,  showing  the  two  kinds  of  gland-structure.     (V.  b. 

Harris.) 

The  Pancreatic  Juice. — The  secretion  of  the  pancreas  has  been 
obtained  for  purposes  of  experiment  from  the  lower  animals,  especially 
the  dog,  by  opening  the  abdomen  and  exposing  the  duct  of  the  gland, 
which  is  then  made  to  communicate  with  the  exterior.  A  pancreatic 
fistula  is  thus  established. 

An  extract  of  pancreas  made  from  the  gland  which  has  been  removed 
from  an  animal  killed  during  digestion  possesses  the  active  properties  of 
pancreatic  secretion.  It  is  made  by  first  dehydrating  the  gland,  cut  up 
into  small  pieces,  by  keeping  it  for  some  days  in  absolute  alcohol,  and 
then,  after  the  entire  removal  of  the  alcohol,  by  pounding  up  these 
pieces  into  a  pulpy  mass  and  placing  it  in  strong  glycerin.  A  glycerin 
extract  is  thus  obtained.  It  is  a  remarkable  fact,  however,  that  the 
amount  of  the  ferment  trypsin  greatly  increases  if  the  gland  be  exposed 
to  the  air  for  twenty-four  hours  before  placing  in  alcohol;  indeed,  a 
glycerin  extract  made  from  the  gland  immediately  upon  the  removal 
from   the  body  often  appears  to  contain  none  of  the  ferments.     This 


FOOD    AND    DIGESTIGlSr.  337 

seems  to  indicate  that  the  conversion  of  zymogen  in  the  gland  into  the 
ferment  only  takes  place  dnring  the  act  of  secretion,  and  that  although 
the  gland  always  contains  in  its  cells  the  materials  (trypsinogen)  oiit 
of  which  trypsin  is  formed,  yet  the  conversion  of  the  one  into  the 
other  only  takes  place  by  degrees.  Dilute  acid  appears  to  assist  and 
accelerate  the  conversion,  and  if  a  recent  pancreas  be  rubbed  up  with 
dilute  acid  before  dehydration,  a  glycerin  extract  made  afterward,  even 
though  the  gland  may  have  been  only  recently  removed  from  the  body, 
is  very  active. 

Many  other  vehicles  may  be  employed  instead  of  glycerin,  e.g.,  brine, 
chloroform,  water,  dilute  methylated  spirit  acidulated  with  acetic  acid. 

Properties. — Pancreatic  juice  is  colorless,  transparent,  and  slightly 
viscid,  alkaline  in  reaction.  It  varies  in  specific  gravity  from  1010  to 
1015,  according  as  it  is  obtained  from  a  permanent  fistula — then  more 
watery — or  from  a  newly-opened  duct.  The  solids  vary  in  a  temporary 
fistula  from  80  to  100  parts  per  thousand,  and  in  a  permanent  one  from 
16  to  50  per  thousand. 

Chemical  Composition  of  the  Pancreatic  Juice. 
From  a  permanent  fistula.      (Bernstein.) 

Water 975 

Solids — Ferm'^nts  (including  trypsin,  amylopsin,  rennet, 

and  steapsin)  : 
Proteids,  including  Serum  Albumin  and  \ 

Casein .    [■      17 

Leucin  and  Tyrosin  ;  Fats  and  Soaps  .       ) 
Inorganic     residue,    especially    Sodium  \_        8 

Carbonate S  25 

1000 

Functions. —  (1.)  By  the  aid  of  its  proteolytic  ferment,  tri/psin,  it 
converts  p7-ofeids  i7ito  pepto)ies,  the  intermediate  products  being  almost 
the  same  as  in  the  case  of  gastric  digestion,  Avith  the  exception  that  the 
initial  change  does  not  produce  syntonin  or  acid-albumin  as  in  gastric 
digestion,  but  alkali-albumin.  Of  the  final  products,  hemi-  and  anti- 
peptone,  the  hemipeptone  is  capable  of  being  converted  by  (?)  the 
action  of  the  pancreatic  ferment  into  leucin  or  amido-caproic  acid 
(CeHisNOo)  and  tyrosin*  or  amido-oxyphenyl-propionic  acid  (CgHnlSrOs), 
but  is  not  so  charged  by  pepsin :  the  antipeptone  cannot  be  further  split 
up  by  the  pancreatic  juice.  The  products  of  pancreatic  digestion  are 
sometimes  further  complicated  by  the  appearance  in  a  pancreatic  diges- 
tive fluid,  of  certain  faecal  substances  of  which  indol  (C3H2N),  skatol 
(C9H9N),  j9/ie?io?  (CeHeN)  and  napthilamine  a.re  the  most  important. 

*  Propionic    acid,    C3H6O2 ;    in  which  one    H    is   replaced  by  the    radicle 
oxyphenyl,  C6H4OH,  and  a  second  H,  by  amidogen  NH2.     Thus  C3H4   (NHj) 
CeH^OH.  0^  =  03, HnNO,. 
22 


338  HANDBOOK    OF    PHYSIOLOGY. 

These  further  products  are  produced  by  the  presence  of  numerous 
micro-organisms  of  the  intestines. 

All  the  albuminous  or  proteid  substances  which  have  not  been  con- 
verted into  pejDtone  and  absorbed  in  the  stomach,  and  the  partially 
changed  substances,  i.e.,  the  proteoses  may  be  converted  into  peptone 
by  the  pancreatic  juice,  and  then  in  part  into  leucin  and  tyrosin. 

The  action  of  the  pancreatic  juice  upon  the  gelatins,  or  nitrogenous 
bodies  other  than  proteids,  is  not  so  distinct.  Mucin  can,  however,  be 
dissolved,  but  not  keratin  in  horny  tissues.  Gelatin  itself  is  formed  into 
l^eptone  [gelatin-peptone').  The  ferment  trypsin  acts  best  in  an  alka- 
line medium,  and  is  by  far  the  most  active  of  the  pancreatic  ferments. 
It  is  more  powerful  than  pepsin  in  its  action  both  on  jiroteids  and 
gelatins. 

(2.)  Starch  is  converted  into  maltose  and  then  into  glucose  in  an 
exactly  similar  manner  to  that  which  happens  with  the  saliva;  erythro- 
and  achroo-dextrine  being  intermediate  jjroducts.  If  the  sugar  which  is 
at  first  formed  is  maltose,  the  ferment  of  the  pancreatic  juice  after  a 
time  completes  the  whole  change  of  starch  into  glucose.  This  distinct 
amylolytic  ferment  in  the  pancreatic  juice  which  cannot  be  distinguished 
from  ptyaline,  is  called  Amylopsin. 

(3.)  Pancreatic  juice  possesses  the  property  of  curdling  milk,  con- 
taining a  special  (rennet)  ferment  for  that  purpose.  The  ferment  is 
distinct  from  trypsin,  and  will  act  in  the  presence  of  an  acid  (W. 
Eoberts).  It  is  best  extracted  by  brine.  The  milk-curdling  ferment  of 
the  pancreas  is,  in  some  pancreatic  extracts,  extremely  powerful,  inso- 
much that  1  cc.  of  a  brine  extract  will  coagulate  50  cc.  of  milk  in  a 
minute  or  two. 

(4.)  Oils  and  fats  are  emtilsiHed  and  sap)07iified  by  pancreatic  secre- 
tion. The  terms  emnlsification  and  saponifcation  may  need  a  little  ex- 
planation. The  former  is  used  to  signify  an  important  mechanical 
change  in  oils  or  fats,  whereby  they  are  made  into  an  emulsion,  or  in 
other  words  are  minutely  subdivided  into  small  particles.  If  a  small 
drop  of  an  emulsion  be  looked  at  under  the  microscope  it  will  be  seen 
to  be  made  up  of  an  immense  number  of  minute  rounded  particles  of 
oil  or  fat,  of  varying  sizes.  The  more  complete  the  emulsion  the  smaller 
are  these  particles.  An  emulsion  is  formed  at  once  if  oil  or  fat,  which 
nearly  always  is  slightly  acid  from  the  presence  of  free  fatty  acid,  is 
mixed  with  an  alkaline  solution.  Saponification  signifies  a  distinct 
chemical  change  in  the  composition  of  oils  and  fats.  An  oil  or  a  fat  be- 
ing made  up  chemically  of  glgcerin,  a  triatomic  alcohol,  and  one  or  more 
fatty  acid  radicles,  when  an  alkali  is  added  to  it,  and  heat  is  applied, 
two  changes  take  place :  firstly,  the  oil  or  fat  is  split  up  into  glycerin, 
and  its  corresponding  fatty  acid;  secondly,  the  fatty  acid  combines  with 
the  alkali,  to  form  a  soap  which  is  chemically  known  as  stearate,  oleate. 


FOOD    AND    DIGESTION".  339 

or  palmitate  of  potassium  or  sodium.  Thus  saponitication  means  a 
chemical  splitting  up  of  oils  or  fats  into  new  compounds,  and  emulsifi- 
cation  means  merely  a  mechanical  splitting  of  them  up  into  minute  par- 
ticles. The  pancreatic  juice  has  been  for  many  years  credited  with  the 
possession  of  a  special  ferment,  which  was  called  by  Claude  Bernard 
steapsin,  and  which  was  supposed  to  aid  in  one  or  both  of  these  pro- 
cesses. It  appears  very  doubtful,  however,  if  the  mechanical  splitting 
up  of  fats  by  the  alkaline  pancreatic  juice  is  a  ferment  action  at  alL 
and  as  regards  the  chemical  action  it  has  been  recently  shown  that  only 
the  pancreatic  juices  of  certain  animals  have  any  power  in  this  direction 
of  a  ferment  character,  and  that  even  in  these  cases  the  ferment  is  only 
present  in  the  fresh  juice  or  gland,  and  that  the  presence  of  alcohol  or 
other  hardening  agent  for  the  latter  entirely  destroys  its  action. 

Several  cases  have  been  recorded  in  which  the  pancreatic  duct  beiug  ob- 
structed, so  that  its  secretion  could  not  be  discharged,  fatty  or  oily  matter  was 
abundantly  discharged  fi'om  the  intestines.  In  nearly  all  these  cases,  indeed, 
the  liver  was  coincidentally  diseased,  and  the  change  or  absence  of  the  bile 
might  appear  to  contribute  to  the  result ;  yet  the  frequency  of  extensive  dis- 
ease of  the  liver,  unaccompanied  by  fatty  discharges  from  the  intestines,  favors 
the  view  that,  in  these  cases,  it  is  to  the  absence  of  the  pancreatic  fluid  from 
the  intestines,  that  the  excretion  or  non-absorption  of  fatty  matter  should  be 
ascribed. 

Conditions  favorable  to  the  Action. — These  are  almost  precisely  sim- 
ilar to  those  which  have  been  mentioned  as  favorable  to  the  action  of 
the  saliva,  and  the  reverse.  The  secretion  of  the  pancreatic  juice  aj)- 
pears  to  be,  at  any  rate  in  some  animals,  e.g.,  the  rabbit  and  dog,  almost 
continuous;  the  flow,  however,  is  not  uniform,  the  amount  increases 
immediately  after  taking  food,  and  the  maximum  amount  occurs  two  or 
four  hours  after,  but  again  between  the  fifth  and  sixth  hour  increases 
somewhat.  The  nervous  mechanism  of  pancreatic  secretion  is  not  at 
present  understood,  and  the  endings  of  its  nerve-fibres  from  the  splanch- 
nics  and  right  vagus  nerves  in  all  probability,  through  the  solar  plexus, 
have  not  been  demonstrated  in  the  gland  cells.  Increased  flow  of  secre- 
tion will  occur  on  stimulation  of  the  spinal  cord  or  bulb,  or  of  the  gland 
itself,  even  after  division  of  the  vagus.  Stimulation  of  the  central  end 
of  the  divided  vagus  will  inhibit  the  secretion,  and  a  similar  effect  is 
produced  on  stimulation  of  other  afferent  nerves.  It  seems  highly  prob- 
able, therefore,  that  there  is  a  central  mechanism  for  the  regulation  of 
tlie  secretion  of  the  pancreas  similar  to  that  which  exists  for  the  sali- 
vary glands,  but  the  nerves  which  pass  to  and  from  the  centre  and  the 
position  of  the  centre  itself,  have  not  yet  been  demonstrated.  The 
gland  will  continue  to  secrete  after  the  section  of  all  of  its  nerves,  and 
in  this  respect  is  said  to  differ  from  the  salivary  glands.  The  secretion 
appears  to  be  called  forth  on  the  introduction  of  food  into  the  stomach, 


340 


HANDBOOK    OF    PHYSIOLOGY. 


when  the  blood-vessels  of  the  gland  become  much  dilated,  and  the  se- 
cretion continues,  as  we  have  seen,  for  many  hours  after  a  meal;  indeed, 
may  be  continuous.  The  pressure  of  the  secretion  is  not  so  great  as  in 
the  case  of  the  salivary  glands;  the  maximum  pressure  in  the  duct  is 
said  not  to  exceed  IT  mm.  of  mercury. 

The  amount  of  secretion  per  diem  is  approximately  estimated  to  be 
200  grms. 

The  Liver. 

The  Liver,  the  largest  gland  in  the  body,  situated  in  the  abdomen 
on  the  right  side  chiefly,  is  an  extremely  vascular  organ,  and  receives 
its  supply  of  blood  from  two  distinct  sources,  viz.,  from  the  portal  vein 
and  from  the  hepatic  artery,  while  the  blood  is  returned  from  it  into  the 


Fig.  253.— The  under  surface  of  the  liver,  g.  b.,  ^all-bladder:  h.  d.,  common  bile-duct;  h.  a.,  hep- 
atic artery;  v.  p.,  portal  vein;  l.  q..  lobulus  quadratus;  l.  s.,  lobulus  spigelii;  l.  c,  lobulus  cauda- 
tus;  D.  v.,  ductus  venosus;  u.  v.,  umbilical  vein.    (Noble  Smith.) 

vena  cava  inferior  by  the  hepatic  vein^.  Its  secretion,  the  hile,  is  con- 
veyed from  it  by  the  hepatic  duct,  either  directly  into  the  intestine,  or, 
when  digestion  is  not  going  on,  into  the  cystic  duct,  and  thence  into 
the  gall-bladder,  where  it  accumulates  until  required.  The  portal  vein, 
hepatic  artery,  and  hepatic  duct  branch  together  throughout  the  liver, 
while  the  hepatic  veins  and  their  tributaries  run  by  themselves. 

On  the  outside,  the  liver  has  an  incomplete  covering  of  peritoneum, 
and  beneath  this  is  a  very  fine  coat  of  areolar  tissue,  continuous  over 
the  whole  surface  of  the  organ.  It  is  thickest  where  the  peritoneum  is 
absent,  and  is  continuous  on  the  general  surface  of  the  liver  with  the 
fine  and,  in  the  human  subject,  almost  imperceptible  areolar  tissue  in- 
vesting the  lobules.  At  the  transverse  fissure  it  is  merged  in  the  areolar 
investment  called  Glisson's  capsule,  which,  surrounding  the  portal  vein^ 
hepatic  artery,  and  hepatic  duct,  as  they  enter  at  this  part,  accompanies 
them  in  their  branches  throufrh  the  substance  of  the  liver. 


FOOD    AXD    DIGESTION". 


341 


Structure. — The  liver  is  made  up  of  small  roundish  or  oval  portions 
called  lobules,  each  of  which  is  about  gV  of  an  inch  (about  1  mm.)  in 
diameter,  and  composed  of  the  minute  branches  of  the  portal  vein,  he- 
patic artery,  hepatic  duct,  and  hepatic  vein;  while  the  interstices  of  these 


Fig.  254.— A.  Liver-cells.    B.  Ditto,  containing  various-sized  particles  of  fat. 

vessels  are  filled  by  the  liver  cells.  The  hepatic  cells  (fig.  254),  which 
form  the  glandular  or  secreting  part  of  the  liver,  are  of  a  spheroidal 
form,  somewhat  polygonal  from  mutual  pressure  about  g^  to  ydVo  ii^ch 
(about  -gig  to  ^V  mm.)  in  diameter,  possessing  one,  sometimes  two  nuclei. 
The  cell-substance  contains  numerous  fatty  molecules,  and  some  yellow- 
ish granules  of  bile-pigment,  as  well  as  a  variable  amount  of  glycogen. 


Fig.  ~55.  -Longitudinal  section  of  a  portal  canal,  containing  a  portal  vein,  hepatic  artery  and 
hepatic  duct,  from  the  pig.  p,  branch  of  vena  nort»,  situate  in  a  portal  canal  formed  among  the 
lobules  ot  the  liver,  /,  i,  and  giving  off  vaginal  branches;  there  are  also  seen  within  the  large  portal 
vein  numerous  orifices  of  the  smallest  interlobular  veins  arising  directly  from  it;  o,  hepatic  artery; 
d,  hepatic  duct,     x  5.     (Kiernan.)  >     >      f  j  - 

The  cells  sometimes  exhibit  slow  amoeboid  movements.     They  are  held 
together  by  a  very  delicate  sustentacular  tissue,  continuous  with  the  in 
terlobular  connective  tissue. 

To  understand  the  distribution  of  the  blood-vessels  in  the  liver,  it 
will  be  well  to  trace,  first,  the  two  blood-vessels  and  the  duct  which  enter 


342 


HANDBOOK    OF    PHYSIOLOGY. 


the  organ  on  the  under  surface  at  the  transverse  fissure,  viz.,  the  portal 
vein,  hepatic  artery,  and  hepatic  duct.  As  before  remarked,  all  three 
run  in  company,  and  their  appearance  on  longitudinal  section  is  shown 
in  fig.  255.  Running  together  through  the  substance  of  the  liver,  they 
are  contained  in  small  channels  called  portal  canals,  their  immediate  in- 
vestment being  a  sheath  of  areolar  tissue  continuous  with  Glisson's  cap- 
sule. 

To  take  the  distribution  of  the  portal  vein  first : — In  its  course  through 
the  liver  this  vessel  gives  olf  small  branches  which  divide  and  subdivide 
between  the  lobules  surrounding  them  and  limiting  them,  and  from  this 
circumstances  called  inter-lohwVAv  veins.  From  these  small  vessels  a 
dense  capillary  network  is  prolonged  into  the  substance  of  the  lobule. 


Fig.  256.— Capillary  network  of  the  lobules  of  the  rabbit's  liver.  The  figure  is  taken  from  a  very 
successful  injectiou  of  the  hepatic  veins,  made  by  Harting:  it  shows  nearly  the  whole  of  two  lo- 
bules, and  parts  of  three  others  :  p,  portal  branches  running  in  the  interlobular  spaces;  h,  hepatic 
veins  penetrating  and  radiating  from  the  centre  of  the  lobules.     X  45.    (Kolliker.) 


and  this  network  gradually  gathering  itself  up,  so  to  speak,  into  larger 
vessels,  converges  finally  to  a  single  small  vein,  occupying  the  centre  of 
the  lobule,  and  hence  called  t;?/r«-lobular.  This  arrangement  is  well 
seen  in  fig.  256,  which  represents  a  transverse  section  of  a  lobule. 

The  small  intra-lohxAskV  veins  discharge  their  contents  into  veins 
called  sub-\6h\x\QX  {li  li  It,  fig,  257);  while  these  again,  by  their  union, 
form  the  main  branches  of  the  hepatic  veins,  which  leave  the  posterior 
border  of  the  liver  to  end  by  two  or  three  principal  trunks  in  the  infe- 
rior vena  cava,  just  before  its  passage  through  the  diaphragm.  The 
5M5-lobular  and  hepatic  veins,  unlike  the  portal  vein  and  its  companions, 
have  little  or  no  areolar  tissue  around  them,  and  their  coats  being  very 
thin,  they  form  little  more  than  mere  channels  in  the  liver  substance 
which  closely  surrounds  them. 

The  manner  in  Avhich  the  lobules  are  connected  with  the  snhlohular 
veins  by  means  of  the  small  intralobular  vein?,  has  been  likened  to  a  twig 


FOOD    AND    DIGESTION. 


343 


having  leaves  without  footstalks — the  lobules  representing  the  leaves, 
and  the  sublobular  vein  the  small  branch  from  which  it  springs. 


Fig.  257. 


Fig.  258. 


Fig.  257.— Section  of  a  portion  of  liver  passing  longitudinally  through  a  considerable  hepatic 
vein,  from  the  pig.  h,  hepatic  venous  trunk,  against  w-iiieh  the  sides  of  the  lobules  (7)  are  applied; 
h,  h,  h,  sublobular  hepatic  veins,  on  which  the  bases  of  tlie  lobules  rest,  and  through  the  coats  of 
which  they  are  seen  as  polygonal  figures;  i,  mouth  of  the  intralobular  veins,  opening  into  the  sub- 
lobular veins;  i',  intralobular  veins  shown  passing  up  the  centre  of  some  divided  lobules;  I,  ?,  cut 
surface  of  the  liver;  c,  c,  walls  of  the  hepatic  venous  canal,  formed  by  the  polygonal  bases  of  the 
lobules.     X  5.     (Kiernan.) 

Fig.  258.— Portion  of  a  lobule  of  liver,  a,  bile  capillaries  between  Uver-cells,  the  network  in 
which  is  well  seen;  b,  blood  capillaries.     X  350.     (Klein  and  Noble  Smith.) 

The  hepatic  artery,  the  chief  function  of  which  is  to  distribute  blood 
for  nutrition  to  Glisson's  capsule,  the  walls  of  the  ducts  and  blood-ves- 
sels, and  other  parts  of  the  liver,  is  distributed  in  a  very  similar  manner 


P/'. 


Fig.  259.— Hepatic  cells  and  bile  capillaries,  from  the  liver  of  a  child  three  months'  old.  Both 
figures  represent  fragments  of  a  section  carried  through  the  periphery  of  a  lobule.  The  red  cor- 
puscles of  the  blood  are  recognized  by  their  circular  contour;  yp,  corresponds  to  an  interlobular 
vem  m  immediate  proximity  with  which  are  the  epithelial  cells  of  the  biliary  ducts,  to  which,  at  the 
lower  part  of  the  figures,  the  much  larger  hepatic  cells  suddenly  succeed.     CE.  Hering.) 

to  the  portal  vein,  its  blood  being  returned  by  small  branches  either 


344  HANDBOOK    OF    PHYSIOLOGY. 

into  tlie  ramifications  of  the  portal  vein,  or  into  the  capillary  plexus  of 
the  lobules  which  connects  the  inter-  and  m^ra-lobular  veins. 

The  hepatic  duct  divides  and  subdivides  in  a  manner  very  like  that 
of  the  portal  vein  and  hepatic  artery,  the  larger  branches  being  lined 
by  cylindrical,  and  the  smaller  by  small  polygonal  epithelium. 

The  bile-capillaries  commence  between  the  hepatic  cells,  and  are 
bounded  by  a  delicate  membranous  wall  of  their  own.  They  appear  to 
be  always  bounded  by  hepatic  cells  on  all  sides,  and  are  thus  separated 
from  the  nearest  blood-capillary  by  at  least  the  breadth  of  one  cell  (figs. 
258  and  259). 

The  Gall-bladdee. 

The  Gall-bladder  (g.  b.  fig.  253)  is  a  pyriform  bag,  attached  to  the 
under  surface  of  the  liver,  and  supported  also  by  the  peritoneum,  which 
passes  below  it.  The  larger  end,  or  ftmckis,  projects  beyond  the  front 
margin  of  the  liver;  while  the  smaller  end  contracts  into  the  cystic  duct. 

Structure. — The  walls  of  the  gall-bladder  are  constructed  of  three 
principal  coats.  (1)  Externally  (excepting  that  part  which  is  in  contact 
with  the  liver),  is  the  serous  coat,  which  has  the  same  structure  as  the 
peritoneum  with  which  it  is  continuous.  Within  this  is  (2)  iha  fibrous 
or  areolar  coat,  constructed  of  tough  fibrous  and  elastic  tissue,  with 
which  is  mingled  a  considerable  number  of  plain  muscular  fibres,  both 
longitudinal  and  circular.  (3)  Internally  the  gall-bladder  is  lined  by 
mucous  membrane,  and  a  layer  of  columnar  epithelium.  The  surface 
of  the  mucous  membrane  presents  to  the  naked  eye  a  minutely  honey- 
combed appearance  from  a  number  of  tiny  polygonal  depressions  with 
intervening  ridges,  by  which  its  surface  is  mapped  out.  In  the  cystic 
duct  the  mucous  membrane  is  raised  up  in  the  form  of  crescentic  folds, 
which  together  appear  like  a  spiral  valve,  and  which  minister  to  the 
function  of  the  gall-bladder  in  retaining  the  bile  during  the  interval  of 
digestion. 

The  gall-bladder  and  all  the  main  biliary  ducts  are  provided  with 
mucous  glands,  which  open  on  the  internal  surface. 

Functions  of  the  Liver. 

The  function  of  the  liver  in  connection  with  digestion  is  to  secrete 
the  bile,  and  may  be  now  considered.  The  other  functions  in  connec- 
tion with  the  general  metabolism  of  the  body,  and  particularly  its  gly- 
cogenic function,  will  be  considered  later  on.  First  of  all  it  will  be  as 
well  to  take  the  composition  and  functions  of  the  bile,  and  afterward  to 
discuss  its  mode  of  secretion. 


FOOD    AND    DIGESTION.  345 


The  Bile. 

Properfies. — The  bile  is  a  somewhat  viscid  fluid,  of  a  yellow  or  reddish- 
yellow  or  green  color,  a  strongly  bitter  taste,  and,  when  fresh,  with  a 
scarcely  perceptible  odor :  it  has  a  neutral  or  slightly  alkaline  reaction, 
and  its  specific  gravity  is  about  1020.  Its  color  and  degree  of  consist- 
ence vary  much,  quite  indeiDendent  of  disease;  but,  as  a  rule,  it  becomes 
gradually  more  deeply  colored  and  thicker  as  it  advances  along  its  ducts, 
■or  when  it  remains  long  in  the  gall-bladder,  wherein,  at  the  same  time, 
it  becomes  more  viscid  and  ropy,  darker,  and  more  bitter,  mainly  from 
its  greater  degree  of  concentration,  on  account  of  partial  absorption  of 
its  water,  but  also  from  being  mixed  with  mucus. 

Chemical  Composition  of  Human  Bile.     (Frerichs.) 

Water 859.3 

Solids— Bile  salts 91.5 

Fat 9.3 

Cholesterin 3.6 

Mucus  and  coloring  matters        .         .  39. 8 

Salts 7.7 

140.8 


1000.0 


(a)  Bile  salts,  sometimes  termed  Bilin,  can  be  obtained  as  colorless, 

'exceedingly  deliquescent  crystals,  soluble  in  Avater,  alcohol,  and  alkaline 

solutions,  giving  to  the  watery  solution  the  taste  and  general  characters 

■of  bile.     They  consist  of  sodium  salts  of  glycocholic  and  taurocholic 

acids.     The  formula  of  the  former  salt  being  C26H43"N'aN06,  and  of  the 

latter  C26H44NaN07S. 

The  bile  acids  are  easily  decomposed  by  the  action  of  dilute  acids  or  alkalies 

thus : 

C.BH43NOe  +  H^O  =  C.HsNO,  +  C.4H4„05 
Glycocholic  Acid.  Glycin.  Cholic  Acid. 

and  C.5H46NO,S  +  H.O  ==  C.2H7NO3S  +  C04H40O5 
Taurocholic  Acid.  Taurin.  Cholic  Acid. 

Glycin,  or  glycocin,  is  amido-aGetic  acid,  i.e.,  acetic  acid  C2H4O2,  with  one 
of  the  atoms  of  H  replaced  by  the  radical  amidogen  NH.2,C2H3(NH2)0.2, 
C2H6N2O.  Taurin  likewise  is  amido-isethionic  acid.  Isethionic  acid  is  sul- 
phurous acid  H2SO3,  in  which  an  atom  of  H  is  replaced  by  the  monotoniic 
radicle  oxy-ethylene,  C2H4OH,  viz.,  H(C2H40H)S03,  and  in  amido-isethionic 
acid,  the  OH  hydroxyl  in  this  radicle  is  replaced  by  amidogen  NH2,  thus 
H(C2H4NH2)S03  =  C2H,NS03.  The  proportion  of  these  two  salts  in  the  bile  of 
different  animals  varies,  e.g..  in  ox  bile  the  glycocholate  is  in  great  excess, 
whereas  the  bile  of  the  dog,  cat,  bear,  and  other  carnivora  contains  taurocho- 
late  alone;  in  human  bile  the  glycocholate  is  in  excess  (4.8  to  1.5). 

Preparation  of  Bile  Salts. — Bile  salts  may  be  prepared  in  tlie  following 
manner :  mix  bile  which   has  been  evaporated  to  a  quarter  of   its  bulk  with 


346  HANDBOOK    OF    PHYSIOLOGY. 

animal  charcoal,  and  evaporate  to  perfect  dryness  in  a  water  bath.  Next  ex- 
tract the  mass  while  still  wai-m  with  absolute  alcohol.  Separate  the  alcoholic 
extract  by  filtration,  and  to  it  add  perfectly  anhydrous  ether  as  long  as  a  pre- 
cipitate is  thrown  down.  The  solution  and  precipitate  should  be  set  aside  in 
a  closely  stoppered  bottle  for  some  days,  when  crystals  of  the  bile  salts  or  bilin 
will  have  separated  out.  The  glycocholate  may  be  separated  from  the  tauro- 
cholate  by  dissolving  bilin  in  water,  and  adding  to  it  a  solution  of  neutral  lead 
acetate,  and  then  a  little  basic  lead  acetate,  when  lead  glycocholate  separates 
out.  Filter  and  add  to  the  filtrate  lead  acetate  and  ammonia,  a  precipitate  of 
lead  taurocholate  will  be  formed,  which  may  be  filtered  off.  In  both  cases,  the 
lead  may  be  got  rid  of  by  suspending  or  dissolving  in  hot  alcohol,  adding 
hydrogen  sulphide,  filtering  and  allowing  the  acids  to  separate  out  by  the  ad- 
dition of  Avater. 

The  Test  for  bile  salts  is  known  as  Pettenkofer's.  If  to  an  aqueous 
solution  of  the  salts  strong  suljjhuric  acid  be  added,  the  bile  acids  are 
first  of  all  precipitated,  but  on  the  further  addition  of  the  acid  are  re- 
dissolved.  If  to  the  solution  a  drop  of  solution  of  cane  sugar  be  added, 
a  fine  deep  cherry  red  to  purjole  color  is  developed. 

The  reaction  will  also  occur  on  the  addition  of  grape  or  fruit  sugar  instead 
of  cane  sugar,  slowly  with  the  first,  quickly  with  the  last ;  and  a  color  similar 
to  the  above  is  produced  by  the  action  of  sulphuric  acid  and  sugar  on  albumen, 
the  crystalline  lens,  nerve  tissue,  oleic  acid,  pure  ether,  cholesterin,  morphia, 
codeia  and  amylic  alcohol.  The  substance  which  gives  the  reaction  is  furfur- 
aldehyde,  formed  by  the  action  of  sulphuric  on  sugar.  Furfur -aldehyde  with 
cholalic  acid  gives  the  red  color. 

The  spectrum  of  Pettenkofer's  reaction,  when  the  fluid  is  moder- 
ately diluted,  shows  four  bands — the  most  marked  and  broadest  at  E, 
and  a  little  to  the  left;  another  at  F;  a  third  between  D  and  E,  nearer 
to  D ;  and  the  fourth  near  D. 

{h)  The  yellow  coloring  matter  of  the  bile  of  man  and  the  Carnivora 
is  termed  Bilirubin  or  Bilifulvin  (C16H18N2O3)  crystallizable  and  in- 
soluble in  water,  soluble  in  chloroform  or  carbon  disulphide;  a  green 
coloring  matter,  Biliverdin  (C16H20N2O5)  which  always  exists  in  large 
amount  in  the  bile  of  Herbivora,  being  formed  from  bilirubin  on  expo- 
sure to  the  air,  or  by  subjecting  the  bile  to  any  other  oxidizing  agency, 
as  by  adding  nitric  acid.  Biliverdin  iB  soluble  in  alcohol  but  insolu- 
ble in  water,  in  chloroform  and  almost  in  ether.  It  is  not  crystalline. 
When  the  bile  has  been  long  in  the  gall-bladder,  a  third  pigment,  Bili- 
prasin,  may  be  also  found  in  small  amount. 

In  cases  of  biliary  obstruction,  the  coloring  matter  of  the  bile  is  re- 
absorbed and  circulates  with  the  blood,  giving  to  the  tissues  the  yellow 
tint  characteristic  of  jaundice. 

The  coloring  matters  of  human  bile  do  not  appear  to  give  character- 
istic absorption  spectra;  but  the  bile  of  the  Guinea-pig,  rabbit,  mouse, 
sheep,  ox,  and  crow  do  so,  the  most  constant  of  which  appears  to  be  a. 


FOOD    AXD    DIGESTIOX.  347 

hand  iit  F.  The  bile  of  the  sheep  and  ox  give  three  bands  in  a  thick 
layer,  and  four  or  five  bauds  with  a  thinner  layer,  one  on  each  side  of 
D,  one  near  E,  and  a  faint  line  at  F.     (McMunn.) 

There  seems  to  be  a  close  relationship  between  the  coloring  matters 
of  the  blood  and  of  the  bile,  and  it  may  be  added,  between  these  and 
that  of  the  urine  {uvohiUti),  and  of  the  faeces  {stercobiU n)  also;  it  is 
probable  they  are,  all  of  them,  varieties  of  the  same  pigment,  or  derived 
from  the  same  source.  Indeed  it  is  maintained  that  Urobilin  is  identi- 
cal with  ffz/drohilirubin,  a  substance  which  in  alkaline  solution  gives  a 
green  fluorescence  with  zinc  chloride,  which  is  obtained  from  bilirubin 
by  the  action  of  sodium  amalgam,  or  by  the  action  of  sodium  amalgam 
on  alkaline  hajraatin;  both  urobilin  and  hydrobilirubin  giving  a  charac- 
teristic absorption  band  between  b  and  F.  They  are  also  identical  with 
stercobiliu,  which  is  formed  in  the  alimentary  canal  from  bile  pigments. 


Fig.  260.— Crystalline  scales  of  cholesterin. 

The  Test  (Gmelin's)  for  the  presence  of  bile-pigment  consists  of  the 
addition  of  a  small  quantity  of  nitric  acid,  yellow  with  nitrous  acid;  if 
bile  be  present,  a  play  of  colors  is  produced,  beginning  with  green  and 
passing  through  blue  and  violet  to  red,  and  lastly  to  yellow.  The  final 
yellow  substance  has  been  called  clioletelin.  The  spectrum  of  Gmelin's 
test  gives  a  black  band  extending  from  near  b  to  beyond  F. 

{r)  Fatty  si(bst(mces  are  found  in  variable  proportions  in  the  bile. 
Besides  these  saponifiable  fats,  there  is  a  small  quantity  of  Cholesterin,. 
which  is  an  alcohol,  and,  with  the  free  fats,  is  probably  held  in  solution 
by  the  bile  salts.  It  is  a  body  belonging  to  the  class  of  monatomic  alco- 
hols (C26II44O),  and  crystallizes  in  rhombic  plates  (fig.  260).  It  is  in- 
soluble in  water  and  cold  alcohol,  but  dissolves  easily  in  boiling  alcohol 
or  in  ether.  It  gives  a  red  color  with  strong  sulphuric  acid,  and  with, 
nitric  acid  and  ammonia;  also  a  play  of  colors  beginning  with  blood  red 
and  ending  with  green  on  the  addition  of  sulphuric  acid  and  chloro- 
form. Lecithin  (C44H90NPO9),  a  phosphorus-containing  body  and  Neu- 
rin  (C5H15NO2),  are  also  found  in  bile,  the  latter  probably  as  a  decom- 
position product  of  the  former. 


348  HANDBOOK    OF    PHYSIOLOGY, 

(d)  Tlie  Mucus  in  bile  is  derived  from  the  mucous  membrane  and 
glands  of  the  gall-bladder,  and  of  the  hepatic  ducts.  It  constitutes  the 
residue  after  bile  is  treated  with  alcohol.  The  epithelium  with  which  it 
is  mixed  may  be  detected  in  the  bile  with  the  microscope  in  the  form  of 
cylindrical  cells,  either  scattered  or  still  held  together  in  layers.  To 
the  presence  of  the  mucus  is  probably  to  be  ascribed  the  rapid  decom- 
position of  the  bile;  for,  according  to  Berzelius,  if  the  mucus  be  sej)a- 
rated,  it  will  remain  unchanged  for  many  days. 

(e)  The  Saline  or  inorganic  constituents  of  the  bile  are  similar  to 
those  found  in  most  other  secreted  fluids.  It  is  possible  that  the  car- 
bonate and  neutral  phosphate  of  sodium  and  potassium,  found  in  the 
ashes  of  bile,  are  formed  in  the  incineration,  and  do  not  exist  as  such  in 
the  fluid.  Oxide  of  iron  is  said  to  be  a  common  constituent  of  the  ashes 
■of  bile,  and  copper  is  generally  found  in  healthy  bile,  and  constantly  in 
biliary  calculi. 

(/)  Gas. — Small  amounts  of  carbonic  acid,  oxygen,  and  nitrogen 
gases,  may  be  extracted  from  bile. 

Functions  of  the  Bile. — Respecting  the  functions  discharged  by  the 
bile  in  digestion,  there  is  little  doubt  that  it  {a)  assists  in  emulsifying 
the  fats  of  the  food,  and  thus  rendering  them  capable  of  passing  into 
the  lacteals  by  absorption.  For  it  has  appeared  in  some  experiments  in 
which  the  common  bile-duct  was  tied,  that,  although  the  process  of 
digestion  in  the  stomach  was  unaffected,  chyle  was  no  'longer  well 
formed;  the  contents  of  the  lacteals  consisting  of  clear,  colorless  fluid, 
instead  of  being  opaque  and  white,  as  they  ordinarily  are,  after  feeding. 
It  is,  however,  the  combined  action  of  the  bile  with  the  pancreatic  juice 
to  which  the  emulsifi cation  is  due  rather  than  to  that  of  the  bile  alone. 
The  bile  itself  has  a  very  feeble  emulsifying  power. 

(5)  It  is  probable,  also,  that  the  moistening  of  the  mucous  membrane 
of  the  intestines  by  bile  facilitates  absorption  of  fatty  matters  through  it. 

(c)  The  bile,  like  the  gastric  fluid,  has  a  certain  but  not  very  con- 
siderable antiseptic  power,  and  may  serve  to  prevent  the  decomposition 
of  food  during  the  time  of  its  sojourn  in  the  intestines.  Experiments 
show  that  the  contents  of  the  intestines  are  much  more  foetid  after  the 
common  bile-duct  has  been  tied  than  at  other  times:  moreover,  it  is 
found  that  the  mixture  of  bile  with  a  fermenting  fluid  stops  or  spoils 
the  process  of  fermentation. 

{d)  The  bile  has  also  been  considered  to  act  as  a  natural  purgative, 
by  promoting  an  increased  secretion  of  the  intestinal  glands,  and  by 
stimulating  the  intestines  to  the  propulsion  of  their  contents.  This  view 
receives  support  from  the  constipation  which  ordinarily  exists  in  jaun- 
dice, from  the  diarrhoea  which  accompanies  excessive  secretion  of  bile, 
.and  from  the  purgative  properties  of  ox-gall. 

(e)  The  bile  appears  to  have  the  power  of  xrreciintating  the  gastric 


FOOD    AXD    DIGESTION.  349' 

proteoses  and  peptones,  together  with  the  pepsin,  which  is  mixed  up  with 
them,  as  soon  as  the  contents  of  the  stomach  meet  it  in  the  duodenum. 
The  purpose  of  this  operation  is  probably  both  to  delay  any  change  in 
the  proteoses  until  the  jiancreatic  juice  can  act  upon  them,  and  also  to 
prevent  the  j)epsin  from  exercising  its  solvent  action  on  the  ferments 
of  tlie  pancreatic  juice. 

(/)  As  an  excrementitious  substance,  the  bile  may  serve  especially  as 
a  medium  for  the  sejjaration  of  certain  highly  carbonaceous  substances 
from  the  blood;  and  its  adaptation  to  this  purjiose  is  well-illustrated  by 
the  peculiarities  attending  its  secretion  and  disposal  in  the  foetus.  Dur- 
ing intra-uterine  life,  the  lungs  and  the  intestinal  canal  are  almost  in- 
active; there  is  no  respiration  of  open  air  or  digestion  of  food;  these 
are  unnecessary,  on  account  of  the  supply  of  well-elaborated  nutriment 
received  by  the  vessels  of  the  fcetus  at  the  placenta.  The  liver,  during 
the  same  time,  is  proportionately  larger  than  it  is  after  birth,  and  the 
secretion  of  bile  is  active,  although  there  is  no  food  in  the  intestinal 
canal  upon  which  it  can  exercise  any  digestive  property.  At  birth, 
the  intestinal  canal  is  full  of  concentrated  bile,  mixed  with  intestinal 
secretion,  and  this  constitutes  the  meconium,  or  fgeces  of  the  foetus. 
In  the  foetus,  therefore,  the  main  purpose  of  the  secretion  of  bile  must 
be  directly  excretive.  Probably  all  the  bile  secreted  in  foetal  life  is 
incorjjorated  in  the  meconium,  and  with  it  discharged,  and  thus  the 
liver  may  be  said  to  discharge  a  function  in  some  sense  vicarious  of 
that  of  the  lungs.  For,  in  the  foetus,  nearly  all  the  blood  coming  from 
the  placenta  passes  through,  the  liver,  j)revious  to  its  distribution  to 
the  several  organs  of  the  body;  and  the  abstraction  of  certain  sub- 
stances will  purify  it,  as  in  extra-uterine  life  it  is  purified  by  the  sejDara- 
tion  of  carbon  dioxide  and  water  at  the  lungs. 

Mode  of  Secretion  and  Discharge. — The  secretion  of  bile  is  contin- 
ually going  on,  but  is  retarded  during  fasting,  and  accelerated  on  taking 
food.  This  has  been  shown  by  tying  the  common  bile-duct  of  a  dog, 
and  establishing  a  fistulous  opening  between  the  skin  and  gall-bladder, 
whereby  all  the  bile  secreted  was  discharged  at  the  surface.  It  was 
noticed  that  when  the  animal  was  fasting,  sometimes  not  a  drop  of  bile 
was  discharged  for  several  hours;  but  that,  in  about  ten  minutes  after 
the  introduction  of  food  into  the  stomach,  the  bile  began  to  flow  abun- 
dantly, and  continued  to  do  so  during  the  whole  period  of  digestion. 

The  bile  is  formed  in  the  hepatic  cells;  thence,  being  discharged 
into  the  minute  hepatic  ducts,  it  passes  into  the  larger  trunks,  and  from 
the  main  hepatic  duct  may  be  carried  at  once  into  the  duodenum. 
This  probably  happens  only  while  digestion  is  going  on,  i.e.,  for  5  to  7 
hours  after  the  introduction  of  food  into  the  stomach;  during  fasting, 
it  regurgitates  from  the  common  bile-duct  through  the  cystic  duct,  into 
the  gall-bladder,  where  it  accumulates  till,  in  the  next  period  of  diges- 


350  HANDBOOK    OF    PHYSIOLOGY. 

tion,  it  is  discharged  into  the  intestine.  The  gall-bladder  tlius  fulfils 
its  office,  that  of  a  reservoir;  for  its  presence  enables  bile  to  be  con- 
stantly secreted,  yet  insures  its  employment  in  the  service  of  digestion, 
although  digestion  is  periodic,  and  the  secretion  of  bile  constant. 

The  mechanism  by  which  the  bile  passes  into  the  gall-bladder  is 
simjjle.  The  orifice  through  which  the  common  bile-duct  communi- 
cates with  the  duodenum  is  narrower  than  the  duct,  and  appears  to  be 
closed,  except  when  there  is  sufficient  j^ressure  behind  to  force  the  bile 
through  it.  The  pressure  exercised  upon  the  bile  secreted  during  the 
intervals  of  digestion  appears  insufficient  to  overcome  the  force  with 
which  the  orifice  of  the  duct  is  closed;  and  the  bile  in  the  common 
duct,  finding  no  exit  in  the  intestine,  traverses  the  cystic  duct,  and  so 
passes  into  the  gall-bladder,  being  probably  aided  in  this  retrograde 
course  by  the  peristaltic  action  of  the  ducts.  The  bile  is  discharged 
from  the  gall-bladder  and  enters  the  duodenum  on  the  introduction  of 
food  into  the  small  intestine:  being  pressed  on  by  the  contraction  of 
the  coats  of  the  gall-bladder,  and  of  the  common  bile-duct  also;  for  both 
these  organs  contain  unstri^jed  muscular  fibre-cells.  Their  contraction 
is  excited  by  the  stimulus  of  the  food  in  the  duodenum  acting  so  as  to 
produce  a  reflex  movement,  the  force  of  which  is  sufficient  to  open  the 
orifice  of  the  common  bile-duct. 

Bile  is  not  pre-formed  in  the  blood.  As  just  observed,  it  is  secreted 
by  the  hepatic  cells,  although  some  of  its  constituents  may  be  brought 
to  them  almost  in  the  condition  for  immediate  secretion.  The  blood 
from  which  the  liver  cells  secrete  the  bile  is  that  applied  to  them  by  the 
portal  vein.  This  is  shown  by  the  alterations  which  occur  in  the  pro- 
cess on  the  alteration  of  the  pressure  in  the  portal  system.  If  the  portal 
vein  be  obstructed,  the  amount  of  bile  secreted  diminishes,  and  is  ulti- 
mately suppressed,  death  resulting.  It  has,  however,  been  shown  that 
under  extraordinary  circumstances  bile  may  be  secreted  by  the  aid  of 
the  blood  from  the  hepatic  artery,  since  if  a  branch  of  the  portal  vein 
be  tied,  the  part  of  the  liver  su^jplied  by  it  continues  to  secrete  bile, 
though  in  diminished  quantity.  When  the  discharge  of  the  bile  into 
the  intestine  is  prevented  by  an  obstruction  of  some  kind,  as  by  a  gall- 
stone blocking  the  hepatic  duct,  it  is  reabsorbed  in  great  excess  into 
the  blood,  and,  circulating  with  it,  gives  rise  to  the  well-known  phenom- 
ena of  jaundice.  This  is  explained  by  tbe  fact  that  the  pressure  of 
secretion  in  the  ducts  although  normally  very  low,  not  exceeding  15 
mm.  in  the  dog,  is  still  higher  than  that  of  the  portal  veins,  and  if  it 
exceeds  16  mm.  the  secretion  although  formed  ceases  to  be  poured  out, 
and  if  the  opposing  force  be  increased,  the  bile  passes  into  the  blood- 
vessels through  the  lymphatics,  and  the  yellow  color  appears  in  the  skin 
and  in  the  secretions,  and  constitutes  the  condition  of  jaundice.  In 
jaundice  the  fseces  are  light  colored  and  highly  offensive,  there  is  con- 


FOOD    AXD    DIGESTION.  351 

stipation,  the  heart  beats  slowly,  and  from  the  presence  of  bile  salts  as 
well  as  bile  pigment  in  the  blood,  the  red  blood  corpuscles  may  be  in 
part  dissolved.  The  latter  action  results  in  the  presence  of  hasmoglobin 
and  of  an  additional  amount  of  bile  pigment  in  the  urine. 

Disposal  of  the  Bile. — The  simple  excretion  of  the  foetal  bile  makes 
it  probable  that  the  bile  in  extra-uterine  life  is  also,  at  least  in  part,  des- 
tined to  be  discharged  as  excrementitious.  The  analysis  of  the  faces 
shows,  however,  that  (except  when  rapidly  discharged  in  purgation)  they 
contain  very  little  of  the  bile  secreted,  probably  not  more  than  one-six- 
teenth part  of  its  weight,  and  that  this  portion  includes  chiefly  its  col- 
oring matter  in  the  form  of  stercobilin,  and  some  of  its  fatty  matters 
and  mucin,  but  its  salts  to  only  a  very  slight  degree,  almost  all  of  Avhich 
have  been  reabsorbed  from  the  intestines  into  the  blood.  The  bilirubin 
is  in  part  converted  into  urobilin  and  is  reabsorbed  and  excreted  by  the 
kidneys  in  the  urine. 

The  elementary  composition  of  bile-salts  shows  such  a  preponderance 
of  carbon  and  hydrogen  that  probabl}^  after  absorption,  they  combine 
with  oxygen,  and  are  excreted  in  the  form  of  carbonic  acid  and  water. 
The  change  after  birth,  from  the  direct  to  the  indirect  mode  of  excre- 
tion of  the  bile  may,  with  much  probability,  be  connected  with  a  purpose 
in  relation  to  the  development  of  heat.  The  temperature  of  the  foetus 
is  largely  maintained  by  that  of  the  parent,  but,  in  extra-uterine  life, 
there  is  (as  one  may  say)  a  waste  of  material  for  heat  when  any  excre- 
tion is  discharged  unoxidized;  the  carbon  and  hydrogen  of  bilin,  there- 
fore, instead  of  being  ejected  in  the  fisces,  to  a  very  large  extent  (viz., 
I),  are  reabsorbed,  in  order  that  they  may  be  combined  with  oxygen,  and 
that  in  the  combination  heat  may  be  generated.  It  appears  that  tauro- 
cholic  acid  may  easily  be  split  up  in  the  intestine  into  taurin  and  chola- 
lic  acid,  and  the  same  is  probable  of  glycocholic  acid.  Taurin,  giycin, 
and  cholalic  acid  have  all  been  detected  in  small  amounts  in  the  fseces. 
So  that  the  bile  is  in  part  excreted,  but  in  part  is  reabsorbed  from  the 
intestine  (chiefly  the  large),  and  returned  to  the  liver.  What  may  be 
the  ultimate  destination  of  these  altered  or  unaltered  constituents  is  un- 
known. Giycin  is  supposed  to  go  partly  to  form  urea,  and  taurin  is  ex- 
creted to  a  slight  extent  in  the  urine  as  tauro-carbamic  acid,  but  it  is 
probable  that  although  part  of  this  may  unite  to  re-form  glycocholic  or 
taurocholic  acid,  the  remainder  is  united  with  oxygen,  and  is  burnt  off 
in  the  form  of  carbonic  acid  and  water. 

A  substance,  contained  in  the  fseces,  and  named  stercorin,  is  closely 
allied  to  cholesterin.  Ten  grains  and  a  half  of  stercorin  are  excreted 
daily  (A.  Flint). 

From  the  peculiar  manner  in  which  the  liver  is  supplied  with  much 
of  the  blood  that  flows  through  it,  it  is  probable  that  this  organ  is  ex- 
cretory, not  only  for  such  hydro-carbonaceous  matters  as  may  need  ex- 


352  HANDBOOK    OF    PHYSIOLOGY. 

pulsion  from  the  blood,  but  that  it  serves  for  the  direct  purification  of 
the  stream  which,  arriving  by  the  portal  vein,  has  just  gathered  up  vari- 
ous substances  in  its  course  through  the  digestive  organs — substances 
which  may  need  to  be  expelled,  almost  immediately  after  their  absorp- 
tion. For  it  is  easily  conceivable  that  many  things  may  be  taken  up 
during  digestion,  which  not  only  are  unfit  for  purposes  of  nutrition,  but 
which  would  be  positively  injurious  if  allowed  to  mingle  with  the  gen- 
eral mass  of  the  blood.  The  liver,  therefore,  may  be  supposed  placed  in 
the  only  road  by  which  such  matters  can  pass  unchanged  into  the  general 
current,  jealously  to  guard  against  their  further  progress,  and  turn  them 
back  again  into  an  excretory  channel.  The  frequency  with  which  me- 
tallic poisons  are  either  excreted  by  the  liver,  or  intercepted  and  retained, 
often  for  a  considerable  time,  in  its  own  substance,  may  be  adduced  as 
evidence  for  the  j^robable  truth  of  this  supposition. 

The  secretion  of  the  bile  by  the  hepatic  cells  is  undoubtedly  influenced 
by  the  amount  of  blood  supj)lied  to  them.  This  is  well  seen  after  a  meal, 
when  the  amount  of  blood  j^assing  through  the  portal  circulation  incon- 
sequence of  the  congestion  of  the  secreting  organs  of  the  abdomen  is 
greatly  increased,  and  with  it  the  bile  secretion.  It  is,  however,  probable 
that  the  secretion  of  the  cells  is  in  some  more  direct  way  under  the  con- 
trol of  the  nervous  system,  but  how  this  influence  is  exercised  is  un- 
known. The  antecedents  of  the  various  substances  of  the  bile  from 
which  the  cells  manufacture  its  chief  constituents  are  not  exactly  known. 
It  is  surmised  that  the  bilirubin  is  formed  from  ha3moglobin  brought- 
from  the  spleen  either  actually  dissolved  in  the  jjlasma  of  the  blood  or 
in  such  a  condition  in  the  corpuscles  as  to  be  easily  acted  upon  by  the 
liver  cells,  by  which  the  iron  is  separated.  The  bile  salts  are,  at  any 
rate  in  part,  formed  simply  by  the  conjunction  of  glycin  and  taurin  with 
cholalic  acid,  all  of  which  may  be  brought  to  the  liver  in  the  portal 
blood,  but  failing  this  it  is  probable  that  the  hepatic  cells  can  produce 
these  substances  anew. 

The  Intestinal  Secretion,  or  Succus  Entericus. 

On  account  of  the  difficulty  in  isolating  the  secretion  of  the  glands 
in  the  wall  of  the  intestine  (Brunner's  and  Lieberkiilin's)  from  other 
secretions  poured  into  the  canal  (gastric  juice,  bile,  and  pancreatic  se- 
cretion), but  little  is  known  regarding  the  comjjosition  of  the  intestinal 
juice,  or  succus  entericus. 

It  is  said  to  be  a  yellowish  alkaline  fluid  with  a  specific  gravity  of 
1011,  and  to  contain  about  2.5  per  cent  of  solid  matters  (Thiry). 

Functions. — The  secretion  is  said  to  be  able  to  convert  proteids  into 
peptones,  and  to  convert  starch  into  sugar,  but  the  evidence  in  favor  of 
these  actions  is  insufficient.     The  chief  function  of  the  juice  is  to  act 


FOOD    AXD    DIGESTION.  353 

upou  sugars.  It  possesses  the  power  of  converting  cane  into  grape 
sugar,  and  maltose  into  glucose.  It  also  contains  a  milk-curdling  fer- 
ment. 

The  reaction  which  represents  the  conversion  of  cane  sugar  into  grape 
sugar  may  be  represented  thus: 

2  C,oHo,0„    +    2  HnO    =     CioH.^Oi,    +    C1.H24O1, 
Saccharose.  Water.  Dextrose.  Lagvulose. 

The  conversion  is  probably  effected  by  means  of  a  hydrolytic  ferment, 
iiivertin  (Bernard). 

Summary  of  the  Digestive  Changes  in  the  Small 
Intestine. 

In  order  to  understand  the  changes  in  the  food  which  occur  during 
its  passage  through  the  small  intestine,  it  will  be  well  to  refer  briefly  to 
the  state  in  which  it  leaves  the  stomach  through  the  pylorus.  It  has 
been  said  before,  that  the  chief  office  of  the  stomach  is  not  only  to  mix 
into  an  uniform  mass  all  the  varieties  of  food  that  reach  it  through  the 
oesophagus,  but  especially  to  dissolve  the  nitrogenous  portion  by  means 
of  its  secretion.  The  fatty  matters,  during  their  sojourn  in  the  stomach, 
become  more  thoroughly  mingled  with  the  other  constituents  of  the 
food  taken,  but  are  not  yec  in  a  state  fit  for  absorption.  The  conversion 
of  starch  into  sugar,  which  began  in  the  mouth,  has  been  interfered 
with,  if  not  altogether  stopped.  The  soluble  matters — both  those  which 
were  so  from  the  first,  as  sugar  and  saline  matter,  and  the  gastric  pejo- 
tones — have  begun  to  disappear  by  absorption  into  tlie  blood-vessels,  and 
the  same  thing  has  befallen  such  fluids  as  may  have  been  swallowed. 

The  thin  pultaceous  chyme,  therefore,  which,  during  the  whole  period 
of  gastric  digestion,  is  being  constantly  squeezed  or  strained  through  the 
pyloric  orifice  into  the  duodenum,  consists  of  albuminous  matter,  broken 
down,  dissolving  and  half  dissolved;  fatty  matter  broken  down  and 
melted,  but  not  dissolved  at  all;  starch  very  slowly  in  process  of  con- 
version into  sugar,  and  as  it  becomes  sugar,  also  dissolving  in  the  fluids 
with  which  it  is  mixed;  while,  with  these  are  mingled  gastric  fluid,  and 
fluid  that  has  been  swallowed,  together  with  such  portions  of  the  food 
as  are  not  digestible,  and  will  be  finally  expelled  as  part  of  the  fasces. 

On  the  entrance  of  the  chyme  into  the  duodenum,  it  is  subjected  to 
the  influence  of  the  bile  and  pancreatic  juice,  which  are  then  poured  out, 
and  also  to  tliat  of  the  succus  entericus.  All  these  secretions  have  a 
more  or  less  alkaline  reaction,  and  by  their  admixture  with  the  gastric 
chyme,  its  acidity  becomes  less  and  less  until  at  length,  at  about  the 
middle  of  the  small  intestine,  the  reaction  becomes  alkaline  and  contin- 
ues so  as  far  as  the  ileo-caecal  valve. 
23 


354  HANDBOOK    OF    PHYSIOLOGY. 

The  special  digestive  functions  of  the  small  intestine  may  be  taken 
in  the  following  order: — 

(1.)  One  important  duty  of  the  small  intestine  is  the  alteration  of 
the  fat  in  such  a  manner  as  to  make  it  fit  for  absorption ;  and  there  is 
no  doubt  that  this  change  is  chiefly  effected  in  the  upper  part  of  the 
small  intestine.  What  is  the  exact  share  of  the  process,  however,  al- 
lotted respectively  to  the  bile  and  to  the  pancreatic  secretion,  is  still  un- 
certain. The  fat  is  changed  in  two  ways,  {a.)  To  a  slight  extent  it 
is  chemically  decomposed  by  the  alkaline  secretions  with  which  it  is 
mingled,  and  a  soap  is  the  result.  (6.)  It  is  emulsionized,  i.e.,  its  par- 
ticles are  minutely  subdivided  and  diffused,  so  that  the  mixture  assumes 
the  condition  of  a  milky  fluid,  or  emulsion.  As  will  be  seen  in  the  next 
Chapter,  most  of  the  fat  is  absorbed  by  the  lacteals  of  the  intestine,  but 
a  small  part,  which  is  saponified,  is  also  absorbed  by  the  blood-vessels. 

(2.)  The  albuminous  substances  which  have  been  partly  dissolved  in 
the  stomach,  and  have  not  been  absorbed,  are  subjected  chiefly  to  the 
action  of  the  pancreatic  juice.  The  pepsin  is  rendered  inert  by  being 
precipitated  together  with  the  gastric  peptones  and  proteoses,  as  soon  as 
the  chyme  meets  with  bile.  By  these  means  the  pancreatic  ferment 
trypsin  is  enabled  to  proceed  with  the  further  conversion  of  the  proteo- 
ses into  peptones,  and  part  of  the  peptones  (hemipeptone)  into  leucin 
and  tyrosin.  Albuminous  substances,  which  are  chemically  altered  in 
the  process  of  digestion  (peptones)  and  gelatinous  matters  similarly 
changed,  are  absorbed  by  the  blood-vessels  and  lymphatics  of  the  intes- 
tinal mucous  membrane.  Albuminous  matters,  in  state  of  solution, 
Avhich  have  not  undergone  the  peptonic  change,  are  probably,  from  the 
difficulty  with  which  they  diffuse,  absorbed,  if  at  all,  almost  solely  by 
the  lymphatics. 

(3.)  The  starchy,  or  amyloid  portions  of  the  food,  the  conversion  of 
which  into  dextrin  and  sugar  was  more  or  less  interrupted  during  its 
stay  in  the  stomach,  is  now  acted  on  briskly  by  the  pancreatic  juice  and 
the  succus  entericus;  and  the  sugar  in  the  form  of  glucose  or  of  maltose 
or  of  both  as  it  is  formed,  is  dissolved  in  the  intestinal  fluids,  and  is 
absorbed  chiefly  by  the  blood-vessels. 

(4.)  Saline  and  saccliarine  matters,  such  as  common  salt,  and  cane 
sugar,  if  not  in  a  state  of  solution  beforehand  in  the  saliva  or  other  fluids 
which  may  have  been  swallowed  with  them,  are  at  once  dissolved  in  the 
stomach,  and  if  not  here  absorbed,  are  soon  taken  up  in  the  small  intes- 
tine; the  blood-vessels,  as  in  the  last  case,  being  chiefly  concerned  in  the 
absorption.  Cane  sugar  is  in  part  or  wholly  converted  into  grape  sugar 
before  its  absorption.  This  is  accomplished  partially  in  the  stomach,  but 
also  by  a  ferment  in  the  succus  entericus. 

(5.)  The  liquids,  including  in  this  term  the  ordinary  drinks,  as  water, 
wine,  ale,  tea,  etc.,  which  may  have  escaped  absorption  in  the  stomach, 


FOOD    AND    DIGESTION.  355 

are  absorbed  probably  very  soou  after  their  entrance  into  the  intestine; 
the  fluidity  of  the  contents  of  the  latter  being  preserved  more  by  the 
•constant  secretion  of  fluid  by  the  intestinal  glands,  pancreas,  and  liver, 
than  by  any  given  portion  of  fluid  whether  swallowed  or  secreted,  re- 
maining long  unabsorbed.  From  this  fact,  therefore,  it  may  be  gathered 
that  there  is  a  kind  of  circulation  constantly  proceeding  from  the  intes- 
tines into  the  blood,  and  from  the  blood  into  the  intestines  again;  for 
as  all  the  fluid — a  very  large  amount— secreted  by  the  intestinal  glands, 
must  come  from  the  blood,  the  latter  w'ould  be  too  much  drained,  were 
it  not  that  the  same  fluid  after  secretion  is  again  reabsorbed  into  the 
current  of  blood— going  into  the  blood  charged  with  nutrient  products 
■of  digestion — coming  out  again  by  secretion  through  the  glands  in  a 
comparatively  uncharged  condition. 

At  the  lower  end  of  the  small  intestine,  the  chyme,  still  thin  and 
pultaceous,  is  of  a  light  yellow  color,  and  has  a  distinctly  faecal  odor. 
This  odor  depends  upon  the  formation  of  indol  and  other  substances  to 
he  again  alluded  to.  In  this  state  it  passes  through  the  ileo-ca3cal  open- 
ing into  the  large  intestine. 

Summary  of  the  Dig-estive  Changes  in  the  Large 
Intestine. 

The  changes  which  take  place  in  the  chyme  in  the  large  intestine 
.are  probably  only  the  continuation  of  the  same  changes  that  occur  in 
the  course  of  the  food's  passage  through  the  upper  part  of  the  intestinal 
■canal.  From  the  absence  of  villi,  however,  we  may  conclude  that  ab- 
sorption, especially  of  fatty  matter,  is  in  great  part  comj^leted  in  the 
small  intestine;  while,  from  the  still  half-liquid,  pultaceous  consistence 
of  the  chyme  when  it  first  enters  the  cgecum,  there  can  be  no  doubt  that 
the  absorption  of  liquid  is  not  by  any  means  concluded.  The  peculiar 
■odor,  moreover,  which  is  acquired  after  a  short  time  by  the  contents  of 
the  large  bowel,  would  seem  to  indicate  a  further  chemical  change  in 
the  alimentary  matters  or  in  the  digestive  fluids,  or  both.  The  acid 
reaction,  which  had  disappeared  in  the  small  bowel,  again  becomes  very 
manifest  in  the  caecum — probably  from  acid  fermentation  processes  in 
■some  of  the  materials  of  the  food. 

There  seems  no  reason  to  conclude  that  any  special  secondary  diges- 
tive process  occurs  in  the  caecum  or  in  any  other  part  of  the  large  in- 
testine. Probably  any  constituent  of  the  food  which  has  escaped 
digestion  and  absorption  in  the  small  bowel  may  be  digested  in  the  large 
intestine;  and  the  power  of  this  part  of  the  intestinal  canal  to  digest 
fatty,  albuminous,  or  other  matters,  may  be  gathered  from  the  good 
effects  of  nutrient  enemata,  so  frequently  given  when  from  any  cause 
ihere  is  difficulty  in  introducing  food  into  the  stomach.     In  ordinary 


356  HANDBOOK    OF    PHYSIOLOGY. 

healthy  digestion,  however,  the  changes  which  ensue  in  tlie  chyme  after 
its  passage  into  the  large  intestine,  are  mainly  the  absorption  of  the 
more  liquid  parts;  the  chief  function  of  the  large  intestine  being  to  act 
as  a  reservoir  for  the  residues  of  digestion  before  their  expulsion  from 
the  body. 

Action  of  Micro-organisms  in  the  Intestines. 

Certain  changes  take  place  in  the  intestinal  contents  independent  of, 
or  at  any  rate  supplemental  to  the  action  of  the  digestive  ferments. 
These  changes  are  brought  about  by  the  action  of  micro-organisms  or 
bacteria.  We  have  indicated  elsewhere  that  the  digestive  ferments  are 
examples  of  i(7iorg((nized  ferments^  so  bacteria  are  examples  of  organized 
ferments.      Organized    ferments,    of    which    the    yeast    plant,    torula 


'ooo' 


,00° 


l,'\ 


$ 


■^^^ 


7 


^ 


Fig.  261. — Types  of  micro-organisms,  a,  micrococci  arranged  singly;  in  twos,  diplococci— if  all 
the  micrococci  at  a  were  grouped  together,  they  would  be  called  staphylococci— and  in  fours,  sar- 
cinae:  6,  micrococci,  in  chains  streptococci ;  c  and  d,  bacilli  of  various  kinds,  one  is  represented 
with  flagellum;  e,  various  forms  of  spirilla;  /,  spores,  either  free  or  in  bacilli. 

{saccharomyces)  cerevisue,  may  be  taken  as  a  typical  example,  consist  of 
unicellular  vegetable  organisms,  which  when  introduced  into  a  suitable 
culture  medium  grow  with  remarkable  rapidity,  and  by  their  growth 
produce  new  substances  from  those  sujDplied  to  them  as  food.  Thus  for 
example,  when  the  yeast  cell  is  introduced  into  a  solution  of  grape  sugar, 
it  grows,  and  on  the  one  hand  alcohol,  and  on  the  other  hand  carbon 
dioxide  are  produced.  These  substances  are  not  the  direct  result  of  the 
life  of  the  cell,  but  probably  arise  from  the  formation  of  some  chemical 
substances  allied  to  the  unorganized  ferments  which  greatly  increase  in 
amount  with  the  multiplication  of  the  original  cell.  In  all  such  fer- 
mentative processes,  organisms  analogous  to  the  yeast  cell  are  present, 
and  it  is  not  strange  that  if  the  ferment  cell  is  introduced  into  a  suit- 
able medium,  it  may  by  its  rapid  reproduction  have  power  to  convert 
an  unlimited  amount  of  one  substance  into  anol^ier.  Speaking  generally 
a  special  variety  of  cell  is  concerned  with  each  ferment  action,  thus  one 
variety  has  to  do  with  alcoholic,  another  with  lactic  and  another  with 
acetous  fermentation.     A  considerable  number  of   species  of  bacteria 


FOOD    AND    DIGESTION.  357 

exist  in  the  body  during  life,  chiefly  in  connection  with  the  mucous 
membranes,  particulurly  of  the  digestive  tract.  These  bacteria  are 
unicellular  organisms,  devoid  of  chlorophyll,  sometimes  called  Jii<sion 
fungi  or  scJiizomycetes.  They  multiply  chiefly  by  division,  but  many  of 
them  also  form  spores — whereas  the  yeast  cell  multiplies  by  gemmation. 
The  bacteria  are  very  much  smaller  than  the  yeast  cells,  being  only 
from  1  to  2,a  in  width.  Morphologically  they  are  classified  into  i.  micro- 
cocci or  globular  bacteria,  ii.  bacilli  or  rod-shaped  bacteria,  and  iii. 
spirilla  or  sinuous  bacteria. 

Many  forms  of  bacteria  have  been  isolated  from  the  mouth,  a  few 
varieties  from  the  stomach,  and  a  very  large  number  from  the  intestines. 
It  is  only  in  the  last  named  locality  that  their  multiplication  has  much 
effect  from  a  physiological  point  of  view.  In  the  intestinal  canal  it 
appears  that  certain  changes  occur  which  are  distinctly  due  to  micro- 
erganisms:  these  changes  are  possibly  kept  within  limits  by  the  presence 
of  bile  in  the  intestine.  The  changes  said  to  be  due  under  ordinary 
eircumstances  are  as  follows : — 

a.  The  formation  of  indol,  sJcatoJ,  cresol  and  plienol,  chiefly  from 
peptone  (?  antipeptone)  in  the  small  intestine,  and  possibly  in  the  large 
intestine  also.  These  substances  are  absorbed  and  excreted  in  the  urine 
as  combined  suli)hates.  In  addition  to  these  as  results  of  decomposition 
of  albuminous  substances,  there  are  many  other  products,  e.g.,  gases,  such 
as  ammonia,  sulphuretted  hydrogen,  volatile  and  fatty  acids,  leucin  and 
tyrosin,  phenyl  acetic,  phenyl-proprionic  and  other  acids. 

h.  The  formation  of  lactic  acid  and  butyric  acid  from  carbo-hydrates. 
This  occurs  in  two  stages,  and  chiefly  results  from  decomposition  of 
sugars. 

c.  The  decomposition  of  cellulose. 

(C6Hio05+H20  =  3COH-3CH4.) 

Movements  of  the  Intestines. 

It  remains  only  to  consider  the  manner  in  which  the  food  and  the 
several  secretions  mingled  with  it  are  moved  through  the  intestinal 
canal,  so  as  to  be  slowly  subjected  to  the  influence  of  fresh  portions  of 
intestinal  secretion,  and  as  slowly  exposed  to  the  absorbent  power  of  all 
the  villi  and  blood-vessels  of  the  mucous  membrane.  The  movement  of 
the  intestines  is  peristaltic  or  vermicular,  und  is  effected  by  the  alternate 
contractions  and  dilatations  of  successive  portions  of  the  muscular  coats. 
The  contractions,  which  may  commence  at  any  point  of  the  intestine, 
extend  in  a  wave-like  manner  along  the  tube.  In  any  given  portion, 
the  longitudinal  muscular  fibres  contract  first,  or  more  than  the  circular; 
they  draw  a  portion  of  the  intestine  upward,  or,  as  it  were,  backward, 
over  the  substance  to  be  propelled,  and  then  the  circular  fibres  of  the 


358  HANDBOOK    OF   PHYSIOLOGY. 

same  portiou  contracting  in  succession  from  above  downward,  or,  as  it 
were,  from  behind  forward,  press  on  the  substance  into  the  portion 
next  below,  in  which  at  once  the  same  succession  of  action  next  ensues. 
These  movements  take  place  slowly,  and,  in  health,  commonly  give  rise 
to  no  sensation;  but  they  are  perceptible  when  they  are  accelerated 
under  the  influence  of  any  irritant.  The  movements  of  the  intestines 
are  sometimes  retrograde;  and  there  is  no  hindrance  to  the  backward 
movement  of  the  contents  of  the  small  intestine.  But  almost  complete 
security  is  afforded  against  the  passage  of  the  contents  of  the  large  into 
the  small  intestine  by  the  ileo-c^cal  valve.  Besides, — the  orifice  of 
communication  between  the  ileum  and  cEecum  (at  the  borders  of  which 
orifice  are  the  folds  of  mucous  membrane  which  form  the  valve)  is  en- 
circled with  muscular  fibres,  the  contraction  of  which  prevents  the 
undue  dilatation  of  the  orifice. 

Proceeding  from  above  downward,  the  muscular  fibres  of  the  large 
intestine  become,  on  the  whole,  stronger  in  direct  proportion  to  the 
greater  strength  required  for  the  onward  moving  of  the  faeces,  which  are 
gradually  becoming  firmer.  The  greatest  strength  is  in  the  rectum,  at 
the  termination  of  which  the  circular  unstriped  muscular  fibres  form  a. 
strong  band  called  the  internal  sphincter;  while  an  external  sphincter 
muscle  with  striped  fibres  is  placed  rather  lower  down,  and  more  ex- 
ternally, and  as  we  have  seen  above,  holds  the  orifice  close  by  a  con- 
stant slight  tonic  contraction. 

Experimental  irritation  of  the  brain  or  cord  produces  no  evident  or 
constant  effect  on  the  movements  of  the  intestines  during  life;  yet  in 
consequence  of  certain  mental  conditions  the  movements  are  accelerated 
or  retarded;  and  in  paraplegia  the  intestines  appear  after  a  time  much 
weakened  in  their  power,  and  costiveness,  with  a  tympanitic  condition^ 
ensues.  Stimulation  of  pneumo-gastric  nerves,  if  not  too  strong,  induces 
genuine  peristaltic  movements  of  the  intestines.  Violent  irritation 
stops  the  movements. 

Influence  of  the  Nervous  System  on  Intestinal  Digestion. 

As  in  the  case  of  the  oesophagus  and  stomach,  the  peristaltic  move- 
ments of  the  intestines  may  be  directly  set  up  in  the  muscular  fibres  by 
the  presence  of  chyme  acting  as  the  stimulus.  Few  or  no  movements 
occur  when  the  intestines  are  empty.  The  intestines  are  connected 
with  the  central  nervous  system  both  by  the  vagi  and  by  the  splanchnic 
nerves,  as  well  as  by  other  branches  of  the  sympathetic  which  come  to 
them  from  the  coeliac  and  other  abdominal  jDlexuses. 

The  relations  of  these  nerves  respectively  to  the  movements  of  the 
intestine  and  the  secretions  are  probably  the  same  as  in  the  case  of  the 
stomach  already  treated  of. 


FOOD    AND    DIGESTION. 


359 


Duration  of  Intestinal  Digestion. — The  time  occupied  by  the  journey 
of  a  given  portion  of  food  from  tlie  stomach  to  the  anus,  varies  consid- 
erably even  in  health,  and  on  this  account  probably  it  is  that  such  dif- 
ferent opinions  have  been  expressed  in  regard  to  the  subject.  About 
twelve  hours  are  occupied  by  the  journey  of  an  ordinary  meal  through 
the  small  intestine,  and  twenty-four  to  thirty-six  hours  by  the  passage 
through  the  large  bowel. 

The  contents  of  the  large  intestine,  as  they  proceed  toward  the  rec- 
tum, become  more  and  more  solid,  and  losing  their  more  liquid  and 
nutrient  parts,  gradually  acquire  the  odor  and  consistence  characteristic 
ot  f(Pces.  After  a  sojourn  of  uncertain  duration  in  the  sigmoid  flexure 
of  the  colon,  or  in  the  rectum,  they  are  finally  expelled  by  the  act  of 
defecation. 

The  average  quantity  of  solid  faecal  matter  evacuated  by  the  human 
adult  in  twenty-four  hours  is  about  six  or  eight  ounces. 

Composition  of  F^ces. 


The  amount  of  water  varies  considerably,  from  68  to  82  per  cent  and 
upward.     The  following  table  is  about  an  average  composition- — 


Water 

Solids, 

a. 


b. 


comprising  : 

Insoluble  residues  of  the  food,  uncooked  starch, 
cellulose,  woody  fibres,  cartilage,  seldom  mus- 
cular fibres  and  other  proteids,  fat,  cholesterin, 
horny  matter,   and  mucin      ..... 

Certain  substances  resulting  from  decomposition 
of  foods,  indol,  skatol,  fatty  and  other  acids, 
calcium  and  magnesium  soaps 

Special  excrementitious  constituents  : — Excretin, 
excretoleic  acid  (Marcet),  and  stercorin  (Austin 
Flint) 

Salts  : — Chiefly  phosphate  of  magnesium  and  phos- 
phate of  calcium,  with  small  quantities  of  iron, 
soda,  lime,  and  silica        ..... 

Insoluble  substances  accidentally  introduced  with 
the  food  ........ 

Mucus,  epitiielium,  altered  coloring  matter  of  bile, 
fatty  acids,  etc.  .  ... 

Varying  quantities  of  other  constituents  of  bile,  and 
derivatives  from  them  ...... 


733.00 


267.00 


1000.00 


The  Gases  contained  in  the  Stomach  and  Intestines. — Under  ordi- 
nary circumstances,  the  alimentary  canal  contains  a  considerable  quan- 
tity of  gaseous  matter.  Any  one  who  has  had  occasion,  in  a  post-mortem 
examination,  either  to  lay  open  the  intestines,  or  to  let  out  the  gas 
which  they  contain,  must  have  been  struck  by  the  small  space  afterward 
occupied  by  the  bowels,  and  by  the  large  degree,  therefore,  in  which  the 
gas,  which  naturally  distends  them,  contributes  to  fill  the  cavity  of  the 
abdomen.     Indeed,  the  presence  of  air  in  the  intestines  is  so  constant. 


360 


HANDBOOK    OF    PHYSIOLOGY. 


and,  within  certain  limits,  the  amount  in  health  so  uniform,  that  there 
can  be  no  doubt  that  its  existence  here  is  not  a  mere  accident,  but  in- 
tended to  serve  a  definite  and  important  purpose,  although,  probably,  a 
mechanical  one. 

Sources. — The  sources  of  the  gas  contained  in  the  stomach  and  bowels 
may  be  thus  enumerated : — 

1.  Air  introduced  in  the  act  of  swallowing  either  food  or  saliva;  2. 
Gases  developed  by  the  decomposition  of  alimentary  matter,  or  of  the 
secretions  and  excretions  mingled  with  it  in  the  stomach  and  intestines; 
3.  It  is  probable  that  a  certain  mutual  interchange  occurs  between  the 
gases  contained  in  the  alimentary  canal,  and  those  present  in  the  blood 
of  these  gastric  and  intestinal  blood-vessels;  but  the  conditions  of  the 
exchange  are  not  known,  and  it  is  very  doubtful  whether  anything  like 
a  true  and  definite  secretion  of  gas  from  the  blood  into  the  intestines  or 
stomach  ever  takes  place.  There  can  be  no  doubt,  however,  that  the 
intestines  may  be  the  proper  excretory  organs  for  many  odorous  and 
other  substances,  either  absorbed  from  the  air  taken  into  the  lungs  in 
inspiration,  or  absorbed  in  the  upper  part  of  the  alimentary  canal,  again 
to  be  excreted  at  a  portion  of  the  same  tract  lower  down — in  either  case 
assuming  rapidly  a  gaseous  form  after  their  excretion,  and  in  this  way, 
perhaps,  obtaining  a  more  ready  egress  from  the  body.  It  is  probable 
that,  under  ordinary  circumstances,  the  gases  of  the  stomach  and  intes- 
tines are  derived  chiefly  from  the  second  of  the  sources  which  has  been 
enumerated. 

Composition  of  Gases  of  the  Alimentary  Canal. 

{Tabulated  from  various  autliorities  hy  Brinton.) 


Composition  by  Volume. 

whence  obtained. 

Oxygen. 

Nitrog. 

Carbon. 
Acid. 

Hydrog. 

Carburet. 
Hydrogen. 

Sulphuj-et. 
Hydrogen. 

Stomach     . 

Small  Intestines     . 

Ceecum 

Colon 

Rectum 

Expelled  per  anum 

11 

71 
32 
67 
35 
46 
22 

14 
30 
12 
51 
43 
40 

4 

38 

8 

6 

19 

13 

8 
11 
19 

1 
1 

J^  trace. 

J 

The  above  table  differs  little  from  the  average  obtained  by  more 
modern  observers,  but  it  emits  an  important  point  to  which  attention 
should  be  drawn,  viz.,  that  the  amounts  of  the  gases  vary  with  the  diet. 
For  all  practical  purposes  oxygen  and  sulphuretted  hydrogen  may  be 
omitted.  An  analysis  of  the  intestinal  gases  (Ruge,  copied  by  Hallibur- 
ton) in  man  is  as  follows: — 


FOOD    AXD    DIGESTION. 


361 


Gases. 

Milk    Diet. 

Meat   Diet. 

Vegetable    Diet. 

Carbon  dioxide   .... 
Hydrogen         .... 
Carburetted  hydrogen 
Nitrogen 

9  to  16 
43  to  54 

0.9 
36  to  38 

8  to  13 

0.7  to  3 

26  to  37 

45  to  64 

21  to  34 
1.5  to   4 
44  to  55 
10  to  19 

Sources  of  the  Carhon  Dioxide. — From  the  carbonates  and  lactates  in 
food;  from  alcoholic  fermentation  of  sugar;  from  pittrefaction  of  car- 
bohydrates and  proteids;  and  from  butyric  acid  fermentation. 

Sources  of  the  Hydrogen. — From  butyric  acid  fermentations  of  lactic 
acid — 


2  CsHeOa 
Lactic  Acid. 


=     CmH^O.^     +     3  CO, 
Butyric  Acid. 


+     2H. 


Source  of  the  Carburetted  Hydrogen. — From  the  decomposition  of 
acetates  and  lactates  and  from  cellulose  (Cg  Hio  O5  +  H2  0  =  3  CO2  + 
3  CH4). 

Source  of  the  Xitrogen. — The  nitrogen  is  derived  from  the  swallowed 
air. 

Defaecation. 

The  act  of  the  expulsion  of  fa?ces  is  in  part  due  to  an  increased  reflex 
peristaltic  action  of  the  lower  part  of  the  large  intestine,  namely  of 
the  sigmoid  flexure  and  rectum,  and  in  part  to  the  more  or  less  volun- 
tary action  of  the  abdominal  muscles.  In  the  case  of  active  voluntary 
efforts,  there  is  usually,  first  an  insisiration,  as  in  the  case  of  coughing, 
sneezing,  and  vomiting;  the  glottis  is  then  closed,  and  the  diaphragm 
fixed.  The  abdominal  muscles  are  contracted  as  in  expiration ;  but  as 
the  glottis  is  closed,  the  whole  of  their  pressure  is  exercised  on  the  ab- 
dominal contents.  The  sphincter  of  the  rectum  being  relaxed,  the  evac- 
uation of  its  contents  takes  place  accordingly;  the  effect  being,  of  course, 
increased  by  the  peristaltic  action  of  the  intestine.  As  in  the  other 
actions  just  referred  to,  there  is  as  much  tendency  to  the  escape  of  the 
contents  of  the  lungs  or  stomach  as  of  the  rectum;  but  the  pressure  is 
relieved  only  at  the  orifice,  the  sphincter  of  which  instinctively  or  in- 
voluntarily yields. 

Nervous  Mechanism. — The  anal  sphincter  muscle  is  normally  in  a 
state  of  tonic  contraction.  The  nervous  centre  which  governs  this  con- 
traction is  probably  situated  in  the  lumbar  region  of  the  spinal  cord,  in- 
asmuch as  in  cases  of  division  of  the  cord  above  this  region  the  sphincter 
regains,  after  a  time,  to  some  extent  the  tonicity  which  is  lost  immedi- 
ately after  the  operation.  By  an  effort  of  the  will,  acting  through  the 
centre,  the  contraction  may  be  relaxed  or  increased.  In  ordinary  cases 
the  apparatus  is  set  in  action  by  the  gradual  accumulation  of  fseces  in 
the  sigmoid  flexure  and  rectum,  pressing  by  the  peristaltic  action  of 


362  HANDBOOK    OF    PHYSIOLOGY. 

these  parts  of  the  large  intestine  against  the  sphincter,  and  causing  hj 
reflex  action  its  rehixation;  this  sensory  impulse  acting  through  the 
brain  and  reflexly  through  the  spinal  centre.  At  the  same  time  that 
the  sphincter  is  inhibited  or  relaxed,  impulses  pass  to  the  muscles  of  the 
lower  intestine  increasing  their  peristalsis,  and,  if  necessary,  to  the  ab- 
dominal muscles  as  well.     The  action  of  the  centre  is  therefore  double. 


CHAPTER  IX. 

ABSORPTION. 

Absorption  is  generally  considered  to  consist  of  two  processes;  the-- 
first,  having  for  its  object  the  introduction  into  the  blood  of  fresh  mate- 
rial, and  which  is  called  absorption  from  without,  takes  place  chiefly 
from  the  alimentary  canal,  and  to  a  less  extent  from  the  skin  and  lungs; 
the  second,  having  for  its  object  the  gradual  removal  of  parts  of  the- 
body  itself  when  they  need  removal,  is  called  absorption  from  within,, 
and  takes  place  everywhere  within  the  tissues  of  the  body. 

The  conditions  of  absorption  from  the  alimentary  canal  which  may 
be  taken  as  an  example  of  the  first  of  these  processes  are  the  following : 
on  one  side  is  a  fluid  containing  matters  wliieh  have  been  so  acted  upon 
by  the  digestive  juices  as  to  be  in  a  fit  condition  to  be  absorbed.  On 
the  other  side  are  blood-capillaries  and  capillaries  of  the  lymphatic  sys- 
tem, and  separating  the  two  are  epithelium  and  connective  tissue,  as 
well  as  the  endothelium  of  the  vessels  themselves.  The  problem  which 
has  to  be  considered  is,  how  does  the  fluid  on  the  one  side  of  the- 
organic  membrane  reach  the  blood  or  lymphatic  vessel  ?  Until  within 
recent  date  it  was  assumed  that  the  passage  of  the  fluid  from  one  side 
of  this  membrane  to  the  other  came  about  solely  by  definite  physical 
laws,  and  these  were  practically  independent  of  the  vital  condition  of" 
the  tissues.  In  the  first  place,  it  was  taught,  came  in  osmosis,  the  pas- 
sage of  fluids  through  an  animal  membrane,  which  occurs  independent 
of  vital  conditions,  and  in  tbe  next  place  came  in  filtration,  the  passage- 
of  fluids  through  the  pores  of  a  membrane  under  pressure.  It  is  now 
believed,  however,  tliat  there  is  another  factor  concerned  in  absorption,, 
viz.,  the  vital  and  selective  action  of  the  epithelium,  and  possibly  of  the- 
tissue  which  separates  the  fluid  to  be  absorbed,  from  the  blood  and 
lymph  stream.  About  this  vital  action  of  the  epithelium  very  little- 
definite  is  known,  but  the  mere  fact  that  fats  are  principally  absorbed 
in  one  part  of  the  intestine,  and  as  we  shall  see  pass  through  the  cells 
of  the  intestinal  villi,  is  some  evidence  in  its  favor.  It  will  be  as  well 
to  consider  briefly  the  two  physical  processes  of  osmosis  and  filtration. 

Methods  of  Absorption. 

Osmosis. — The  phenomenon  of  the  passage  of  fluids  through  animal 
membrane,  which  occurs  quite  independently  of  vital  conditions,  was^ 
first  demonstrated  by  Dutrochet.     The  instrument  which  he  employed. 

363 


364 


HANDBOOK    OF    PHYSIOLOGY. 


in   his  experiments   was  named  an  endosinometer.     One  form  of  this, 
represented  in  the  figure,  consists  of  a  graduated  tube  expanded  into  an 
•open-mouthed  bell  at  one  end,  over  which  a  portion   of  membrane  is 
tied.     If  the  bell  be  filled  with  a  solution  of  a  salt — say  sodium  chloride, 
.and  be  immersed  in  water,  the  water  will  pass  into  the  solution,  and 
part  of  the  salt  will  pass  out  into  the  water;  the  water,  however,  will 
pass  into  the  solution  much  more  rapidly  tlian  the  salt  will  pass  out  into 
the  water,  and  the  diluted  solution  will  rise  in  the  tube.     It  is  to  this 
passage  of  fluids  through  membrane  that  the  term  osmosis  is  applied. 
The  nature  of  the  membrane  used  as  a  sepium,  ana  its  affinity  for 
the  fluids  subjected  to  experiment  have  an  important  influ- 
ence, as  might   be  anticipated,  on  the  rapidity  and  dura- 
tion of  the  osmotic  current.     Thus,  if  a  piece  of  ordinary 
bladder  be  used  as  the  septum  between  water  and  alcohol, 
the  current  is  almost  solely  from  the  water  to  the  alcohol, 
on  account  of  the  much  greater  affinity  of  water  for  this 
kind  of  membrane;  while,  on  the  other  hand,  in  the  case 
of  a  membrane  of  caoutchouc,  the  alcohol,  from  its  greater 
affinity  for  this  substance,  would  pass  freely  into  the  water. 
Absorption  by  blood-vessels  is  the  consequence  of  their 
walls  being,  like  the  membranous  septum  of  the  endosmo- 
meter,  porous  and  capable  of  imbibing  fluids,  and  of  the 
blood  being  so  composed  that  most  fluids  will  mingle  with 
it.     Thus  the  relation  of  the  chyme  in  the  stomach  and 
intestines   to  the  blood  circulating  in  the  vessels  of  the 
gastric  and  intestinal  mucous  membrane  is  evidently  just 
that  which  is  required  for  osmosis.     The   chyme  contains 
substances  which   have   been    so  acted  upon    by   the   di- 
gestive juices  as  to  have  become  quite  able  to  pass  through 
an  animal  membrane,  or  to  dialyze  as  it  is  called.     The  thin  animal 
membrane  is  the  coat  of  the  blood-vessels  with  the  intervening  mucous 
membrane.     The  nature  of  the  fluid  within  the  vessels,  the  very  feeble 
power  of  dialyzation  which  the  albuminous  blood  possesses,  determines 
the  direction  of  the  osmotic  current,  viz.,  into  and  not  out  of  the  blood- 
vessels.    The  current  is  of  course  aided  by  the  fact  of  the  constant 
change  in  the  blood  presented  to  the  osmotic  surface,  as  it  rapidly  circu- 
lates within  the  vessels.     As  a  rule  the  current  is  from  the  stomach  or 
intestine  into  the  blood,  but  the  reversed  action  may  occur,  when,  for 
example,  sulphate  of  magnesia,  is  taken  into  the  stomach,  in  which  case 
there  is  a  rapid  discharge  of  water  from  the  blood-vessels  into  the  ali- 
TTientary  canal  resulting   in  purgation.     The  presence  of  various  sub- 
stances in  the  food  has  the  power  of  diminishing  the  rate  of  absorption, 
their  influence  is  probably  exerted  upon  the  membrane,  diminishing  its 
power  of  permitting  osmosis.     Whereas  the  presence  of  a  little  hydro- 


Fig.  262. 
ILndosQiometer 


ABSORPTION.  365 

chloric  acid  in  the  contents  of  the  stomach  appears  to  determine  the 
direction  of  the  osmosis,  or  at  any  rate  to  diminish  or  prevent  exosraosis. 

The  conditions  for  osmosis  exist  not  only  in  the  alimentary  mucous 
membrane,  but  also  in  the  serous  cavities  and  the  tissues  elsewhere. 

Various  substances  have  been  classified  according  to  the  degree  in 
which  they  possess  the  property  of  passing,  when  in  a  state  of  solution 
in  water,  through  membrane;  those  which  pass  freely,  inasmuch  as  they 
are  usually  capable  of  crystallization,  being  termed  cri/stalloids,  and  those 
which  pass  with  difficulty,  on  account  of  their  physically,  glue-like  char- 
acter, colloids. 

This  distinction,  however,  between  colloids  and  crystalloids  which 
is  made  the  basis  of  their  classification,  is  by  no  means  the  only  differ- 
ence between  them.  The  colloids,  besides  the  absence  of  power  to  assume 
a  crystalline  form,  are  characterized  by  their  inertness  as  acids  or  bases, 
and  feebleness  in  all  ordinary  chemical  relations.  Examples  of  them 
are  found  in  albumin,  gelatin,  starch,  hydrated  alumina,  hydrated  silicic 
acid,  etc. ;  while  the  crystalloids  are  characterized  by  qualities  the  reverse 
of  those  just  mentioned  as  belonging  to  colloids.  Alcohol,  sugar,  and 
ordinary  saline  substances  are  examples  of  crystalloids. 

Fntration,  or  transudation,  means  the  passage  of  fluids  through  the 
pores  of  a  membrane  under  pressure.  The  greater  the  pressure  the 
greater  the  amount  wliich^ passes  through  the  membrane.  Colloids  will 
filter,  although  less  easily  than  crystalloids.  The  nature  of  the  substance 
to  be  filtered  and  the  nature  of  the  membrane  which  acts  as  the  filter 
materially  affect  the  activity  of  the  process.  No  doubt  both  osmosis 
and  filtration  go  on  together  in  the  process  of  absorption.  An  excellent 
example  of  filtration  or  transudation  occurs  in  the  pathological  condition 
known  as  dropsy,  in  which  the  connective  tissues  become  infiltrated 
with  serous  fluid.  The  fluid  passes  out  of  the  vein  when  the  intra-ven- 
ous  pressure  passes  a  certain  point,  the  fluid  being,  as  it  were,  squeezed 
through  the  walls  of  the  vessels  by  this  excess  of  pressure. 

Rajjidity  of  Alsoiyt ion. — The  rapidity  with  which  matters  may  be 
absorbed  from  the  stomach,  probably  by  the  blood-vessels  chiefly,  and 
diffused  through  the  textures  of  the  body,  has  been  found  by  experiment. 
It  appears  that  lithium  chloride  may  be  diffused  into  all  the  vascular 
textures  of  the  body,  and  into  some  of  the  non-vascular,  as  the  cartilage 
of  the  hip-joint,  as  well  as  into  the  aqueous  humor  of  the  eye,  in  a  quar- 
ter of  an  hour  after  being  given  on  an  empt}^  stomach.  Into  the  outer 
part  of  the  crystalline  lens  it  may  pass  after  a  time,  varying  from  half 
an  hour  to  an  hour  and  a  half.  Lithium  carbonate,  when  taken  in  five 
or  ten-grain  doses  on  an  empty  stomach,  may  be  detected  in  the  urine 
in  5  or  10  minutes;  or,  if  the  stomach  be  full  at  the  time  of  taking  the 
dose,  in  20  minutes.  It  may  sometimes  be  detected  in  the  urine,  more- 
over, for  six,  seven,  or  eight  days. 


366  HANDBOOK    OF    PHYSIOLOGY. 

Some  experiments  on  the  absorption  of  various  mineral  and  vegeta- 
ble poisons,  have  brought  to  light  the  singular  fact,  that,  in  some  cases, 
absorption  takes  place  more  rapidly  from  the  rectum  than  from  the 
stomach.  Strychnia,  for  example,  when  in  solution,  produces  its  poi- 
sonous effects  much  more  speedily  when  introduced  into  the  rectum 
than  into  the  stomach.  When  introduced  in  the  solid  form,  however, 
it  is  absorbed  more  rapidly  from  the  stomach  than  from  the  rectum, 
doubtless  because  of  the  greater  solvent  property  of  the  secretion  of  the 
former  than  of  the  latter. 

Conditions  for  Ahsoiytion. — 1.  The  diffusibility  of  the  substance  to 
be  absorbed  is  one  of  the  chief  conditions  for  its  absorption — a  col- 
loid, as  we  have  seen,  dialyzes  very  little.  It  must  be  also  in  the  liquid  or 
gaseous  state.  Mercury  may,  however,  be  absorbed  even  in  the  metallic 
state;  and  in  that  state  may  pass  into  and  remain  in  the  blood-vessels, 
or  be  deposited  from  them;  and  such  substances  as  exceedingly  finely- 
divided  charcoal,  when  taken  into  the  alimentary  canal,  have  been  found 
in  the  mesenteric  veins.  Oil,  minutely  divided,  as  in  an  emulsion,  will 
pass  slowly  into  blood-vessels,  as  it  will  through  a  filter  moistened  with 
water;  and,  without  doubt,  fatty  matters  find  their  way  into  the  blood- 
Tessels  as  well  as  into  the  lymph-vessels  of  the  intestinal  canal. 

3.  The  less  dense  the  fluid  to  he  al)sor'bed,  the  more  speedy,  as  a  gen- 
eral rule,  is  its  absorption  by  the  living  blood-vessels.  Hence  the  rapid 
absorption  of  w^ater  from  the  stomach;  also  of  weak  saline  solutions;  but 
with  strong  solutions,  there  appears  less  absorption  into,  than  effusion 
irom,  the  blood-vessels. 

3.  The  absorption  is  tlie  less  rapid  the  fuller  and  tenser  the  llood-ves- 
^els  are;  and  the  tension  may  be  so  great  as  to  hinder  altogether  the 
■entrance  of  more  fluid.  Thus,  if  water  is  injected  into  a  dog's  veins  to 
repletion,  poison  is  absorbed  very  slowly;  but  when  the  tension  of  the 
Tessels  is  diminished  by  bleeding,  the  poison  acts  quickly.  So,  when 
cupping-glasses  are  placed  over  a  poisoned  wound,  they  retard  the  ab- 
sori^tion  of  the  poison  not  only  by  diminishing  the  velocity  of  the  eir- 
oulation  in  the  part,  but  by  filling  all  its  vessels  too  full  to  admit  more. 

4.  On  the  same  ground,  absorption  is  the  quicker  the  more  rapid  the 
circulation  of  the  Hood;  not  because  the  fluid  to  be  absorbed  is  more 
quickly  imbibed  into  the  tissues,  or  mingled  with  the  blood,  but  because 
as  fast  as  it  enters  the  blood,  it  is  carried  away  from  the  jDart,  and  the 
blood  being  constantly  renewed,  is  constantly  as  fit  as  at  the  first  for 
the  reception  of  the  substance  to  be  absorbed. 

These  four  conditions  are  physical,  but  (5)  the  vital  condition  of  the 
absorptive  epithelium  must  not  be  forgotten.  It  has  been  shown,  for 
example,  that  the  absorption  by  the  frog's  skin  is  hastened  by  alcohol 
and  retarded  by  chloroform.  It  appears  also  that  absorption  is  retarded 
rather  than  hastened  by  removal  of  the  intestinal  epithelium. 


ABSOKPTION. 


367 


The  Lymphatic  System. 

Having  now  discussed  the  methods  and  conditions  of  absorption  in 
general,  we  must  next  turn  to  the  system  of  vessels  in  which,  on  the 
one  hand,  materials  of  the  food  not  taken  directly  into  the  blood-vessels 
of  the  alimentary  canal  are  received  and  carried  into  the  blood-stream; 
and,  on  the  other,  fluid  which  has  exuded  from  the  blood-vessels  into  the 


Xiymphatics    of    head    and 
neck,  right. 

Eight  internal  jugular  vein. 
Right  subclavian  vein. 

Lymphatics  of  right  arm. 


Receptaculum  chyli. 


LjTnphatics  of  lower  extrem- 
ities. 


Lymphatics  of   head   and 
neck,  left. 


Thoracic  duct. 

Left  subclavian  vein. 


Thoracic  duct. 


Lacteals. 


Ljrmphatics  of   lower   ex- 
tremities. 


Fig.  263.— Diagram  of  the  principal  groups  of  Lymphatic  vessels  (from  Quain). 


tissues  is  gathered  up  and  carried  back  again  into  the  blood.  This  sys- 
tem of  vessels  is  called  the  Lymphatic  System,  and  the  vessels  themselves 
are  named  Lymjjhatics  or  Absorben  ts.  They  have  often  been  incidentally 
mentioned  in  former  chapters. 

The  principal  vessels  of  the  lymphatic  system  are,  in  structure  and 
general  appearance,  like  very  small  and  thin-walled  veins.  They  are 
provided  with  valves.  They  commence  in  fine  microscopic  lymph-cap- 
illaries,  in  the  organs  and  tissues  of  the  body,  and  they  end  directly  or 
indirectly  in  two  trunks  which  open  into  the  large  veins  near  the  heart 


368 


HANDBOOK    OF    PHYSIOLOGY. 


(fig.  2G3).  The  fluid  which  they  contain,  unlike  the  blood,  passes  only 
in  one  direction,  namely,  from  the  fine  branches  to  the  trunk  and  so  to 
the  large  veins,  on  entering  which  they  are  mingled  with  the  stream  of 
blood  and  form  part  of  its  constituents.  The  course  of  the  fluid  in  the 
lymphatic  vessels  is  always  toward  the  large  veins  in  the  neighborhood 
of  the  heart,  and  in  fig.  263  the  greater  part  of  the  contents  of  the  lym- 


Fig.  264. 


Fig.  265. 


Fig.  264.— Superficial  lymphatics  of  right  groin  and  upper  part  of  thigh,  |-.— 1.  Upper  inguinal 
glands.  2,2'.  Lower  or  inguinal  or  femoral  glands.  3,  3'.  Plexus  of  lymphatics  in  the  course  of  the 
long  saphenous  vein.     (Maseagni.) 

Fig.  265.— Lymphatic  vessels  of  the  head  and  neck  and  the  upper  part  of  the  trunk  (Maseagni). 
i.— The  chest  and  pericardium  have  been  opened  on  the  left  side,  and  the  left  mamma  detached  and 
thrown  outward  over  the  left  arm,  so  as  to  expose  a  great  part  of  its  deep  surface.  The  principal 
iyniphatic  vessels  and  glands  are  shown  on  the  side  of  the  head  and  face,  and  in  the  neck,  axilla, 
and  mediastinum.  Between  ttie  left  internal  jugular  vein  and  the  common  carotid  artery,  the  upper 
ascending  part  of  the  thoracic  duct  marked  i,  and  above  this,  and  descending  to  2,  the  arch  and  last 
part  of  the  duct.  The  termination  of  the  upper  lymphatics  of  the  diaphragm  in  the  mediastinal 
glands,  as  well  as  the  cardiac  and  the  deep  mammary  lymphatics,  is  also  shown. 


phatic  system  of  vessels  will  be  seen  to  pass  through  a  comparatively 
large  trunk  called  the  tJioracic  chief,  which  finally  empties  its  contents 
into  the  blood-stream,  at  the  junction  of  the  internal  jugular  and  sub- 
clavian veins  of  the  left  side.  There  is  a  smaller  duct  on  the  right  side. 
The  lymphatic  vessels  of  the  intestinal  canal  are  called  ladeals,  because 
during  digestion  the  fluid  contained  in  them  resembles  milk  in  appear- 


ABSORPTION". 


369 


ance;  and  the  lymph  in  the  lacteals  during  the  period  of  digestion  is 
called  chyle.     There  is  no  essential  distinction,  however,  between  lacteals 
and  lymphatics.     In  some  parts  of  its   course  the  lymph-stream  must 
pass  through  lympliatic  glands. 

Lymphatic  vessels  are  distributed  in  nearly  all 
parts  of  the  body.  Their  existence,  however,  has 
not  yet  been  determined  in  the  placenta,  the  um- 
bilical cord,  the  membranes  of  the  ovum,  or  in 
any  of  the  so  called  non-vascular  parts,  as  the 
nails,  cuticle,  hair,  and  the  like. 

Origin  of  Lymph  Capillaries.~The  lymphatic 
capillaries  commence  most  commonly  either  (a) 
in  closely  meshed  networks,  or  {b)  in  irregular 
lacunar  spaces  between  the  various  structures  of 
which  the  different  organs  are  composed.  Such 
irregular   spaces,  forming   what   is   now    termed 


m 


W 


mm 


Fig.  ^66. 


Fig.  267 


Fig.  300.— Superficial  lymphatics  of  the  forearm  and  palm  of  the  hand,  ^. — 5.  Two  small  glands 
at  the  bend  of  the  arm.  0.  Radial  l3^mpliatic  vessels.  7.  Ulnar  lymphatic  vessels.  8,  8.  Palmar 
arch  of  lymphatics.  9,  9'.  Outer  and  inner  sets  of  vessels,  b.  Cephalic  vein.  d.  Radial  vein. 
e  Median  vein.  /.  Ulnar  vein.  The  lymphatics  are  represented  as  lying  on  the  deep  fascia. 
(Mascagni.) 

Fig.  207.  —Lymphatics  of  central  tendon  of  rabbit's  diaphragm,  stained  with  silver  nitrate.  The 
ground  substance  has  been  shaded  diagramniatically  to  bring  out  the  lymphatics  clearly.  I.  Lym- 
phatics lined  by  long  narrow  endothelial  cells,  and  showing  u.  valves  at  frequent  intervals,  (^cho- 
field.J 


the  lymph-canalicular  system,  have  been  shown  to  exist  in  many  tis- 
sues. In  serous  membranes  such  as  the  omentum  and  mesentery  they 
occur  as  a  connected  system  of  very  irregular  branched  spaces  partly 
occupied  by  connective  tissue-corpuscles,  and  both  in  these  and  in  many 
other  tissues  are  found  to  communicate  freely  with  regular  lymphatic 
24 


370  HANDBOOK    OF    PHYSIOLOGY. 

vessels.  In  many  cases,  though  they  are  formed  mostly  by  the  chinks 
and  crannies  between  the  blood-vessels,  secreting  ducts,  and  other  parts 
which  may  happen  to  form  the  framework  of  the  organ  in  which  they 
exist,  they  are  lined  by  a  distinct  layer  of  endothelium. 

The  lacteals  offer  an  illustration  of  another  mode  of  origin,  namely, 
(c)  in  blind  dilated  extremities;  but  there  is  no  essential  diiference  in 
structure  between  these  and  the  lymphatic  cajnllaries  of  other  parts. 

Structure  of  Lymph  Capillaries. — The  structure  of  lymphatic  capil- 
laries is  very  similar  to  that  of  blood-capillaries :  their  walls  consist  of 
a  single  layer  of  elongated  endothelial  cells  with  sinuous  outline,  which 
cohere  along  their  edges  to  form  a  delicate  membrane.  They  dilfer 
from  blood  capillaries  mainly  in  their  larger  and  very  variable  calibre, 
and  in  their  numerous  communications  with  the  spaces  of  the  lymjih- 
canalicular  system. 

Com nvunicat ions  of  the  Lymphatics. — The  fluid  part  of  the  blood 
constantly  exudes  from  or  is  strained  through  the  walls  of  the  blood- 
capillaries,  so  as  to  moisten  all  the  surrounding  tissues,  and  occupies 
the  interspaces  which  exist  among  their  different  elements,  which  form 
the  beginnings  of  the  lymph-capillaries;  and  the  latter,  therefore,  are  the 
means  of  collecting  the  exuded  blood  plasma,  and  returning  that  part 
which  is  not  directly  absorbed  by  the  tissues  into  the  blood-stream.  It 
is  not  necessary  to  assume  the  presence  of  any  siDecial  channels  between 
the  blood  and  lymphatic  vessels,  inasmuch  as  even  blood-corpuscles  can 
pass  bodily,  without  much  difficulty,  through  the  walls  of  the  blood- 
capillarie^  and  small  veins,  and  could  pass  with  still  less  trouble,  proba- 
bly, through  the  comparatively  ill-defined  walls  of  the  capillaries  which 
contain  lymph. 

It  has  been  already  mentioned  (p.  29)  that  in  certain  parts  of  the 
body,  stomata  exist,  by  which  lymphatic  capillaries  directly  communi- 
cate with  parts  hitherto  supposed  to  be  closed  cavities. 

Stomata  have  been  found  in  the  pleura;  and  as  they  may  be  pre- 
sumed to  exist  in  other  serous  membranes,  it  would  seem  as  if  the  serous 
cavities,  hitherto  supposed  closed,  form  but  a  large  lymph-sinus  or 
widening  out,  so  to  speak,  of  the  lymph-capillary  system  with  which 
they  directly  communicate. 

When  absorption  into  the  lymphatic  system  takes  piace  in  mem- 
branes covered  by  epithelium  or  endothelium  through  the  interstitial  or 
intercllular  cement-substance,  it  is  said  to  take  place  through  pseudo- 
stomata,  already  alluded  to  (p.  30). 

Demonstration  of  Lymphatics  of  Diaphragm. — The  stomata  on  the  peritoneal 
surface  of  the  diaphragm  are  the  openings  of  short  vertical  canals  which  lead 
up  into  the  lymphatics,  and  are  lined  by  cells  like  those  of  germinating  endo 
thelium.     B}"  introducing  a  solution  of  Berlin   blue  into   the  peritoneal   cavity 
of  an  animal  shortly  after  death,  and  suspending  it,  head  downward,  an  in- 


ABSOKPTION.  371 

jection  of  the  lymphatic  vessels  of  the  diaphragm,  through  the  stomata  on  its 
peritoneal  surface,  may  readily  be  obtained  if  artificial  respiration  be  carried 
on  for  about  half  an  hour.  In  this  way  it  has  been  found  that  in  the  rabbit 
the  lymphatics  are  arranged  between  the  tendon  bundles  of  the  centrum  ten- 
diueum ;  and  they  are  hence  termed  interfascicular.  The  centrum  tendineum 
is  coated  by  endothelium  on  its  pleural  and  peritoneal  surfaces,  and  its  substance 
consists  of  tendon  bundles  arranged  in  concentric  rings  toward  the  pleural 
side  and  in  x-adiating  bundles  toward  the  peritoneal  side. 

The  lymphatics  of  the  anterior  half  of  the  diaphragm  open  into  those  of  the 
anterior  mediastinum,  while  those  of  the  posterior  half  pass  into  a  lymphatic 
vessel  in  the  posterior  mediastinum,  which  soon  enters  the  thoracic  duct. 
Both  these  sets  of  vessels,  and  the  glands  into  which  they  pass,  are  readily 
injected  by  the  method  above  described ;  and  there  can  be  little  doubt  that 
during  life  the  flow  of  lymph  along  these  channels  is  chiefly  caused  by  the 
action  of  the  diaphragm  during  respiration.  As  it  descends  in  inspiration, 
the  spaces  between  the  radiating  tendon  bundles  dilate,  and  lymph  is  sucked 
from  the  peritoneal  cavity,  through  the  widely  open  stomata,  into  the  inter- 
fascicidar  lymphatics.  During  expiration,  the  spaces  between  the  concentric 
tendon  bundles  dilate,  and  the  lymph  is  squeezed  into  the  lymphatics  toward 
the  pleural  surface  (Klein).  It  thus  appears  probable  that  during  health  there 
IS  a  continued  sucking  in  of  lymph  from  the  peritoneum  into  the  lymphatics 
by  the  "  pumping"  action  of  the  diaphragm  ;  and  there  is  doubtless  an  equally 
continuous  exudation  of  fluid  from  the  general  serous  surface  of  the  perito- 
neum. When  this  balance  of  transudation  and  absorption  is  disturbed  either 
by  increased  transudation  -or  some  impediment  to  absorption,  an  accumulation 
of  fluid  necessarily  takes  place  (ascites) . 

Structure  of  Lymphatic  Vessels. — The  larger  vessels  as  before  men- 
tioned are  very  like  veins,  having  an  external  coat  of  areolar  tissue,  with 
elastic  filaments;  within  this,  a  thin  layer  of  areolar  tissue,  with  un- 
striped  muscular  fibres,  which  have,  principally,  a  circular  direction, 
and  are  much  more  abundant  in  the  small  than  in  the  larger  vessels; 
and  again,  within  this,  an  inner  elastic  layer  of  longitudinal  fibres,  and 
a  lining  of  epithelium;  and  numerous  valves.  The  valves,  constructed 
like  those  of  veins,  and  with  the  free  edges  turned  toward  the  heart, 
are  usually  arranged  in  pairs,  and,  in  the  small  vessels,  are  so  closely 
placed,  that  when  the  vessels  are  full,  the  valves  constricting  them 
where  their  edges  are  attached,  give  them  a  peculiar  beaded  or  knotted 
appearance. 

The  Lymph  Flow. 

The  flow  of  the  lymph  toward  the  point  of  its  discharge  into  the  veins 
is  brought  about  by  several  agencies.  With  the  help  of  the  valvular 
mechanism  (1)  all  occasional  pressure  on  the  exterior  of  the  lymphatic 
and  lacteal  vessels  propels  the  lymph  onward:  thus  muscular  and  other 
external  pressure  accelerates  the  flow  of  the  lymph  as  it  does  that  of 
the  blood  in  the  veins.     The  actions  of  (2)  the  muscular  fibres  of  the 


373  HANDBOOK    OF    PUYSIOLOGY. 

small  intestine,  and  probably  the  layer  of  unstripod  muscle  present  in 
each  intestinal  villus,  seem  to  assist  in  propelling  the  chyle :  for,  in  the 
small  intestine  of  a  mouse,  the  chyle  has  been  seen  moving  with  inter- 
mittent propulsions  that  appeared  to  correspond  with  the  peristaltic 
movements  of  the  intestine.  But  for  the  general  propulsion  of  the 
lymph  and  chyle,  it  is  probable  that,  together  with  (3)  the  vis  a  terrjo 
resulting  from  absorption  (as  in  the  ascent  of  sap  in  a  tree),  and  from 
external  pressure,  some  of  the  force  may  be  derived  (4)  from  the  con- 
tractility of  the  vessel's  own  walls.  The  respiratory  movements,  also, 
(5)  favor  the  current  of  lymph  through  the  thoracic  duct  as  they  do  the 
current  of  blood  in  the  thoracic  veins. 

Lymph-Hearts. — In  reptiles  and  some  birds,  an  important  auxiliary  to  the 
movement  of  the  lymph  and  chyle  is  supplied  in  certain  muscular  sacs,  named 
lympli-hearts,  and  it  has  been  shown  that  the  caudal  heart  of  the  eel  is  a 
lymph-heart  also.  The  number  and  position  of  these  organs  vary.  In  frogs 
and  toads  there  are  usually  four,  two  anterior  and  two  posterior  ;  in  the  frog, 
the  posterior  lymph-heart  on  each  side  is  situated  in  the  ischiatic  region,  just 
beneath  the  skin  ;  the  anterior  lies  deeper,  just  over  the  transverse  process  of 
the  third  vertebra.  Into  each  of  these  cavities  several  lymphatics  open,  the 
orifices  of  the  vessels  being  guarded  by  valves,  w-hich  prevent  the  retrograde 
passage  of  the  lymph.  From  each  heart  a  single  vein  proceeds,  and  conveys 
the  lymph  directly  into  tlie  venous  system.  In  the  frog,  the  inferior  lymphatic 
heart,  on  each  side,  pours  its  lymph  into  a  branch  of  the  ischiatic  vein  ;  by 
the  superior,  the  lymph  is  forced  into  a  branch  of  the  jugular  vein,  which 
issues  from  its  anterior  surface,  and  which  becomes  turgid  each  time  that  the 
sac  contracts.  Blood  is  prevented  from  passing  fi'om  the  vein  into  the  lym- 
phatic heart  by  a  valve  at  its  orifice. 

The  muscular  coat  of  these  hearts  is  of  variable  thickness  ;  in  some  cases  it 
can  only  be  discovered  by  means  of  the  microscope ;  but  in  every  case  it  is 
composed  of  striped  fibres.  The  contractions  of  the  hearts  are  rhythmical, 
occurring  about  sixty  times  in  a  minute,  slowly,  and,  in  comparison  with 
those  of  the  blood-hearts,  feebly.  The  pulsations  of  the  cervical  pair  are  not 
always  synchronous  with  those  of  the  pair  in  the  ischiatic  region,  and  even 
the  corresponding  sacs  of  opposite  sides  are  not  always  synchronous  in  their 
action. 

Unlike  the  contractions  of  the  blood-heart,  those  of  the  lymph-heart  ai^pear 
to  be  directly  dependent  upon  a  certain  limited  portion  of  the  spinal  cord. 
For  Volkmann  found  that  so  long  as  the  portion  of  spinal  cord  corresponding 
to  the  third  vertebra  of  the  frog  was  uninjured,  the  cervical  pair  of  lymphatic 
hearts  continued  pulsating  after  all  the  rest  of  the  spinal  cord  and  the  brain 
were  destroyed;  while  destruction  of  this  portion,  even  though  all  other  parts 
of  the  nervous  centi-es  were  uninjured,  instantly  arrested  the  heart's  move- 
ments. The  posterior,  or  ischiatic,  pair  of  lymph-hearts  were  found  to  be 
governed,  in  like  manner,  by  the  portion  of  spinal  cord  corresponding  to  the 
eighth  vertebra.  Division  of  the  posterior  spinal  roots  did  not  arrest  the  move- 
ments ;  but  division  of  the  anterior  roots  caused  them  to  cease  at  once. 

Lymphatic  Glands. — Lymphatic  glands  are   small  round  or  oval 
compact  bodies  varying  in  size  from  a  hemp-seed  to  a  bean,  interposed 


ABSORPTION". 


373 


in  the  course  of  the  lymphatic  vessels,  and  through  which  the  chief  part 
of  the  lymph  passes  in  its  course  to  be  discharged  into  the  blood-vessels. 
They  are  found  in  great  numbers  in  the  mesentery,  and  along  the  great 
vessels  of  the  abdomen,  thorax,  and  neck;  in  the  axilla  and  groin;  a 


Fig.  268. — Section  of  a  mesenteric  gland  from  the  ox,  slightly  magnified,  a,  Hilus  ;  b  (in  the 
central  part  of  the  figure),  medullary  substance;  c,  cortical  substance  with  indistinct  alveoU;  d, 
capsule.     (^KuUiker.j 

few  in  the  popliteal  spacq,  but  not  further  down  the  leg,  and  in  the 
arm  as  far  as  the  elbow.  Some  lymphatics  do  not,  however,  pass  through 
glands  before  entering  the  thoracic  duct. 

Strndiire. — A  lymphatic  gland  is  covered  externally  by  a  capsule  of 
connective  tissue,  generally  containing  some  unstriped  muscle.  At  the 
inner  side  of  the  gland,  which  is  somewhat  concave  {hilus),  (fig.  268,  a), 


Fig.  209.— Section  of  medullary  substance  of  an  inguinal  gland  of  an  ox.  «,  a,  glandular  sub- 
stance or  pulp  forming  rounded  cords  joining  in  a  continuous  net  (dark  in  the  figure);  c,  c,  tra- 
becula?;  the  space,  6.  6,  between  these  and  the  glandular  substance  is  the  lymph  sinus,  washed  clear 
of  corpuscles  and  traversed  by  filaments  of  retiform  connective-tissue.     X  90.    (KoUiker.) 


the  capsule  sends  inward  processes  called  troheculm  in  which  the  blood- 
vessels are  contained,  and  these  join  with  other  processes  prolonged  from 
the  inner  surface  of  the  part  of  the  capsule  covering  the  convex  or  outer 
par!  of  the  gland;  they  have  a  structure  similar  to  that  of  the  capsule, 
and  entering  the  gland  from  all  sides,  and  freely  communicating,  form 


374 


HANDBOOK    OF    PHYSIOLOGY. 


a  fibrous  supporting  stroma.  The  interior  of  the  gland  is  seen  on  sec- 
tion, even  when  examined  with  the  naked  eye,  to  be  made  up  of  two 
parts,  an  outer  or  cortical  (fig.  270,  c,  c),  which  is  light  colored,  and  an 
inner  of  redder  appearance,  the  medullary  j)ortion  (fig,  268).  In  the 
outer  or  cortical  part  of  the  gland  (fig.  270)  the  intervals  between  the 
trabecular  are  comparatively  large,  and  form  more  or  less  triangular  in- 
tercommunicating spaces  termed  alveoli;  while  in  the  more  central  or 
medullary  part  is  a  finer  meshwork  formed  by  the  more  free  anastomosis 
of  the  trabecular  process.  Within  the  alveoli  of  the  cortex  and  in  the 
meshwork  formed   by  the  trabecule  in  the  medulla,  is  contained  the 


Fi?.  370.— Diagrammatic  section  of  lymphatic  gland,  a.l.,  afferent ;  e.l.,  efferent  lymphatics; 
C,  cortical  substance;  l.h.,  reticulating  cords  of  medullary  substance;  /.s.,  lymph-sinus;  c,  fibrous 
coat  sending  in  trabeculge  ;  tr.,  into  the  substance  ol:  the  gland.     (Sharpey.) 

proper  gland  structure.  In  the  former  it  is  arranged  as  follows:  occu- 
pying the  central  and  chief  part  of  each  alveolus,  is  a  more  or  less  wedge- 
shaped  mass  of  adenoid  tissue,  densely  packed  with  lymph  corpuscles; 
but  at  the  periphery  surrounding  the  central  portion  and  immediately 
next  the  capsule  and  trabeculae,  is  a  more  open  meshwork  of  adenoid 
tissue  constituting  the  lymph  sinus  or  channel,  and  containing  fewer 
lymph-corpuscles.  The  central  mass  is  inclosed  in  endothelium,  the 
cells  of  which  join  by  their  processes,  the  processes  of  the  adenoid  frame- 
work of  the  lymph  sinus.  The  trabecule  are  also  covered  with  endothe- 
lium. The  lining  of  the  central  mass  does  not  prevent  the  passage  of 
fluids  and  even  of  corpuscles  into  the  lymph  sinus.  The  framework  of 
adenoid  tissue  of  the  lymph  sinus  is  nucleated,  that  of  the  central  mass 
is  non-nucleated.     At  the  inner  part  of  the  alveolus,  the  wedge-shaped 


ABSORPTION". 


375 


central  mass  divides  into  two  or  more  smaller  rounded  or  cord-like- 
masses  which  joining  with  those  from  the  other  alveoli,  form  a  much 
closer  arrangement  of  the  gland  tissue  than  in  the  cortex;  spaces  (fig. 
271,  b),  are  left  within  those  anastomosing  cords,  in  which  are  found 
portions  of  the  trabecular  meshwork  and  the  continuation  of  the  lymph 
sinus. 

The  essential  structure  of  lymphatic-gland  substance  resembles  that 
which  was  described  as  existing,  in  a  simple  form,  in  the  interior  of  the 
solitary  and  agminated  intestinal  follicles. 

The  lymph  enters  the  gland  by  several  afferent  vessels,  which  open 


Fig.  271.— A  small  portion  of  medullary  substance  from  a  mesenteric  gland  of  the  ox.  d,  d,  tra- 
beculse;  a.  part  of  a  cord  of  glandular  substances  from  which  all  but  a  few  of  the  lymph-corpuscles 
have  been  washed  out  to  show  its  supporting  meshwork  of  retiform  tissue  and  its  capillary  blood- 
vessels (which  have  been  injected,  and  are  dark  in  the  figure);  6,  6,  lymph-sinus,  of  which  the  reti- 
form tissue  is  represented  only  at  c,  c.     X  200.    (Kolliker.) 


beneath  the  capsule  into  the  lymph-channel  or  lymph-path;  at  the  same 
time  they  lay  aside  all  their  coats  except  the  endothelial  lining,  which 
is  continuous  with  the  lining  of  the  lymph-path.  The  efferent  vessels 
begin  in  the  medullary  part  of  the  gland,  and  are  continuous  with  the 
lympli-path  here  as  the  afferent  vessels  were  with  the  cortical  portion; 
the  endothelium  of  one  is  continuous  with  that  of  the  other. 

The  efferent  vessels  leave  the  gland  at  the  Itilus,  the  more  or  less 
concave  inner  side  of  the  gland,  and  generally  either  at  once  or  very 
soon  after  join  together  to  form  a  single  vessel. 

Blood-vessels  which  enter  and  leave  the  gland  at  the  hilus  are  freely 
distributed  to  the  trabecular  tissue  and  to  the  gland-pulp. 


376  HANDBOOK    OF    PHYSIOLOGY. 


The  Lymph  and  Chyle. 

Lymph  is,  under  ordinary  circumstances,  a  clear,  transparent,  and 
yellowish  fluid,  of  a  specific  gravity  varying  from  1012 — 1033.  It  is 
devoid  of  smell,  is  slightly  alkaline,  and  has  a  saline  taste.  As  seen  with 
the  microscope  in  the  small  transparent  vessels  of  the  tail  of  the  tad- 
pole, it  usually  contains  no  corpuscles  or  particles  of  any  kind;  and  it  is 
only  in  the  larger  trunks  that  any  corpuscles  are  to  be  found.  These 
corpuscles  are  similar  to  colorless  blood-corpuscles.  The  fluid  in  which 
the  corpuscles  float  is  albuminous,  and  contains  no  fatty  particles;  but 
is  liable  to  variations  according  to  the  general  state  of  the  blood,  and  to 
that  of  the  organ  from  which  the  lymph  is  derived.  It  may  clot  on  ex- 
posure to  the  air.  As  it  advances  toward  the  thoracic  duct,  after  pass- 
ing through  the  lymphatic  glands,  it  becomes  spontaneously  coagulable 
and  the  number  of  corpuscles  is  much  increased. 

Chi/Ie,  found  in  the  lacteals  after  a  meal, is  an  opaque,  whitish,  milky 
fluid,  neutral  or  slightly  alkaline  in  reaction.  Its  whiteness  and  opacity 
are  due  to  the  presence  of  innumerable  particles  of  oily  or  fatty  matter, 
of  exceedingly  minute  though  nearly  uniform  size,  measuring  on  the 
average  about  3,7^-17  of  an  inch  (0.8//).  These  constitute  what  is  termed 
the  molecular  base  of  chyle.  Their  number,  and  consequently  the  opac- 
ity of  the  chyle,  are  dependent  upon  the  quantity  of  fatty  matter  con- 
tained in  the  food.  The  fatty  nature  of  the  molecules  is  made  manifest 
by  their  solubility  in  ether.  Each  molecule  probably  consists  of  a  drop- 
let of  oil  coated  over  with  albumen,  in  the  manner  in  which  minute 
drops  of  oil  always  become  covered  in  an  albuminous  solution.  This  is 
proved  when  water  or  dilute  acetic  acid  is  added  to  chyle,  many  of  the 
molecules  are  lost  sight  of,  and  oil-drops  appear  in  their  place,  as  the 
investments  of  the  molecules  have  been  dissolved,  and  their  oily  con- 
tents have  run  together. 

Except  these  molecules,  the  chyle  taken  from  the  villi  or  from  lac- 
teals near  them,  contains  no  other  solid  or  organized  bodies.  The  fluid 
in  which  the  molecules  float  is  albuminous,  and  does  not  spontaneously 
coagulate.  But  as  the  chyle  passes  on  toward  the  thoracic  duct,  and 
especially  while  traversing  one  or  more  of  the  mesenteric  glands,  it  is 
elaborated.  The  quantity  of  molecules  and  oily  particles  gradually  di- 
minishes; cells,  to  which  the  name  of  chi/Ie-corjjnsdes  is  given,  aj)pear 
in  it;  and  it  acquires  the  property  of  coagulating  spontaneously.  The 
higher  in  the  thoracic  duct  the  chyle  advances,  the  greater  is  the  num- 
ber of  chyle-corpuscles,  and  the  larger  and  firmer  is  the  clot  which  forms 
in  it  when  withdrawn  and  left  at  rest.  Such  a  clot  is  like  one  of  blood 
without  the  red  corpuscles,  having  the  chyle-corpuscles  entangled  in  it, 
and  the  fatiy  matter  forming  a  white  creamy  film  on  the  surface  of  the 


ABSORPTION.  377 

iserum.  But  the  clot  of  chyle  is  softer  and  moister  than  that  of  blood. 
Lik6  blood,  also,  the  chyle  often  remains  for  a  long  time  in  its  vessels 
without  coagulating,  but  coagulates  rapidly  on  being  removed  from  them. 
The  existence  of  the  materials  which,  by  their  union,  form  fibrin,  is, 
therefore,  certain;  and  their  increase  appears  to  be  commensurate  with 
that  of  the  corpuscles. 

The  structure  of  the  chyle-corpuscles  was  described  when  speaking 
of  the  white  corpuscles  of  the  blood,  with  which  they  are  identical.  The 
lymph,  ill  chemical  composition,  I'esemhles  diluted  plasma,  and  from  what 
has  been  said,  it  will  appear  that  perfect  chyle  and  lymph  are,  in  essen- 
tial cliaracters,  nearly  similar,  and  scarcely  differ,  excejjf  in  the  prepon- 
derance of  fatty  and  proteid  matter  in  the  chyle. 

Chemical  Composition  of  Lymph  and  Chyle. 


I. 

II. 

III. 

Lj-mph. 

Chyle. 

Mixed  Lymph  & 

(Donkey^. 

(Donkey). 

Chyle  (Human). 

Water 

96.536 

90.287 

90.48 

Solids 

3.454 

9.763 

9.52 

Solids— 

Proteids,   including  Serum-Albu-  \ 
min,  Fibrinogen,  and  Globulin.  \ 

1.320 

3.886 

7.08 

Extractives,    including  in  (I  and  i 

II)    Sugar,  Urea,     Leucin    and  > 

1.559 

1.565 

1.08 

Cholesterin          .         .  '       .         .  ) 

Fatty  matter  and  Soaps 

a  trace 

8.601 

.93 

Salts 

.585 

.711 

.44 

Quantity. — The  quantity  which  would  pass  into  a  cat's  blood  in 
"twenty-four  hours  has  been  estimated  to  be  equal  to  about  one-sixth  of 
"the  weight  of  the  whole  body.  And,  since  the  estimated  weight  of  the 
'blood  in  cats  is  to  the  weight  of  their  bodies  as  1  to  7,  the  quantity  of 
'lymph  daily  traversing  the  thoracic  duct  would  appear  to  be  about  equal 
to  the  quantity  of  blood  at  any  time  contained  in  the  animals.  By  an- 
■  other  series  of  experiments,  the  quantity  of  lymph  traversing  the  tho- 
racic duct  of  a  dog  in  twenty-four  hours  was  found  to  be  about  equal  to 
two-thirds  of  the  blood  in  the  body. 

Chaxnels  of  Ai^sorption. 

The  Lacteals. — During  the  passage  of  the  chyme  along  the  intestinal 
canal,  its  completely  digested  parts  are  absorbed  into  the  blood  and 
distributed  in  the  mucous  membrane.  The  absorption  into  both  sets  oi 
vessels  is  carried  on  most  actively  hut  not  exclusively ,  in  the  villi  of  tha- 
small  intestine;  for  in  them  both  the  capillary  blood-vessels  and  the 
■lacteals  are  brought  almost  into  contact  with  the  intestinal  contents. 
There  seems  to  be  no  doubt  that  absorption  of  fatty  matters  during 
I  digestion,  from  the  contents  of  the  intestines,  is  effected  chiefly  through 


378  HANDBOOK    OF    PHYSIOLOGY. 

the  epithelial  cells  which  line  the  intestinal  tract,  and  especially  those 
which  clothe  the  surface  of  the  villi.  Thence,  the  fatty  particles  are 
passed  on  into  the  interior  of  the  lacteal  vessels,  but  how  they  pass,  and 
what  laws  govern  their  passage,  are  not  at  present  exactly  known.  The 
lymph-corpuscles  of  the  villi  are  however,  in  some  animals,  e.g.,  the  rat 
and  frog,  important  agents  in  effecting  the  passage  of -fat-joarticles  into 
the  lacteals.  These  cells  take  up  the  fat  whicli  has  passed  through  the 
columnar  cells  and  then,  by  reason  of  their  amseboid  movement,  carry 


Fig,  272.— Section  of  the  villus  of  a  rat  killed  during;  fat  absorption,  ep,  epithelium ;  str,  striated 
border;  c,  lymph-cells  ;  c',  lymph-cells  in  the  epithelium;  1,  central  lacteal  containing  disintegrating 
lymph-corpuscles.    (E.  A.  Schafer.) 

it  in  to  the  lacteal.  When  arrived  there  they  break  up  and  set  free 
both  fat  and  proteid  matter  thereby. 

The  process  of  absorption  is  assisted  by  the  pressure  exercised  on 
the  contents  of  the  intestines  by  their  contractile  walls;  and  the  absorp- 
tion of  fatty  particles  is  also  facilitated  by  the  presence  of  the  bile,  and 
the  pancreatic  and  intestinal  secretions,  which  moisten  the  absorbing 
surface. 

TJie  Lymphatics. — The  lymph  is  diluted  liquor  sangi(inis,  which  is 
always  exuding  from  the  blood-capillaries  into  the  interstices  of  the  tis- 
sues in  which  they  lie;  and  as  these  interstices  form  in  most  parts  of 
the  body  the  beginnings  of  the  lymphatics,  the  source  of  the  lymph  is 
sufficiently  obvious.  In  connection  with  this  may  be  mentioned  the 
fact  that  changes  in  the  character  of  the  lymph  correspond  very  closely 
with  changes  in  the  character  of  either  the  whole  mass  of  blood,  or  of  that  • 


ABSORPTIOX. 


379 


in  the  vessels  of  the  part  from  which  the  lymph  is  exuded.  Thus  it  ap- 
pears that  the  coagulability  of  the  lymph,  although  always  less  than,  is 
directly  proportionate  to  that  of  the  blood;  and  that  when  fluids  are  in- 
jected into  the  blood-vessels  in  sufficient  quantity  to  distend  them,  the 
injected  substance  may  be  almost  directly  afterward  found  in  the 
lymphatics. 

Some  other  matters  than  those  originally  contained  in  the  exuded 
liquor  sanguinis  may,  however,  find  their  way  with  it  into  the  lymphatic 
vessels.  Parts  which  having  entered  into  the  composition  of  a  tissue, 
md,  having  fulfilled  their  purpose,  require  to  be  removed,  may  not  be 
altogether  excrementitious,  but  may  admit  of  being  reorganized  and 
adapted  again  for  nutrition;  and  these  maj  be  absorbed  by  the  lym- 


Fig.  273. — Mucous  membrane  of  frog's  intestine  during  fat  absorption,  ep,  epithelium;  str,  striated 
border;  C,  lymph  corpuscles  ;  i,  lacteal.     (E.  A.  Schafer.) 

phatics,  and  elaborated  with  the  other  contents  of  the  lymph  in  passing 
through  the  glands. 

The  Blood-  Vessels. — In  the  absorption  by  the  lymphatic  or  lacteal 
vessels  just  described  tbere  appears  something  like  the  exercise  of  choice 
in  the  materials  admitted  into  them.  This  is  not  the  case  with  the 
blood-vessels;  it  apjjears  that  every  substance,  whether  gaseous,  liquid, 
or  a  soluble,  or  minutely  divided  solid,  may  be  absorbed  by  the  blood- 
vessels, provided  it  is  capable  of  permeating  their  walls,  and  of  mixing 
with  the  blood. 


Where  absorption  may  take  place. 

In  the  alimentary  canal. — The  greatest  activity  of  absorption  occurs 
in  the  alimentary  canal.  In  it  the  materials  of  the  duly  digested  food 
find  their  way  by  means  of  this  process  on  the  one  hand  into  the  blood- 
vessels of  the  portal  circulation,  and  on  the  other  into  the  lacteal  vessels 
which  are,  as  we  shall  see  presently,  the  commencements  of  the  lym- 
phatic vessels  of  the  intestines. 

Through  the  shin. — It  has  been  shown  that  metallic  preparations 
rubbed  into  the  skin  have  the  same  action  as  when  given  internally, 
only  in  a  less  degree.     Mercury  applied  in  this  manner  exerts  its  spe- 


380  HANDBOOK    OF    PHYSIOLOGY. 

cific  influence  upon  syphilis,  and  excites  salivation;  potassio-tartrate  of 
antimony  may  excite  vomiting,  or  an  eruption  extending  over  the  whole 
body;  and  arsenic  may  produce  poisonous  effects.  Vegetable  matters, 
also,  if  soluble,  or  already  in  solution,  give  rise  to  their  peculiar  effects, 
as  cathartics,  narcotics,  and  the  like,  when  rubbed  into  the  ski?i.  The 
effect  of  rubbing  is  probably  to  convey  the  particles  of  the  matter  into 
the  orifices  of  the  glands,  whence  they  are  more  readily  absorbed  than 
they  would  be  through  the  epidermis.  When  simply  left  in  contact 
with  the  skin,  substances,  unless  in  a  fluid  state,  are  seldom  absorbed. 

It  has  long  been  a  contested  question  whether  the  skin  covered  with 
the  epidermis  has  the  power  of  absorbing  water;  and  it  is  a  point  the 
more  difficult  to  determine  because  the  skin  loses  water  by  evaporation. 
But,  from  the  result  of  many  experiments,  it  may  now  be  regarded  as  a 
well-ascertained  fact  that  such  absorption  really  occurs.  The  absorption 
of  water  by  the  surface  of  the  body  may  take  place  in  the  lower  animals 
very  rapidly,  Not  only  frogs,  which  have  a  thin  skin,  but  lizards,  in 
which  the  cuticle  is  thicker  than  in  man,  after  having  lost  weight  by 
being  kept  for  some  time  in  a  dry  atmosphere,  are  found  to  recover  both 
their  weight  and  plumpness  very  rapidly  when  immersed  in  water. 
When  merely  the  tail,  posterior  extremities,  and  posterior  j^art  of  the 
body  of  the  lizard  are  immersed,  the  water  absorbed  is  distributed 
throughout  the  system.  And  a  like  absorption  through  the  skin,  though 
to  a  less  extent,  may  take  place  also  in  man. 

In  severe  cases  of  dysphagia,  when  not  even  fluids  can  be  taken  into 
the  stomach,  immersion  in  a  bath  of  warm  water  or  of  milk  and  water 
may  assu:ige  the  thirst;  and  it  has  been  found  in  such  cases  that  the 
weight  of  the  body  is  increased  by  the  immersion.  Sailors  also,  when 
destitute  of  fresh  water,  find  their  urgent  thirst  allayed  by  soaking  their 
clothes  in  salt  water,  and  wearing  them  in  that  state;  but  these  effects 
are  in  part  due  to  the  hindrance  to  the  evaporation  of  water  from  the 
skin. 

Through  the  Lung  a. — It  is  a  remarkable  fact  that  not  only  is  the 
epithelium  of  the  pulmonary  epithelium  able  to  allow  the  passage 
through  it  of  gases  and  volatile  substances,  but  that  also  under  certain 
conditions  fluids  such  as  water  may  also  be  absorbed,  and  besides  this, 
the  presence  of  carbon  particles  in  the  bronchial  glands  and  elsewhere 
in  connection  with  the  lungs  must  point  to  the  pulmonary  epithelium 
as  the  only  possible  channel  of  their  absorption. 


CHAPTER  X. 

EXCRETION. 

We  have  now  considered  the  methods  by  which  the  food  is  digested 
and  prepared  for  absorption  as  well  as  the  methods  by  which  the 
changed  materials  reach  the  general  blood-stream,  either  by  means  of 
the  lymphatics  of  the  intestinal  walls  or  by  the  capillaries  of  the  portal 
circnlation.  The  most  difficult  problems  of  jDhysiology  yet  remain  to  be 
discussed,  and  these  are  those  concerned  with  the  exact  changes  which 
take  place  in  the  tissues  and  organs  of  the  body,  when  they  are  supplied 
with  the  food  necessary  for  their  life.  In  order  to  be  in  a  condition  to 
discuss  these  questions  from  the  best  possible  standpoint,  it  will  be  as 
well  first  of  all  to  consider  the  forms  in  Avhich  the  waste  materials  re- 
sulting from  the  metabolism  of  the  tissues  leave  the  body,  and  the 
methods  of  their  elimination.  This  has  to  a  certain  extent  been  already 
considered,  we  have  seen  how  carbon  dioxide  and  other  matters  are  elim- 
inated by  the  lungs,  and  further,  we  have  devoted  some  time  to  the  con- 
sideration of  the  amount  and  composition  of  the  fgeces.  The  highly 
important  functions  of  the  kidneys,  in  excreting  the  urine,  and  of  the 
skin  remain,  and  it  is  to  these  that  we  must  now  direct  our  attention. 

The  Structure  and  Functions  of  the  Kidneys. 

The  Kidneys  are  two  in  number,  and  are  situated  deeply  in  the  lum- 
bar region  of  the  abdomen  on  either  side  of  the  spinal  column  behind 
the  peritoneum.  They  correspond  in  position  to  the  last  two  dorsal  and 
two  upper  lumbar  vertebra?;  the  right  being  slightly  below  the  left  in 
consequence  of  the  position  of  the  liver  on  the  right  side  of  the  abdo- 
men. They  are  about  4  inches  long,  2^  inches  broad,  and  l-j  inch  thick. 
The  weight  of  each  kidney  is  about  4|  oz. 

Structure. — The  kidney  is  covered  by  a  tough  fibrous  capsule,  which 
is  slightly  attached  by  its  inner  surface  to  the  proper  substance  of  the 
organ  by  means  of  very  fine  fibres  of  areolar  tissue  and  minute  blood- 
vessels. From  the  healthy  kidney,  therefore,  it  may  be  easily  torn  off 
without  injury  to  the  subjacent  cortical  j)ortion  of  the  organ.  At  the 
hiliis  or  notch  of  the  kidney,  it  becomes  continuous  with  the  external 
coat  of  the  upper  and  dilated  part  of  the  ureter  (fig.  274). 

On  dividing  the  kidney  into  two  equal  parts  by  a  section  carried 

381 


38y 


HANDBOOK    OF    PHYSIOLOGY. 


through  its  long  convex  border  (fig.  274),  the  main  part  of  its  substance 
is  seen  to  be  composed  of  two  chief  portions  called  respectively  cortical 
and  medullary,  the  latter  being  also  sometimes  called  pyramidal,  from 
the  fact  of  its  being  composed  of  about  a  dozen  conical  bundles  of  urine 
tubes,  each  bundle  forming  what  is  called  a  pyramid.  The  upper  part 
of  the  ureter  or  duct  of  the  organ,  is  dilated  into  the  pelvis  ;  and  this, 
again,  after  separating  into  two  or  three  principal  divisions,  is  finally 
subdivided  into  still  smaller  portions,  varying  in  number  from  about  8 
to  12,  or  even  more,  and  called  calyces.  Each  of  these  little  calyces  or 
cups,  which  are  often  arranged  in  a  double  row,  receives  the  pointed 


/ 


^< 


'tmiP^^' 


Fig.  274. 


Fig:.  275. 


Fig.  374.— Plan  of  a  longitudinal  section  through  the  pelvis  and  substance  of  the  right  kidney, 
J^  ;  a,  the  cortical  substance  ;  6,  b.  broad  part  of  the  pyramids  of  Malpighi ;  c,  c,  the  divisions  of  the 
pelvis  named  calyces,  laid  open  ;  c',  one  of  those  unopened  ;  d,  summit  of  the  pyramids  of  papillae 
projecting  into  calyces  ;  e,  e,  section  of  the  narrow  part  of  two  pyramids  near  the  calyces;  p,  pel- 
vis or  enlarged  divisions  of  the  ureter  within  the  kidney;  m,  the  ureter;  s,  the  sinus;  h,  the  hilus. 

Fig.  275.— A.  Portion  of  a  secreting  tubule  from  the  cortical  substance  of  the  kidney,  b.  The  epi- 
thelial or  gland-cells.     X  700  times. 

extremity  or  papilla  of  a  pyramid.  Sometimes,  however,  more  than  one 
papilla  is  received  by  a  calyx. 

The  kidney  is  a  compound  tubular  gland,  and  both  its  cortical  and 
medullary  portions  are  composed  essentially  of  tubes,  the  tuhuli  urini- 
feri,  which,  by  one  extremity,  in  the  cortical  portion,  end  commonly  in 
little  saccules  containing  blood-vessels,  called  Malpigkian  bodies,  and, 
by  the  other,  opened  through  the  papillae  into  the  pelvis  of  the  kidney, 
and  thus  discharge  the  urine  which  flows  through  them. 

In  the  pyramids  the  tubes  are  chiefly  straight — dividing  and  diverg- 
ing as  they  ascend  through  these  into  the  cortical  portion;  while  in  the 
latter  region  they  spread  out  more  irregularly,  and  become  much 
branched  and  convoluted. 

Tuhuli  Uriniferi. — The  tubuli  uriniferi  (fig.  275)  are  composed  of 


EXCRETION. 


383 


a  nearly  homogeneous  membrane,  and  are  lined  internally  by  epithelium. 
They  vary  considerably  in  size  in  different  parts  of  their  course,  but  are, 
on  an  average,  about  g^Jo  of  an  inch  {^^  mm.)  in  diameter,  and  are  found 


Fig.  276— A  diagram  of  the  sections  of  uriniferous  tubes.  A,  Cortex  limited  externaUy  by  the 
capsule:  u,  subcapsular  layer  not  containing:  Malpighian  corpuscles;  a',  inner  stratum  of  cortex, 
also  without  Malpighian  capsules  :  B,  boundary  layer;  C,  papillary  part  next  the  boundary  layer; 
1,  Bowman  s  capsule  of  Malpighian  corpuscle;  2,  neck  of  capsule;  3,  proximal  convoluted  tubule;  4. 
spiral  tubule;  5.  descending  limb  ot  Henle's  loop;  (5,  the  loop  proper;  7,  thick  part  of  the  ascending 
hmb  ;  8,  spiral  part  of  ascending  limb;  9.  narrow  ascending  limb  in  the  medullarv  ray;  10,  the  ir- 
regular tubule;  11,  the  intercalated  section,  or  the  distal  convoluted  tubule;  13,  the  curved  collect- 
ing tubule;  13,  the  straight  collecting  tubule  of  the  medullary  ray  ;  14,  the  collecting  tube  of  the 
boundary  layer;  15,  the  large  collecting  tube  of  the  papillary  part  which,  joining  with  similar 
tubes,  forms  the  duct.     (Klein.) 

to  be  made  up  of  several  distinct  sections  which  differ  from  one  another 
very  markedly,  both  in  situation  and  structure.  According  to  Klein, 
the  following  segments  may  be  made  out:  (1)  The  Malpighian  corpus- 


384 


HANDBOOK    OF    PHYSIOLOGY. 


cle  (figs.  276,  281),  composed  of  a  hyiiline  membrana  propria,  thickened 
by  a  varying  amount  of  fibrous  tissue,  and  lined  by  flattened  nucleated 
epithelial  plates.  This  capsule  is  the  dilated  extremity  of  the  urinif- 
erous  tubule,  and  contains  within  it  a  glomerulus  of  convoluted  capil- 
lary blood-vessels  supported  by  connective  tissue,  and  covered  by  flat- 
tened epithelial  plates.  The  glomerulus  is  connected  with  an  efferent 
and  an  afferent  vessel.  (2)  The  constricted  7ieck  of  the  capsule  (fig. 
276,  2),  lined  in  a  similar  manner,  connect  it  with  (3)  The  Proximal 
convoluted  tubule,  which  forms  several  distinct  curves  and  is  lined  with 


Fig.  277. — From  a  vertical  section  through  the  kidney  of  a  dog — the  capsule  of  which  is  supposed 
to  be  on  the  right,  a,  the  capillaries  of  the  Malpighian  corpuscle — viz.,  the  glomerulus,  are  ar- 
ranged in  lobules;  n,  neck  of  capsule  ;  c,  convoluted  tubes  cut  in  various  directions  ;  6,  irregular 
tubule  ;  d,  e,  and/,  are  straight  tubes  running  toward  capsules  forming  a  so-called  medullary  ray; 
d,  collecting  tube  ;  e,  spiral  tube;  /,  narrow  section  of  ascending  limb.  X  380.  (Klein  and  Noble 
Smith.) 

short  columnar  cells,  which  vary  somewhat  in  size.  The  tube  next 
passes  almost  vertically  downward,  forming  (4)  The  Spiral  Tubule, 
which  is  of  much  the  same  diameter,  and  is  lined  in  the  same  way  as 
the  convoluted  portion.  So  far  the  tube  has  been  contained  in  the  cortex 
of  the  kidney;  it  now  passes  vertically  downward  through  the  most 
external  part  (boundary  layer)  of  the  Malpighian  pyramid  into  the  more 
internal  part  (papillary  layer),  where  it  curves  up  sharply,  forming 
altogether  the  (5  and  6)  Loop  of  Ilenle,  which  is  a  very  narrow  tube 
lined  with  flattened  nucleated  cells.  Passing  vertically  upward  just  as 
the  tube  reaches  the  boundary  layer  (7),  it  suddenly  enlarges  and  be- 
comes lined  with  polyhedral  cells.     (8)  About  midway  in  the  boundary 


EXCRETION.  385 

layer  the  tube  again  narrows,  forming  the  ascending  sjnral  of  Henh's 
hop,  but  is  still  lined  with  polyhedral  cells.  At  the  point  where  the  tube 
enters  the  cortex  (9)  the  ascending  limb  narrows,  but  the  diameter 
varies  considerably;  here  and  there  the  cells  are  more  flattened,  but 
both  in  this  as  in  (8),  the  cells  are  in  many  places  very  angular,  branched, 
and  imbricated.  It  then  joins  (10)  the  "irregular  tuhule,"  which  has  a 
very  irregular  and  angular  outline,  and  is  lined  with  angular  and  imbri- 
cated cells.  The  tube  next  becomes  convoluted  (11),  forming  the  distal 
convoluted  tube  or  intercalated  sectioti  of  Schweig ger-Seidel,  which  is 
identical  in  all  respects  with  the  j)roximal  convoluted  tube  (12  and  13). 
The  curved  and  straight  collecting  tubes,  the  former  entering  the  latter 


Fig.  278. — Transverse  section  of  arenal  papilla;  o,  large  tubes  or  papillary  ducts;  6,  c,  and  d,  smaller 
tubes  of  Henle;  e,  /,  blood  capillaries,  distinguished  by  their  flatter  epithelium.    (Cadiat.) 

at  right  angles,  and  the  latter  passing  vertically  downward,  are  lined 
with  polyhedral,  or  spindle-shaped,  or  flattened,  or  angular  cells.  The 
straight  collecting  tube  now  enters  the  boundary  layer  (14)  and  passes 
on  to  the  papillary  layer,  and,  joining  with  other  collecting  tubes,  forms 
larger  tubes,  which  finally  open  at  the  apex  of  the  papilla.  These  col- 
lecting tubes  are  lined  with  transparent  nucleated  columnar  or  cubical 
cells  (U,  15). 

The  cells  of  the  tubules  with  the  exception  of  Henle's  loop  and  all 
parts  of  the  collecting  tubules,  are,  as  a  rule,  possessed  of  the  intra- 
nuclear as  well  as  of  the  intra-cellular  network  of  fibres,  of  which  the 
vertical  rods  are  most  conspicuous. 

Heidenhain  observed  that  indigo-sulphate  of  sodium,  and  other  pig- 
ments injected  into  the  jugular  vein  of  an  animal,  were  apparently  ex- 
creted by  the  cells  which  possessed  these  rods,  and  therefore  concluded 
25 


386 


HANDBOOK    OF    PHYSIOLOGY. 


that  the  pigment  passes  through  the  cells,  rods,  and  nucleus  themselves. 
Klein,  however,  believes  that  the  pigment  passes  through  the  intercel- 
lular substances,  and  not  through  the  cells. 

In  some  places,  it  is  stated  that  a  distinct  membrane  of  flattened  cells 
can  be  made  out  lining  the  lumen  of  the  tubes  {centrotuhular  mem- 
brane). 

Blood-supplij. — In  connection  with 
the  general  distribution  of  blood-ves- 
sels to  the  kidney,  the  Malpigliian 
Corpuscles  may  be  further  considered. 
They  (fig.  280)  are  found  only  in  the 
cortical  part  of  the  kidney,  and  are 
confined  to  the  central  part,  which, 
however,  makes  up  about  seven- 
eighths  of  the  whole  cortex.  On  a 
section  of  the  organ,  some  of  them 
are  just  visible  to  the  naked  eye  as 
minute  red  points;  others  are  too 
small  to  be  thus  seen.  Their  average 
diameter  is  about  ^^-^  of  an  inch 
{\  mm.).  Each  of  them  is  composed, 
as  we  have  seen  above,  of  the  diluted 
extremity  of  an  uriniferous  tube,  or 
Malpigliian  capsule,  which  incloses  a 
tuft  of  blood-vessels. 

The  renal  artery  divides  into  sev- 
eral branches,  which,  passing  in  iit 
the  hilus  of  the  kidney,  and  covered 
by  a  fine  sheath  of  areolar  tissue  de- 
rived from  the  capsule,  enter  the 
substance  of  the  organ  chiefly  in  the 
intervals  between  the  papillae,  and 
at  the  junction  between  the  cortex 
and  the  boundary  layer.  The  main 
branches  then  pass  almost  horizon- 
llXna^rfatemlSlFeftl^^  tally,  forming  more   or  less  complete 

up- 
ward to  the  cortex  and  downward  to 
the  medulla.  The  former  are  for  the  most  part  straight;  they  pass 
almost  vertically  to  the  surface  of  the  kidney,  giving  off  laterally  in 
all  directions  longer  and  shorter  branches,  which  ultimately  supply  the 
Malpigliian  bodies. 

The  small  afferent  artery  (figs.  380  and  281)  which  enters  the  Mal- 
pigliian corpuscle,  breaks  up  in  the  interior  as  before  mentioned  into  a 


Fig.  279. — Vascular  supply  of  kidney,    a, 
part  of  arterial  arch ;  6.  iaterlobular  artery;  c, 


cortex;/,  capillaries  of  medulla;  g,  venous  „„„],„„  .,„.]  „ivino-  nflF  l-.vinr.lioo 
arch;  7i,  straight  veins  of  medulla;  J,  vena  stel-  aiCUCS,  ana  glVlUg  On  DianCUCS 
lula;  i,  interlobular  vein.    (Cadiat.) 


EXCRETIOX. 


387 


dense  convoluted  and  looped  capillary  plexus,  which  is  ultimately  gath- 
ered up  again  into  several  small  efferent  vessels,  comparable  to  minute 
veins,  which  leave  the  capsule  at  one  or  more  places  near  the  point  at 


Fig  280.— Diagram  showing  the  relation  of  the  Malpighian  body  to  the  uriniferous  ducts  and 
blood-vessels,  a.  one  of  the  interlobular  arteries;  a',  afferent  artery  passing  into  the  glomerulus  ; 
c,  capsule  of  the  Malpighian  body,  forming  the  termination  of  and  continuous  with  t,  the  uriniferous 
tube  :  e',  e',  efferent  vessels  which  subdivide  in  the  plexus,  p,  surrounding  the  tube,  and  finally 
terminate  in  the  branch  of  the  renal  vein  e  (after  Bowman). 

which  the  afferent  artery  enters  it.  On  leaving,  it  does  not  immediately 
join  other  small  veins  as  might  have  been  expected,  but  again  breaking 
up  into  a  network  of  capillary  vessels,  is  distributed  on  the  exterior  of 


Fig.  281.— Malpighian  capsule  and  tuft  of  capillaries,  injected  through  the  renal  artery  with 
colored  gelatin,  a,  glomerular  vessels  :  h.  capsule  ;  c,  anterior  capsule;  d,  glomerular  artery  ;  e, 
efferent  veins;  /,  epithelium  of  tubes.     (Cadiat.) 

the  tubule,  from  whose  dilated  end  it  liad  just  emerged.  After  this 
second  breaking  up  it  is  finally  collected  into  a  small  vein,  which,  by 
union  with  others  like  it,  helps  to  form  the  radicles  of  the  renal  vein. 
These  small  veins  piss  into  others  which  form  venous  arclies  correspond- 


388 


HANDBOOK    OF    I'HYSIOLOGY. 


ing  to  the  arterial  arches,  but  which  are  more  distinct,  situated  between 
the  medulla  and  cortex. 

Thus  in  the  kidney,  the  blood  entering  by  the  renal  artery  traverses 
two  sets  of  capillaries  before  emerging  by  the  renal  vein,  an  arrangement 
which  may  be  compared  to  the  portal  system  in  miniature. 

The  tuft  of  vessels  in  the  course  of  development  is  tlirust  into  the 
dilated  extremity  of  the  urinary  tubule,  which  finally  com})letely  invests 
it.  Thus  the  Malpighian  capsule  is  lined  by  a  parietal  layer  of  squa- 
mous cells  and  a  visceral  or  reflected  layer  immediately  covering  the  vas- 
cular tuft  (fig,  282),  and  sometimes  dipping  down  into  its  interstices. 
This  reflected  layer  of  epithelium 
is  readily  seen  in  young  subjects,  but  \  V*^ 

cannot   always  be  demonstrated   in  (-^hj^^-^  I  ^  J 

the  adult.     (See  figs.  282  and  283.)  /  j[      \> '^^^  ]  \ 

'  J 


r^.  1 


Fig.  282. 


Fig.  2a3. 


Fig.  282.— Transverse  section  of  a  developing  Malpighian  capsule  and  tuft  (human).  X  300. 
From  a  fcetus  at  about  the  fourth  month:  o,  flattened  cells  growing  to  form  the  capsule;  b,  more 
rounded  cells,  continuous  with  the  above,  reflected  round  c,  and  finally  enveloping  it ;  c,  mass  of 
embryonic  cells  which  will  later  become  developed  into  b'ood-ves.sels.    (W.  Pye. ) 

Fig.  283. — Epithelial  elements  of  a  Malpighian  capsule  and  tuft,  with  the  commencement  of  a 
urinary  tubule  showing  the  afferent  and  efferent  vessel ;  a,  layer  of  flat  epithelium  forming  the 
capsule;  b,  similar,  but  rather  larger  epithelial  ceUs,  placed  in  the  walls  of  the  tube;  c,  cells,  covering 
the  vessels  of  the  capillary  tuft;  cl,  commencement  of  the  tubule,  somewhat  narrower  that  the  rest 
of  it.     (W.  Pye.) 


The  vessels  which  enter  the  medullary  layer  break  up  into  smaller 
arterioles,  which  pass  through  the  boundary  layer,  and  proceed  in  a 
straight  course  between  the  tubules  of  the  papillary  layer,  giving  off  on 
their  way  branches,  which  form  a  fine  arterial  meshwork  around  the 
tubes,  and  ending  in  a  similar  plexus  from  which  the  venous  radicles 
arise. 

Besides  the  small  afferent  arteries  of  the  Malpighian  bodies,  there 
are,  of  course,  others  which  are  distributed  in  the  ordinary  manner,  for 
the  nutrition  of  the  different  parts  of  the  organ;  and  in  the  pyramids,, 
between  the  tubes,  there  are  numerous  straight  vessels,  the  vasa  recta, 
some  of  which  are  branches  of  vasa  eff'erentia  from  Malpighian  bodies, 
and  therefore  comparable  to  the  venous  plexus  around  the  tubules  in 


EXCRETION. 


389 


the  cortical  portion,  while  others  arise  directly  as  small  branches  of  the 
renal  arteries. 

Between  the  tubes,  vessels,  etc.,  which  make  uj)  the  substance  of 
the  kidney,  there  exists,  in  small  quantity,  a  fine  matrix  of  areolar 
tissue. 

Nerves. — The  nerves  of  the  kidney  are  derived  from  the  renal  plexus 
of  each  side.  This  consists  of  both  medullated  and  uon-medullated 
nerve-fibres,  the  former  of  varying  size,  and  of  nerve-cells.  The  renal 
plexus  is  derived  from  the  solar  plexus,  particularly  from  the  semilunar 
ganglion.  The  renal  plexus  is  thus  indirectly  connected  with  the  vagi  and 
with  the  splanchnic  nerves.  It  is  also  directly  connected  with  them  by 
fibres  which  pass  to  them  without  first  joining  the  solar  plexus.  Fibres 
from  the  anterior  roots  of  the  eleventh,  twelfth,  and  thirteenth  dorsal 
nerves  in  the  dog  also  pass  to  the  same  plexus,  either  directly  through 
the  sympathetic  chain  or  by  first  passing  into  the  solar  plexus. 


Fig.  2&i.— Epithelium  of  the  bladder:  a,  one  of  the  cells  of  the  first  row;  b,  a  cell  of  the  second  row; 
c.  cells  i)i  situ,  of  first,  second,  and  deepest  layers.    (Obersteiner.) 


The  Ureters. — The  duct  of  each  kidney,  or  nreter,  is  a  tube  about 
the  size  of  a  goose-quill,  and  from  twelve  to  sixteen  inches  in  length, 
which,  continuous  above  with  the  pelvis  of  the  kidney,  ends  below  by 
perforating  obliquely  the  walls  of  the  bladder,  and  opening  on  its  inter- 
nal surface. 

Structure. — It  is  constructed  of  three  principal  coats  {a)  an  outer, 
tow g\\,  fibrous  and  elastic  coat;  {h)  a  middle  muscular  coat,  of  which  the 
fibres  are  unstriped,  and  arranged  in  three  layers — the  fibres  of  the  cen- 
tral layer  being  circular,  and  those  of  the  other  two  longitudinal  in 
direction;  and  (r)  an  internal  mucous  lining  continuous  with  that  of 
the  pelvis  of  the  kidney  above,  and  of  the  urinary  bladder  below.  The 
epithelium  of  all  these  parts  (fig.  284)  is  alike  stratified  and  of  a  some- 
what peculiar  form ;  the  cells  on  the  free  surface  of  the  mucous  mem- 
brane being  usuuUy  spheroidal  or  polyhedral  with  one  or  more  spherical 
or  oval  nuclei;  while  beneath  these  are  pear-shaped  cells,  of  which  the 
broad  ends  are  directed  toward  the  free  surface,  fitting  in  beneath  the 
cells  of  the  first  row,  and  the  apices  are  prolonged  into  processes  of  va- 


390  HANDBOOK    OF    PHYSIOLOGY. 

rions  lengths,  among  wliich,  again,  the  deepest  cells  of  the  epithelium 
are  found  spheroidal,  irregularly  oval,  spindle-shai^ed  or  conical. 

The  Urinary  Bladder. — The  urinary  bladder,  which  forms  a  re- 
ceptacle for  the  temporary  lodgment  of  the  urine  in  the  intervals  of  its 
expulsion  from  the  body,  is  more  or  less  pyriform,  its  widest  part,  which 
is  situate  above  and  behind,  being  termed  the  fundus;  and  the  narrow 
constricted  portion  in  front  and  below,  by  which  it  becomes  continuous 
with  the  urethra,  being  called  its  cervix  or  neck. 

Sti  uctiire. — It  is  constructed  of  four  principal  coats —  serous,  mus- 
cular, areolar  or  submucous,  and  mucous,  {a.)  The  serous  coat,  which 
covers  only  the  posterior  and  upper  part  of  the  bladder,  has  the  same 
structure  as  that  of  the  peritoneum,  with  which  it  is  continuous,  (b) 
The  fibres  of  the  muscular  coat,  which  are  unstriped,  are  arranged  in 
three  principal  layers,  of  which  the  external  and  internal  have  a  general 
longitudinal,  and  the  middle  layer  a  circular  direction.  The  latter  are 
especially  developed  around  the  cervix  of  the  organ,  and  are  described 
as  forming  a  sphincter  vesicce.  The  muscular  fibres  of  the  bladder,  like 
those  of  the  stomach,  are  arranged  not  in  simple  circles,  but  in  figure- 
of-8  loops,  (c)  The  areolar  or  submucous  coat  is  constructed  of  connec- 
tive tissue  with  a  large  proportion  of  elastic  fibres.  {(I)  The  mucous 
membrane,  which  is  rugose  in  the  contracted  state  of  the  organ,  does 
not  differ  in  essential  structure  from  mucous  membranes  in  general. 
Its  epithelium  is  stratified  and  closely  resembles  that  of  the  pelvis  of  the 
kidney  and  the  ureter  (fig.  284). 

The  mucous  membrane  is  provided  with  mucous  glands,  which  are 
more  numerous  near  the  neck  of  the  bladder. 

The  bladder  is  well  provided  with  blood-  and  lympli-vessels,  and  with 
nerves.  The  latter  are  both  medullated  and  non-medullated  fibres, 
both  branches  from  the  sacral  plexus  (spinal)  and  hypogiistric  plexus 
(sympathetic).  Ganglion-cells  are  found,  here  and  there,  in  the  course 
of  the  nerve-fibres. 

The  Urine. 

Physical  Properties. — Healthy  urine  is  a  perfectly  transparent,  am- 
ber-colored liquid,  with  a  peculiar,  but  not  disagreeable  odor,  a  bitterish 
taste,  and  slight  acid  reaction.  Its  specific  gravity  varies  from  1015  to 
1025.  On  standing  for  a  short  time,  a  little  mucus  appears  in  it  as  a 
flocculent  cloud. 

Chemical  Composition. — The  urine  consists  of  water,  holding  in  solu- 
tion certain  organic  and  saline  matters,  as  its  ordinary  constituents,  and 
occasionally  various  other  matters;  some  of  the  latter  are  indications 
of  diseased  states  of  the  system,  and  others  are  derived  from  unusual 
articles  of  food  or  drugs  taken  into  the  stomach. 


EXCRETION.  391 


Chemical  Composition  of  the  Urixe. 

Water 967 

Solids- 
Urea       14.230 

Other  nitrogenous  crystalline  bodies — 

Uric  acid,    principally  in  the  form  of  alka- 
line Urates,  a  trace  only  free. 
Creatinin,  Xanthin,  Hypoxathin. 
Hippuric  acid. 

Mucus,  Pigments,  and  Ferments. 
Salts : — 

Inorganic— 

Principally  Sulphates,  Phosphates,  and 
Chlorides  of  Sodium  and  Potassium,  with 
Phosphates  of  Magnesium  and  Calcium, 
traces  of  Silicates  and  Chlorides. 


10.635 


}        8.135 
Organic — 

Lactates,  Hippurates,  Oxalates,  Acetates  and 
Formates,  which  only  appear  occasion- 
ally, j  —    33 

Sugar a  trace  sometimes. 

Gases  (nitrogen  and  carbonic  acid  principally) . 

1000 

Reaction. — The  normal  reaction  of  the  urine  is  slightly  acid.  This 
acidity  is  due  to  acid  phosphate  of  sodium,  and  is  less  marked  soon  after 
meals.  The  urine  contains  no  appreciable  amount  of  free  acid,  as  it 
gives  no  precipitate  of  sulphur  with  sodium  hyposulphite.  After  stand- 
ing for  sometime  the  acidity  increases  from  a  Jiind  of  acid  fermentation, 
due  in  all  probability  to  the  presence  of  mucus  and  fungi,  and  acid 
urates  or  free  uric  acid  is  deposited.  After  a  time,  varying  in  length 
according  to  the  temperature,  the  reaction  becomes  strongly  alkaline 
from  the  change  of  urea  into  ammonium  carbonate,  due  to  the  presence 
of  one  or  more  specific  micro-organisms  {micrococcus  urece).  The  urea 
takes  up  two  molecules  of  water — a  strong  ammoniacal  and  foetid  odor 
appears,  and  deposits  of  triple  phosphates  and  alkaline  urates  take  place. 
This  does  not  occur  unless  the  urine  is  freely  exj)osed  to  the  air,  or, 
at  least,  until  air  has  had  access  to  it. 

Reaction  of  Urine  in  Different  Classes  of  Animals. — In  most  herbivorous  ani- 
mals the  urine  is  alkaline  and  turbid.  The  difference  depends  not  on  any 
peculiarity  in  the  mode  of  secretion,  but  on  the  difference  in  the  food  on  which 
the  two  classes  subsist;  for  when  carnivorous  animals,  such  as  dogs,  are  re- 
stricted to  a  vegetable  diet,  their  urine  becomes  pale,  turbid,  and  alkaline  like 
that  of  an  herbivorous  animal,  but  resumes  its  former  acidity  on  the  return  to 
an  animal  diet;  while  the  urine  voided  by  herbivorous  animals,  e.g.,  rabbits, 
fed  for  some  time  exclusively  upon  animal  substances,  presents  the  acid  reac- 
tion and  other  qualities  of  the  urine  of  Carnivora,  its  ordinary  alkalinity 
being  restored  only  on  the  substitution  of  a  vegetable  for  the  animal  diet. 
Human  urine  is  not  usually  rendered  alkaline  by  vegetable  diet,  but  it  becomes 
so  after  the  free  use  of  alkaline  medicines,  or  of  the  alkaline  salts  with  car- 


392 


HANDBOOK    OF    PHYSIOLOGY. 


bonic  or  vegetable  acids ;  for  these  latter  are  changed  into  alkaline  carbonates 
previous  to  elimination  by  the  kidneys. 


Average  daily  quantity  of  the  chief  urinary  constituents  (modified  from  Parkes). 


Water        .       '  . 
Solids — 

Urea 

Creatinin    . 

Uric  Acid 

Hippuric  Acid    . 

Pigment  and  Extract- 
tives 

Sulphuric  Acid  . 

Phosphoric  Acid     . 

Chlorine 

Ammonia 

Potassium  . 

Sodiuni 

Calcium 

Magnesium     . 


1500 

cc. 

or 

52i  oz. 

Per  Kilo  of 
body  weight. 
23.         grms. 

33.180  grms 
.910     " 

" 

512.4  grains. 
14.0 

.5 
.0140     " 

.555 

" 

" 

8.569 

" 

.0084     " 

.400 

" 

" 

6.16 

" 

.0060     " 

10. 

.. 

« 

154. 

" 

.1510     " 

2.013 

" 

" 

30.98 

" 

. 0480     " 

3.164 

" 

" 

48.80 

" 

.0305     " 

7. 000 

" 

*' 

107.8 

" 

.1260     " 

.770 

" 

" 

11.8 

" 

2. 500 

" 

" 

38.5 

•' 

11.090 

" 

" 

170.78 

" 

.260 

" 

" 

4. 

" 

.207 

" 

" 

3. 

" 

72. 


Variations  in  the  Quantity  of  the  Constituents. — From  the  propor- 
tions given  in  the  above  table,  most  of  the  constituents  are,  even  in 
health,  liable  to  variations.  The  variations  of  the  water  in  different 
seasons,  and  according  to  the  quantity  of  drink  and  exercise,  have  al- 
ready been  mentioned.  The  water  of  the  urine  is  also  liable  to  be  influ- 
enced by  the  condition  of  the  nervous  system,  being  sometimes  greatly 
increased,  e.g.,  in  hysteria  and  in  some  other  nervous  affections;  and  at 
other  times  diminished.  In  some  diseases  it  is  enormously  increased; 
and  its  increase  may  be  either  attended  with  an  augmented  quantity  of 
solid  matter,  as  in  ordinary  diabetes,  or  may  be  nearly  the  sole  change, 
as  in  the  affection  termed  diabetes  insipidus.  In  other  diseases,  e.(j., 
the  various  forms  of  albuminuria,  the  quantity  may  be  considerably 
diminished.  A  febrile  condition  almost  always  diminishes  the  quantity 
of  water;  and  a  like  diminution  is  caused  by  any  affection  which  draws 
off  a  large  quantity  of  fluid  from  the  body  through  any  other  channel 
than  that  of  the  kidneys,  e.g.,  the  bowels  or  the  skin. 

Method  of  Estimating  the  Solids.— A  useful  rule  for  approximately  estimating 
the  total  solids  in  any  given  specimen  of  healthy  urine  is  to  multiply  the  last 
two  figures  representing  the  specific  gavity  by  2.33.  Thus,  in  urine  of  sp. 
gr.  1025,  2.33  X  25  =  58.25  grains  of  solids,  are  contained  in  1000  grains  of  the 
urine.  In  using  this  method  it  must  be  remembered  that  the  limits  of  errors 
are  much  wider  in  diseased  than  in  healthy  urine. 

Variations  in  the  Specific  Gravity.— The  average  specific  gravity  of 
the  human  urine  is  about  1020.  The  relative  quantity  of  water  and  of 
solid  constituents  of  which  it  is  composed  is  materially  influenced  by 
the  condition  and  occupation  of  the  body  "during  the  time  at  which  it  is 


EXCRETION.  393 

secreted;  by  the  length  of  time  which  has  elapsed  since  the  last  meal; 
and  by  several  other  accidental  circumstances.  The  existence  of  these 
causes  of  difference  in  the  composition  of  the  urine  has  led  to  the  secre- 
tion being  describe^l  under  the  three  heads  of  Urina  sanguinis,  Urina 
potus,  and  Urina  cibi.  The  first  of  these  names  signifies  the  urine,  or 
that  part  of  it  which  is  secreted  from  the  blood  at  times  in  which 
neither  food  nor  drink  has  been  recently  taken,  and  is  applied  especially 
to  the  urine  which  is  evacuated  in  the  morning  before  breakfast.  The 
terms  lirifia  jjotus  indicates  the  urine  secreted  shortly  after  the  intro- 
duction of  any  considerable  quantity  of  fluid  into  the  body:  and  the 
iurina  cibi,  the  portions  secreted  during  the  period  immediately  succeed- 
ing a  meal  of  solid  food.  The  last  kind  contains  a  larger  quantity  of 
solid  matter  than  either  of  the  others;  the  first  or  second,  being  largely 
diluted  with  water,  possesses  a  comparatively  low  specific  gravity.  Of 
these  three  kinds,  the  morning  urine  is  the  best  calculated  for  analysis 
in  health,  since  it  represents  the  simple  secretion  unmixed  with  the 
elements  of  food  or  drink;  if  it  be  not  used,  the  whole  of  the  urine 
passed  during  a  period  of  twenty-four  hours  should  be  taken.  The 
specific  gravity  of  the  urine  may  thus,  consistently  with  health,  range 
widely  on  both  sides  of  the  usual  average.  It  may  vary  from  1015  in 
the  winter  to  1025  the  summer;  but  variations  of  diet  and  exercise,  and 
many  other  circumstances,  may  make  even  greater  differences  than  these. 
In  disease,  the  variation  may  be  greater;  sometimes  descending,  in  albu- 
minuria, to  1004,  and  frequently  ascending  in  diabetes,  when  the  urine 
is  loaded  with  sugar,  to  1050,  or  even  to  1060. 

Quant  it  II. — The  total  quantity  of  urine  passed  in  twenty-four  hours 
is  affected  by  numerous  circumstances.  On  taking  the  mean  of  many 
observations  by  several  experiments,  the  average  quantity  voided  in 
twenty-four  hours  by  healthy  male  adults  from  20  to  -40  years  of  age 
has  been  found  to  amount  to  about  Ir-l^  fluid  ounces  (1^  to  2  litres). 

Abnormal  Constituents. — In  disease,  or  after  the  ingestion  of  special 
foods,  various  abnormal  substances  occur  in  urine,  of  which  the  follow- 
ing may  be  mentioned — Serum-albumin,  Globulins,  Ferments  (appa- 
rently present  in  health  also),  Proteoses,  Peptone,  Blood,  Sugar,  Bile 
acids  and  pigments,  Casts,  Fats,  various  Salts  taken  as  medicine,  Micro- 
organisms of  various  kinds,  and  other  matters. 

The  Solids  of  the  Urine. 

Urea  (CH4X2O). — Urea  is  the  principal  solid  constituent  of  the 
urine,  forming  nearly  one-half  of  the  total  quantity.  It  is  also  the 
most  important  ingredient,  since  it  is  the  chief  substance  by  which  the 
■nitrogen  which  is  derived  from  the  metabolic  changes  iii  the  tissues  as 
well  as  that  which  is  derived  from  any  superfluous  food  is  excreted 


394 


HANDBOOK    OF    PHYSIOLOGY. 


from  the  body.  For  its  removal,  the  secretion  of  urine  seems  especially- 
provided  ;  and  by  its  retention  in  the  blood  the  most  pernicious  effects 
are  produced. 

Properties. — Urea,  like  the   other  solid   constituents  of  the  urine, 
exists  in  a  state  of  solution.     When  in  the  solid  state,  it  appears  in  the 


Fig.  2S5. — Crystals  of  Urea. 

form  of  delicate  silvery  acicular  crystals,  which,  under  the  microscope, 
appear  as  four-sided  prisms  (fig.  285).  It  may  be  obtained  in  this  state 
by  evaporating  urine  carefully  to  the  consistence  of  honey,  acting  on 
the  inspissated  mass  with  four  parts  of  alcohol,  then  evaporating  the 
alcoholic  solution  to  dryness,  and  purifying  the  residue  by  repeated 
solution  in  water  or  in  alcohol,  and  finally  allowing  it  to  crystallize.  It 
readily  combines  with  some  acids,  like  a  weak  base:  and  may  thus  be 
conveniently  procured  in  the  form  of  crystals  of  nitrate  or  oxalate  of 
urea  (figs.  286  and  287). 

Urea  is  colorless  when  pure;    when  impure  it   may  be  yellow  or 


Fig.  286.— Crystals  of  Urea  nitrat^e. 


Fig.  387.— Crystals  of  Urea  oxalate. 


brown:  it  is  without  smell,  and  of  a  cooling  nitre-like  taste;  it  has 
neither  an  acid  nor  an  alkaline  reaction,  and  deliquesces  in  a  moist  and 
warm  atmosphere.  At  15°  C.  (59°  ¥.)  it  requires  for  its  solution  less 
than  its  own  weight  of  water;  it  is  dissolved  in  all  proportions  by  boil- 
ing water;  but  it  requires  five  times  its  weight  of  cold  alcohol  for  its 
solution.     It  is  insoluble  in  ether.     At  120°  C.  (248°  F.)  it  melts  with- 


EXCRETION.  395 

out  undergoing  decomposition;  at  a  still  higher  temperature  ebullition 
takes  place,  and  carbonate  of  ammonium  sublimes.  When  heated  with 
water  in  a  sealed  tube  to  100°  C,  urea  splits  up  into  carbonic  acid  and 
ammonia;  when  heated  to  a  high  temperature  urea  loses  ammonia  and 
lirst  yields  biuret,  C2H5N3O2,  which  gives  a  rose  color  with  caustic  potash 
and  a  trace  of  copper  sulphate,  and  afterward  cyanuric  acid,  C3H3O3N3, 
which  gives  a  violet  color  with  caustic  potash  and  a  trace  of  copper  sul- 
phate. It  is  decomposed  by  sodium  hypochlorite  or  hypobromite  or  by- 
nitrous  acid,  with  evolution  of  N.  It  forms  compounds  with  acids,  of 
which  the  chief  are  urea  hydrochloride,  CH4jSr20.HCL;  urea  nitrate, 
CH4lSroOHN03;  and  urea  phosphate,  CH4N2O.H3PO4.  It  forms  com- 
pounds with  metals  such  as  HgO.CH4N20;  with  silver  CH2N20Ag2; 
and  with  salts  such  as  HgClo  and  IIgN03. 

Chemical  Nature. — Urea  is  isomeric  with  ammonium  cyanate 
NH4,CN0.     It  was  first  of  all  artificially  prepared  from  that  substance. 

It  may  also  he  produced   artificially  by  treating    carbonyl  chloride  (CO  CI2) 
v^\i\\  ammonia;  or  hy  heating  ethyl  carbonate  with  ammonia  CO  qq'jj'*  +  2  NH3  = 

TyJTT 

CONoHi  2C2H6O ;  by  heating  ammonium  carbonate  CO  Q]sf|j  =  CON2H4  -|- 
H2O ;  by  adding  water  to  cyanamide  CN.NH2,  or  by  evaporating  ammonium 
cyanate  in  aqueous  solution.- 

It  is  usually  considered  to  be  a  diamide  of  carbonic  acid,  in  other 
words,  carbonic  acid,  CO  (OH) '2,  with  two  of  hydroxyl,  (OH) '2,  replaced 
by  two  of  amidogen  (NH2)'2.  It  may  also  be  written  as  if  it  were  a 
monamide  of  carbamic  acid  (COOHNHo),  thus  CONH2.NH2;  one  of 
amidogen,  NH2,  in  the  latter  replacing  one  of  hydroxyl  in  the  former. 
Decomposition  of  the  urea  with  development  of  ammonium  carbonate 
takes  place  from  the  action  of  the  bacteria  (micrococcus  urese),  when 
urine  is  kept  for  some  days  after  being  voided,  and  explains  the  ammo- 
niacal  odor  then  evolved.  The  urea  is  sometimes  decomposed  before  it 
leaves  the  bladder,  when  the  mucous  membrane  is  diseased,  and  the 
mucus  secreted  by  it  is  both  more  abundant,  and,  probably,  more  prone 
to  act  as  a  ferment;  but  decompositLon  does  not  often  occur  unless 
atmospheric  germs  have  had  access  to  the  urine. 

Variations  in  the  Quantitfi  excreted. — The  quantity  of  urea  excreted 
is,  like  that  of  the  urine  itself,  subject  to  considerable  variation.  For 
a  healthy  adult  about  512.4  grains  (about  33.18  grms.)  per  diem  may  be 
taken  as  rather  a  high  average.  Its  percentage  in  healthy  urine  is  from 
1.5  to  2.5.  Its  amount  is  materially  influenced  by  diet,  being  greater 
when  animal  food  is  exclusively  used,  less  when  the  diet  is  mixed,  and 
least  of  all  with  a  vegetable  diet.  As  a  rule,  men  excrete  a  larger  quan- 
tity than  women,  and  persons  in  the  middle  periods  of  life  a  larger 
quantity  than  infants  or  old  people.     The  quantity  of  urea  excreted  by 


396  HANDBOOK    OF    PHYSIOLOGY. 

•children,  relatively  to  their  body-weight,  is  much  greater  than  by  adults; 
Thus  the  quantity  of  urea  excreted  per  kilogram  of  weight  was  found  to 
be,  in  a  child,  0.8  grm.;  in  an  adult  only  0.4  grm.  Regarded  in  this 
way,  too,  the  excretion  of  carbonic  acid  gives  similar  results,  the  pro- 
portions in  the  child  and  adult  being  as  82 :  34. 

The  quantity  of  urea  does  not  necessarily  increase  and  decrease  with 
that  of  the  urine,  tliough  on  the  whole  it  would  seem  that  whenever  the 
amount  of  urine  is  much  augmented,  the  quantity  of  urea  also  is  usually 
increased;  and  it  appears  that  the  quantity  of  urea,  as  of  urine,  may  be 
especially  increased  by  drinking  large  quantities  of  water.  In  various 
diseases  the  quantity  is  reduced  considerably  below  the  healthy  stan- 
dard, while  in  other  affections  it  is  above  it. 


Quantitative  Estimation. — There  are  two  chief  methods  of  estimating  the 
amount  of  urea  in  the  urine.  (1.)  By  decomposing  it  by  means  of  an  alkaline 
solution  of  sodium  hypobromite,  or  hypochlorite,  and  calculating  the  amount 
in  a  measured  quantity,  by  collecting  and  measuring  the  amount  of  nitrogen 
evolved  under  such  circumstances.  Urea  contains  nearly  half  its  weight  of 
nitrogen,  hence  the  amount  of  the  gas  collected  may  be  taken  as  a  measure  of 
the  urea  decomposed,  remembering  that  1  litre  of  nitrogen  at  the  standard 
temperature  and  pressure  weighs  14  X  -08936,  or  1.251  grms.  The  percentage 
of  urea  can  thus  be  readily  calculated  from  the  volume  of  nitrogen  evolved 
from  a  measured  quantity  of  the  urine,  but  this  calculation  is  avoided  by 
graduating  the  tube  in  which  the  nitrogen  is  collected  with  numbers  which 
indicate  the  corresponding  percentage  of  urea.  The  reaction  is  CONn  H4  -\- 
3NaBrO  +  2NaH0  =  3NaBr  +  3HoO  +  NaoCOs  +  N^.  (2. )  By  precipitating  the 
urea  by  adding  to  a  given  amount  of  urine,  freed  from  sulphates  and  phos- 
phates, a  standard  solution  of  mercuric  nitrate  from  a  burette,  vmtil  the  whole 
of  it  has  been  thrown  down  in  an  insoluble  form  ;  then  reading  oflF  the  exact 
amount  of  the  mercuric  nitrate  solution,  which  it  was  necessary  to  use.  As 
the  amount  of  urea  which  each  cubic  centimetre  of  the  standard  solution  will 
precipitate  is  previously  known,  it  is  easy  to  calculate  the  amount  in  the  sam- 
ple of  urine  taken.  The  precipitate  which  is  formed  was  generally  said  to  be 
composed  of  mercuric  oxide  and  urea.  Some,  liowever,  now  consider  that  it 
is  a  mixture  of  mercuric  nitrate  itself  and  urea. 


Uric  Acid  (C5H4N4O3), — Uric  or  lithic  acid  is  rarely  absent  from 
the  urine  of  man  or  animals,  though  in  the  feline  tribe  it  seems  to  be 
sometimes  entirely  replaced  by  urea. 

Properties. — Uric  acid  when  pure  is  colorless,  but  when  deposited 
from  the  urine  is  yellowish-brown.  It  crystallizes  in  various  forms,  of 
which  the  most  common  are  smooth  transparent,  rhomboid  plates, 
diamond-shaped  plates,  hexagonal  tables,  etc.  (fig.  288).  It  is  odorless 
and  tasteless.  It  is  very  slightly  soluble  in  cold  water,  and  a  little  more 
so  in  hot  water,  quite  insoluble  in  alcohol  and  ether.  It  dissolves  freely 
in  solution  of  the  alkaline  carbonates  and  other  salts. 


EXCRETION.  ■  397 

The  proportionate  quantity  of  uric  acid  varies  considerably  in  different 
animals.  In  man,  and  Mammalia  generally,  especially  the  Herbivora,  it  is 
comparatively  small.  In  the  whole  tribe  of  birds,  and  of  serpents,,  on  the  other 
hand,  the  quantity  is  very  large,  greatly  exceeding  that  of  the  urea.  In  the 
urine  of  granivorous  birds,  indeed,  urea  is  rarely  if  ever  found,  its  place  being 
entirely  supplied  by  uric  acid. 

Variations  in  Qaanfitij. — The  quantity  of  uric  acid,  like  that  of 
nrea,  in  human  urine,  is  increased  by  the  use  of  animal  food,  and  de- 
creased by  the  use  of  food  free  from  nitrogen,  or  by  an  exclusively  vege- 
table diet.  In  most  febrile  diseases,  and  in  plethora,  it  is  formed  in 
unnaturally  large  quaiitities;  and  in  gout  it  is  deposited  in  and  around 
joints,  in  the  form  of  urate  of  soda,  of  which  the  so-called  chalk-stones; 
of  this  disease  are  principally  composed.  The  average  amount  secreted 
in  twenty-four  hours  is  about  one-third  of  a  gramme. 

Condition  in  the  Urine. — The  condition  in  which  uric  acid  exists  in 
solu  ion  in  the  urine  has  formed  the  subject  of  some  discussion.  The 
uric  acid  exists  as  urate  of  soda,  produced  by  the  uric  acid  as  soon  as  it 
is  formed  combining  with  part  of  the  base  of  the  alkaline  sodium  phos- 
phate of  the  blood.  Ilippuric  acid,  which  exists  in  human  urine  also,. 
acts  upon  the  alkaline  phosphate  in  the  same  way,  and  increases  still 
more  the  quantity  of  acixl  phosphate,  on  the  presence  of  which  it  is- 
probable  that  a  part  of  the  natural  acidity  of  the  urine  depends.  'It  is. 
scarcely  possible  to  say  whether  the  union  of  uric  acid  with  the  bases- 
sodium  and  ammonium  takes  place  in  the  blood,  or  in  the  act  of  secre- 
tion in  the  kidney:  the  latter  is  more  likely;  but  the  quantity  of  either 
uric  acid  or  urates  in  the  blood  is  probably  too  small  to  allow  of  this 
question  being  solved. 

Owing  to  its  existence  in  combination  in  healthy  urine,  uric  acid  for 
examination  must  generally  be  precipitated  from  its  bases  by  a  stronger 
acid,  e.g.,  hydrochloric  or  nitric.  When  excreted  in  excess,  however,  it 
is  deposited  in  a  crystalline  form  (fig.  288),  mixed  with  large  quanti- 
ties of  ammonium  or  sodium  urate.  In  such  cases  it  may  be  produced 
for  microscopic  examination  by  gently  warm^ing  the  portion  of  urine 
containing  the  sediment;  this  dissolves  urate  of  ammonium  and  sodium, 
while  the  comparatively  insoluble  crystals  of  uric  acid  subside  to  the 
bottom. 

The  most  common  form  in  which  uric  acid  is  deposited  in  urine,  is- 
that  of  a  brownish  or  yellowish  powdery  substance,  consisting  of  gran- 
ules of  ammonium  or  sodium  urate.  When  deposited  in  crystals,  it  is 
most  frequently  in  rhombic  or  diamond-shaped  lamina?,  but  other  forms- 
are  not  uncommon  (fig.  288).  When  deposited  from  urine,  the  crystals- 
are  generally  more  or  less  deeply  colored,  from  being  combined  with 
the  Coloring  principles  of  the  i^rine. 

Tests. — There  are  two  chief  tests  for  uric  acid  besides  the  micro- 


398 


HANDBOOK    OF    PHYSIOLOGY. 


scopic  evidence  of  its  crystalline  structure:  (1)  The  Mi<rexide  test, 
which  consists  of  evaporating  to  dryness  a  mixture  of  strong  nitric  acid 
and  uric  acid  in  a  water  bath.  This  leaves  a  yellowish-red  residue  of 
Alloxan  (C4H2N2O4)  and  urea,  and  on  addition  of  ammonium  hydrate,  a 
beautiful  purple  color  (ammonium  purpurate,  C8H4(NH4)N506),  deep- 
ened on  addition  of  caustic  potash,  takes  place.  (2)  Schiff's  test  con- 
sists of  dissolving  the  uric  acid  in  sodium  carbonate  solution,  and  of 
dropping  some  of  it  on  a  filter  paper  moistened  with  silver  nitrate.  A 
black  spot  appears,  which  corresponds  to  the  reduction  of  silver  by  the 
uric  acid. 

Hippuric  Acid    (C9H9NO3)   has  long  been  known  to  exist  in  the 
urine  of  herbivorous  animals  in  combination  with  soda.     It  also  exists 


Fig.  288.— Various  forms  of  uric  acid  crystals. 


Fig.  ;289.— Crystals  of  hippuric  acid. 


naturally  in  the  urine  of  man,  in  a  quantity  equal  or  rather  exceeding 
that  of  the  uric  acid. 

The  quantity  of  hippuric  acid  excreted  is  increased  by  a  vegetable 
diet.  It  appears  to  be  formed  in  the  body  from  benzoic  acid  or  from 
some  allied  substance.  The  benzoic  acid  unites  with  glycin,  probably 
in  the  kidneys,  and  hippuric  acid  and  water  are  formed  thus,  CrlleOa 
(Benzoic  acid)  +  C2H5NO2  (Glycin)  =  C9H9NO3  (Hippuric  acid)  +  H.O 
(water).     It  may  be  decomposed  by  acids  into  benzoic  acid  and  glycin. 

Properties. — It  is  a  colorless  and  odorless  substance  of  bitter  taste, 
crystallizes  in  semi-transparent  rhombic  prisms  (fig.  289).  It  is  more 
soluble  in  cold  water  than  uric  acid,  and  much  more  soluble  in  hot 
water.     It  is  soluble  in  alcohol. 

Pigments. — The  pigments  of  the  urine  are  the  following: — 1.  Uro- 
r/irowp,  a  yellow  coloring  matter,  giving  no  absorption  band;  of  which 
but  little  is  known.  Urine  owes  its  yellow  color  mainly  to  the  pres- 
ence of  this  body.  2.  Urobilin,  an  orange  pigment,  of  which  traces  may 
be  found  in  nearly  all  urines,  and  which  is  especially  abundant  in  the 
urines  passed  by  febrile  patients.  It  is  characterized  by  a  well-marked 
spectroscopic  absorption  band  at  the  junction  of  green  and  blue,  best 


EXCRETIOX.  399 

seen  in  acid  solutions;  and  by  giving  a  green  fluorescence  when  excess 
of  ammonia  with  a  little  chloride  of  zinc  is  added  to  it.  The  very 
vexed  question  of  the  relation  of  the  pigments  of  urine  to  bile  pigments 
turns  largely  upon  the  spectroscopic  appearances  of  urobilin ;  for  orange- 
colored  solutions  having  the  same  absorption  band  as  urobilin  may  be 
prepared  from  bile  pigments  in  two  different  ways — i,  by  reduction  with 
sodium  amalgam — Hijdrohiliruhin  (Maly);  ii,  by  oxidation  with  nitric 
acid — ClioleteUn  (Jaffe),  and  both  these  bile  derivatives  give  a  fluores- 
cence v»^ith  ammonia  and  a  drop  of  chloride  of  zinc.  It  is  not  satisfac- 
torily settled  which  of  these,  if  either,  is  the  same  as  urobilin  of  urine. 
It  is  worth  noting  that  choletelin  may  be  oxidized  a  stage  further;  it 
then  loses  its  absorption  band,  remaining  however  of  a  yellow  color.  It 
is  very  possible  that  the  urochrome  of  normal  urine  may  be  this  oxi- 
dized choletelin,  and  that  the  presence  of  the  absorption  band  of  urobilin 
in  urines  may  mean  that  some  of  the  pigment  is  in  the  stage  of  cholete- 
lin ;  i.e.,  that  its  oxidation  is  not  quite  completed. 

Those  who  believe  urobilin  to  be  identical  with  hydrobilirubm  sup- 
pose that  the  bilirubin  is  reduced  by  the  putrefactive  processes  in  the 
intestines,  and  is  conveyed  in  its  reduced  form  by  the  blood  stream  to 
the  kidneys. 

3.  Uro-erytJii-in  is  the  pigment  which  is  found  in  the  pink  de|)Osits 
of  urates  which  are  sometimes  seen  in  urines;  it  communicates  a  rich 
red-orange  color  to  urine  when  in  solution,  and  its  solutions  have  two 
broad  faint  absorption  bands  in  the  green. 

4.  Uromelanin.  When  urine  is  boiled  with  strong  acids  it  darkens 
to  a  reddish-brown  color.  This  change,  once  described  to  the  forma- 
tion of  a  new  pigment  uromelanin,  is  now  believed  to  be  due  to  the 
presence  in  urine  of  pyrocatechin  aud  allied  bodies  which  are  capable 
of  taking  up  oxygen  when  boiled  with  acids,  yielding  CO2  and  brown 
or  black  residual  products. 

5.  Indigo  is  rarely  found  in  urines,  to  which  it  may  communicate  a 
blue  or  green  color.  Urine  frequently  contains  a  compound  which  is 
either  a  g\\xco?>id.e,  Indiccm;  or  more  probably  a  salt  of  indoxyl-sulphuric 
acid.  It  yields  indigo  blue  when  treated  with  strong  hydrochloric  acid 
and  left  to  stand  for  some  hours  exposed  to  the  air;  the  indigo  may  be 
separated  by  treatment  with  boiling  chloroform,  which  takes  it  up, 
forming  a  blue  solution. 

There  is  a  similar  compound  of  skatol  and  sulphuric  acid  which  is 
sometimes  recognized  in  the  urine,  by  the  production  of  a  red  color 
when  nitric  acid  is  added  to  it. 

Many  medicinal  substances  color  the  urine,  for  instance  Rhubarb, 
Santonin,  Senna,  Fuchsine,  Carbolic  Acid. 

Bromides  and  Iodides  yield  Bromine  or  Iodine,  when  nitric  acid  is 
added  to  the  urine  of  patients  taking  these  drugs.     In  the  case  of  iodides 


400  HANDBOOK    OF    PHYSIOLOGY. 

the  liberated  iodine  communicates  a  strong  mahogany  color  to  the  urine 
thus  treated. 

Mucus. — Mucus  in  the  urine  consists  principally  of  the  epithelial 
debris  from  the  mucous  surface  of  the  urinary  passages.  Particles  of 
epithelium,  in  greater  or  less  abundance,  may  be  detected  in  most  sam- 
ples of  urine,  especially  if  it  has  remained  at  rest  for  some  time,  and  the 
lower  strata  are  then  examined  (fig.  290).  As  urine  cools,  the  mucus  is. 
sometimes  seen  suspended  in  it  as  a  delicate  opaque  cloud,  but  generally 
it  falls.  In  inflammatory  affections  of  the  urinary  passages,  especially 
of  the  bladder,  mucus  in  large  quantities  is  poured  forth,  and  speedily 
undergoes  decomjjosition.  The  presence  of  the  decomposing  mucus- 
excites  chemical  changes  in  the  urea,  whereby  carbonate  of  ammoniumi 
is  formed,  which,  combining  with  the  excess  of  acid  in  the  superphos- 
phates in  the  urine,  produces  insoluble  neutral  or  alkaline  phosiDhates 
of  calcium  and  magnesium,  and  phosphate  of  ammonium  and  magne- 
sium. These,  mixing  with  the  mucus,  constitute  the  peculiar  white, 
viscid,  mortar-like  substance  which  collects  upon  the  mucous  surface  of 
the  bladder,  and  is  often  passed  with  the  urine,  forming  a  thick  tena- 
cious sediment. 

Extractives. — In  addition  to  those  already  considered,  urine  cow- 
tains  a  considerable  number  of  nitrogenous  compounds.  These  are 
usually  described  under  the  generic  name  of  Extractives.  Of  these,  the 
chief  are:  (1)  Kreatinin  (C4H7N3O),  a  substance  derived,  probably,  from 
the  metamorj^hosis  of  muscular  tissue,  crystallizing  in  colorless  oblique 
rhombic  prisms;  a  fairly  definite  amount  of  this  substance,  about  15 
grains  (1  grm.),  appears  in  the  urine  daily,  so  that  it  must  be  looked 
upon  as  a  normal  constituent;  it  is  increased  on  an  increase  of  the 
nitrogenous  constituents  of  the  food;  (2)  Xanthin  (C5N4H4O2),  when 
isolated,  is  an  amorjDhous  powder  soluble  in  hot  water;  (3)  SarTcin, 
or  hypo-xantliin  (C5N4H4O);  (4)  Oxalnric  acid  (C3H4N2O4),  in  combi- 
nation with  ammonium  in  the  urine  of  the  new-born  child;  (5)  Allantoin 
(C4H6N4O3).  All  these  extractives  are  chiefly  interesting  as  being  closely 
connected  with  urea,  and  mostly  yielding  that  substance  on  oxidation. 
Leucin  and  tyrosin  can  scarcely  be  looked  ujjon  as  normal  constitueiits 
of  urine. 

Saline  Matter. — (a)  The  Sulphuric  acid  in  the  urine  is  combined 
chiefly  or  entirely  with  sodium  or  potassium;  forming  salts  which  are 
taken  in  very  small  quantity  with  the  food,  and  are  scarcely  found  in 
other  fluids  or  tissues  of  the  body;  for  the  sulphates  commonly  enumer- 
ated among  the  constituents  of  the  ashes  of  the  tissues  and  fluids  are 
for  the  most  part,  or  entirely,  produced  by  the  changes  that  take  place 
in  the  burning.  Only  about  one-third  of  the  sulphuric  acid  found  in 
the  urine  is  derived  directly  from  the  food  (Parkes).  Hence  the  greater 
part  of  the  sulphuric  acid  which  the  sulphates  in  the  urine  contain. 


EXCRETIO]Sr. 


401 


must  be  formed  in  the  blood,  or  in  the  act  of  secretion  of  urine ;  the 
sulj^hur  of  which  the  acid  is  formed  being  probably  derived  from  the 
decomposing  nitrogenous  tissues,  the  other  elements  of  which  are  re- 
solved into  urea  and  uric  acid.  It  may  be  in  part  derived  also  from  the 
sulphur-holding  taurin  and  n/.sii)i,  which  can  be  found  in  the  liver, 
lungs,  and  other  parts  of  the  body,  but  not  generally  in  the  excretions; 
and  which,  therefore,  must  be  broken  up.  The  oxygen  is  supplied 
through  the  lungs,  and  the  heat  generated  during  combination  with  the 
sulphur  is  one  of  the  subordinate  means  by  which  the  animal  tempera- 
ture is  maintained. 

Besides  the  sulphur  in  these  salts,  some  also  appears  to  be  in  the 
urine  uncombined  with  oxygen;  for  after  all  the  sulphates  have  been 
removed  from  urine,  sulphuric  acid  may  be  formed  by  drying  and  burn- 


Fig.  290. 


Fig.  291. 


Fig.  290. — Mucus  deposited  from  urine. 

Fig.  291. — Urinarj'  sediment  of  triple  phosphates  (large  'prismatic  crystals)  and  urate  of  ammo- 
nium, from  urine  which  had  undergone  alkaline  fermentation. 


ing  it  with  nitre.  From  three  to  five  grains  of  sulphur  are  thus  daily 
excreted.  The  combination  in  which  it  exists  is  uncertain :  possibly  it 
is  in  some  compound  analogous  to  cystin  or  cystic  oxide.  Sulphuric 
acid  also  exists  normally  in  the  urine  in  combination  with  phenol 
(C'eHeO)  as  phenol-sulphuric  acid  or  its  corresponding  salts,  with 
sodium,  etc. 

(1)  The  pliospTioric  acid  in  the  urine  is  combined  jjartly  with  the 
alkalies,  partly  with  the  alkaline  earths — about  four  or  five  times  as 
much  with  the  former  as  with  the  latter.  In  blood,  saliva,  and  other 
alkaline  fluids  of  the  body,  phosi^hates  exist  in  the  form  of  alkaline, 
neutral,  or  acid  salts.  In  the  urine  they  are  acid  salts,  viz.,  the  sodium, 
ammonium,  calcium,  and  magnesium  phosphates,  the  excess  of  acid 
being  (Liebig)  due  to  the  appropriation  of  the  alkali  with  which  the 
phosphoric  acid  in  the  blood  is  combined,  by  the  several  new  acids 
which  are  formed  or  discharged  at  the  kidneys,  namely,  the  uric,  hip- 
puric,  and  sulphuric  acids,  all  of  which  are  neutralized  with  soda, 
26 


402 


HANDBOOK    OF    PHYSIOLOGY. 


The  phosphates  are  taken  largely  in  both  vegetable  and  animal  food; 
some  thus  taken  are  excreted  at  once;  others,  after  being  transformed 
and  incorporated  with  the  tissues.  Calcium  phosphate  forms  the  prin- 
cipal earthy  constituent  of  bone,  and  from  the  decomposition  of  the 
osseous  tissue  the  urine  derives  a  large  quantity  of  this  salt.  The  de- 
composition of  other  tissues  also,  but  especially  of  the  brain  and  nerve- 
substance,  furnishes  large  supplies  of  phosjihorus  to  the  urine,  which 
pliosphorus  is  supposed,  like  the  sulphur,  to  be  united  with  oxygen,  and 
tlien  combined  with  bases.  This  quantity  is,  however,  liable  to  consid- 
erable variation.  Any  undue  exercise  of  the  brain  and  all  circumstances 
producing  nervous  exhaustion  increase  it.  The  earthy  jjhosphates  are 
more  abundant  after  meals,  whether  of  animal  or  vegetable  food,  and 
are  diminished  after  long  fasting.     The  alkaline  phosphates   are    in- 


Fig.  292.— Crystals  of  Cjstiii. 


Fig:.  293.— Crj'stals  of  Calcium  Oxalate. 


creased  after  animal  food,  diminished  after  vegetable  food.  Exercise 
increases  the  alkaline,  but  not  the  earthy  phosphates.  Phosphorus 
uncombined  with  oxygen  appears,  like  sulphur,  to  be  excreted  in  the 
urine.  When  the  urine  undergoes  alkaline  fermentation  phosphates  are 
deposited  in  the  form  of  a  urinary  sediment,  consisting  chiefly  of 
ammonio-mangesium  phosphates  (triple  phosphate)  (fig.  291).  This 
compound  does  not,  as  such,  exist  in  healthy  urine.  The  ammonia  is 
chiefly  or  wholly  derived  from  the  decomposition  of  urea. 

(r.)  The  Chlorine' ol  the  urine  occurs  chiefly  in  combination  with 
sodium  (next  to  urea,  sodium  chloride  is  the  most  abundant  solid  con- 
stituent of  the  urine),  but  slightly  also  with  ammonium,  and,  perhaps, 
potassium.  As  the  chlorides  exist  largely  in  food,  and  in  most  of  the 
animal  fluids,  their  occurrence  in  the  urine  is  easily  understood. 

Occasional  Constituents.— (7?/.?^m  (C3H7N  SO2)  (fig.  292)  is  an 
occasional  constituent  of  urine.  Tt  resembles  taurin  in  containing  a 
large  quantity  of  sulphur— more  than  25  per  cent.  It  does  not  exist  in 
hetdthy  urine. 

Another  common  morbid  constituent  of  the  urine  is   Oxalic  acid, 


EXCKETION.  403 

which  is  frequently  deposited  in  combination  with  calcium  (fig.  293)  as 
a  urinary  sediment.  Like  cystin,  but  much  more  commonly^  it  is  the 
chief  constituent  of  certain  calculi. 

Of  the  other  abnormal  constituents  of  the  urine  which  were  men- 
tioned on  p.  393,  it  will  be  unnecessary  to  speak  at  length  in  this  work. 

Gases. — A  small  quantity  of  gas  is  naturally  present  in  the  urine  in 
a  state  of  solution.  It  consists  of  carbonic  acid  (chiefly)  and  nitrogen 
and  a  small  quantity  of  oxygen. 

The  Method  of  the  Excretion  of  Urine. 

The  excretion  of  the  urine  by  the  kidney  is  believed  to  consist  of 
two  more  or  less  distinct  processes — viz.,  (1)  of  Filtration,  by  which 
the  water  and  the  ready-formed  salts  are  eliminated;  and,  (2)  of  True 
Secretion,  by  which  certain  substances  forming  the  chief  and  more  im- 
portant part  of  the  uriruiry  solids  are  removed  from  the  blood.  This 
division  of  function  corresponds  more  or  less  to  the  division  in  the 
functions  of  other  glands  of  which  we  have  already  treated.  It  will  be 
as  well  to  consider  them  separately. 

Filtration. — This  part  of  the  renal  function  is  performed  within 
the  Malpighian  corpuscles  by  the  renal  glomeruli.  By  it  not  only  the  water 
is  strained  off,  but  also  certain  other  constituents  of  the  urine,  e.g., 
sodium  chloride,  are  separated.  The  amount  of  the  fluid  filtered  off  de- 
pends almost  entirely  upon  the  blood-jDressure  in  the  glomeruli. 

The  greater  the  blood-pressure  in  the  arterial  system  generally,  and 
consequently  in  the  renal  arteries,  the  greater,  cceteris  j^aribiis,  will  be 
the  blood-pressure  in  the  glomeruli,  and  the  greater  the  quantity  of 
urine  separated;  but  even  without  increase  of  the  general  blood-pres- 
sure, if  the  renal  arteries  be  locally  dilated,  the  pressure  in  the  glomeruli 
will  be  increased  and  with  it  the  secretion  of  urine.  All  the  causes, 
therefore,  which  increase  the  general  blood-pressure  will  secondarily 
increase  the  secretion  of  urine.     Of  these — 

(1)  The  heart's  action  is  amongst  the  most  important.  When  the 
cardiac  contractions  are  increased  in  force  or  frequency,  increased 
diuresis  is  the  result. 

(2)  Since  the  connection  between  the  general  blood-pressure  and  the 
nervous  system  is  so  close  it  will  be  evident  that  the  amount  of  urine 
secreted  depends  greatly  upon  the  influence  of  the  latter.  This  may  be 
demonstrated  experimentally.  Thus,  division  of  the  spinal  cord,  by 
producing  general  vascular  dilatation,  causes  a  great  diminution  of  blood- 
pressure,  and  so  diminishes  the  amount  of  water  passed;  since  the  local 
dilatation  in  the  renal  arteries  is  not  sufficient  to  counteract  the  general 
diminution  of  pressure.  Stimulation  of  the  cut  cord  produces,  strangely 
enough,  the  same  results — i.e.,  a  diminution  in  the  amount  of  the  urine 


404 


HANDBOOK    OF    PHYSIOLOGY. 


passed,  but  in  a,  different  way,  viz.,  by  constricting  the  arteries  generally, 
and,  among  others,  the  renal  arteries;  the  diminution  of  blood-pressure 
resulting  from  tlie  local  resistance  in  the  renal  arteries  being  more 
potent  to  diminish  blood-pressure  in  the  glomeruli  than  the  general 
increase  of  blood-pressure  is  to  increase  it.  Section  of  the  renal  nerves 
which  produces  local  dilatation  without  greatly  diminishing  the  general 
blood-pressure  will  cause  an  increase  in  the  quantity  of  fluid  passed. 

(3)  The  fact  that  in  summer  or  in  hot  weather  the  urine  is  dimin- 
ished may  be  attributed  partly  to  the  copious  elimination  of  water  by 
the  skin  in  the  form  of  sweat  which  occurs  in  summer,  as  contrasted 
with  the  greatly  diminished  functional  activity  of  the  skin  in  winter, 


Fig.  294.— Diagram  of  Roy's  Oncometer,  o,  represents  tlie  kidney  inclosed  in  a  metal  box, 
which  opens  by  hinge/;  b,  the  renal  vessels  and  duct.  Surrounding  the  kidney  are  two  chambers 
formed  by  membranes,  the  edges  of  which  are  tirmly  fixed  by  being  clamped  between  the  outside 
metal  capsule,  and  one  mot  representeil  in  the  figiwe)  inside,  the  two  being  firmly  screwed  together 
by  screws  at  /i,  and  below.  The  membranous  chamber  below  is  filled  witli  a  varying  amount  of 
warm  oil,  accorchng  to  the  size  of  tl.e  kiilney  experimented  with,  through  ihe  opening  then  closed 
with  the  plug  i.  After  the  kidney  has  been  inclosed  in  the  capsule,  the  membrano'is  chamber  above 
is  filled  with  warm  oil  through  the  tube  e,  which  is  then  closed  by  a  tap  (not  represented  in  the 
diagram);  the  tube  d  communicates  with  a  recording  apparatus,  and  any  alteration  in  the  volume 
of  tne  kidney  is  communicated  by  the  oil  in  the  tube  to  the  chamber  d  of  the  Oncograph,  fig.  295. 

but  also  to  the  dilated  condition  of  the  vessels  of  the  skin  causing  a 
decrease  in  the  general  blood-pressure.  Thus  we  see  that  in  regard  to 
the  elimination  of  water  from  the  system,  the  skin  and  kidneys  perform 
similar  functions,  and  are  capable  to  some  extent  of  acting  vicariously, 
one  for  the  other.  Their  relative  activities  are  inversely  jji-oportional 
to  each  other. 

The  intimate  conuection  which  exists  between  the  volume  of  the  kidney 
and  the  variations  of  blood -pressure  is  exceedingly  w^ell  shown  with  the 
Oncometer,  introduced  by  Roy,  which  is  a  modification  of  the  plethysmo- 
graph,  fig.  394.  By  means  of  this  apparatus  any  alteration  in  the  volume  of 
the  kidney  is  communicated  to  an  apparatus  [oncograph],  capable  of  recording 
graphically,  with  a  writing  lever,  siich  variations. 


EXCRETION. 


405 


It  has  been  found  that  the  kidney  is  extremely  sensitive  to  any 
alteration  in  the  general  blood-pressure,  every  fall  in  the  general  blood- 
pressure  being  accompanied  by  a  decrease  in  the  volume  of  the  kidney, 
and  every  rise,  unless  produced  by  considerable  constriction  of  the 
peripheral  vessels,  including  those  of  the  kidney,  being  accomjaanied  by 
a  corresponding  increase  of  volume.  Increase  of  volume  is  followed 
uy  an  increase  in  the  amount  of  urine  secreted,  and  decrease  of  volume 
by  a  decrease  in  the  secretion.  In  addition,  however,  to  the  response  of 
the  kidney  to  alterations  in  the  general  blood-pressure,  it  has  been 
further  observed  that  certain  substances,  when  injected  into  the  blood, 
will  also  produce  an  increase  in  volume  of  the  kidney,  a;id  consequent 
increased  flow  of  urine,  without  affecting  the  general  blood-pressure — 


Fig:.  295. — Roy's  Oncograph,  or  apparatus  for  recording  alterations  in  the  volume  of  the  kidney, 
etc.,  as  shown  by  the  oncometer — (,',  upright,  supporting  recording  lever  I,  which  is  raised  or  lowered 
by  needle  b,  which  works  through/,  and  which  is  attached  to  the  piston  e,  worlving  in  the  chamber 
d.  witli  which  the  tube  from  the  oncometer  comnumicates.  The  oil  is  preventi'd  fi(  mi  lii-ing  squeezed 
out  as  tlie  piston  descends  by  a  meaibraue,  which  is  clamped  between  the  ring-shaped  surfaces  of 
cylinder  by  the  screw  i  worliing  upward;  the  tube  h  is  for  filling  the  instrument. 


such  bodies  as  sodium  acetate  and  other  diuretics.  These  observations 
appear  to  prove  that  local  dilatation  of  the  renal  vessels  may  be  produced 
by  alterations  in  the  blood  acting  upon  a  local  nervous  mechanism,  as  this 
happens  when  all  of  the  renal  nerves  have  been  divided.  The  altera- 
tions are  not  only  produced  by  the  addition  of  drugs,  but  also  by  the  in- 
troduction of  comparatively  small  quantities  of  water  or  saline  solution. 
To  this  alteration  of  the  blood  acting  upon  the  renal  vessels  (either 
directly  or)  through  a  local  vaso-motor  mechanism,  and  not  to  any  great 
alteration  in  the  general  blood -pressure,  must  we  attribute  the  effects  of 
meals,  etc.,  observed  by  Roberts.  The  renal  excretion  is  increased  after 
meals  and  diminished  during  fasting  and  sleep.  The  increase  begins 
within  the  first  hour  after  breakfast,  and  continues  during  the  succeed- 
ing two  or  three  hours;  then  a  diminution  sets  in,  and  continues  until 
an  hour  or  two  after  dinner.     The  effect  of  dinner  does  not  appear  until 


406  HANDBOOK    OF    PHYSIOLOGY. 

two  or  three  hours  after  the  meal;  and  it  reaches  its  maximum  about 
the  fourth  hour.  From  this  period  the  excretion  steadily  decreases 
until  bed-time.  During  sleep  it  sinks  still  lower,  and  reaches  its  mini- 
mum— being  not  more  than  one-third  of  the  quantity  excreted  during 
the  hours  of  digestion.  The  increased  amount  of  urine  passed  after 
drinking  large  quantities  of  fluid  probably  depends  upon  the  diluted 
condition  of  the  blood  thereby  induced. 

The  following  table  *  will  help  to  explain  the  dependence  of  the 
filtration  function  upon  the  blood-pressure  and  the  nervous  system: — 

Table  of  the  jielation  of  the  secretion  of  Urine  to  Arterial  Pressure. 

A.  Secretion  of  urine  may  be  increased— 

a.   By  increasing  the  general  blood-pressure;  by 

1.  Increase  of  the  force  or  frequency  of  heart-beat, 

2.  Constriction  of  the  small   arteries  of  areas  other  than  that  of  the 

kidney. 
h.   By   increasing   the    local   blood-pressure,    by    relaxation    of   tlie    renal 
artery,  -without  compensating  relaxation  el'seivhere ;  by 

1.  Division  of  the  renal  nerves  (causing  polj'uria). 

2.  Division  of  the  renal  nerves  and  stimulation  of  the  cord,  below 

tlie  medulla  (causing  greater  polyuria) . 

3.  Division  of  the  splanchnic   nerves  ;    but  the  polyuria  produced  is 

less  than  in  1  or  2,  as  these  nerves  are  distributed  to  a  wider 
area,  and  tlie  dilatation  of  the  renal  arterj^  is  accompanied  by 
dilatation  of  other  vessels,  and  therefore  with  a  somewhat  di- 
minished general  blood  supply. 

4.  Puncture  of  the  floor  of  fourth  ventricle  or  mechanical  irritation 

of  the  superior  cervical  ganglion  of  the  sympathetic,  possibly 
from  the  production  of  dilation  of  the  renal  arteries. 

B.  Secretion  of  urine  may  be  diminished 

a.  By  diminishing  the  general  blood-pressiire;  by 

1.  Diminution  of  tlie  force  or  frequency  of  the  heart-beats. 

2.  Dilatation  of  capillary  areas  other  than  that  of  the  kidney. 

3.  Division  of  spinal  cord  below  the  inedulla,  which  causes  dilata- 

tion of  general  abdominal  area,    and  urine  generally   ceases 
being  secreted. 
6.  By  increasing  the  blood-presstire,  by  stimulation  of  the  spinal  cord 
below^  the  medulla,  the  constriction  of  the  renal  arterj^,  which  follows, 
not  being  compensated  for  by  the  increase  of  general  blood -pressure. 
c.  By   constriction   of  the    renal   artery,    by    stimulating    the    renal    or 
splanchnic  nerves,  or  the  spinal  cord. 

Although  it  is  convenient  to  call  the  processes  which  go  on  in  the 
renal  glomeruli,  filtration,  there  is  reason  to  believe  that  they  are  not 
absolutely  mechanical,  as  the  term  might  seem  to  imply,  since,  when  the 
epithelium  of  the  Malpighian  capsule  has  been,  as  it  were,  put  out  of 


*  Modified  from  Foster. 


EXCRETION". 


407 


order  by  ligature  of  the  renal  artery,  on  removal  of  the  ligature,  the 
urine  has  been  found  temporarily  to  contain  albumen,  indicating  that  a 
selective  power  resides  in  the  healthy  epithelium,  which  allows  certain 
constituent  parts  of  the  blood  to  be  filtered  oft',  and  not  others. 

Secretion. — That  there  is  a  second  part  in  the  process  of  the  excre- 
tion of  urine,  which  is  true  secretion,  is  suggested  by  the  structure  of 
the  tubnli  uriniferi,  tind  the  idea  is  supported  by  various  experiments. 
It  will  be  remembered  that  the  convoluted  portions  of  the  tubules  are 
lined  with  an  epithelium,  which  bears  a  close  resemblance  to  the  secre- 
tory epithelium  of  other  glands,  whereas  the  Malpighian  capsules  and 
portions  of  the  loops  of  Henle  are  lined  simply  by  flattened  epithelium. 
The  two  functions  of  the  different  parts  of  an  uriniferous  tube  are,  then, 
suggested  by  the  ditTerences  of  epithelium,  and  also  by  the  fact  that  the 
blood  supply  to  the  different  parts  is  different,  since,  as  we  have  seen, 


Fig.  296. — Curve  taken  by  renal  oncometer  compressed — with  that  of  ordinary  blood-pressure, 
o,  Kidney  curve;  6,  blood-pressure  curve.    (Roy.) 


the  convoluted  tubes  are  surrounded  by  capillary  vessels  derived  from 
the  breaking  up  of  the  efferent  vessels  of  the  Malpighian  tufts.  As  to 
the  functions  of  the  different  parts  of  the  uriniferous  tubes  in  the 
secretion  of  urine,  two  chief  theories  have  been  brought  forward.  The 
first,  suggested  by  Bowman  (1843),  and  still  generally  accepted,  is  that 
the  cells  of  the  convoluted  tubes,  by  a  process  of  true  secretion,  separate 
from  the  blood  substances  such  as  urea,  whereas  from  the  glomeruli 
are  separated  the  water  and  the  inorganic  salts.  The  second,  suggested 
by  Ludwig  (1844),  is  that  in  the  glomeruli  are  filtered  off  from  the 
blood  all  the  constituents  of  the  urine  in  a  very  diluted  condition. 
When  this  passes  along  the  tortuous  uriniferous  tube,  part  o£  the  water 
is  re-absorbed  into  the  vessels  surrounding  them,  leaving  the  urine  in 
a  more  concentrated  condition — retaining  all  its  proper  constituents. 
This  osmosis  is  j)romoted  by  the  high  specific  gravity  of  the  blood  in 
the  capillaries  surrounding  the  convoluted  tubes,  but  the  return  of  the 
urea  and  similar  substances  is  prevented  by  the  secretory  epithelium  of 
the  tubules.  The  first  theory  is,  however,  more  strongly  supported  by 
direct  experiment. 

By  using  the  kidney  of  the  newt,  which  has  two  distinct  vascular 


408  HANDBOOK    OF    PHYSIOLOGY. 

supplies,  one  from  the  renal  artery  to  the  glomeruli,  and  the  other  from 
the  renal-portal  vein  to  the  convoluted  tubes,  Nussbaum  has  shown  that 
certain  substances,  e.g.,  peptones  and  sugar,  when  injected  into  the 
blood,  are  eliminated  by  the  glomeruli,  and  so  are  not  got  rid  of  when 
the  renal  arteries  are  tied;  whereas  certain  other  substances,  e.g.,  urea, 
when  injected  into  the  blood,  are  eliminated  by  the  convoluted  tubes, 
even  when  the  renal  arteries  have  been  tied.  This  evidence  is  very 
direct  that  urea  is  excreted  by  the  convoluted  tubes,  that  is  to  say,  if  it 
is  certain  that  ligature  of  the  renal  artery  assists  the  circulation  through 
the  glomeruli,  which,  however,  is  denied  by  Adami. 

Heidenhain  also  has  shown  by  experiment  that  if  a  substance  (sodium 
sulph-indigotate),  which  ordinarily  produces  blue  urine,  be  injected 
into  the  blood  after  section  of  the  medulla  which  causes  lowering  of  the 
blood-pressure  in  the  renal  glomeruli,  that  when  the  kidney  is  examined, 
the  cells  of  the  convoluted  tubules  (and  of  these  alone)  are  stained  with 
the  substance,  which  is  also  found  in  the  lumen  of  the  tubules.  This 
appears  to  show  that  under  ordinary  circumstances  the  pigment  at  any 
rate  is  eliminated  by  the  cells  of  the  convoluted  tubules,  and  that  when 
by  diminishing  the  blood-pressure,  the  filtration  of  urine  ceases,  the 
pigment  remains  in  the  convoluted  tubes,  and  is  not,  as  it  is  under 
ordinary  circumstances,  swept  away  from  them  by  the  flushing  of  them 
which  ordinarily  takes  place  with  the  watery  part  of  urine  derived  from 
the  glomeruli.  It  therefore  is  jirobable  that  the  cells,  if  they  excrete 
the  pigment,  excrete  urea  and  other  substances  also.  But  urea  acts 
somewhat  differently  to  the  pigment,  as  when  it  is  injected  into  the 
blood  of  an  animal  in  which  the  medulla  has  been  divided,  and  the 
secretion  of  urine  stopped,  a  copious  secretion  of  urine  results,  which 
is  not  the  case  when  the  pigment  is  used  instead  under  similar  condi- 
tions. The  flow  of  urine,  independent  of  the  general  blood-pressure, 
might  be  supposed  to  be  due  to  the  action  of  the  altered  blood  upon 
some  local  vaso-motor  mechanism;  and,  indeed,  the  local  blood-pressure 
is  directly  affected  in  this  way,  but  there  is  reason  for  believing  that 
part  of  the  increase  of  the  secretion  is  due  to  the  direct  stimulation  of 
the  cells  by  the  urea  continued  in  the  blood. 

To  sum  up, then, the  relation  of  the  two  functions:  (1.)  The  process 
of  filtration,  by  which  the  chief  part,  if  not  the  whole,  of  the  fluid  is 
eliminated,  together  with  certain  inorganic  salts  and  possibly  other 
solids,  is  directly  dependent  upon  blood-pressure,  is  accomplished  by 
the  renal  glomeruli,  and  is  accompanied  by  a  free  discharge  of  solids 
from  the  tubules.  (2.)  The  process  of  secretion  proper,  by  which  urea 
and  the  principal  urinary  solids  are  eliminated,  is  only  indirectly,  if  at 
all,  dependent  upon  blood-pressure,  is  accomplished  by  the  cells  of  the 
convoluted  tubes,  and  is  sometimes  (as  in  the  case  of  the  elimination  of 
urea  and  similar  substances)  accompanied  by  the  elimination  of  copious 


EXCKETION.  409 

fluid,  produced  by  the  chemical  stimulation  of  the  epithelium  of  the 
same  tubules. 

The  Passage  of  Urine  into  the  Bladder. 

As  each  portion  of  urine  is  secreted  it  propels  that  which  is  already 
in  the  uriniferous  tubes  onward  into  the  pelvis  of  the  kidney.  Theuce 
through  the  ureter  the  urine  passes  into  the  bladder,  into  which  its  rate 
and  mode  of  entrance  has  been  watched  in  cases  of  ectopia  vesicce,  i.e., 
of  such  tissures  in  the  anterior  or  lower  j^art  of  the  walls  of  the  abdo- 
men, and  of  the  front  wall  of  the  bladder,  as  expose  to  view  its  hinder 
wall  together  with  the  orifices  of  the  ureters.  The  urine  does  not  enter 
the  bladder  at  any  regular  rate,  nor  is  there  a  synchronism  in  its  move- 
ment through  the  two  ureters.  During  fasting,  two  or  three  drojDS 
enter  the  bladder  every  minute,  each  drop  as  it  enters  first  raising  up 
the  little  papilla  on  which,  in  these  cases,  the  ureter  opens,  and  then 
passing  slowly  through  its  orifice,  which  at  once  again  closes  like  a 
sphincter.  In  the  recumbent  posture,  the  urine  collects  for  a  little  time 
in  the  ureters,  then  flows  gently,  and,  if  the  body  be  raised,  runs  from 
them  in  a  stream  till  they  are  empty.  Its  flow  is  aided  by  the  peristaltic 
contractions  of  the  ureters,  and  is  increased  in  deep  inspiration,  or  by 
straining,  and  in  active  exercise,  and  in  fifteen  or  twenty  minutes  after 
a  meal.  The  urine  collecting  is  jarevented  from  regurgitation  into  the 
ureters  by  the  mode  in  which  these  pass  through  the  walls  of  the  blad- 
der, namely,  by  their  lying  for  between  half  and  three-quarters  of  an 
inch  between  the  muscular  and  mucous  coats  before  they  turn  rather 
abruptly  forward,  and  oj^en  through  the  latter  into  the  interior  of  the 
bladder. 

Micturition. — The  contraction  of  the  muscular  walls  of  the  bladder 
may  by  itself  expel  the  urine  with  little  or  no  help  from  other  muscles. 
In  so  far,  however,  as  it  is  a  voluntary  act,  it  is  performed  by  means  of 
the  abdominal  and  other  expiratory  muscles,  which  in  their  contraction, 
as  before  explained,  press  on  the  abdominal  viscera,  the  diaphragm  being 
fixed,  and  cause  the  expulsion  of  the  contents  of  those  whose  siDhincter 
muscles  are  at  the  same  time  relaxed.  The  muscular  coat  of  the  blad- 
der co-operates,  in  micturition,  by  reflex  involuntary  action,  with  the 
abdominal  muscles;  and  the  act  is  completed  hy  the  accelerator  urinm, 
which,  as  its  name  implies,  quickens  the  stream,  and  expels  the  last 
drop  of  urine  from  the  urethra.  The  act,  so  far  as  it  is  not  directed  by 
volition,  is  under  the  control  of  a  nervous  centre  in  the  lumbar  spinal 
cord,  through  which,  as  in  the  case  of  the  similar  centre  for  defaecation, 
the  various  muscles  concerned  are  harmonized  in  their  action.  It  is 
well  known  that  the  act  may  be  reflexly  induced,  e.g.,  in  children  who 
suffer  from  intestinal  worms,  or  other  such  irritation.     Generally  the 


410  HANDBOOK    OF    PHYSIOLOGY. 

afferent  impulse  which  calls  into  action  the  desire  to  micturate  is  excited 
by  over-distentiou  of  the  bladder,  or  even  by  a  few  drojDS  of  urine^ 
passing  into  the  urethra.  This  passes  up  to  the  lumbar  centre  (or  cen- 
tres) and  produces  on  the  one  hand  inhibition  of  the  sphincter  and  on 
the  other  hand  contraction  of  the  necessary  muscles  for  the  expulsion  of 
the  contents  of  the  bladder. 

The  Structure  and  Functions  of  the  Skin. 

The  skin  serves — (1),  as  an  external  integument  for  the  protection 
of  the  deeper  tissues,  and  (3),  as  a  sensitive  organ  in  the  exercise  of 
touch,  a  subject  to  be  considered  in  the  Chapter  on  the  Special  Senses; 
it  is  also  (3),  an  important  secretory  and  excretory,  and  (4),  an  absorb- 
ing organ,  already  noticed,  p.  412;  wliile  it  plays  an  important  part  in 
5)  the  regulation  of  the  temperature  of  the  body.  (See  the  Chapter  on 
Animal  Heat.) 

Structure. — The  skin  consists  principally  of  a  vascular  tissue  named 
the  corium,  derma,  or  cutis  vera,  and  of  an  external  covering  of  epithe- 
lium termed  the  epidermis  or  cuticle.  Within  and  beneath  tiie  corium 
are  imbedded  several  organs  with  special  functions,  namely,  .S'?yc?or(/(?ro%s 
glands,  seiaceous  glands,  and  hair  follicles ;  and  on  its  surface  are  sensi- 
tive papillcB.  The  so-called  appendages  of  the  skin — the  hair  and  nails 
— are  modifications  of  the  epidermis. 

Epidermis. — The  epidermis  is  composed  of  several  strata  of  cells  of 
various  shapes  and  sizes;  it  closely  resembles  in  its  structure  the  epithe- 
lium of  the  mucous  membrane  that  lines  the  mouth.  The  following 
four  layers  may  be  distinguished  in  a  more  or  less  developed  form.  1. 
Stratum  corneum  (fig.  297,  a),  consisting  of  superposed  layers  of  horny 
scales.  The  different  thickness  of  the  epidermis  in  different  regions  of 
the  body  is  chiefly  due  to  variations  in  the  thickness  of  this  layer;  e.g., 
on  the  horny  parts  of  the  jialms  of  the  hands  and  soles  of  the  feet  it  is 
of  great  thickness.  The  stratum  corneum  of  the  buccal  epithelium 
chiefly  differs  from  that  of  the  epidermis  in  the  fact  that  nuclei  are  to 
be  distinguished  in  some  of  the  cells  even  of  its  most  superficial  layers. 

2.  Stratum  lucidum,  a  bright  homogeneous  membrane  consisting  of 
squamous  cells  closely  arranged,  in  some  of  which  a  nucleus  can  be  seen. 

3.  Stratum  granulosum,  consisting  of  one  layer  of  flattened  cells 
which  appear  fusiform  in  vertical  section,  they  are  distinctly  nucleated, 
and  a  number  of  granules  extend  from  the  nucleus  to  the  margins  of 
the  cell. 

4.  Stratum  Malpighii  or  Rete  mucosmn  consists  of  many  strata. 
The  deepest  cells,  placed  immediately  above  the  cutis  vera,  are  columnar 
with  oval  nuclei:  this  layer  of  columnar  cells  is  succeeded  by  a  number 
of  layers  of  more  or  less  polyhedral  cells  with  spherical  nuclei;  the  cells 


EXCRETION.  411 

of  the  more  superficial  layers  are  considerably  flattened.  The  deeper 
surface  of  the  rete  mucosum  is  accurately  adapted  to  the  i^apillse  of  the 
true  skin,  being,  as  it  were,  moulded  on  them.  It  is  very  constant  in 
thickness  in  ail  parts  of  the  skin.  The  cells  of  the  middle  layers  of 
the  stratum  Malpighii  are  almost  all  connected  by  processes,  and  thus 
form  prickle  cells  (fig.  35).  The  pigment  of  the  skin,  the  varying  quan- 
tity of  which  causes  the  various  tints  observed  in  difl'erent  individuals 
and  different  races,  is  contained  in  the  deeper  cells  of  rete  mucosum; 
the  pigmented  cells  as  they  approach  tlie  free  surface  gradually  losing 
their  color.     Epidermis  maintains  its  thickness  in  spite  of  the  constant 


...  .7 


0/ 

■I 


r\   \ 


Fig.  297.— Vertical  section  of  the  epidermis  of  the  prepuce,  a,  stratum  corneum,  of  very  few 
layers,  the  stratum  luciduni  anil  sti-atum  granulosum  not  being  distinctly  represented;  b.  c,  d  and  e, 
the  layers  of  the  stratum  .Alalpifj:!!!!.  a  certain  number  of  the  cells  in  layers  (/  and  e  showing  signs  of 
segmentation;  layer  c  consists  ohietly  of  prickle  or  ridge  and  furrow  cells;  /,  basement  membrane; 
g,  cells  in  cutis  vera.    (Cadiat.) 

wear  and  tear  to  which  it  is  subjected.  The  columnar  cells  of  the  deep- 
est layer  of  the  rete  mucosum  elongate,  and  their  nuclei  divide  into  two 
(fig.  297,  e).  Lastly  the  upper  part  of  the  cell  divides  from  the  lower; 
thus  from  a  long  columnar  cell  are  produced  a  polyhedral  cell  and  a 
short  columnar  cell:  the  latter  elongates  and  the  process  is  repeated. 
The  polyhedral  cells  thus  formed  are  pushed  up  toward  the  free  surface 
by  the  production  of  fresh  ones  beneath  them,  and  become  flattened 
from  pressure:  they  also  become  gradually  horny  by  evaporation  and 
transformation  of  their  protoplasm  into  ceratin,  till  at  last  by  rubbing 
in  ordinary  wear  and  tear  they  are  detached  as  dry  horny  scales  at  the 
free  surface.     There  is  thus  a  constant  production  of  fresh  cells  in  the 


412  HANDBOOK    OF    PHYSIOLOGY. 

deeper  layers,  and  a  constant  throwing  off  of  old  ones  from  the  free  sur- 
face. When  these  two  processes  are  accurately  balanced,  the  epidermis 
maintains  its  thickness.  When,  by  intermittent  pressure  a  more  active 
cell-growth  is  stimulated,  the  production  of  cells  exceeds  their  waste  and 
the  epidermis  increases  in  thickness,  as  we  see  in  the  horny  hands  of  the 
laborer. 

The  thickness  of  the  epidermis  on  the  different  portions  of  the  skin 
is  directly  proportioned  to  the  friction,  pressure,  and  other  sources  of 
injury  to  which  it  is  exposed;  for  it  serves  as  well  to  protect  the  sensi- 
tive and  vascular  cutis  from  injury  from  without,  as  to  limit  the  evap- 
oration of  fluid  from  the  blood-vessels.  The  adaptation  of  the  epider- 
mis to  the  latter  purposes  may  be  well  shown  by  exposing  to  the  air  two 
dead  hands  or  feet,  of  which  one  has  its  epidermis  perfect,  and  the 
other  is  deprived  of  it;  in  a  day,  the  skin  of  the  latter  will  become 
brown,  dry  and  horn-like,  while  that  of  the  former  will  almost  retain  its 
natural  moisture. 

Cutis  vera. — The  corium  or  cutis  vera,  which  rests  upon  a  layer  of 
adipose  and  cellular  tissue  of  varying  thickness,  is  a  dense  and  tough, 
but  yielding  and  highly  elastic  structure,  composed  of  fasciculi  of  areolar 
tissue,  interwoven  in  all  directions,  and  forming,  by  their  interlace- 
ments, numerous  spaces  or  areolae.  These  areolae  are  large  in  the  deeper 
layers  of  the  cutis,  and  are  there  usually  filled  with  little  masses  of  fat 
(fig.  398) :  but,  in  the  superficial  parts,  they  are  small  or  entirely  oblit- 
erated.    Unstriped  muscular  fibres  are  also  abundantly  present. 

Papillae. — The  cutis  vera  presents  numerous  conical  papillae,  with  a 
single  or  divided  free  extremity,  which  are  more  prominent  and  more 
densely  set  at  some  parts  than  at  others.  This  is  especially  the  case  on 
the  palmar  surface  on  the  hands  and  fingers,  and  on  the  soles  of  the  feet 
— parts,  therefore,  in  which  the  sense  of  touch  is  most  acute.  On  these 
parts  they  are  disposed  in  double  rows,  in  parallel  curved  lines,  separated 
from  each  other  by  depressions.  Thus  they  may  be  easily  seen  on  the 
palm,  whereon  each  raised  line  is  composed  of  a  double  row  of  papillae, 
and  is  intersected  by  short  transverse  lines  or  furrows  corresponding 
with  the  interspaces  between  the  successive  pairs  of  papillae.  Over 
other  parts  of  the  skin  they  are  more  or  less  thinly  scattered,  and  are 
scarcely  elevated  above  the  surface.  Their  average  length  is  about  yto 
of  an  inch  (^  mm.),  and  at  their  base  they  measure  about  -^  of  an 
inch  in  diameter.  Each  papilla  is  abundantly  supplied  with  blood,  re- 
ceiving from  the  vascular  plexus  in  the  cutis  one  or  more  minute  arte- 
rial twigs,  which  divide  into  capillary  loops  in  its  substance,  and  then 
reunite  into  a  minute  vein,  which  passes  out  at  its  base.  This  abun- 
dant supply  of  blood  explains  the  turgescence  or  kind  of  erection  which 
they  undergo  when  the  circulation  through  the  skin  is  active.  The 
majority,  but  not  all,  of  the  papillae  contain  also  one  or  more  terminal 


EXCRETIOJiT. 


413 


nerve-fibres,  from  the  ultimate  ramifications  of  the  cutaneous  plexus, 
on  which  their  exquisite  sensibility  depends. 

The  7ierve-terminations  in  the  skin  have  been  described  under  the 
Sensory  Xerve  Terminations  (p.  104  et  seq.). 

Glands  of  the  Skin. — The  skin  possesses  glands  of  two  kinds:  [a) 
Sudoriferous,  or  Sweat  Glands;  {b)  Sebaceous  glands. 

{a)  Sudoriferous,  or  Sweat  Glands. — Each  of  these  glands  consists 
of  a  small  lobular  mass,  formed  of  a  coil  of  tubular  gland-duct,  sur- 


c — 


7'rV^H^ 


w 


Fig.  298. — Vertical  section  of  skin.  A.  Sebaceous  gland  opening  into  hair  follicle.  B.  Muscular 
fibres.  C.  Sudoriferous  or  sweat-gland.  D.  Subcutaneous  fat.  E.  Fundus  of  hair-follicle,  with 
hair-papillae.    (Klein.) 

rounded  by  blood-vessels  and  embedded  in  the  subcutaneous  adipose 
tissue  (fig.  298,  C).  From  this  mass,  the  duct  ascends,  for  a  short  dis- 
tance in  a  spiral  manner  through  the  deeper  part  of  the  cutis,  then 
passing  straight,  and  then  sometimes  again  becoming  spiral,  it  passes 
through  the  epidermis  and  opens  by  an  oblique  valve-like  aperture. 
In  the  parts  where  the  epidermis  is  thin,  the  ducts  themselves  are 
thinner  and  more  nearly  straight  in  their  course  (fig.  298).  The  duct, 
which  maintains  nearly  the  same  diameter  throughout,  is  lined  M'ith  a 


414  HANDBOOK    OF    PHYSIOLOGY. 

layer  of  columnar  epithelium  (fig.  299)  continuous  with  the  epidermis; 
while  the  part  which  passes  through  the  epidermis  is  a  mere  passage 
through  the  epidermal  cells  not  being  bounded  by  any  special  lining; 
but  the  cells  which  immediately  form  the  boundary  of  the  canal  in  this 
part  are  somewhat  ditlerently  arranged  from  those  of  the  adjacent  cuti- 
cle. The  coils  or  terminal  portions  of  the  gland  are  lined  with  at  least 
two  layers  of  short  columnar  cells  with  very  distinct  nuclei  (fig.  299), 
and  possess  a  large  lumen  distinctly  bounded  by  a  special  lining  of 
cuticle. 

The  sudoriferous  glands  are  abundantly  distributed  over  the  whole 
surface  of  the  body;  but  are  especially  numerous,  as  well  as  very  large, 
in  the  skin  of  the  palm  of  the  hand  and  of  the  sole  of  the  foot.  The 
glands  by  which  the  peculiar  odorous  matter  of  the  axillae  is  secreted 


Fig.  299. — Terminal  tubules  of  sudoriferous  glands,  cut  in  various  directions  from  the  skin'^of  the 

pig's  ear.     (V.  D.  Harris.) 

form  a  nearly  complete  layer  under  the  cutis,  and  are  like  the  ordinary 
sudoriferous  glands,  except  in  being  larger  and  having  very  short  ducts. 

The  peculiar  bitter  yellow  substance  secreted  by  the  skin  of  the  ex- 
ternal auditory  jDassage  is  named  cerumen,  and  the  glands  themselves 
cernuiinous  glands;  but  they  do  not  much  differ  in  structure  from  the 
ordinary  sudoriferous  glands. 

{b)  Sebaceous  Glands. — The  sebaceous  glands  (figs.  298,  303),  like 
sudoriferous  glands,  are  abundant  in  most  parts  of  the  surface  of  the 
l)ody,  particularly  in  parts  largely  supplied  with  hair,  as  the  scalp  and 
face.  They  are  thickly  distributed  about  the  entrances  of  the  various 
passages  into  the  body,  as  the  anus,  nose,  lips,  and  external  ear.  They 
are  entirely  absent  from  the  palmar  surface  of  the  hand  and  the 
plantar  surfaces  of  the  feet.  They  are  racemose  glands  composed  of  an 
aggregate  of  small  tubes  or  sacculi  lined  with  columnar  epithelium  and 
filled  with  an  opaque  white  substance,  like  soft  ointment,  which  consists 
of  broken-up  epithelial  cells  which  have  undergone  fatty  degeneration. 
Minute   capillary  vessels  overspread  them;    and  their   ducts   open    on 


excretions". 


415 


•either  the  surface  of  the  skin,  close  to  a  hair,  or,  which  is  more  usual, 
directly  into  the  follicle  of  the  hair.  In  the  latter  case,  there  are  gener- 
ally two  or  more  glands  to  each  hair  (fig.  298). 

Hair. — A  hair  is  produced  by  a  peculiar  growth  and  modification  of 
the  epidermis.  Externally  it  is  covered  by  a  layer  of  fine  scales  closely 
imbricated,  or  overlapping  like  the  tiles  of  a  house,  but  with  the  free 
edges  turned  upward  (fig.  301,  a).  It  is  called  the  cuticle  of  the  hair. 
Beneath  this  is  a  much  thicker  layer  of  elongated  horny  cells,  closely 
packed  together  so  as  to  resemble  a  fibrous  structure.  This,  very  com- 
monly, in  the  human  subject,  occupies  the  whole  inside  of  the  hair;  but 


Fig.  300. — Transverse  section  of  a  hair  and  hair-follicle  made  below  the  opening  of  the  sebace. 
gland,    o,  medulla  or  pith  of  the  hair:  b.  fibrous  layer  or  cortex;  c,  cuticle;  d,  Huxley's  layer     .,'. 
Henle's  layer  of  mternal  root-sheath;  /and  g.  layers  of  external  roo^sheath,  outside  of  ^  is  a  li.;Ot 
layer,  or  "glassy  membrane,"  which  is  equivalent  to  the  basement  membrane;  h,  fibrous  coat  of 
hair  sac ;  2,  vessels.    (Cadiat.) 


in  some  cases  there  is  left  a  small  central  space  filled  by  a  subsw'.nce 
called  the  mef/?f//rt  or  ^j?77^,  composed  of  small  collections  of  irregularly 
shaped  cells,  containing  sometimes  pigment  granules  or  fat,  bnt  inostly 
air. 

The  follicle,  in  which  the  root  of  each  hair  is  contained  (fig  302), 
forms  a  tubular  dej)ression  from  the  surface  of  the  skin, — descending 
into  the  subcutaneous  fat,  generally  to  a  greater  depth  than  the  sudor- 
iferous glands,  and  at  its  deepest  part  enlarging  in  a  bulbous  form,  and 
often  curving  from  its  previous  rectilinear  course.  It  is  lined  through- 
out by  cells  of  epithelium,  continuous  with  those  of  the  epidermis,  and 
its  v.alls  are  formed  of  pellucid  membrane,  which  commonly  in  the 
follicles  of  the  larc-est  hairs  has  the  structure  of  vascular  fibrous  tissue. 


416 


HANDBOOK    OF    PHYSIOLOGY. 


At  the  bottom  of  the  follicle  is  a  small  papilla,  or  projection  of  true 
skin,  and  it  is  by  the  jjroduction  and  outgrowth  of  epidermal  cells  from 
the  surface  of  this  papilla  that  the  hair  is  formed.  The  inner  wall  of 
the  follicle  is  lined  by  epidermal  cells  continuous  with  those  covering 


Fig.  301.— Surface  of  a  white  hair,  magnified  160  diameters.    The  wave  lines  mark  the  upper  or  free 
edges  of  the  cortical  scales.    B,  separated  scales,  magnified  350  diameters.    (Kolliker.) 

the  general  surface  of  the  skin;  as  if  indeed  the  follicle  had  been  formed 
by  a  simple  thrusting  in  of  the  surface  of  the  integument  (fig.  302). 
This  epidermal  lining  of  the  hair-follicle,  or  roof-sheath  of  the  hair,  is 
composed  of  two  layers,  the  inner  one  of  which  is  so  moulded  on  the 
imbricated  scaly  cuticle  of  the  hair,  that  its  inner  surface  becomes  im- 
bricated also,  but  of  course  in  the  opposite  direction.     When  a  hair  is 


Fig.  .302.— Longitudinal  section  of  a  hair  follicle,  o,  Stratum  of  Blalpighi,  deep  layer  forming 
the  external  root-sheath,  and  continued  to  the  surface  of  the  papilla  to  form  the  medullary  sheath 
of  the  hair;  6,  second  external  sheath;  c.  internal  root-sheath;  d,  fibroid  sheath  of  the  hair:  e, 
medullary  sheath  or  medulla;  /,  hair  papilla;  g,  blood-vessels  of  the  hair-papilla;  h,  fibro-vascular 
sheath.     (Cadiat.) 

pulled  out,  the  inner  layer  of  the  root-sheath  and  part  of  the  outer 
layer  also  are  commonly  pulled  out  with  it. 

Nails. — A  nail,  like  a  hair  is  a  peculiar  arrangement  of  epidermal 
cells,  the  undermost  of  which,  like  those  of  the  general  surface  of  the 
integument,  are  rounded  or  elongated,  while  the  superficial  are  flat- 
tened, and  of  more  horny  consistence.     That  specially  modified  portion 


EXCRETION".  417 

of  the  corium,  or  true  skin,  by  which  the  nail  is  secreted  is  called  the 
matrix. 

The  back  edge  of  the  nail,  or  the  root  as  it  is  termed,  is  received  into 
a  shallow  crescentic  groove  in  the  matrix,  while  the  front  part  is  free 
and  projects  beyond  the  extremity  of  the  digit.  The  intermediate  por- 
tion of  the  nail  rests  by  its  broad  under  surface  on  the  front  part  of  the 
matrix,  which  is  here  called  the  hed  of  the  nail.  This  part  of  the  matrix 
is  not  uniformly  smooth  on  the  surface,  but  is  raised  in  the  form  of 
longitudinal  and  and  nearly  parallel  ridges  or  lamina?,  on  which  are 
moulded  the  epidermal  cells  of  which  the  nail  is  made  up. 

The  growth  of  the  nail,  like  that  of  the  hair,  or  of  the  epidermis  gen- 
erally, is  effected  by  a  constant  production  of  cells  from  beneath  and 
behind,  to  take  the  place  of  those  which  are  worn  or  cut  away.  Inas- 
much, however,  as  the  posterior  edge  of  the  nail,  from  its  being  lodged  in 
a  groove  of  the  skin,  cannot  grow  backward,  on  additions  being  made 
to  it,  so  easily  as  it  can  pass  in  the  opposite  direction,  any  growth  at  its 
hinder  part  pushes  the  whole  forward.  At  the  same  time  fresh  cells 
are  added  to  its  under  surface,  and  thus  each  portion  of  the  nail  becomes 
gradually  thicker  as  it  moves  to  the  front,  until,  projecting  beyond  the 
surface  of  the  matrix,  it  can  receive  no  fresh  addition  from  beneath,  and 
is  simply  moved  forward  hj  the  growth  at  its  root,  to  be  at  last  worn 
away  or  cut  off. 

Functions  of  the  Skin. 

The  function  of  the  skin  to  be  considered  in  this  chapter  is  that  of 
the  excretion  of  the  sweat.  The  fluid  secreted  by  the  sweat-glands  is 
usually  formed  so  gradually  that  the  watery  portion  of  it  escapes  by 
evaporation  as  fast  as  it  reaches  the  surface.  But  during  strong  exer- 
cise, exposure  to  great  external  warmth,  in  some  diseases,  and  when 
evaporation  is  prevented,  the  secretion  becomes  more  sensible,  and  col- 
lects on  the  skin  in  the  form  of  drops  of  fluid. 

The  perspiration,  as  the  term  is  sometimes  employed  in  physiology, 
includes  all  that  portion  of  the  secretions  and  exudations  from  the  skin 
which  passes  off  by  evaporation ;  the  siveat  includes  that  which  may  be 
collected  only  in  drops  of  fluid  on  the  surface  of  the  skin.  The  two 
terms  are,  however,  most  often  used  synonymously;  and  for  distinction, 
the  former  is  called  insensible  perspiration;  the  latter  sensible  perspira- 
tion. The  fluids  are  the  same,  except  that  the  sweat  is  commonly  mingled 
with  various  substances  lying  on  the  surface  of  the  skin.  The  contents 
of  the  sweat  are,  in  part,  matters  capable  of  assuming  the  form  of  vapor, 
such  as  carbonic  acid  and  water,  and  in  part,  other  matters  which  are 
deposited  on  the  skin,  and  mixed  with  the  sebaceous  secretions. 

The  secretion  of  the  sebaceous  glands  and  hair-follicles  consists  of 
cast-off  epithelium  cells,  with  nuclei  and  granules,  together  with  an  oily 
27 


418 


HANDBOOK    OF    PHYSIOLOGY. 


matter,  extractive  matter,  and  stearin;  in  certain  parts,  also,  it  is  mixed 
with  a  peculiar  odorous  principle,  which  contains  caproic,  butyric,  and 
rutic  acids.  It  is,  perhaps,  nearly  similar  in  composition  to  the  unctu- 
ous coating,  or  vernix  caseosa,  which  is  formed  on  the  body  of  the 
foetus  while  in  the  uterus,  and  which  contains  large  quantities  of 
ordinary  fat.  Its  purpose  seems  to  be  that  of  keeping  the  skin  moist 
and  supple,  and,  by  its  oily  nature,  of  both  hindering  the  evaporation 
from  the  surface,  and  guarding  the  skin  from  the  effects  of  the  long- 


Fig.  303.— Sebaceous  gland  from  human  skin.    (Klein  and  Noble  Smith.) 

continued  action  of  moisture.  But  while  it  thus  serves  local  purposes, 
its  removal  from  the  body  entitles  it  to  be  reckoned  among  the  excre- 
tions of  the  skin. 

Chemical  Composition  of  Sweat. 

Water .995 

Solids  :— 

Organic  Acids  (formic,  acetic,  butyric,  pro-  )         q 

picnic,  caproic,  caprylic)  .         .  )        ' 

Salts,  chiefly  sodium  chloride  .         .         .         .1.8 
Neutral  fats  and  cholesterin  .         .         .  .7 

Extractives  (including  urea),  with  epithelium     1.6  5 

1000 
The  sweat  is  a  colorless,  slightly  turbid  fluid,  alkaline,  neutral  or 

acid  in  reaction,  of  a  saltish  taste,  and  peculiar  characteristic  odor. 

Of  the  several  substances  it  contains,  however,  only  the  carbonic  acid 

and  water  need  particular  consideration. 

Watery  Vapor. — The  quantity  of  watery  vapor  excreted  from  the 


EXCRETIOX.  419 

skin  is  on  an  average  between  1^  and  2  lb  daily  (about  1  kilo).  This 
subject  has  been  very  carefully  investigated  by  Lavoisier  and  Sequin. 
The  latter  chemist  enclosed  his  body  in  an  air-tight  bag,  with  a  mouth- 
piece. The  bag  being  closed  by  a  strong  band  above,  and  the  mouth- 
piece adjusted  and  gummed  to  the  skin  around  the  mouth,  he  was 
weighed,  and  then  remained  quiet  for  several  hours,  after  which  time 
he  was  again  weighed.  The  difference  in  the  two  weights  indicated  the 
amount  of  loss  by  pulmonary  exhalation.  Having  taken  off  the  air- 
tight dress,  he  was  immediately  weighed  again,  and  a  fourth  time  after 
a  certain  interval.  The  difference  between  the  two  weights  last  ascer- 
tained gave  the  amount  of  the  cutaneous  and  pulmonary  exhalation  to- 
gether; by  subtracting  from  this  the  loss  by  pulmonary  exhalation 
alone,  while  he  was  in  the  air-tight  dress,  he  ascertained  the  amount  of 
cutaneous  transpiration.  During  a  state  of  rest,  the  average  loss  by 
cutaneous  and  pulmonary  exhalation  in  a  minute,  is  eighteen  grains, — • 
the  minimum  eleven  grains,  the  maximum  thirty-two  grains;  and  of  the 
eighteen  grains,  eleven  pass  off  by  the  skin,  and  seven  by  the  lungs. 

The  quantity  of  watery  vapor  lost  by  transpiration  is  of  course  influ- 
enced by  all  external  circumstances  which  affect  the  exhalation  from 
other  evaporating  surfaces,  such  as  the  temperature,  the  hygrometric 
state,  and  the  stillness  of  the  atmosphere.  But,  of  the  variations  to 
which  it  is  subject  under  the  influence  of  these  conditions,  no  calcula- 
tion has  been  exactly  made. 

Carbonic  Acid. — The  quantity  of  carbonic  acid  exhaled  by  the  skin 
on  an  average  is  about  yl-g-  to  ^^  of  that  furnished  by  the  pulmonary 
respiration. 

The  cutaneous  exhalation  is  most  abundant  in  the  lower  classes  of  animals, 
more  particularly  the  naked  Amphibia,  as  frogs  and  toads,  whose  skin  is  thin  and 
moist,  and  readily  permits  an  interchange  of  gases  between  the  blood  circulating 
in  it,  and  the  surrounding  atmosphere.  Bischoff  found  that,  after  the  lungs  of 
frogs  had  been  tied  and  cut  out,  about  a  quarter  of  a  cubic  inch  of  carbonic 
acid  gas  was  exhaled  by  the  skin  in  eight  hours.  And  this  quantity  is  very 
large,  when  it  is  remembered  that  a  full-sized  frog  will  generate  only  about 
half  a  cubic  inch  of  carbonic  acid  by  his  lungs  and  skin  together  in  six  hours. 

The  importance  of  the  respiratory  function  of  the  skin,  which  was  once 
thought  to  be  proved  by  the  speedy  death  of  animals  whose  skins,  after  removal 
of  the  hair,  were  covered  with  an  impermeable  varnish,  has  been  shown  by 
further  observations  to  have  no  foundation  in  fact ;  the  immediate  cause  of 
death  in  such  cases  being  the  loss  of  temperature.  A  varnished  animal  is  said 
to  have  suffered  no  harm  when  surrounded  by  cotton  M-adding,  and  to  have  died 
when  the  wadding  was  removed. 

Influence  of  the  Xervous  System. 

Experiments  seem  to  show  that  the  mode  of  the  secretion  of  sweat 
is  more  or  less  like  that  of  the  secretion  of  saliva.  The  chief  difference 
between  the  two  processes  appears  to  be  this,  that  increased  blood  sup- 


420  HANDBOOK    OF    PHYSIOLOGY. 

ply,  of  itself,  is  able  to  produce  a  secretion  of  sweat,  whereas  this  is  not 
the  case  with  the  salivary  secretion  In  the  case  of  the  sweat-glands,  it 
is  practically  certain  that  they  are  also  under  the  control  of  efferent  im- 
pulses passing  to  them  from  the  sjiecial  sweat  centres  in  the  brain  and 
spinal  cord  through  special  sweat  nerves.  Thus,  if  the  sciatic  nerve 
be  divided  in  a  cat  and  the  peripheral  end  be  stimulated,  beads  of  sweat 
are  seen  to  appear  upon  the  pad  of  the  corresponding  foot,  although  at 
the  same  time  the  blood-vessels  are  constricted  or  whilst  the  aorta  is 
pressed  upon,  whereas  if  atropin  have  been  injected  previously  to  the 
stimulation,  no  sweat  appears,  although  dilatation  of  the  vessels  be 
present.     Secretion  of  sweat,  too,  may  be  reflexly  brought  about. 

The  exact  way  in  which  various  conditions  producing  an  extra  secre- 
tion of  sweat  act,  is  somewhat  uncertain.  The  circulation  of  venous 
blood  in  the  central  nervous  system,  however,  appears  to  be  the  cause 
of  the  sweating  of  phthisis  and  of  dyspnoea  generally.  If  the  cat  whose 
sciatic  nerve  be  divided  be  rendered  dyspnoeic,  abundant  sweat  occurs 
upon  the  foot  of  the  uninjured,  arid  none  on  the  injured  side.  The 
effect  of  heat  in  producing  sweating  may  be  both  local  and  general,  and 
again,  the  various  drugs  which  produce  an  increased  secretion  of  sweat 
do  not  all  act  in  the  same  way;  thus,  there  is  reason  for  thinking  that 
pilocarjnn  acts  upon  the  local  apparatus,  that  stryclmia  and  picrotoxin 
act  upon  the  sweat  centres,  and  that  nicotin  acts  both  upon  the  central 
and  upon  the  local  apparatus. 

The  special  sweat-nerves  appear  to  issue  from  the  spinal  cord,  in  the 
case  of  the  hind  limb  of  the  cat  by  the  last  two  or  three  dorsal  and  first 
two  or  four  lumbar  nerves,  pass  to  the  abdominal  sympathetic  and  from 
thence  to  the  sciatic  nerve.  In  the  case  of  the  fore  limb,  the  nerves 
leave  the  cord  by  the  5th  and  6th  cervical  nerves  into  the  thoracic  sym- 
pathetic, and  then  join  the  brachial  plexus,  reaching  the  arm  through 
the  median  and  ulnar  nerves. 

It  will  be  as  well  to  repeat  here  the  other  functions  which  the  skin 
subserves.  In  addition  to  its  excretory  oflSce,  we  have  seen  that  it  acts 
as  a  channel  for  absorption.  It  is  also  concerned  with  a  special  sense, 
viz.,  that  of  touch,  to  the  consideration  of  which  as  well  as  to  its  func- 
tion of  regulating  the  temperature  of  the  body  we  shall  presently  return. 
It  should  be  recollected,  however,  that  apart  from  these  special  func- 
tions, by  means  of  its  toughness,  flexibility  and  elasticity,  the  skin  is 
eminently  qualified  to  serve  as,  the  general  integument  of  the  body,  for 
defending  the  internal  parts  from  external  violence,  while  readily  yield- 
ing and  adapting  itself  to  their  various  movements  and  changes  of 
position. 


CHAPTER  XI 

THE    METABOLISM    OF    THE   TISSUES. 

We  have  now  to  consider  the  various  changes  occurring  in  the  tissues 
and  organs  of  the  body  which  maybe  considered  as  intermediate  between 
those  already  described,  viz.,  the  digestion  and  absorption  of  food  on  the 
one  hand,  and  the  excretion  of  waste  products  on  the  other.  These 
processes  take  place  principally  in  the  muscles  and  glands  of  the  body, 
and  it  will  be  as  well  to  direct  our  attention  to  the  metabolism  first  of 
all  in  muscle,  and  secondly  in  the  glands  not  directly  concerned  in  the 
digestive  processes. 

Muscular  Metabolism. 

The  muscles  make  up  about  one-half  of  the  total  body  weight.  The 
principal  substance  which  can  be  extracted  from  muscle,  when  examined 
after  death,  is  the  proteid  body,  JIi/osi»,  some  of  the  reactions  of  which 
have  been  already  discussed,  p.  108.  I'his  body  appears  to  bear  some- 
what the  same  relation  to  the  living  muscle,  as  fibrin  does  to  the  living 
blood,  since  the  coagulation  of  muscle  after  death  is  due  to  the  formation 
of  myosin.  Thus,  if  coagulation  be  delayed  in  muscles  removed  imme- 
diately from  recently  killed  animals,  by  subjecting  them  to  a  temperature 
below  0°C„,  it  is  possible  to  obtain  from  them  by  expression  a  viscid 
fluid  of  slightly  alkaline  reaction,  called  musde-jilasma  (Klihne,  Halli- 
burton). And  muscle  plasma,  if  exposed  to  the  ordinary  temperature  of 
the  air  (and  more  quickly  at  37°-40°  C),  undergoes  coagulation  much 
in  the  same  way  as,  under  similar  circumstauces,  does  blood  i)lasma, 
separated  from  the  blood  corpuscles  by  the  action  of  a  low  temperature. 
The  appearances  presented  by  the  fluid  during  the  process  are  also  very 
similar  to  the  phenomena  of  blood-clotting,  viz.,  that  first  of  all  an  in- 
creased viscidity  appears  on  the  surface  of  the  fluid,  and  at  the  sides  of 
the  containing  vessel,  which  gradually  extends  throughout  the  entire 
mass,  until  a  fine  transparent  clot  is  obtained.  In  the  course  of  some 
hours  the  clot  begins  to  contract,  and  to  squeeze  out  of  its  meshes  a  fluid 
corresponding  to  blood-serum.  In  the  course  of  coagulation,  therefore, 
muscle  plasma  separates  into  muscU-dot  and  miisde-serum.  The  muscle 
clot  is  the  substance  myosin.  It  differs  from  fibrin  in  being  easily  soluble 
in  a  2  per  cent  solution  of  hydrochloric   acid,  and  in  a  10  per  cent  solu- 


422  HANDBOOK    OF    PHYSIOLOGY. 

tion  of  sodium  chloride.  It  is  insoluble  in  distilled  water,  and  its  solu- 
tions coagulate  on  aj)plication  of  heat.  It  is  in  short  a. globulin.  During 
the  process  the  reaction  of  the  fluid  becomes  distinctly  acid. 

The  coagulation  of  muscle  plasma  cannot  only  be  prevented  by  cold, 
but  also,  as  Halliburton  has  shown,  by  the  presence  of  neutral  salts  in 
certain  proportions;  for  example,  of  sodium  chloride,  of  magnesium 
sulphate,  or  of  sodium  sulphate.  It  will  be  remembered  that  this  is 
also  the  case  with  blood  plasma.  Dilution  of  the  salted  muscle  plasma 
will  produce  its  slow  coagulation,  which  is  prevented  by  the  presence  of 
the  neutral  salts  in  strong  solution. 

It  is  highly  probable  that  the  formation  of  muscle-clot  is  due  to  the 
presence  of  a  ferment  (myosin-ferment).  The  antecedent  myosin  in  liv- 
ing muscle  has  received  the  name  of  myosinogen,  in  the  same  way  as  the 
fibrin-forming  element  in  the  blood  is  called  fibrinogen.  Myosinogen 
is,  however,  made  up  of  two  globulins,  which  coagulate  at  the  tempera- 
tures 47°  C.  and  56°  C.  respectively.  Myosin  may  also,  as  we  have  before 
mentioned,  p.  421,  be  obtained  from  dead  muscle  by  subjecting  it,  after 
all  the  blood,  fat,  and  fibrous  tissue,  and  substances  soluble  in  water  have 
been  removed,  to  a  10  per  cent  solution  of  sodium  chloride,  or  5  per 
cent  solution  of  magnesium  sulphate,  or  10  to  15  per  cent  solution  of 
ammonium  chloride,  filtering  and  allowing  the  filtrate  to  drop  into  a 
large  quantity  of  water;  the  myosin  separates  out  as  a  white  flocculent 
precipitate. 

A  very  remarkable  fact  with  regard  to  the  properties  of  myosin  has 
been  demonstrated  by  Halliburton,  namely,  that  a  solution  of  dead 
muscle  in  strong  neutral  saline  solution,  possesses  very  much  the  same 
properties  as  muscle  plasma,  and  that  if  diluted  with  twice  or  three 
times  its  bulk  of  water,  myosin  will  separate  out  as  a  clot,  which  clot  can 
be  again  dissolved  in  a  strong  neutral  saline  solution,  and  the  solution 
can  be  again  made  to  clot  on  dilution.  This  process  can  often  be  re- 
peated ;  but  in  the  fluid  which  exudes  from  the  clot  there  is  no  proteid 
present.  Myosin  when  dissolved  in  neutral  saline  fluids  is  converted  in- 
to myosinogen,  but  reappears  on  dilution  of  the  fluid.  Muscle  clot  is 
almost  pure  myosin;  but  it  appears  to  be  combined  with  a  certain 
amount  of  salts,  for  if  it  be  freed  of  salts,  especially  of  those  of  calcium, 
by  prolonged  dialysis,  it  loses  its  solubility.  If  a  small  amount  of  cal- 
cium salts  be  added,  however,  it  regains  that  pro^Derty. 

Muscle  serum  is  acid  in  reaction,  and  almost  colorless.  It  contains 
three  proteid  bodies,  viz. — («)  kglohuUn  (myoglobulm),  which  can  be  pre- 
cipitated by  saturation  with  sodium  chloride,  or  magnesium  sulphate,  and 
which  can  be  coagulated  at  63°  C.  (145°  F.).  (b)  Serum-albumin  {myo- 
albnmin),  which  coagulates  at  73°  C.  (163°  F.),  but  is  not  precipitated 
by  saturation  with  either  of  those  salts.     And    (c)  Myo-albumose,  which. 


THE    METABOLISM    OF   THE   TISSUES.  423 

is  neither  precipitated  by  heat,  nor  by  saturation  with  sodium  chloride 
or  magnesium  sulphate,  but  may  be  precipitated  by  saturation  with  am- 
monium sulphate.  It  is  closely  connected  with,  even  if  it  is  not  itself, 
myosin  ferment.  Neither  casein  nor  peptone  has  been  found  by  Halli- 
burton in  muscle  extracts.  In  extracts  of  muscles,  especially  of  red 
muscles,  there 'is  a  certain  amount  of  Hmmoglobin^  and  also  of  a  pigment 
special  to  muscle,  called  by  McMunn  Mijo-lmmatin,  which  has  a  spectrum 
quite  distinct  from  haemoglobin,  viz.,  a  narrow  band  just  before  D,  two 
very  narrow  between  D  and  E,  and  two  other  faint  bands,  nearly  violet, 
E  b,  and  between  E  and  F  close  to  F. 

In  addition  to  muscle  ferments,  already  mentioned,  muscle  extracts 
contain  certain  small  amounts  ot pepsin  and Jibrin  ferment,  and  also  an 
amylolytic  ferment. 

Certain  acids  are  also  present,  particularly  sarco-lactic,  as  well  as 
acetic  and  formic. 

Of  carbohydrates,  glycogen  and  glucose  (or  maltose),  also  inosite. 

Nitrogenous  crystalline  bodies,  such  as  lcreatin,hreatinin,xanthin, 
"hypo-xantliin,  or  carnin,  taurin,  urea,  in  very  small  amount,  uric  acid 
and  inosmic  acid. 

Salts,  the  chief  of  whicli  is  potassium  phosphate. 

Muscle  at  Rest. 

Physical  Condition. — During  rest  or  inactivity  a  muscle  has  a  slight 
but  very  perfect  Elasticity;  it  admits  of  being  considerably  stretched, 
but  returns  readily  and  completely  to  its  normal  condition.  In  the  liv- 
ing body  the  muscles  are  always  stretched  somewhat  beyond  their  natural 
length,  they  are  always  in  a  condition  of  slight  tension;  an  arrangement 
which  enables  the  whole  force  of  the  contraction  to  be  utilized  in  ap- 
proximating the  points  of  attachment.  It  is  obvious  that  if  the  muscles 
were  lax,  the  first  part  of  the  contraction  until  the  muscle  became  tight 
would  be  wasted. 

There  is  no  d6ubt  that  even  in  a  condition  of  rest  Oxygen  is  abstracted 
from  the  Mood,  and  carbonic  acid  is  given  out  by  a  muscle;  for  the  blood 
becomes  venous  in  the  transit,  and  since  the  muscles  form  by  far  the 
largest  element  in  the  composition  of  the  body,  chemical  changes  must 
be  constantly  going  on  in  them  as  in  other  tissues  and  organs,  although 
not  necessarily  accompanied  by  contraction.  When  cut  out  of  the  body 
such  muscles  retain  their  contractility  longer  in  an  atmosphere  of  oxygen 
than  in  an  atmosphere  of  hydrogen  or  carbonic  acid,  and  during  life,  an 
amount  of  oxygen  is  no  doubt  necessary  to  the  manifestation  of  energy 
as  well  as  for  the  metabolism  going  on  in  the  resting  condition. 

The  reaction  of  living  muscle  in  a  resting  or  inactive  condition  is 
neutral  or  faintly  cdkaline. 


424 


HANDBOOK    OF    PHYSIOLOGY, 


In  muscles  whicli  have  been  removed  from  the  body,  it  lias  been  found 
that  for  some  little  time  electrical  currents  can  be  dcnionsirated  jmssing 
from  point  to  point  on  their  surface;  but  as  soon  as  the  muscles  die  or 
enter  into  rigor  mortis,  these  currents  disapjjear. 

The  demonstration  of  muscle  currents  is  usually  done  as  follows  : — The  frog'& 
muscles  are  the  most  convenient  for  experiment ;  and  a  muscle  of  regular 
shape,  in  which  the  fibres  are  parallel,  is   selected.     The  ends  are  cut  off  by- 


Fig.  304.— Reflecting  galvanometer.  (Thomson.)  A.  The  galvanometer,  which  consists  of 
two  systems  of  small  astatic  needles  suspended  by  a  fine  hair  from  a  support,  so  that  each  set  of 
needles  is  within  a  coil  of  fine  insulated  copper  wire,  that  forming  the  lower  coil  is  wound  in  an 
opposite  direction  to  the  upper.  Attached  to  the  upper  set  of  needles  is  a  small  mirror  about 
54  inch  in  diameter;  the  light  from  the  lamp  at  B  is  thrown  upon  this  Uttle  mirror,  and  is  re- 
flected upon  the  scale  on  tlie  other  side  of  B,  not  shown  in  figure.  The  coils  /  I  are  arranged 
upon  brass  uprights,  and  their  ends  are  carried  to  the  binding  screws.  The  whole  apparatus  is 
placed  upon  a  vulcanite  plate  capable  of  being  levelled  by  the  screw  supports,  and  is  covered 
by  a  brass-bound  glass  shade,  L.  the  cover  of  which  is  also  of  brass,  and  supports  a  brass  rod, 
6,  on  which  moves  a  weak  curved  magnet,  m.  C  is  the  shunt  by  means  of  which  the  amount  of 
the  current  sent  into  the  galvanometer  may  be  regulated.  When  in  use  the  scale  is  placed 
about  three  feet  from  the  galvanometer,  which  is  arranged  east  and  west,  the  lamp  is  lighted, 
the  mirror  is  made  to  swing,  and  the  light  from  the  lamp  is  adjusted  to  fall  upon  it,  and  it  is 
then  regulated  until  the  reflected  spot  of  light  from  it  falls  upon  the  zero  of  the  scale.  The 
wires  from  the  non-polarizable  electrodes  touching  the  muscU^  are  attached  to  the  outer  binding 
screws  of  the  galvanometer,  a  key  intervening  for  short-circuiting,  or  if  a  portion  only  of  the 
current  is  to  pass  into  the  galvanometer,  the  shunt  should  interv<>iie  as  well  with  the  appropriate 
plug  in.  When  a  current  passes  into  the  galvanometer  the  needles  and,  with  them,  the  mirror, 
are  turned  to  the  right  or  left  according  to  the  direction  of  the  current.  The  amount  of  the  de- 
flection of  the  needle  is  marked  on  the  scale  by  the  spot  of  light  travelling  along  it. 

clean  vertical  cuts,  and  the  resulting  piece  of  muscle  is  called  a  regular  muscle 
prism.  The  muscle  prism  is  insulated,  and  a  pair  of  non-polarizable  electrodes 
connected  with  a  very  delicate  galvanometer  (fig.  304)  is  applied  to  various 
points  of  the  prism,  and  by  a  deflection  of  the  needle  to  a  greater  or  less  extent 


THE    METABOLISM    OF   THE   TISSUES. 


425 


in  one  direction  or  anothex',  the  strength  and  direction  of  the  currents  in  the 
piece  of  muscle  can  be  estimated.  It  is  necessary  to  use  non-polarizable  and 
not  metallic  electrodes  in  this  experiment,  as  otherwise  there  is  no  certainty 
that  the  whole  of  the  current  observed  is  communicated  from  the  muscle  itself, 
and  is  not  derived  from  the  metallic  electrodes  arising  in  consequence  of  the 
action  of  the  saline  juices  of  the  tissues  upon  them.  The  form  of  the  non- 
polarizable  electrodes  is  a  modification  of  Du  Bois  Eeymond's  apparatus  (fig. 
305),  which  consists  of  a  somewhat  flattened  glass  cylinder,  a,  drawn  abruptly 


Fig.  305.— Diagram  of  Du  Bois  Reymond's  non-polarizable  electrodes,  a.  Glass  tube  filled 
with  a  saturated  solution  of  zinc  sulphate,  in  the  end,  c,  of  which  is  china  clay  drawn  out  to  a 
point;  in  the  solution  a  well  amalgamated  zinc  rod  is  immersed  and  connected,  by  means  of  the 
wire  which  passes  through  a,  with  the  galvanometer.  The  remainder  of  the  apparatus  is  simply 
for  convenience  of  application.  The  muscle  and  the  end  of  the  second  electrode  are  to  the 
right  of  the  figure. 

to  a  point,  and  fitted  to  a  socket  capable  of  movement,  and  attached  to  a  stand, 
A,  so  that  it  can  be  raised  or  lowered  as  required.  The  lower  portion  of  the 
cylinder  is  filled  with  china  clay  moistened  with  saline  solution,  part  of  which 
projects  through  its  drawn-out  point ;  the  rest  of  the  cylinder  is  fitted  with  a 
saturated  solution  of  zinc  sulphate  into  which  dips  a  well  amalgamated  piece 
of  zinc  connected  by  means  of  a  wire  with  the  galvanometer.  In  this  way 
the  zinc  sulphate  forms  a  homogeneous  and  non-polarizable  conductor  between 
the  zinc  and  the  china  clay.  A  second  electrode  of  the  same  kind  is,  of  course, 
necessary. 

In  a  regular  muscle  prism  the  currents  are  found  to  be  as  follows: — 
If  from  a  point  in  the  surface  a  line — the  equator — be  drawn  across  the 
muscle  prism  equally  dividing  it,  currents  pass  from  this  point  to  points 
away  from  it,  which  are  weak  if  the  points  are  near,  and  increased  in 
strength  as  the  points  are  further  and  further  away  from  the  equator ; 
the  strongest  passing  from  the  equator  to  a  point  representing  the  middle 
of  the  cut  ends  (fig.  306,  2) ;  currents  also  pass  from  j^oints  nearer  the 
equator  to  those  more  remote  (fig.  300,  1,  3,  4,),  but  not  from  points 
equally  distant  or  iso-electric  points  (fig.  306,  6,  7,  8).  The  cut  ends 
are  always  negative  to  the  equator.  These  currents  are  constant  for  some 
time  after  removal  of  the  muscle  from  the  body,  and  in  fact  remain  as 


426 


HANDBOOK    OF    PHYSIOLOGY 


long  as  the  muscle  retains  its  life.     They  are  in  all  ])robaLility  due  to 
chemical  changes  going  on  in  the  muscles. 

The  currents  are  diminished  by  fatigue  and  are  increased  by  an  increase 
of  temperature  within  natural  limits.  If  the  uninjured  tendon  be  used  as 
the  end  of  the  muscle,  and  the  muscle  be  examined  without  re- 
moval from  the  body,  the  currents  are  very  feeble,  but  they  are  at  once 
much  increased  by  injuring  the  muscle,  as  by  cutting  off  its  tendon. 
The  last  observation  appears  to  show  that  they  are  right  who  believe 
that  the  currents  do  not  exist  in  uninjured  muscles  in  situ,  but  that  in- 
jury, either  mechanical,  chemical  or  thermal,  will  render  the  injured 
part  electrically  negative  to  other  points  on  the  muscle.  In  a  frog's 
heart  it  has  been  shown,  too,  that  no  currents  exist  during  its  inactivity, 
but  that  as  soon  as  it  is  injured  in  any  way  they  are  developed;  the  in- 
jured part  being  negative  to  the  rest  of  the  muscle.     The  currents  which 


Fig.  306. — Diagram  of  the  currents  in  a  muscle  prism.     (Du  Bois  Reymond.) 

have  been  above  described  are  called  either  natural  muscle  currents  or 
currents  of  rest,  according  as  they  are  looked  upon  as  always  existing  in 
muscle  or  as  developed  when  a  part  of  the  muscle  is  subjected  to  injury; 
in  either  case,  up  to  a  certain  point,  it  is  agreed  that  the  strength  of  the 
currents  is  in  direct  proportion  to  the  injury. 

Muscle  in  Activity. 

The  property  of  muscular  tissue,  by  which  its  peculiar  functions  are 
exercised,  is  its  Contractility,  which  is  excited  by  all  kinds  of  stimuli  ap- 
plied either  directly  to  the  muscles,  or  indirectly  to  them  through  the 
medium  of  their  motor  nerves.  This  property,  although  commonly 
brought  into  action  through  the  nervous  system,  is  inherent  in  the 
muscular  tissue.  For — (1.)  it  may  be  manifested  in  a  muscle  which  is 
isolated  from  the  influence  of  the  nervous  system  by  division  of  the  nerves 
supplying  it,  so  long  as  the  natural  tissue  of  the  muscle  is  duly  nourished; 
and  (2.)  it  is  manifest  in  a  portion  of  muscular  fibre,  in  which,  under 
the  microscope,  no  nerve-fibre  can  be  traced.      (3.)  Substances  such  as 


THE    METABOLISM    OF   THE   TISSUES.  427 

urari.,  which  paralyze  the  nerve-endings  in  muscles,  do  not  at  all  dimin- 
ish the  irritability  of  the  muscle  itself. 

(4.)  When  a  muscle  is  fatigued,  a  local  stimulation  is  followed  by  a 
contraction  of  a  small  part  of  the  fibre  in  the  immediate  vicinity  without 
any  regard  to  the  distribution  of  nerve-fibres. 

If  the  removal  of  nervous  influence  be  long  continued,  as  by  division 
of  the  nerves  supplying  a  muscle,  or  in  cases  of  paralysis  of  long-standing, 
the  irritability,  I.e.,  the  power  of  responding  to  a  stimulus,  maybe  lost; 
but  probably  this  is  chiefly  due  to  the  impaired  nutrition  of  the  muscular 
tissue,  which  ensues  through  its  inaction.  The  irritability  of  muscles 
is  also  soon  lost,  unless  a  suj^ply  of  arterial  blood  to  them  is  kept  up. 
Thus,  after  ligature  of  the  main  arterial  trunk  of  a  limb,  the  power  of 
moving  the  muscles  is  partially  or  wholly  lost,  until  the  collateral  cir- 
culation is  established;  and  when,  in  animals,  the  abdominal  aorta  is 
tied,  the  hind  legs  are  rendered  almost  powerless. 

The  same  fact  may  be  readily  shown  by  compressing  the  abdominal 
aorta  in  a  rabbit  for  about  10  minutes;  if  the  pressure  be  released  and 
the  animal  be  placed  on  the  ground,  it  will  work  itself  along  with  its 
front  legs,  while  the  hind  legs  spra,wl  helplessly  behind.  Gradually  the 
muscles  recover  their  power  and  become  quite  as  efficient  as  before. 

So,  also,  it  is  to  the  imperfect  supply  of  arterial  blood  to  the  muscular 
tissue  of  the  heart,  that  the  cessation  of  the  action  of  this  organ  in  as- 
phyxia is  in  some  measure  due. 

The  Phenomena  of  Muscular  Contraction. 

The  power  which  muscles  possess  of  contraction  may  then  be  called 
forth  by  stimuli  of  various  kinds,  and  these  stimuli  may  also  be  applied  di- 
rectly to  the  muscle  or  indirectly  to  the  nerve  supplying  it.  There  are 
distinct  advantages,  however,  in  applying  the  stimulus  to  the  nerve,  as 
it  is  more  convenient,  as  well  as  more  potent.  The  stimuli  are  of  four 
kinds,  viz. : — 

(1.)  Mechanical  stimuli^  as  by  a  blow,  pinch,  prick  of  the  muscle  or 
its  nerve,  will  produce  a  contraction,  repeated  on  the  repetition  of  the 
stimulus;  but  if  applied  to  the  same  point  for  a  limited  number  of  times 
only,  as  such  stimuli  will  soon  destroy  the  irritability  of  the  preparation. 

(2.)  Thermal  Stimuli. — If  a  needle  be  heated  and  applied  to  a  muscle 
or  its  nerve,  the  muscle  will  contract.  A  temperature  of  over  37.8°  C. 
(100°  F.)  will  cause  the  muscles  of  a  frog  to  pass  into  a  condition  known 
as  heat  rigor. 

(3.)  Chemical  Stimuli. — A  great  variety  of  chemical  substances  will 
excite  the  contraction  of  muscles,  some  substances  being  more  potent  in 
irritating  the  muscle  itself,  and  other  substances  having  more  effect  upon 
the  nerve.     Of  the  former  mav  be  mentioned,  dilute  acids,  salts  of  cer- 


428 


HANDBOOK    OF    PHYSIOLOGY, 


tain   metals,  e.g.^  zinc,    copper  and   iron;  to  the  latter  belong  strong 
glycerin,  strong  acids,  ammonia  and  bile  salts  in  strong  solution. 

(4.)  Electrical  Stimuli. — For  the  purpose  of  experiment  electrical 
stimuli  are  most  frequently  used,  as  the  strength  of  the  stimulus  may  be 
more  conveniently  regulated.  Any  form  of  electrical  current  may  be 
employed  for  this  purpose,  but  galvanism  or  the  induced  current  is  usu- 
ally chosen. 

Galvanic  currents  are  usually  obtained  by  the  employment  of  a  continuous 
current  battery  such  as  that  of  Daniell,  by  which  an  electrical  current  which 
varies  but  little  in  intensity  is  obtained  The  battery  (fig.  307)  consists  of  a 
positive  plate  of  well -amalgamated  zinc  immersed  in  a  porous  cell,  containing 
dilute  sulphuric  acid  ;  and  this  cell  is  again  contained  within  a  large  copper 
vessel  (forming  the  negative  plate) ,  containing  besides  a  saturated  solution  of 
copper  sulphate.  The  electrical  current  is  made  continuous  by  the  use  of  the 
two  fluids  in  the  following  manner.  The  action  of  the  dilute  sulphuric  acid 
upon  the  zinc  plate  partly  dissolves  it,  and  liberates  hydrogen,  and  this  gas 
passes  through  the  porous  vessel,  and  decomposes  the  copper  sulphate  into  copper 


ChSO-^ 


Fig.  307.— Diagram  of  a  Dauiell's  battery. 

and  sulphuric  acid.  The  former  is  deposited  upon  the  copper  plate,  and  the 
latter  passes  through  the  porous  vessel  to  renew  the  sulphuric  acid  which  is 
being  used  up.  The  copper  sulphate  solution  is  renewed  by  spare  crystals  of 
the  salt,  which  are  kept  on  a  little  shelf  attached  to  the  copper  plate,  and 
slightly  below  the  level  of  the  solution  in  the  vessel.  The  current  of  electricity 
supplied  by  this  battery  will  continue  without  variation  for  a  considerable  time. 
Other  continuous  current  batteries,  such  as  Grove's,  may  be  used  in  place  of 
Daniell 's.  The  way  in  which  the  apparatus  is  arranged  is  to  attach  wires  to 
the  copper  and  zinc  plates,  and  to  bring  them  to  a  key,  which  is  a  little  appa- 
ratus for  connecting  the  wires  of  a  battery.  One  often  employed  is  Du  Bois 
Reymond's  (fig.  308)  ;  it  consists  of  two  pieces  of  brass  about  an  inch  long,  in 
each  of  which  are  two  holes  for  wires  and  binding  screw,  to  hold  them  tightly; 
these  pieces  of  brass  are  fixed  upon  a  vulcanite  plate,  to  the  under  surface  of 
which  is  a  screw  clamp  by  which  it  can  be  secured  to  the  table.  The  interval 
between  the  pieces  of  brass  can  be  bridged  over  by  means  of  a  third  thinner 
piece  of  similar  metal  fixed  by  a  screw  to  one  of  the  brass  pieces,  and  capable 
of  movement  by  a  handle  at  right  angles,  so  as  to  touch  the  other  piece  of 
brass.     If  the  wires  from  the  battery  are  brought  to  the  inner  binding  screws, 


THE    METABOLISM    OF   THE   TISSUES, 


429 


and  the  bridge  connects  them,  the  current  passes  across  it  and  back  to  the 
battery.  Wires  are  connected  with  the  outer  binding  screws,  and  the  other 
ends  are  joined  together  for  about  two  inches,  but,  being  covered  except  at 
their  points,  are  insulated ;  the  uncovered  points  are  about  an  eighth  of  an 


Fig.  308.— A.  Du  Bois  Reymond's  Key. 


B.  Mercury  Key. 


inch  apart.  These  wires  are  ihe  electrodes,  and  the  electrical  stimulus  is  applied 
to  the  muscle  through  them,  if  they  are  placed  behind  its  nerve.  When  the 
connection  between  the  two  brass  plates  of  the  key  is  broken  by  depressing  the 
handle  of  the  bridge,  the  key  is  then  said  to  be  opened. 

An  induced  current  is  developed  by  means  of  an  apparatus,  called  an  induc- 


Fig.  309.  — Du  Bois  Reymond's  induction  coil. 

tion  coil,  and  the  one  employed  for  physiological  purposes  is  mostly  Du  Bois 
Reymond's,  the  one  seen  in  fig.  309. 

Wires  from  a  battery  are  brought  to  the  two  binding  screws  d'  and  d,  a  key 
intervening.     These  binding  screws  are  the  ends  of  a  coil  of  coarse  covered  wire 


430 


HANDBOOK    OF    PHYSIOLOGY. 


c,  called  the  primary  coil.  The  ends  of  a  coil  of  finer  covered  wire  g,  are  attached 
to  two  binding  screws  to  the  left  of  the  figure,  one  only  of  which  is  visible. 
This  is  the  secondary  coil,  and  is  capable  of  being  moved  nearer  to  c  along  a 
gi-oove  and  graduated  scale.  To  the  binding  screws  to  the  left  of  g,  the  wires 
of  electrodes  used  to  stimulate  the  muscle  are  attached.  If  the  key  in  the  cir- 
cuit of  wires  from  the  battery  to  the  primary  coil  (primary  circuit)  be  closed, 
the  current  from  the  battery  passes  through  the  primary  coil,  and  across  the 
key  to  the  battery,  and  continues  to  pass  as  long  as  the  key  continues  closed. 
At  the  moment  of  closure  of  the  key,  at  the  exact  instant  of  the  completion  of 
the  primary  circuit,  an  instantaneous  current  of  electricity  is  induced  in  the 
secondary  coil,  g,  if  it  be  sufficiently  near  and  in  line  with  the  primary  coil ; 
and  the  nearer  it  is  to  e,  the  stronger  is  the  cvirrent  induced.  The  current 
is  only  momentary  in  duration  and  does  not  continue  during  the  w^hole  of  the 
period  while  the  primary  circuit  is  complete.  When,  however,  the  primary 
current  is  broken  by  opening  the  key,  a  second,  also  momentary,  current  is 
induced  in  g.  The  former  induced  current  is  called  the  making  and  the  latter 
the  breaking  shock  ;  the  former  is  in  the  opposite  direction  to,  and  the  latter  in 
the  same  as,  the  primary  current. 

The  induction  coil  may  be  used  to  produce  a  rapid  series  of  shocks  by  means 
of  another  and  accessory  part  of  the  apparatus  at  the  right  of  the  fig. ,  called 
the  magnetic  intemipter.  If  the  wires  from  a  battery  are  connected  with  the 
two  pillars  by  the  binding  screws,  one  below  c,  and  the  other,  a,  the  course  of 


Fig.  310.  —Diagram  of  the  course  of  the  current  in  the  magnetic  interrupter  of  Du  Bois  Rey- 
mond's  induction  coil.     (Helmholz's  modification.) 


the  cun-ent  is  indicated  in  fig.  310,  the  direction  being  indicated  by  the  arrows. 
The  current  passes  up  the  pillar  from  e,  and  along  the  springs  if  the  end  of  d 
is  close  to  the  spring,  the  current  passes  to  the  primary  coil  c,  and  to  wires 
covering  two  upright  pillars  of  soft  iron,  from  them  to  the  pillar  a,  and  out 
by  the  wires  to  the  battery  ;  in  passing  along  the  wire,  h,  the  soft  iron  is  con- 
verted into  a  magnet,  and  so  attracts  the  hammer,  /,  of  the  spring,  breaks  the 
connection  of  the  spring  with  d\  and  so  cuts  off  the  current  from  the  primary 
coil,  and  also  from  the  electro-magnet.  As  the  pillars,  h,  are  no  longer  mag- 
netized the  spring  is  released,  and  the  current  passes  in  the  first  direction, 
and  is  in  like  manner  interrupted.  At  each  make  and  break  of  the  primary 
current,  currents  corresponding  are  induced  in  the  secondary  coil.  These  cur- 
rents are  opposite  in  direction,  but  are  not  equal  in  intensity,  the  break  shock 
being  greater.  In  order  that  the  shocks  should  be  nearly  equal  at  the  make 
and  break,  a  wire  (fig.  310,  e')  connects  e  and  d' ,  and  the  screw  d'  is  raised  out 
of  reach  of  the  spring,  and  d  is  raised  (as  in  fig.  310) ,  so  that  part  of  the  cur- 


THE    METABOLISM    OF   THE   TISSUES, 


431 


rent  always  passes  through  the  primary  coil  and  electromagnet.  When  the 
spring  touches  d,  the  current  in  b  is  diminished,  but  never  entirely  withdrawn, 
and  the  primary  current  is  altered  in  intensity  at  each  contact  of  the  spring 
with  d,  but  never  entirely  broken. 

Record  of  Muscular  Contraction  under  Stimuli. — The  muscles  of  the  frog  are 
most  convenient  for  the  purpose  of  recording  contractions.  The  frog  is  pithed, 
that  is  to  say,  its  central  nervous  system  is  entirely  destroyed  by  the  insertion 
of  a  stout  needle  into  tlie  spinal  cord,  and  the  parts  above  it.  One  of  its  lower 
extremities  is  used  in  the  following  manner.  The  large  trunk  of  the  sciatic 
nerve  is  dissected  out  at  the  back  of  the  thigh,  and  a  pair  of  electrodes  is 


Fig.  311. — An'anffement  of  the  apparatus  necessary  for  recording;  muscle  contractions 
■with  a  revolving  cylinder  carrying'  smoked  y)aper.  A,  Revolving  cylinder;  B,  the  frog  arranged 
upon  a  cork-covered  board  which  is  capable  of  being  raised  or  lowered  on  the  upright,  which 
also  can  be  moved  along  a  solid  triangular  bar  of  metal  attached  to  the  base  of  the  recording 
apparatus— the  tendon  of  the  gastrocnemius  is  attached  to  the  writing  lever,  properly  weiglited, 
by  a  ligature.  The  electrodes  from  the  secondary  coil  pass  to  the  apparatus— being,  for  the 
■sake  of  convenience,  first  of  all  brought  to  a  key,  D  ( Du  Bois  Reymond's) ;  C,  the  induction 
■coil;  F,  the  battery  (in  this  fig.  a  bichromate  one);  E,  the  key  (Morse's)  in  the  primary  circuit. 

inserted  behind  it.  The  tendo-achillis  is  divided  from  its  attachment  to  the 
OS  calcis,  and  a  ligature  is  tightly  tied  round  it.  This  tendon  is  part  of  the 
broad  muscle  of  the  thigh  (gastrocnemius),  which  arises  from  above  the  con- 
dyles of  the  femur.  The  femur  is  now  fixed  to  a  board  covered  with  cork, 
and  the  ligature  attached  to  the  tendon  is  tied  to  the  upright  of  a  piece  of 
metal  bent  at  right  angles  (fig.  311,  b),  which  is  capable  of  moverment  about  a 
pivot  at  its  knee,  the  horizontal  portion  caiTving  a  writing  lever  (myograph) . 
When  the  muscle  contracts,  the  lever  is  raised.  It  is  necessary  to  attach  a 
small  weight  to  the  lever.  In  this  arrangement  the  muscle  is  in  situ,  and  the 
nerve  disturbed  from  its  relations  as  little  as  possible. 

The  muscle  may,  however,  be  detached  from  the  body  with  the  lower  end  of 


432 


HANDBOOK    OF    PHYSIOLOCiV 


Fig.  312.— Moist  Chamber. 

the  femur  from  which  it  arises,  and  the  nerve  going  to  it  may  be  taken  away 
with  it.  The  femur  is  divided  at  about  the  lower  third.  The  bone  is  held  in  a 
firm  clamp,  the  nerve  is  placed  upon  two  electrodes  connected  with  an  induc- 
tion apparatus,  and  the  lower  end  of  the  muscle  is  connected  by  means  of  a 
ligature  attached  to  its  tendon  with  a  lever  which  can  write  on  a  recording 
apparatus. 

To  prevent  evaporation  this  so-called  nerve-muscle  preparation  is  placed  under 


Fig.  313.— Simple  form  of  pendulum  myograph  and  accessory  parts.  A,  Pivot  upon  which 
pendulum  swings :  2?,  catch  on  lower  end  of  myograph  opening  the  key,  C,  in  its  swing ;  D,  a 
spring-catch  which  retains  myograph,  as  indicated  by  dotted  lines,  and  on  pressing  down  the 
handle  of  which  the  pendulum  swings  along  the  arc  to  D  on  the  left  of  figure,  and  is  caught  by 
its  spring. 


THE    METABOLISM    OF   THE   TISSUES. 


433 


a  glass  shade  {moist  cltamber,  fig.  312),  the  air  in  which  is  kept  moist  by  means 
of  blotting  paper  saturated  with  saline  solution. 

Effects  of  a  Single  Induction  Shock. — With  a  nerve-muscle  preparation 
arranged  in  either  of  the  above  ways,  on  closing  or  opening  the  key  in  the  pri- 
mary circuit,  we  obtain  and  can  record  a  contraction,  and  if  we  use  the  clock- 
work apparatus  revolving  rapidly,  a  curve  is  traced  such  as  is  shown  in  fig.  314. 

Another  way  of  recording  the  contraction  is  by  the  use  of  the  pendulum 
myograph  (fig.  313) .  Here  the  movement  of  the  pendulum  along  a  certain  arc 
is  substituted  for  the  clockwork  movement  of  the  other  apparatus.  The  pen- 
dulum carries  a  smoked  glass  plate  uj^on  which  the  writing  lever  of  a  myo- 
graph is  made  to  mark.  The  opening  or  breaking  shock  is  sent  into  the 
nerve-muscle  preparation  by  the  pendulum  in  its  swing  opening  a  key  (fig. 
313,  C.)  in  the  primary  circuit. 

Single  Muscle  Contractions. — The  tracing  {muscle  curve)  ob- 
tained of  a  single  muscle  contraction  or  twitch  is  seen  in  fig.  314,  and 
may  be  thus  explained. 

The  upper  line  (m)  represents  the  curve  traced  by  the  end  of  the  lever 
in  connection  with  a  muscle  after  stimulation  of  the  muscle  by  a  single 


Fi^.  314. — Muscle-curve  obtained  by  means  of  the  pendulum  myograph,  .s,  indicates  the 
exact  instant  of  the  induction  sliock;  c,  commencement;  and  m  x,  the  maximum  elevation  of 
lever;  t,  the  line  of  a  vibrating  tuning-fork.     (M.  Foster.) 

induction-shock:  the  middle-line  (/)  is  that  described  by  the  marking- 
lever,  and  indicates  by  a  sudden  drop  the  exact  instant  at  which  the 
induction-shock  was  given.  The  lower  wavy  line  (t)  is  traced  by  a 
vibrating  tuning-fork,  and  serves  to  measure  precisely  the  time  occupied 
in  each  part  of  the  contraction. 

It  will  be  observed  that  after  the  stimulus  has  been  applied,  as  indi- 
cated by  the  vertical  line  s,  there  is  an  interval  before  the  contraction 
commences,  as  indicated  by  the  line  r.  This  interval,  termed  (a)  the 
latent  period,  when  measured  by  the  number  of  vibrations  of  the  tun- 
ing-fork between  the  lines  .s  and  r,  is  found  to  be  about  y^  sec.  The 
latent  period  is  longer  in  some  muscles  than  in  others,  and  differs  also 
according  to  the  condition  of  the  muscie,  being  longer  in  fatigued  mus- 
28 


434  HANDBOOK    OF    PHYSIOLOGY. 

cles,  and  the  kind  of  stimulus  employed.     During  the  latent  period  there 
is  no  apjJcweiit  change  in  the  muscle. 

The  second  part  is  the  {h)  stage  of  contraction  proper.  The  lever 
is  raised  by  the  sudden  contraction  of  the  muscle.  The  contraction  is  at 
first  very  rapid,  but  then  progresses  more  slowly  to  its  maximum,  indi- 
cated by  the  line  m  x,  drawn  through  its  highest  point.  It  occupies  in 
the  figure  y|o  sec.  {<;)  The  next  stage,  stage  of  elongation.  After 
reaching  its  highest  point,  the  lever  begins  to  descend,  in  consequence 
of  the  elongation  of  the  muscle.  At  first  the  fall  is  rapid,  but  then  be- 
<;omes  more  gradual  until  the  lever  reaches  the  abscissa  or  baseline,  and 
the  muscle  attains  its  pre-con traction  length,  indicated  in  the  figure  by 
the  line  c'.  The  stage  occujjies  jf  ^  second.  Very  often  after  the  main 
xjoutraction  the  lever  rises  once  or  twice  to   a  slight  degree,  producing 


Fig.  315.— Tracing  of  a  double  muscle-curve.  To  be  read  from  left  to  right.  While  the 
muscle  was  engaged  in  the  first  contraction  (whose  complete  course,  had  nothing  intervened,  is 
indicated  by  the  dotted  line),  a  second  induction-shock  was  thrown  in,  at  such  a  time  that  the 
second  contraction  began  just  as  the  fir.st  was  beginning  to  decline.  The  second  curve  is  seen 
to  start  from  the  first,  as  does  the  first  from  the  base  line.     (M.  Foster.) 

curves,  one  of  which  is  seen  in  fig.  315.  These  contractions,  due  to  the 
elasticity  of  the  muscle,  are  called  most  "in-operly  {d)  Stage  of  elastic 
after-vibration,  or  contraction  remainder. 

The  muscle  curve  obtained  from  the  heart  differs  from  that  of  other 
striped  muscles  in  the  longer  duration  of  the  effect  of  stimulation;  the 
descending  curve  also  is  more  prolonged. 

The  greater  part  of  the  latent  period  is  taken  up  by  changes  in  the 
muscle  itself,  and  the  remainder  occupied  in  the  propagation  of  the 
shock  along  the  nerve. 

Tetanus. — If  we  stimulate  the  nerve-muscle  preparation  with  two 
induction  shocks,  one  immediately  after  the  other,  when  the  point  of 
stimulation  of  the  second  one  corresponds  to  the  maximum  of  the  first, 
a  second  curve  (fig.  315)  will  occur,  which  will  commence  at  the 
highest  point  of  the  first  and  will  rise  nearly  as  high,  so  that  the  sum  of 
the  height  of  the  two  curves  almost  exactly  equals  twice  the  height  of  the 
first.     If  a  third  and  a  fourth  shock  be  passed,  a  similar  effect  will  en- 


THE    METABOLISM    OF   THE    TISSUES. 


•435 


sue,  and  curves  one  above  the  other  will  be  traced,  the  third  being 
slightly  lower  than  the  second,  and  the  fourth  than  the  third.  If  a  more 
numerous  series  of  shocks  occur,  however,  the  lever  after  a  time  ceases 
to  rise  any  further,  and  the  contraction,  which  has  reached  its  maxi- 
mum, is  maintained.     The  condition  which  ensues  is  called   Tetanus. 


Fig.  316.— Curve  of  tetanus,  ootained  from  the  gastrocnemius  of  a  frog,  where  the  shocks 
were  sent  in  from  an  induction  coil,  about  sixteen  times  a  second,  by  the  interruption  of  tlie 
primary  current  by  means  of  a  vibrating  spring,  which  dipped  into  a  cup  of  mercury,  and  broke 
the  primary  current  at  each  vibration. 

A  tetanus  is  really  a  summation  of  contractions,  but  unless  the  stimuli 
become  very  rapid  indeed,  the  muscle  will  still  be  in  a  condition  of  vi- 
bratory contraction  and  not  of  unvarying  contraction. 

If  the  shocks,  however,  be  repeated  at  very  short  intervals,  being  15 
per  second  for  the  frog's  muscle,  but  varying  in  each  animal,  the  muscle 
contracts  to  its  utmost  suddenly  and  continues  at  its  maximum  contrac- 
tion for  some  time  and  the  lever  rises  almost  perpendicularly,  and  then 
describes  a  straight  line  (fig.  317).     If  the  stimuli  are  not  quite  so  rapid 


Fig.  317.— Curve  of  tetanus,  from  a  series  of  very  rapid  shocks  from  a  magnetic  interrupter. 

the  line  of  maximum  contraction  becomes  somewhat  wavy,  indicating  a 
slight  tendency  of  the  muscle  to  relax  during  the  intervals  between  the 
stimuli  (fig.  316). 

Muscular  Work. — We  have  seen  that  icorh  is  estimated  by  multi- 
plying the  weight  raised,  by  the  height  through  which  it  has  been  lifted. 
It  has  been  found  that  in  order  to  obtain  the  maximum  of  work  a  mus- 
cle must  be  moderately  loaded:  if  the  weight  is  increased  beyond  a  cer- 
tain point,  however,  the  muscle  becomes  strained  and  raises  it  through 


436  HANDBOOK    OF    PHYSIOLOGY. 

SO  small  a  distance  tliat  less  work  is  accomplished.  If  the  load  is  still 
further  increased,  the  muscle  is  completely  overtaxed  and  cannot  raise 
the  weight.  No  work  is  then  done  at  all.  Practical  illustrations  of 
these  facts  must  be  familiar  to  every  one. 

The  power  of  a  muscle  is  usually  measured  by  the  maximum  weight  which 
it  will  support  without  stretching.  In  man  this  is  readily  determined  by  weight- 
ing the  body  to  such  an  extent  that  it  can  no  longer  be  raised  on  tiptoe  :  thus 
the  power  of  the  calf-muscles  is  determined.  The  power  of  a  muscle  thus  esti- 
mated depends  of  course  upon  its  cross-section.  The  power  of  a  human  muscle 
is  from  two  to  three  times  as  great  as  a  frog's  muscle  of  the  same  sectional  area. 

• 

Fatigue  of  Muscle, — A  muscle  becomes  rapidly  exhausted  from  re- 
peated stimulation,  and  the  more  rapidly,  the  more  quickly  the  induc- 
tion-shocks succeed  each  other.  This  is  indicated  by  the  diminished 
height  of  the  muscular  contractions. 

A  fatigued  muscle  has  a  much  longer  latent  period  than  a  fresh  one. 
The  slowness  with  which  muscles  respond  to  the  will  when  fatigued  must 
be  familiar  to  every  one. 

In  a  muscle  which  is  exhausted,  stimulation  only  causes  a  contraction 
producing  a  local  bulging  near  the  point  irritated,  A  similar  effect 
may  be  produced  in  a  fresh  muscle  by  a  sharp  blow,  as  in  striking  the 
biceps  smartly  with  the  edge  of  the  hand,  when  a  hard  muscular  swelling 
is  instantly  formed. 

Accompaniments  of  Muscular  Contraction. 

(1.)  Heat  is  developed  in  the  contraction  of  muscles.  Becquerel  and 
Breschet  found,  with  the  thermo-multiplier  about  ,5°  C.  of  heat 
produced  by  each  forcible  conti-aption  of  a  man's  biceps;  and  when  the 
actions  were  long  continued,  the  temperature  of  the  muscle  increased  1°. 
This  estimate  is  probably  high,  as  in  the  frog's  muscle  a  considerable 
contraction  has  been  found  to  produce  an  elevation  of  temperature  equal 
on  an  average  to  less  than  ^°  C.  It  is  not  known  whether  this  develop- 
ment of  heat  is  due  to  chemical  changes  ensuing  in  the  muscle,  or  to  the 
friction  of  its  fibres  vigorously  acting :  in  either  case,  we  may  refer  to  it 
a  part  of  the  heat  developed  in  active  exercise. 

(2.)  Sound  is  produced  as  mentioned  above,  when  muscles  contract 
forcibly.  Wollaston  showed  that  this  sound  might  be  easily  heard  by 
placing  the  tip  of  the  little  finger  in  the  ear,  and  then  making  some 
muscles  contract,  as  those  oi  the  ball  of  the  thumb,  whose  sound  may  be 
conducted  to  the  ear  through  the  substance  of  the  hand  and  finger.  A 
low  shaking  or  rumbling  sound  is  heard,  the  height  and  loudness  of  the 
note  being  in  direct  proportion  to  the  force  and  quickness  of  the  mus- 
cular action,  and  to  the  number  of  fibres  that  act  together,  or,  as  it 
were,  in  time. 


THE    METABOLISM    OF    THE   TISSUES.  437 

(3.)  Changes  in  Shape. — There  is  a  considerable  difference  of  opinion 
as  to  the  mode  in  which  the  transversely  striated  muscular  fibres  con- 
tract. The  most  probable  account  is,  that  the  contraction  is  effected 
by  an  approximation  of  the  constituent  parts  of  the  fibrils,  which,  at 
the  instant  of  contraction,  without  any  alteration  in  their  general  direc- 
tion, become  closer,  flatter,  and  wider;  a  condition  which  is  rendered 
evident  by  the  approximation  of  the  transverse  strias  seen  on  the  surface 
of  the  fasciculus,  and  by  its  increased  breadth  and  thickness.  The 
appearance  of  the  zigzag  lines  into  which  it  was  supposed  the  fibres  are 
thrown  in  contraction,  is  due  to  the  relaxation  of  a  fibre  which  has  been 
recently  contracted,  and  is  not  at  once  stretched  again  by  some  antago- 
nist fibre,  or  whose  extremities  are  kept  close  together  by  the  contractions 
of  other  fibres.  The  contraction  is  therefore  a  simple  and,  according  to 
Ed.  "Weber,  a  uniform,  simultaneous,  and  steady  shortening  of  each  fibre 
and  its  contents.  What  each  fibril  or  fibre  loses  in  length,  it  gains  in 
thickness :  the  contraction  is  a  change  of  form  not  of  size ;  it  is,  there- 
fore, not  attended  with  any  diminution  in  bulk,  from  condensation  of 
the  tissue.  This  has  been  proved  for  entire  muscles,  by  making  a  mass 
of  muscles,  or  many  fibres  together,  contract  in  a  vessel  full  of  water, 
with  which  a  fine,  perpendicular,  graduated  tube  communicates.  Any 
diminution  of  the  bulk  of  the  contracting  muscle  would  be  attended  by 
a  fall  of  fluid  in  the  tube;  but  when  the  experiment  is  carefully  per- 
formed, the  level  of  the  water  in  the  tube  remains  the  same,  whether 
the  muscle  be  contracted  or  not. 

In  thus  shortening,  muscles  appear  to  swell  vp,  becoming  rounder,  more 
prominent,  harder,  and  apparently  tougher.     But  this  hardness  of  muscle 


■I 


EL 


Fig.  318. — The  microscopic  appearances  during  a  muscular  contraction  in  the  individual 
fibrillar,  after  Engehnaun.  1.  A  passive  muscle-fibre;  c  to  d  =  doubly  refractive  discs,  with 
median  disc  a  b  in  it:  h  and  g  are  lateral  discs:  f  and  e  are  secondary  discs,  only  slightly  doubly 
refractive;  fig.  on  right  same  fibre  in  polarized  light:  bright  part  is  doubly  refracted,  black  ends 
not  so.  2.  Transition  stage;  and  ;^.  Stage  of  entire  contraction:  in  each  case  the  right-hand 
figure  represents  the  effect  of  polarized   light.  cLandois  after  Engelmaun.) 

in  the  state  of  contraction  is  not  due  to  increased  firmness  or  condensa- 
tion of  the  muscular  tissue,  but  to  the  increased  tension  to  which  the 
fibres,  as  well  as  their  tendons  and  other  tissues,  are  subjected  from  the 
resistance  ordinarily  opposed  to  their  contraction.  When  no  resistance 
is  offered,  as  when  a  muscle  is  cut  off  from  its  tendon,  not  only  is  no 
hardness  perceived  during  contraction,  but  the  muscular  tissue  is  even 


438  HANDBOOK    OF    PHYSIOLOGY. 

softer,  more  extensile,  and  less  elastic  than  in  its  ordinary  uncontracted 
state.  During  contraction  in  each  fibre  it  is  said  that  the  anisotropous 
or  doubly  refractive  elements  become  less  refractive  and  the  singly  re- 
fractive more  so  (fig.  318). 

(4.)  Chemical  Changes. — (a)  The  reaction  of  the  muscle  which  is 
normally  alkaline  or  neutral  becomes  decidedly  acid,  from  the  develop- 
ment of  sarcolactic  acid,  {h)  The  muscle  gives  out  carbonic  acid  gas 
and  takes  up  oxygen,  the  amount  of  the  CO^  given  out  not  appearing  to 
be  entirely  dependent  upon  the  0  taken  in,  and  so  doubtless  in  part 
arising  from  some  other  source.  (c)  Certain  imperfectly  understood 
chemical  changes  occur,  in  all  probability  connected  with  {a)  and  {b). 
Glycogen  is  diminished,  and  glucose,  or  muscle  sugar  (inosite)  appears; 
the  extractives  are  increased. 

(5.)  Electrical  Changes. — AVhen  a  muscle  contracts  the  natural  muscle 
current  or  currents  of  rest  undergo  a  distinct  diminution,  which  is  due 
to  the  appearance  in  the  actively  contracting  muscle  of  currents  in  an 
opposite  direction  to  those  existing  in  the  muscle  at  rest.  This  causes 
a  temporary  deflection  of  the  needle  of  a  galvanometer  in  a  direction 
opposite  to  the  original  current,  and  is  called  by  some  the  negative  vari- 
ation of  the  muscle  current,  and  by  others  a  current  of  action. 

Conditions  of  Contraction. —  {a)  The  irritability  of  muscle,  as 
indicated  by  length  of  latent  period,  velocity  and  extent  of  contraction, 
is  greatest  at  a  certain  mean  tern i:)eratu re;  {b)  after  a  number  of  con- 
tractions a  muscle  gradually  becomes  exhausted;  (r)  the  activity  of 
muscles  after  a  time  disappears  altogether  when  they  are  removed  from 
the  body  or  the  arteries  are  tied ;  [d)  oxygen  is  used  up  in  muscular 
contraction,  but  a  muscle  Aviil  act  for  a  time  in  vacuo  or  in  a  gas  which 
contains  no  oxygen;  in  this  case  it  is  of  course  using  up  the  oxygen 
already  in  store;  {e)  the  contraction  is  greater  if  the  stimulus  is  applied 
to  the  nerve,  than  if  it  be  applied  to  the  muscle  directly. 

Response  to  Stimuli. — The  two  kinds  of  fibres,  the  striped  and 
the  unstriped,  have  characteristic  differences  in  the  mode  in  which  they 
act  on  the  application  of  the  same  stimulus;  differences  which  may  be 
ascribed  in  great  part  to  their  respective  differences  of  structure.,  but  in 
some  degree,  possibly,  to  their  respective  modes  of  connection  with  the 
nervous  system.  When  irritation  is  applied  directly  to  a  muscle  with 
striated  fibres,  or  to  the  motor  nerve  supplying  it,  contraction  of  the 
part  irritated,  and  of  that  only,  ensues;  and  this  contraction  is  instan- 
taneous, and  ceases  on  the  instant  of  withdrawing  the  irritation.  But 
when  any  part  with  unstriped  muscular  fibres,  e.g.,  the  intestines  or 
bladder,  is  irritated,  the  subsequent  contraction  ensues  more  slowly, 
extends  beyond  the  part  irritated,  and,  witli  alternating  relaxation,  con- 
tinues for  some  time  after  the  withdrawal  of  the  irritation.      The  differ- 


THE    METABOLISM    OF   THE   TISSUES.  439 

ence  in  the  modes  of  coutractiou  of  the  two  kinds  of  muscular  fibres 
may  be  particularly  illustrated  by  the  effects  of  the  repeated  stimuli 
with  the  magnetic  interrupter.  The  rapidly  succeeding  shocks  given 
by  this  means  to  the  nerves  of  muscles  excite  in  all  the  transversely  stri- 
ated muscles,  except  in  the  case  of  the  heart,  a  fixed  state  of  tetanic 
contraction  as  previously  described,  which  lasts  as  long  as  the  stimulus 


Fig:.  319. — Muscle-curves  from  the  gastrocnemius  of  a  frog,  illustrating  effects  of  alterations  in 

temperature. 

is  continued,  and  on  its  withdrawal  instantly  ceases;  but  in  the  muscles 
with  unstriped  fibres  they  excite  a  slow  vermicular  movement,  which  is 
comparatively  slight  and  alternates  with  rest.  It  continues  for  a  time 
after  the  stimulus  is  withdrawn. 

In  their  mode  of  responding  to  these  stimuli,  all  the  skeletal  mviscles,  or 
those  with  transverse  stria?,-  are  alike  ;  but  among  those  with  unstriped  fibres 
there  are  many  differences — a  fact  which  tends  to  confirm  the  opinion  that 
their  pecviliarity  depends  as  well  on  their  connection  with  nerves  and  ganglia 
as  on  their  own  properties.  The  ureters  and  gall-bladder  are  the  parts  least 
excited  by  stimuli ;  they  do  not  act  at  all  till  the  stimulus  has  been  long  applied, 
and  then  contract  feebly,  and  to  a  small  extent.  The  contractions  of  the  caecum 
and  stomach  are  quicker  and  wider  spread  :  still  quicker  those  of  the  iris,  and  of 
the  urinary  bladder  if  it  be  not  too  full.  The  actions  of  the  small  and  large 
intestines,  of  the  vas  deferens,  and  pregnant  uterus,  are  j^et  more  vivid,  more 
regular,  and  more  sustained  ;  and  they  require  no  more  .stimulus  than  thijt  of  the 
air  to  excite  them.  The  heart,  on  account,  doubtless,  of  its  striated  muscle,  is 
the  quickest  and  most  vigorous  of  all  the  muscles  of  organic  life  in  contracting 
upon  irritation,  and  appears  in  this,  as  in  nearly  all  other  respects,  to  be  the  con- 
necting member  of  the  two  classes  of  muscles. 

All  the  muscles  retain  their  property  of  contracting  under  the  influence  of 
stimuli  applied  to  thena  or  to  their  nerves  for  some  time  after  death,  the  period 
being  longer  in  cold-blooded  than  in  warm-blooded  Vertebrata,  and  shorter  in 
Bii'ds  than  in  Mammalia.  It  would  seem  as  if  the  more  active  the  respiratory 
process  in  the  living  animal,  the  shorter  is  the  time  of  dviration  of  the  irrita- 
bility in  the  muscles  aft^-r  death  ;  and  this  is  confirmed  by  the  comparison  of 
different  species  in  the  same  order  of  Vertebrata.  But  the  i:)eriod  during  which 
this  irritability  lasts  is  not  the  same  in  all  persons,  nor  in  all  the  muscles  of 
the  same  person.  In  a  man  it  ceases,  according  to  Nysten,  in  the  following 
order: — first  in  the  left  ventricle,  then  in  the  intestines  and  stomach,  the 
urinary  bladder,  right  ventricle,  oesophagus,  iris ;  then  in  the  voluntary  mus- 
cles of  the  trunk,  lower  and  upper  extremities ;  lastly,  in  the  right  and  left 
auricle  of  the  heart. 


440  HANDBOOK    OF    PHYSIOLOGY. 

Muscle  in  Rigor  Mortis. 

After  the  muscles  of  the  dead  body  have  lost  their  irritability  or  capa- 
bility of  being  excited  to  contraction  by  the  application  of  a  stimulus, 
they  spontaneously  pass  into  a  state  of  contraction,  apparently  identical 
with  that  which  ensues  during  life.  It  affects  all  the  muscles  of  the 
body;  and,  when  external  circumstances  do  not  prevent  it,  commonly 
fixes  the  limbs  in  that  which  is  their  natural  posture  of  equilibrium  or 
rest.  Hence,  and  from  the  simultaneous  contraction  of  all  the  muscles 
of  the  trunk,  is  produced  a  general  stiffening  of  the  body,  constituting 
the  rigor  mortis  or  post- mortem  rigidity. 

When  this  condition  has  set  in,  the  muscle  [a)  'becomes  acid  in  reaction 
(due  to  development  of  sarcolactic  acid),  (Z*)  gives  off  carhonic  acid  in 
great  excess,  (c)  diminishes  in  volume  slightly,  (d)  becomes  shortened  and 
opaque,  its  substance  setting  firm.  Eigor  comes  on  much  more  rapidly 
after  muscular  activity,  and  is  hastened  by  Avarmth.  It  may  be  brought 
on,  in  muscles  exposed  for  experiment,  by  the  action  of  distilled  water 
and  many  acids,  also  by  freezing  and  thawing. 

Cause. — The  immediate  cause  of  rigor  seems  to  be  a  chemical  one, 
namely,  the  coagulation  of  the  muscle  plasma.  We  may  distinguish 
three  main  stages — (1.)  Gradual  coagulation.  (2.)  Contraction  of  coag- 
ulated muscle-clot  (myosin),  and  squeezing  out  of  muscle-serum.  (3.) 
Putrefaction.  After  the  first  stage,  restoration  is  possible  through  the 
circulation  of  arterial  blood  through  the  muscles,  and  even  when  the 
second  stage  has  set  in,  vitality  may  be  restored  by  dissolving  the  coag- 
ulum  of  the  muscle  in  salt  solution,  and  j^assing  arterial  blood  through 
the  vessels.     In  the  third  stage  recovery  is  impossible. 

It  has  been  noticed  that  the  relaxation  in  muscles  after  rigor  some- 
times occurs  too  quickly  to  be  caused  by  putrefaction,  and  the  suggestion 
that  in  such  cases  at  any  rate  such  relaxation  is  due  to  a  ferment-action 
is  very  plausible.  It  is  known  that  pepsin  is  present  in  muscles,  and 
that  this  ferment  will  act  in  an  acid  medium.  The  conditions  for  the 
solution  of  the  coagulated  myosin  are  therefore  present  as  the  reaction 
of  rigored  muscle  is  acid. 

Order  of  Occurrence. — The  muscles  are  not  affected  simu*ltaneously  oy 
rigor  mortis..  It  affects  the  neck  and  lower  jaw  first;  next,  the  upper 
extremities,  extending  from  above  downward;  and  lastly,  reaches  the 
lower  limbs;  in  some  rare  instances  only,  it  affects  the  lower  extremities 
before,  or  simultaneously  Mdth,  the  upper  extremities.  It  usually  ceases 
in  the  order  in  which  it  begins:  first  at  the  head,  then  in  the  upper 
extremities,  and  lastly  in  the  lower  extremities.  It  never  commences 
earlier  than  ten  minutes,  and  never  later  than  seven  hours  after  death; 
and  its  duration  is  greater  in  proportion  to  the  lateness  of  its  accession. 


THE    METABOLISM    OF   THE   TISSUES,  441 

Heat  is  developed  during  the  passage  of  a  muscular  fibre  into  the  condi- 
tion of  rigor  mortis. 

Since  rigidity  does  not  ensue  until  muscles  have  lost  the  capacity  of 
being  excited  by  external  stimuli,  it  follows  that  all  circumstances  which 
cause  a  speedy  exhaustion  of  muscular  irritability,  induce  an  early  oc- 
currence of  the  rigidity,  while  conditions  by  which  the  disappearance  of 
the  irritability  is  delayed,  are  succeeded  by  a  tardy  onset  of  this  rigidity. 
Hence  its  speedy  occurrence,  and  equally  speedy  departure  in  the  bodies 
of  persons  exhausted  by  chronic  diseases;  and  its  tardy  onset  and  long 
continuance  after  sudden  death  from  acute  diseases.  In  some  cases  of 
sudden  death  from  lightning,  violent  injuries,  or  paroxysms  of  passion, 
rigor  mortis  has  been  said  not  to  occur  at  all;  but  this  is  not  always  the 
case.  It  may,  indeed,  be  doubted  whether  there  is  really  a  comj^lete 
absence  of  the  post-mortem  rigidity  in  any  such  cases;  for  the  experi- 
ments of  Brown-Sequard  make  it  probable  that  the  rigidity  may  supervene 
immediately  after  death,  and  then  pass  away  with  such  rapidity  as  to  be 
scarcely  observable. 

The  occurrence  of  rigor  mortis  is  not  prevented  by  the  previous  exist- 
ence of  paralysis  in  a  part,  provided  the  j^aralysis  has  not  been  attended 
with  very  imperfect  nutrition  of  the  muscular  tissue. 

The  rigidity  affects  the  involuntary  as  well  as  the  voluntary  muscles, 
whether  they  be  constructed  of  striped  or  unstriped  fibres.  The  rigidity 
of  involuntary  muscles  with  striped  fibres  is  shown  in  the  contraction  of 
the  heart  after  death.  The  contraction  of  the  muscles  with  unstriped 
^res  is  shown  by  an  experiment  of  Valentin,  who  found  that  if  a  grad- 
uated tube  connected  with  a  portion  of  intestine  taken  from  a  recently- 
killed  animal,  be  filled  with  water,  and  tied  at  the  opposite  end,  the 
water  will  in  a  few  hours  rise  to  a  considerable  height  in  the  tube, 
owing  to  the  contraction  of  the  intestinal  walls.  It  is  still  better  shown 
in  the  arteries,  of  which  all  that  have  muscular  coats  contract  after 
death,  and  thus  present  the  roundness  and  cord-like  feel  of  the  arteries 
of  a  limb  lately  removed,  or  those  of  a  body  recently  dead.  Subsequently 
they  relax,  as  do  all  the  other  muscles,  and  feel  lax  and  flabby,  and  lie 
as  if  flattened,  and  with  their  walls  nearly  in  contact. 

Action  of  the  Voluntary  Muscles. 

The  greater  part  of  the  voluntary  muscles  of  the  body  act  as  sources 
of  power  for  moving  levers, — the  latter  consisting  of  the  various  bones  to 
which  the  muscles  are  attached. 

Examples  of  the  three  orders  of  levers  in  the  Human  Body. — All  levers  have 
been  divided  into  three  kinds,  according  to  the  relative  position  of  the  power, 
the  tceight  to  be  removed,  and  the  axis  of  motion  or  fulcrum.  In  a  lever  of 
the  first  kind  the  potver  vi  at  oneexti-emity  of  the  lever,  the  iceight  at  the  other. 


442 


HANDBOOK    OF    PHYSIOLOGY, 


and  the  fulcrum  between  the  two.  If  the  initial  letters  only  of  the  power, 
weight,  and  fulcrum  be  used,  the  arrangement  will  stand  thus :— P.  F.  W.  A 
poker  as  ordinarily  used,  or  the  bar  in  fig.  320,  may  be  cited  as  an  example  of 
this  variety  of  lever ;  while,  as  an   instance   in  which  the  bones  of  the  human 


9 


-au 


Fig.  320. 

skeleton  are  used  as  a  lever  of  the  same  kind,  may  be  mentioned  the  act  of 
raising  the  body  from  the  stooping  posture  by  means  of  the  hamstring  muscles 
attached  to  the  tuberosity  of  the  ischium  (fig.  320) . 

In  a  lever  of  the  second  kind,  the  arrangement  is  thus : — P.  W.  F.  ;  and  this 
leverage  is  employed  in  the  act  of  raising  the  handles  of  a  wheelbarrow,  or  in 
stretching  an  elastic  band,  as  in  fig.  321.  In  the  human  body  the  act  of  open- 
ing the  mouth  by  depressing  the  lower   jaw  is  an  example  of   the  same  kind — 


ClasticHBano 


Fig.  321. 

the  tension  of  the  muscles  which  close  the  jaw  representing  the  weight 
(fig.  321). 

In  a  lever  of  the  third  kind  the  arrangement  is — F.  P.  "W. ,  and  the  act  of 
raising  a  pole,  as  in  fig.  322,  is  an  example.  In  the  human  body  there  are 
numerous  examples  of  the  employment  of  this  kind  of  leverage.  The  act  of 
bending  the  fore-arm  may  be  mentioned  as  an  instance  (fig.  322).  The  act  of 
biting  is  another  example. 

At  the  ankle  we  have  examples  of  all  three  kinds  of  lever.  1st  kind — Ex- 
tending the  foot.  3d  kind — Flexing  the  foot.  In  both  these  cases  the  foot 
represents  the  weight :  the  ankle  joint  the  fulcrum,  the  power  being  the  calf 
muscles  in  the  first  case  and  the  tibialis  anticus  in  the  second  case.     2d  kind — 


THE    METABOLISM    OF   THE   TISSUES. 


443 


When  the  body  is  raised  on  tiptoe.  Here  the  ground  is  the  fulcrum,  the 
weight  of  the  body  acting  at  the  ankle  joint  the  weight,  and  the  calf  muscles 
the  power. 

In  the  human  body,  levers  are  most  frequently  used  at  a  disadvantage  as 
regards  power,  the  latter  being  sacrificed  for  the  sake  of  a  greater  range  of 
motion.  Thus  in  the  diagrams  of  the  first  and  third  kinds  it  is  evident  that 
the  power  is  so  close  to  the  fulcrum,  that  great  force  must  be  exercised  in  order 
to  produce  motion.     It  is  also  evident,  however,  from  the  same  diagrams,  that 


Fig.  .322. 

by  the  closeness  of  the  power  to  tlie  fulcrum  a  great  range  of  movement  can 
be  obtained  by  means  of  a  comparatively  slight  shortening  of  the  muscular 
fibres. 

The  greater  number  of  the  more  important  muscular  actions  of  the 
human  body — those,  namely,  which  are  arranged  harmoniously  so  as  to 
subserve  some  definite  purpose  or  other  in  the  animal  economy — are  de- 
scribed in  various  parts  of  this  work,  in  the  sections  which  treat  of  the 
physiology  of  the  processes  by  which  these  muscular  actions  are  resisted 
or  carried  out.  There  are,  however,  one  or  two  very  important  and 
somewhat  complicated  muscular  acts  which  may  be  best  described  in 
this  place. 

Walking. — In  the  act  of  walking,  almost  every  voluntary  muscle  in  the  body 
is  brought  into  play,  either  directly  for  purposes  of  progression,  or  indirectly 
for  the  proper  balancing  of  the  head  and  trunk.  The  muscles  of  the  arms  are 
least  concerned ;  but  even  these  are  for  the  most  part  instinctively  in  action  to 
some  extent. 

Among  the  chief  muscles  engaged  directly  in  the  act  of  walking  are  those  of 
the  calf,  which,  by  pulling  up  the  heel,  pull  up  also  the  astragalus,  and  with  it, 
of  course,  the  whole  body,  the  weight  of  which  is  transmitted  through  the 
tibia  to  this  bone  (fig.  328) .  When  starting  to  walk,  say  with  the  left  leg, 
this  raising  of  the  body  is  not  left  entirely  to  the  muscles  of  the  left  calf,  but 
the  trunk  is  thrown  forward  in  such  a  way,  that  it  would  fall  prostrate  were 
it  not  that  the  right  foot  is  brought  forward  and  planted  on  the  ground  to  sup- 
port it.  Thus  the  muscles  of  the  left  calf  are  assisted  in  their  action  by  those 
muscles  on  the  front  of  the  trunk  and  legs  which,  by  their  contraction,  pull  the 
body  forward ;  and,  of  course,  if  the  trunk  form  a  slanting  line,  with  the  in- 
clination forward,  it  is  plain   that  when  the  heel  is  raised  by  the  calf-muscles. 


444 


HAXDBOOK    OF    PHYSIOLOGY, 


the  whole  body  will  be  raised,  and  pushed  obliquely  forward  and  upward. 
The  successive  acts  in  taking  the  first  step  in  walking  are  represented  in 
fig.  323,  1,  2,  3. 

Now  it  is  evident  that  by  the  time  the  body  has  assumed  the  position  No.  3, 
it  is  time  that  the  right  leg  should  be  brought  forward  to  support  it  and  pre- 
vent it  from  falling  prostrate.  This  advance  of  the  other  leg  (in  this  case  the 
right)  is  effected  partly  by  its  mechanically  swinging  forward,  pendulum- 
wise,  and  partly  by  muscular  action  ;  the  muscles  used  being — 1st,  those  on  the 
front  of  the  thigh,  which  bend  the  thigh  forward  on  the  pelvis,  especially  the 
rectus  femoris,  with  the  psoas  and  the  iliacus ;  2dly,  the  hamstring  muscles, 
which  slightly  bend  the  leg  on  the  thigh ;  and,  Sdly,  the  muscles  on  the 
front  of  the  leg,  which  raise  the  front  of  the  foot  and  toes,  and  so  prevent  the 
latter  in  swinging  forward  from  hitching  in  the  ground. 

The  second  part  of  the  act  of  walking,  which  has  been  just  described,  is 
shown  in  the  diagram  (4,  fig.  323) . 

When  the  right  foot  has  reached  the  ground  the  action  of  the  left  leg  has  not 
ceased.  The  calf-muscles  of  the  latter  continue  to  act,  and  by  pulling  up  the 
heel,  throw  the  body  still  more  forward  over  the  right  leg,  now  bearing  nearly 
the  whole  weight,  until  it  is  time  that  in  its  turn  the  left  leg  should  swing 
forward,  and  the  left  foot  be  planted  on  the  ground  to  prevent  the  body  from 
falling  prostrate.  As  at  first,  while  the  calf-muscles  of  one  leg  and  foot  are 
preparing,  so  to  tpeak,  to  pws/i  the  body  forward  and  upward  from  behind 
by  raising  the  heel,  the  muscles  on  the  front  of  the  trunk  and  the  same  leg 
(and  of  the  other  leg,  except  when   it  is  swinging  forward)    are  helping  the 


Fig.  323. 

act  by  pulling  the  legs  and  trunk,  so  as  to  make  them  incline  forward,  the 
rotation  in  the  inclining  forward  being  effected  mainly  at  the  ankle  joint. 
Two  main  kinds  of  leverage  are,  therefore,  employed  in  the  act  of  walking, 
and  if  this  idea  be  firmly  grasped,  the  details  muII  be  understood  with  com- 
parative ease.  One  kind  of  leverage  employed  in  walking  is  essentially  the 
same  with  that  employed  in  pulling  forward  the  pole,  as  in  fig.  322.  And  the 
other,  less  exactly,  is  that  employed  in  raising  the  handles  of  a  wheelbarrow. 
Now,  supposing  the  lower  end  of  the  pole  to  be  placed  in  the  barrow,  we 
should  have  a  very  rough  and  inelegant,  but  not  altogether  bad  representation 
of  the  two  main  levers  employed  in  the  act  of  walking.  The  body  is  pttZ/ed 
forward  by  the  muscles  in  front,  much  in  the  same  way  that  the  pole  might  be 
by  the  force  applied  at  P.,  while  the  raising  of  the  heel  and  2iushing  forward 
of  the  trunk  by  the  calf- muscles  is  roughly  represented  on  raising  the  handles 
of  the  barrow.  The  manner  in  which  these  actions  are  performed  alternately 
by  each  leg,  so  that  one  after  the  other  is  swung  forward  to  support  the 
trunk,  which  is  at  the  same  time  pushed  and  p>uUed  forward  by  the  muscles 
of  the  other,  may  be  gathered  from  the  the  previous  description. 


THE    METABOLISM    OF   THE   TISSUES, 


■445 


There  is  one  more  tiling  to  be  especially  noticed  in  the  act  of  walking.  In- 
asmuch as  the  body  is  being  constantly  supported  and  balanced  on  each  leg 
alternately,  and  therefore  on  onl}-  one  at  the  same  moment,  it  is  evident  that 
there  must  be  some  provision  made  for  throwing  the  centre  of  gravity  over  the 
line  of  support  formed  by  the  bones  of  each  leg,  as,  in  its  turn,  it  supports  the 
weight  of  the  body.  This  may  be  done  in  various  wajs,  and  the  manner  in 
which  it  is  effected  is  one  element  in  the  differences  which  exist  in  the  walk- 
ing of  different  people.  Thus  it  may  be  done  by  an  instinctive  slight  rotation  of 
the  pelvis  on  the  head  of  each  femur  in  turn,  in  such  a  manner  that  the  centre 
of  gi'avity  of  the  body  shall  fall  over  the  foot  of  this  side.  Thus  when  the  body 
is  pushed  onward  and  upward  by  the  raising,  say,  of  the  right  heel,  as  in  fig. 
323,  3,  the  pelvis  is  instinctively  by  various  muscles  made  to  rotate  on  the 
head  of  the  left  femur  at  the  acetabulum,  to  the  left  side,  so  that  .the  weight 
may  fall  over  the  line  of  support  formed  by  the  left  leg  at  the  time  that  the 


Fig.  3*4. 


iHght  leg  is  swinging  forward,  and  leaving  all  the  work  of  support  to  fall  on 
its  fellow.  Such  a  "  rocking"  movement  of  the  trunk  and  pelvis,  however,  is 
accompanied  by  a  movement  of  the  whole  trunk  and  leg  over  the  foot  which 
is  being  planted  on  the  ground  (fig.  324)  :  the  action  being  accompanied  with 
a  compensatory  outward  movement  at  the  hip,  more  easily  appreciated  by 
looking  at  the  figure  (in  which  this  movement  is  shown  exaggerated)  than 
described. 

Thus  the  body  in  walking  is  continually  rising  and  swaying  alternately 
from  one  side  to  the  other,  as  its  centre  of  gravity  has  to  be  brought  alternately 
over  one  or  other  leg ;  and  the  curvatures  of  tlie  spine  are  altered  in  corre- 
spondence with  the  varying  position  of  the  weight  which  it  has  to  support.  The 
extent  to  which  the  body  is  raised  or  swayed  differs  much  in  different  people. 

In  walking,  one  foot  or  the  other  is  always  on  the  ground.  Tlie  act  of  leaping 
or  jumping,  consists  in  so  sudden  a  raising  of  the  heels  by  the  sharp  and  strong 
contraction  of  the  calf-muscles,  that  the  body  is  jerked  off  the  groimd.  At  the 
same  time  the  effect  is  much  increased  by  first  bending  the  thighs  on  the  pel- 


446  HANDBOOK    OF    PHYSIOLOGY. 

vis,  and  the  legs  on  the  thighs,  and  then  suddenly  straightening  out  the  angles 
thus  formed.  The  share  which  this  action  has  in  producing  the  effect  may  be 
easily  known  by  attempting  to  leap  in  the  upright  posture,  with  the  legs  quite 
straight. 

Running  is  performed  by  a  series  of  rapid  low  jumps  with  each  leg  alter- 
nately ;  so  that,  during  each  complete  muscular  act  concerned,  there  is  a  moment 
when  both  feet  are  off  the  ground. 

In  all  these  cases,  however,  the  description  of  the  manner  in  which  any 
given  effect  is  produced,  can  give  but  a  very  imperfect  idea  of  the  infinite 
number  of  combined  and  harmoniously  arranged  muscular  contractions  which 
are  necessary  for  even  the  simplest  acts  of  locomotion. 

Action  of  the  Involuntary  Muscles. — The  involuntary  muscles 
are  for  the  most  part  not  attached  to  bones  arranged  to  act  as  levers,  but 
enter  into  the  formation  of  such  hollow  parts  as  require  a  diminution  of 
their  calibre  by  muscular  action,  under  particular  circumstances.  Ex- 
amples of  this  action  are  to  be  found  in  the  intestines,  urinary  bladder, 
heart  and  blood-vessels,  gall-bladder,  gland-ducts,  etc. 

The  difference  in  the  manner  of  contraction  of  the  striated  and  non- 
striated  fibres  has  been  already  referred  to  (p.  438) ;  and  the  peculiar 
vermicular  or  peristaltic  action  of  the  latter  fibres  has  also  been  described. 

Electkical  Cureents  IX  Nerves. 

The  electrical  condition  of  nerves  is  so  closely  connected  with  the 
phenomena  of  muscular  contraction,  that  it  will  be  convenient  to  con- 
sider it  in  the  present  chapter. 

If  a  piece  of  nerve  be  removed  from  the  body  and  subjected  to  exami- 
nation in  a  way  similar  to  that  adopted  in  the  case  of  muscle,  which  has 
been  described,  electrical  currents  are  found  to  exist  which  correspond 
exactly  to  the  natural  muscle  currents,  and  which  are  called  natural 
nei've  currents  or  currents  of  rest,  according  as  one  or  other  theory  of 
their  existence  be  adopted,  as  in  the  case  with  muscle.  One  point 
(equator)  on  the  surface  being  positive  to  all  other  points  nearer  to  the 
cut  ends,  and  the  greatest  deflection  of  the  needle  of  the  galvanometer 
taking  place  when  one  electrode  is  aj)plied  to  the  equator  and  the  other 
to  the  centre  of  either  cut  end.  As  in  the  case  of  muscle,  these  nerve 
currents  undergo  a  negative  variation  when  the  nerve  is  stimulated,  the 
variation  being  momentary  and  in  the  opposite  direction  to  the  natural 
currents;  and  are  similarly  known  as  the  currents  of  action.  The  cur- 
rents of  action  are  propagated  in  both  directions  from  the  point  of  the 
application  of  the  stimulus,  and  are  of  momentary  duration. 

Rheoscopic  Frog. — This  negative  variation  may  be  demonstrated  by  means  of 
the  following  experiment.— The  new  current  produced  by  stimulating  the  nerve 
of  one  nerve-muscle  preparation  may  be  used  to  stimulate  the  neiwe  of  a  second 
nerve-muscle  preparation.     The  foreleg  of  a  frog  with  the  nerve  going  to  the 


THE    METABOLISM    OF   THE   TISSUES.  447 

gastrocnemius  cut  long  is  placed  upon  a  glass  plate,  and  arranged  in  such  way 
that  its  nerve  touches  in  two  places  the  sciatic  nerve,  exposed  but  preserved 
in  situ  in  the  opposite  thigh  of  the  frog.  The  electrodes  from  an  induction 
coil  are  placed  behind  the  sciatic  nerve  of  the  second  preparation,  high  up. 
On  stimulating  it  with  a  single  induction  shock,  the  muscles  not  only  of  the 
same  leg  are  found  to  undergo  a  twitch,  but  also  those  of  the  first  preparation, 
although  this  is  not  near  the  electrodes,  and  so  the  stimulation  cannot  be  due 
to  an  escape  of  the  current  into  the  first  nerve.  This  experiment  is  known 
under  the  name  of  the  rheoscopic  frog. 

Nerve-stimuli. — Xerve-fibres  require  to  be  stimulated  befor  ethey  can 
manifest  any  of  their  properties,  since  they  have  no  power  of  themselves 
of  generating  force  or  of  originating  impulses.  The  stimuli  which  are 
capable  of  exciting  nerves  to  action  are,  as  in  the  case  of  muscle,  very 
diverse.  They  are  very  similar  in  each  case.  The  mechanical,  chem- 
ical, thermal,  and  electric  stimuli  which  may  be  used  in  the  one  case 
are  also,  with  certain  differences  in  the  methods  employed,  efficacious  in 
the  other.  The  chemical  stimuli  are  chiefly  these:  withdrawal  of  water, 
as  by  drying,  strong  solutions  of  neutral  salts  of  potassium,  sodium,  etc., 
free  inorganic  acids,  except  phosphoric;  some  organic  acids;  ether, 
chloroform,  and  bile  salts.  The  electrical  stimuli  employed  are  the 
induction  and  continuous  currents  concerning  which  the  observations  in 
reference  to  muscular  contraction  should  be  consulted,  \yeaker  efec- 
trical  stimuli  will  excite  nerve  than  will  excite  muscle;  the  nerve  stimuli 
appears  to  gain  strength  as  it  descends,  and  a  weaker  stimulus  applied 
far  from  the  muscle  will  have  the  same  effect  as  a  stronger  one  applied 
to  the  nerve  near  the  muscle. 

It  will  be  ouly  necessary  here  to  add  some  account  of  the  effect  of  a 
constant-  curvent^  such  as  that  obtained  from  a  Daniell's  battery,  upon  a 
nerve.  This  effect  may  be  studied  with  the  apparatus  described  before. 
A  pair  of  electrodes  is  placed  behind  the  nerve  of  the  nerve-muscle  prep- 
aration, with  a  Du  Bois  Reymond's  key  arranged  for  short  circuiting 
the  battery  current,  in  such  a  way  that  when  the  key  is  opened  the  cur- 
rent is  sent  into  the  nerve,  and  when  closed  the  current  is  cut  off.  It 
will  be  found  that  with  a  current  of  moderate  strength  there  will  be  a 
contraction  of  the  muscle  both  at  the  opening  and  at  the  closing  of  the 
key  (called  respectively  making  and  breaking  contractions),  but  that 
during  the  interval  between  these  two  events  the  muscle  remains  flaccid, 
provided  the  battery  current  continues  of  constant  intensity.  If  the 
current  be  a  very  weak  or  a  very  strong  one  the  effect  is  not  quite  the 
same;  one  or  other  of  the  contractions  may  be  absent.  Which  of  these 
contractions  is  absent  depends  upon  another  circumstance,  viz.,  the 
direction  of  the  current.  The  direction  of  the  current  may  be  ascending 
or  descending:  if  ascending,  the  anode  or  positive  pole  is  nearer  the 
muscle  than  the  cathode  or  negative  pole,  and  the  current  to  return  to 


448  HANDBOOK    OF    PHYSIOLOGY. 

the  battery  has  to  pass  up  the  nerve;  if  descending,  the  position  of  tht 
electrodes  is  reversed.  It  will  be  necessary  before  considering  this  ques- 
tion further  to  return  to  the  apparent  want  of  effect  of  the  constant 
current  during  the  interval  between  the  make  and  break  contraction :  to 
all  appearances  no  change  is  produced,  but  in  reality  a  very  important 
alteration  of  the  irritability  is  brought  about  in  the  nerve  by  the  passage 
of  this  constant  (polarizing)  current.  This  may  be  shown  in  two  ways, 
first  of  all  by  the  galvanometer.  If  a  piece  of  nerve  be  taken,  and  if  at 
either  end  an  arrangement  be  made  to  test  the  electrical  condition  of 
the  nerve  by  means  of  a  pair  of  non-polarizable  electrodes  connected  with 
a  galvanometer,  while  to  the  central  portion  a  pair  of  electrodes  con- 
nected with  a  Dauiell's  battery  be  applied,  it  will  be  found  that  the 
natural  nerve-currents  are  profoundly  altered  on  the  passage  of  the  con- 
stant current  in  the  neighborhood.  If  the  polarizing  current  be  in  the 
same  direction  as  the  latter  the  natural  current  is  increased,  but  if  in 
the  direction  opposite  to  it,  the  natural  cuiTcnt  is  diminished.  This 
change,  produced  by  the  continual  passage  of  the  battery-current  through 
a  portion  of  the  nerve,  is  to  be  distinguished  from  the  negative  varia- 
tion of  the  natural  current  to  which  allusion  has  been  already  made,  and 
which  is  a  momentary  change  occurring  on  the  sudden  application  of 
the  stimulus.  The  condition  produced  by  the  passage  of  a  constant 
current  is  known  by  the  name  of  Electrotonus. 

A  second  way  of  showing  the  effect  of  the  polarizing  current  is  by 
taking  a  nerve-muscle  preparation  and  applying  to  the  nerve  a  pair  of 
electrodes  from  an  induction  coil,  while  at  a  point  further  removed  from 
the  muscle,  electrodes  from  a  Daniell's  battery  are  arranged  with  a  key 
for  short  circuiting  and  an  apparatus  (reverser)  by  which  the  battery 
current  may  be  reversed  in  direction.  If  the  exact  point  be  ascertained 
to  which  the  secondary  coil  should  be  moved  from  the  primary  coil  in 
order  that  a  minimum  contraction  be  obtained  by  the  induction  shock, 
and  the  secondary  coil  be  removed  slightly  further  from  the  primary, 
the  induction  current  cannot  now  produce  a  contraction;  but  if  the 
polarizing  current  be  sent  in  a  descending  direction,  that  is  to  say,  with 
the  cathode  nearest  the  other  electrodes,  the  induction  current,  which 
was  before  insufficient,  will  prove  sufficient  to  cause  a  contraction; 
whereby  indicating  that  with  a  descending  current  the  irritability  of 
the  nerve  is  increased.  By  means  of  a  somewhat  similar  experiment  it 
may  be  shown  that  an  ascending  current  will  diminish  the  irritability 
of  a  nerve.  Similarly,  if  instead  of  applying  the  induction  electrodes 
below  the  other  electrodes  they  are  applied  between  them,  like  effects 
are  demonstrated,  indicating  that  in  the  neighborhood  of  the  cathode 
the  irritability  of  the  nerve  is  increased  by  the  passage  of  a  constant 
current,  and  in  the  neighborhood  of  the  anode  diminished.     This  in- 


THE    METABOLISM    OF   THE   TISSUES, 


449 


crease  in  irritability  is  called  catelectrotonus,  and  similarly  the 
decrease  is  called  anelectrotonus.  As  there  is  between  the  electrodes 
both  an  increase  and  a  decrease  of  irritability  on  the  passage  of  a  po- 
larizing current,  it  must  be  evident  that  the  increase  must  shade  off  into 
the  decrease,  and  that  there  must  be  a  neutral  point  where  there  is 
neither  increase  nor  decrease  of  irritability.  The  position  of  this 
neutral  point  is  found  to  yary  with  the  intensity  of  the  polarizing  cur- 
rent— when  the  current  is  weak  the  point  is  nearer  the  anode,  when 


-<-sr« 


J: 


Fig.  325. — Diagram  iUustrating  the  effects  of  various  intensities  of  the  polarizing  currents. 
n,  n',  nerve;  a,  auode:  A-,  cathode;  the  curves  above  indicate  increase,  and  those  below  decrease 
of  irritability,  and  when  the  current  is  small  the  increase  and  decrease  are  both  small,  with  the 
neutral  point  near  a,  and  so  on  as  the  current  is  increased  in  strength. 

strong  nearer  the  cathode  (fig.  325) ;  when  a  constant  current  passes 
into  a  nerve,  therefore,  if  a  contraction  result,  it  may  be  assumed  that 
it  is  due  to  the  increased  irritability  produced  in  the  neighborhood  of 
the  cathode,  but  the  breaking,  contraction  must  be  produced  by  a  rise 
in  irritability  from  a  lowered  state  to  the  normal  in  the  neighborhood 
of  the  anode.  The  contractions  produced  in  the  muscle  of  a  nerve- 
muscle  preparation  by  a  constant  current  have  been  arranged  in  a  table 
which  is  known  as  Pfliiger's  Law  of  Contractions.  It  is  really  only  a 
statement  as  to  when  a  contraction  may  be  expected : — 


Strength  of  Current  used. 

Descending  Current. 

Ascending  Current. 

Make. 

Break. 

Make. 

Break. 

Very  Weak 

Weak 

Moderate 

Yes. 
Yes. 
Yes. 
Yes. 

No. 
No. 
Yes. 

No. 

No. 
Yes. 
Yes. 

No. 

No. 
No. 

Yes 

Strong 

Yes 

The  difficulty  in  this  table  is  chiefly  in  the  effect  of  a  weak  ascending 
current,  but  the  following  statement  may  remove  it.  The  increase  of 
irritability  at  tlie  cathode  when  the  current  is  made  is  more  potent  to 
produce  a  contraction  than  the  rise  of  irritability  at  the  anode  when  the 
current  is  broken ;  and  so  with  weak  currents  the  only  effect  is  a  con- 
traction at  the  make  of  both  currents.     The  descending  current  is  more 


450 


HANDBOOK    OF    PHYSIOLOGY. 


potent  than  the  ascending  (and  with  still  weaker  currents  is  the  only 
one  which  produces  any  effect),  since  the  cathode  is  near  the  muscle. 
In  the  case  of  the  ascending  current  the  stimulus  has  to  pass  through  a 
district  of  diminished  irritability,  which  with  a  very  strong  current 
acts  as  a  block,  being  of  considerable  amount  and  extent,  but  with  a 
weak  current  being  less  considerable  both  in  intensity  and  extent,  only 
slightly  affects  the  contraction.  As  the  current  is  stronger  however, 
recovery  from  anelectrotonus,  is  able  to  produce  a  contraction  as  well 
as  catelectrotonus ;  a  contraction  occurs  both  at  the  make  and  the 
break  of  the  current.  The  absence  of  contraction  with  a  very  strong 
■current  at  the  break  of  the  ascending  current  maybe  explained  by  sup- 
posing that  the  region  of  fall  in  irritability  at  the  cathode  blocks  the 
istimulus  of  the  rise  in  irritability  at  the  anode. 

Thus  we  have  seen  that  two  circumstances  influence  the  effect  of  the 
■constant  current  upon  a  nerve,  viz.,  the  strength  and  direction  of  the 
current.  It  is  also  necessary  that  the  stimulus  should  be  applied  swf7- 
denly  and  not  gradually,  and  that  the  irritability  of  the  nerve  sliould  he 
normal;  not  increased  or  diminished.  Sometimes  (when  the  prepara- 
tion is  sj^ecially  irritable?)  instead  of  a.  simple  contraction  a  tetanus 
occurs  at  the  make  or  break  of  the  constant  current.  This  is  especially 
liable  to  occur  at  the  break  of  a  strong  ascending  current  which  has 
been  passing  for  some  time  into  the  preparation;  this  is  called  Ritter'r 
tetanus,  and  may  be  increased  by  passing  a  current  in  an  opposite  di- 
rection or  stopped  by  passing  a  current,  in  the  same  direction. 


Muscular  and    Nervous   Metabolism. 

The  question  of  the  metabolism  of  muscle  both  in  a  resting  and  in  an 
active  condition  has  for  many  years  occupied  the  attention  of  physiolo- 
gists. It  cannot  be  said  even  now  to  be  thoroughly  understood.  Most 
■of  the  facts  with  reference  to  the  subject  have  been  already  mentioned. 
We  may  shortly  recapitulate  them  here: — First,  muscle  during  rest  ab- 
sorbs oxygen  and  gives  out  carbon  dioxide.  This  has  been  shown  by  an 
analysis  of  the  gases  of  the  blood  going  to  and  leaving  muscles.  During 
activity,  e.  g.,  during  tetanus,  the  same  interchange  of  gases  takes  place. 
but  the  quantities  of  the  oxygen  absorbed  and  of  the  carbon  dioxide 
given  up  are  increased,  and  the  23roj)ortion  between  them  is  altered  thus : — 


Venous  Blood. 

O,  less  than  Arterial 
Blood. 

CO2,  more  than  Arterial 
Blood. 

Of  resting  muscle 

9  per  cent. 

6.71  per  cent. 

Of  active  muscle 

12.26  per  cent. 

10.79  per  cent. 

THE    METABOLISM    OF   THE   TISSUES.  451 

There  is  then  a  greater  proportion  of  carbon  dioxide  produced  in 
muscle  during  activity  than  during  rest. 

During  rigor  mortis  there  is  also  an  increased  production  of  carbon 
dioxide. 

Second,  muscle  during  rest  produces  nitrogenous  crystallizable  sub- 
stances, such  as  kreatin,  from  the  metabolism  which  is  constantly  going 
on  in  it  during  life ;  in  addition  there  is  in  all  probability  sarcolactic 
acid  formed  and  other  non-nitrogenous  matters. 

During  activity  the  nitrogenous  substances,  such  as  kreatin,  undergo 
very  slight,  if  any,  increase — about  the  amount  produced  during  rest — • 
but  the  sarcolactic  acid  is  distinctly  increased;  sugar  (whether  glucose 
or  maltose  is  uncertain)  is  also  increased,  whereas  the  glycogen  is  dimin- 
ished. 

During  rigor  mortis  the  sarcolactic  acid  is  also  increased,  and  in  ad- 
dition myosin  is  formed. 

From  these  data  it  is  assumed  that  the  processes  which  take  place  in 
resting  and  active  muscle  are  somewhat  different,  at  any  rate  in  degree. 
From  actively  contracting  muscle,  also,  there  are  obtained  an  increased 
amount  of  heat  and  mechanical  work,  more  potential  is  converted  into 
kinetic  energy. 

Many  theories  have  been  proposed  to  explain  the  facts  of  muscular 
energy.  It  has  been  suggested  by  Herman  that  muscular  activity  de- 
pends upon  the  splitting  up  and  subsequent  re-formation  of  a  complex 
nitrogenous  body,  called  by  him  Inogen.  When  this  body  so  splits  up 
there  result  from  its  decomposition,  carbon  dioxide,  sarcolactic  acid, 
and  a  gelatin o-albuminous  body.  Of  these  the  carbon  dioxide  is  carried 
away  by  the  blood  stream ;  the  albuminous  substance  and  possibly  the 
acid,  at  any  rate  in  part,  go  to  re-form  the  inogen.  The  other  materials 
of  which  the  inogen  is  formed  are  supplied  by  the  blood ;  of  these  mate- 
rials we  know  that  some  carbohydrate  substance  and  oxygen  form  a  part. 
The  decomposition,  although  taking  place  in  resting  muscle,  reaches  a 
climax  in  active  muscle,  but  in  that  condition  the  destruction  of  inogen 
largely  exceeds  restoration,  and  so  there  must  be  a  limit  to  muscular 
activity.  But  this  is  not  the  only  change  going  on  in  muscle,  there  are 
others  which  afiect  the  nitrogenous  elements  of  the  tissue,  and  from 
them  result  the  nitrogenous  bodies  of  which  kreatin  is  the  chief;  these 
changes  may  be  unusually  large  during  severe  exercise. 

It  has  been  further  suggested  that,  as  myosin  is  undoubtedly  formed 
in  rigor  mortis,  when  the  muscle  becomes  acid  and  gives  off  carbon 
dioxide,  that  myosin  is  also  formed  when  muscle  contracts,  and  that,  in 
other  words,  contraction  is  a  condition  akin  to  partial  death.  The 
electrical  reaction  appears  to  justify  this;  both  contracted  and  dead 
muscle  are  negative  to  living  muscle,  when  at  rest.     What  happens  to 


452  HANDBOOK    OF    PIIYSIOLOGy, 

the  myosin  which  is  formed  when  muscle  contracts,  if  this  view  be  the 
correct  one,  is  unknown.  Halliburton  suggests  that  the  myosin  which 
can  be  made  to  clot  and  unclot  easily  enough  outside  the  body,  is  able 
to  do  the  same  thing  in  the  body.  It  is  possible  that  the  clotting  of 
myosinogen  which  is  supposed  to  occur  during  contraction,  is  not  of  the 
same  intensity  or  extent  as  that  which  occurs  post  mortem.  The  rela- 
tion of  the  hypothetical  inogen  to  the  rest  of  the  muscle-fibre  is  unde- 
termined. It  may  be  that  tlie  inogen  is  formed  by  the  activity  of  the 
muscle-protoplasm,  and  stored  up  within  itself,  and  that  duriug  rest  of 
muscle  it  is  gradually  used  up,  whereas  in  activity  it  is  suddenly  and 
explosively  decomposed.  In  the  rest  of  the  fibre  the  nitrogenous  meta- 
bolism continues  much  the  same  during  rest  as  during  activity. 

Again,  histologically,  the  question  as  to  which  is  the  contractile  and 
which  is  the  non-contractile  part  of  muscle,  has  been,  as  we  have  seen 
(p.  84  et  seq.),  a  matter  of  much  controversy. 

As  regards  nervous  metabolism,  we  have  little  knowledge  of  anything 
except  the  electrical  phenomena  which  have  been  already  considered. 
For  the  maintenance  of  nervous  irritability,  oxygen  is  required ;  to  form 
this,  it  has  been  suggested  that  the  nervous  impulse  is  the  result  of 
processes  of  an  oxidative  character,  etc.  The  chief  seat  of  the  metabo- 
lism is  no  doubt  the  axis-cylinder.  The  question  whether  a  nervous 
impulse  is  possibly  an  electrical  change,  as  has  been  asserted  by  some, 
cannot  be  at  present  settled,  but  if  it  be  so,  at  any  rate  it  differs  essenti- 
ally from  an  ordinary  current,  if  in  no  other  respect,  at  any  rate  in  the 
rate  of  transmission, 


CHAPTEE  XII. 

METABOLISM  OF  THE  TISSUES. 

Glandular  Metabolism, 

It  is  the  function  of  gland  cells  to  produce  by  the  metabolism  of  their 
protoplasm  certain  substances  called  secretions.  These  materials  are  of 
two  kinds;  viz.,  those  which  are  employed  for  the  purpose  of  serving 
some  ulterior  office  in  the  economy,  and  those  which  are  discharged  from 
the  body  as  useless  or  injurious.  In  the  former  case,  the  separated 
materials  are  termed  true  secretions;  in  the  latter  they  are  termed  excre- 
tions. 

The  secretions  as  a  rule  consist  of  substances  which  do  not  pre-exist 
in  the  same  form  in  the  blood,  but  require  special  cells  and  a  process 
of  elaboration  for  their  formation,  e.g.,  the  liver  cells  for  the  forma- 
tion of  bile,  the  mammary  glaud-cells  for  the  formation  of  milk.  The 
excretions,  on  the  other  hand,  conmiouly  consist  of  substances  which 
exist  ready-formed  in  the  blood,  and  are  merely  abstracted  therefrom. 
If  from  any  cause,  such  as  extensive  disease  or  extirpation  of  an  excre- 
tory organ,  the  separation  of  an  excretion  is  prevented,  and  an  accumu- 
lation of  it  in  the  blood  ensues,  it  frequently  escapes  through  other 
organs,  and  may  be  detected  in  various  fluids  of  the  body.  But  this  is 
never  the  case  with  secretions;  at  least  Avith  those  that  are  most  elabo- 
rated ;  for  after  the  removal  of  the  sj^ecial  organ  by  which  each  of  them 
is  manufactured,  the  secretion  is  no  longer  formed.  Cases  sometimes 
occur  in  which  the  secretion  continues  to  be  formed  by  the  natural 
organ,  but  not  being  able  to  escape  toward  the  exterior,  on  account  of 
some  obstruction,  is  re-absorbed  into  the  blood,  and  afterward  discharged 
from  it  by  exudation  in  other  ways;  but  these  are  not  instances  of  true 
vicarious  secretions,  and  must  not  be  so  regarded. 

The  circumstances  of  their  formation,  and  their  final  destination,  are, 
however,  the  only  particulars  in  which  secretions  and  excretions  can  be 
distinguished;  for,  in  general,  the  structure  of  the  jmrts  engaged  in 
eliminating  excretions  is  as  complex  as  that  of  the  parts  concerned  in  the 
formation  of  secretions.  And  since  the  diiierences  of  the  two  processes 
of  separation,  corresponding  with  those  in  the  several  purposes  and  des- 
tinations of  the  fluids,  are  not  3'et  ascertained,  it  will  be  sufficient  to 
speak  in  general  terms  of  the  process. 


454  HANDBOOK    OF    PHYSIOLOGY. 

Every  secreting  apparatus  possesses,  a  sessential  parts  of  its  structure, 
a  simple  and  almost  textureless  membrane,  named  the  primary  or  iase- 
ment-membrane;  certain  cells;  and  hlood-vessels.  These  three  structural 
elements  are  arranged  together  in  various  ways;  but  all  the  varieties  may 
be  classed  under  one  or  other  of  two  principal  divisions,  namely,  mem- 
branes and  glands. 

Organs  and  Tissues  of  Secretion. 

The  principal  secreting  organs  are  the  following: — (1)  the  serous  and 
synovial  membranes;  (2)  the  mucous  membranes  with  their  special 
glands,  e.g.,  the  buccal,  gastric,  and  intestinal  glands;  (3)  the  salivary 
glands  and  pancreas;  (4)  the  mammary  glands;  (5)  the  liver;  (6)  the 
lachrymal  gland;   (7)  the  kidney  and  skin;  and  (8)  the  testes. 

The  structure  and  functions  of  the  glands  secreting  materials  used  in 
digestion  we  have  already  considered,  and  they  need  not  detain  us  here. 
The  functions  of  the  kidney  and  skin  have  also  been  dealt  with. 

The  lachrymal  gland  will  be  considered  with  the  rest  of  the  optic 
apparatus  and  the  testes  in  the  Chapter  on  Generation.  There  remain, 
then,  the  serous  and  mucous  membranes  and  the  mammary  gland  to  be 
here  described,  and  also  that  part  of  the  secreting  function  of  the  liver 
which  is  concerned  with  the  formation  of  glycogen  and  of  urea. 

(1.)  Serous  and  Synovial  Membranes. — Serous  membranes  are  of 
two  principal  kinds:  1st.  Those  which  line  visceral  cavities, — the  arach- 
noid, pericardium,  pleurcB,  peritoneum,  and  timicce  vaginales.  2d.  The 
synovial  memhranes  lining  the  joints,  and  the  sheaths  of  tendons 
and  ligaments,  with  which,  also,  are  usually  included  the  synovial  bursce, 
or  burscB  mucosa',  whether  these  be  subcutaneous,  or  situated  beneath 
tendons  and  glide  over  bones. 

The  serous  membranes  form  closed  sacs,  and  exist  wherever  the  free 
surfaces  of  viscera  come  into  contact  with  each  other  or  lie  in  cavities 
unattached  to  surrounding  parts.  The  viscsra  invested  by  a  serous 
membrane  are,  as  it  were,  j^ressed  into  the  shut  sac  which  it  forms, 
carrying  before  them  a  portion  of  the  membrane,  which  serves  as  their 
investment.  To  the  law  that  serous  membranes  form  shut  sacs,  there 
is,  in  the  human  subject,  one  exception,  viz. :  the  opening  of  the  Fal- 
lopian tubes  into  the  abdominal  cavity, — an  arrangement  which  exists 
in  man  and  all  Vertebrata,  with  the  exception  of  a  few  fishes. 

The  serous  membranes  are  especially  distinguished  by  the  characters 
of  the  endothelium  covering  their  free  surface:  it  always  consists  of  a 
single  layer  of  polygonal  cells.  The  ground  substance  of  most  serous 
membranes  consists  of  connective-tissue  corpuscles  of  various  forms 
lying  in  the  branching  spaces  which  constitute  the  lymph  canalicular 
system,  and  interwoven  with    bundles  of  white  fibrous  tissue,  and    nu- 


METABOLISM    OF   THE    TISSUES. 


455 


meroiis  delicate  elastic  fibrill*,  together  with  blood-vessels,  nerves,  and 
lymphatics.  In  relation  to  the  process  of  secretion,  the  layer  of  connec- 
tive tissue  serves  as  a  groundwork  for  the  ramification  of  blood-vessels, 
nerves,  and  lymphatics.  But  in  its  usual  form  it  is  absent  in  some  in- 
stances, as  in  the  arachnoid  covering  the  dura  mater,  and  in  the  interior 
of  the  ventricles  of  the  brain.     The  primary  membrane  and  epithelium 


Fig.  326.— Section  of  synovial  membrane,  a.  Endothelial  covering  of  the  elevations  of  the 
membrane;  6,  subserous  tissue  containing  fat  and  blood-vessels;  c,  ligament  covered  by  the  sy- 
novial membrane.     (Cadiat.) 

are  alwa\s  present,  and  are  concerned  in  the  formation  of  the  fluid  by 
which  the  free  surface  of  the  membrane  is  moistened. 

Fimctions. — The  principal  purpose  of  the  serous  and  synovial  mem- 
branes is  to  furnish  a  smooth,  moist  surface,  to  facilitate  the  movements 
of  the  invested  organ,  and  to  prevent  the  injurious  effects  of  friction. 
This  purpose  is  especially  manifested  in  joints,  in  which  free  and  exten- 
sive movements  take  place;  and  in  the  stomach  and  intestines,  which, 
from  the  varying  quantity  and  movements  of  their  contents,  are  in  al- 
most constant  motion  upon  one  another  and  the  walls  of  the  abdomen. 

Fluid. — The  fluid  secreted  from  the  free  surface  of  the  serous  mem- 
branes is,  in  health,  rarely  more  than  sufficient  to  ensure  the  mainte- 
nance of  their  moisture.  The  opposed  surfaces  of  each  serous  sac  are  at 
every  point  in  contact  with  each  other.  After  death,  a  larger  quantity  of 
fluid  is  usually  found  in  each  serous  sac;  but  this,  if  not  the  product  of 
manifest  disease,  is  probably  such  as  has  transuded  after  death,  or  in 
the  last  hours  of  life.  An  excess  of  such  fluid  in  any  serous  sac  consti- 
tutes dropsy  of  the  sac. 


456  HANDBOOK    OF    PHYSIOLOGY, 

The  fluid  naturally  secreted  by  the  serous  membranes  appears  to  be 
identical,  in  general  and  chemical  characters,  with  very  dilute  liquor 
sanguinis.  It  is  of  a  pale  yellow  or  straw-color,  slightly  viscid,  alkaline, 
and  on  account  of  the  presence  of  albumen,  coagulable  by  heat.  This 
similarity  of  the  serous  fluid  to  the  liquid  part  of  blood,  and  to  the  fluid 
with  which  most  animal  tissues  are  moistened,  renders  it  probable  that 
it  is,  in  great  measure,  separated  by  simple  transudation,  through  the 
walls  of  the  blood-vessels.  The  probability  is  increased  by  the  fact  that, 
in  jaundice,  the  fluid  in  the  serous  sacs  is,  equally  with  the  serum  of  the 
blood,  colored  with  the  bile.  But  there  is  reason  for  supposing  that  the 
fluid  of  the  cerebral  ventricles  and  of  the  arachnoid  sac  are  exceptions  to 
this  rule ;  for  they  diifer  from  the  fluids  of  the  other  serous  sacs  not  only 
in  being  pellucid,  colorless,  and  of  much  less  specific  gravity,  but  in  that 
they  seldom  receive  the  tinge  of  bile  when  present  in  the  blood,  and  are 
not  colored  by  madder,  or  other  similar  substances  introduced  abundantly 
into  the  blood. 

It  is  also  probable  that  the  formation  of  synovial  fluid  \&  a  process  of 
more  genuine  and  elaborate  secretion,  by  means  of  the  epithelial  cells  on 
the  surface  of  the  membrane,  and  especially  of  those  which  are  accumu- 
lated on  the  edge  and  processes  of  the  synovial  fringes;  for,  in  its  pecu- 
liar density,  viscidity,  and  abundance  of  albumen,  synovia  differs  alike 
from  the  serum  of  blood  and  from  the  fluid  of  any  of  the  serous  cavities. 

(2.)  Mucous  Membranes. — The  mucous  memhranes  line  all  those 
passages  by  v/hich  internal  parts  communicate  with  the  exterior,  and 
by  which  either  matters  are  eliminated  from  the  body  or  foreign  sub- 
stances taken  into  it.  They  are  soft  and  velvety,  and  extremely  vascu- 
lar. The  external  surfaces  of  mucous  membranes  are  attached  to  various 
other  tissues;  in  the  tongue,  for  example,  to  muscle;  on  cartilaginous 
parts,  to  perichondrium;  in  the  cells  of  the  ethmoid  bone,  in  the 
frontal  and  sphenoidal  sinuses,  as  well, as  in  the  tympanum,  to  perios- 
teum ;  in  the  intestinal  canal,  it  is  connected  with  a  firm  submucous 
membrane,  which  on  its  exterior  gives  attachment  to  the  fibres  of  the 
muscular  coat.  The  mucous  membranes  line  certain  principal  tracts — 
Gastro-pulmonary  &nd  Genito-urinary;  the  former  being  subdivided  into 
the  Digestive  and  Respiratory  tracts. 

1.  The  Digestive  tract  commences  in  the  cavity  of  the  mouth,  from 
which  prolongations  pass  into  the  ducts  of  the  salivary  glands.  From 
the  mouth  it  passes  through  the  fauces,  pharynx,  and  oesophagus,  to  the 
stomach,  and  is  thence  continued  along  the  whole  tract  of  the  intestinal 
canal  to  the  termination  of  the  rectum,  being  in  its  course  arranged  in 
the  various  folds  and  depressions  already  described,  and  prolonged  into 
the  ducts  of  the  intestinal  glands,  the  pancreas  and  liver,  and  into  the 
ffall-bladder. 


METABOLISM    OF    THE    TISSUES.  457 

2.  The  Eespiratory  tract  includes  the  mucous  membrane  lining  the 
cavity  of  the  nose,  and  the  various  sinuses  communicating  with  it,  the 
lachrymal  canal  and  sac,  the  conjunctiva  of  the  eye  and  eyelids,  and  the 
prolongation  which  passes  along  the  Eustachian  tubes  and  lines  the  tym- 
panum and  the  inner  surface  of  the  membrana  tympani.  Crossing  the 
pharynx,  and  lining  that  part  of  it  which  is  above  the  soft  palate,  the 
respiratory  tract  leads  into  the  glottis,  whence  it  is  continued,  through 
the  larynx  and  trachea,  to  the  bronchi  and  their  divisions,  which  it 
lines  as  far  as  the  branches  of  about  -^  of  an  inch  {},-  mm.)  in  diameter, 
and  continuous  with  it  is  a  layer  of  delicate  epithelial  membrane  which 
extends  into  the  pulmonary  cells. 

3.  The  Genito-urinary  tract,  which  lines  the  whole  of  the  urinary  pas- 
sages, from  their  external  orifice  to  the  termination  of  the  tubuli  uriniferi 
of  the  kidneys,  extends  also  into  the  organs  of  generation  in  both  sexes, 
and  into  the  ducts  of  the  glands  connected  with  them :  and  in  the  female 
becomes  continuous  Avith  the  serous  membrane  of  the  abdomen  at  the 
fimbria  of  the  Fallopian  tubes. 

Structure. — These  mucous  tracts,  and  different  portions  of  each  of 
them,  jiresent  certain  structural  peculiarities,  adapted  to  the  functions 
which  each  part  has  to  discharge;  yet  in  some  essential  characters  the 
mucous  membrane  is  the  same,  from  whatever  part  it  is  obtained.  In 
all  the  principal  and  larger  parts  of  the  several  tracts,  it  j^resents,  as 
just  remarked,  an  external  layer  of  epithelium,  situated  upon  a  basement 
membrane,  and  beneath  this,,  a  stra-tum  of  vascular  tissue  of  variable 
thickness,  containing  lymphatic  vessels  and  nerves.  The  vascular 
stratum,  together  with  the  basement  membrane  and  epithelium,  in  differ- 
ent cases,  is  elevated  into  minute  papilhi?  and  villi,  or  depressed  into 
involutions  in  the  form  of  glands.  But  in  the  prolongations  of  the 
tracts,  where  they  pass  into  gland-ducts,  these  constituents  are  reduced 
in  the  finest  branches  of  the  ducts  to  the  epithelium,  the  primary  or  base- 
ment-membrane, and  the  capillary  blood-vessels  spread  over  the  outer 
surface  of  the  latter  in  a  single  layer. 

The  primary  or  basement  membrane  is  a  thin  transparent  layer,  sim- 
ple, homogeneous,  or  composed  of  endothelial  cells.  In  the  minuter 
divisions  of  the  mucous  membranes,  and  in  the  ducts  of  glands,  it  is  the 
layer  continuous  and  correspondent  with  this  basement-membrane  that 
forms  the  proper  walls  of  the  tubes.  The  cells  also,  which,  lining  the 
larger  and  coarser  mucous  membranes,  constitute  their  epithelium,  are 
continuous  with  and  often  similar  to  those  which,  lining  the  gland-ducts, 
are  called  gland-cells.  No  certain  distinction  can  be  drawn  between  the 
epithelium-cells  of  mucous  membranes  and  gland -cells. 

Mucous  Fluid:  Mucus. — From  all  mucous  membranes  there  is  secreted 
either  from  the  surface  or  from  certain  special  glands,  or  from  both,  a 


458  HANDBOOK    OF    PHYSIOLOGY. 

more  or  less  viscid,  grayish,  or  semi-transparent  fluid,  of  alkaline  reac- 
tion and  high  specific  gravity,  named  mucus.  It  mixes  imperfectly 
with  water,  but,  rapidly  absorbing  liquid,  it  swells  considerably  when 
water  is  added.  Under  the  microscope  it  is  found  to  contain  epithelium 
and  leucocytes.  It  is  found  to  be  made  up,  chemically,  of  mucin, 
which  forms  its  chief  bulk,  of  a  little  albumen,  of  salts  chiefly  chlorides 
and  phosphates,  and  water  with  traces  of  fats  and  extractives. 

Secreting  Glands. 

The  secreting  glands  present,  amid  manifold  diversities  of  form  and 
composition,  a  general  plan  of  structure;  all  contain,  and  appear  con- 
structed with  particular  regard  to  the  arrangement  of  the  cells,  which,  as 
already  expressed,  both  line  their  tubes  or  cavities  as  an  epithelium,  and 
elaborate,  as  secreting  cells,  the  substances  to  be  discharged  from  them. 

Ty2)es  of  Secreting  Glands. — Secreting  glands  may  be  classified  accord- 
ing to  certain  types,  which  are  the  following: — 1.  The  simjile  tubular 
gland  (a,  fig.  327),  examples  of  which  are  furnished  by  the  follicles  of 
Lieberkiihn,  and  the  tubular  glands  of  the  stomach.  They  are  simple 
tubular  depressions  of  the  mucous  membrane,  the  wall  of  which  is  formed 
of  primary  membrane  and  is  lined  with  secreting  cells  arranged  as  an 
epithelium.  To  the  same  class  may  be  referred  the  elongated  and  tor- 
tuous sudoriferous  glands. 

2.  The  co7npou7id  tubular  glands  (d,  fig.  327)  form  another  division. 
These  consist  of  main  gland-tubes,  which  divide  and  subdivide.  Each 
gland  may  be  made  up  of  the  subdivisions  of  one  or  more  main  tubes. 
The  ultimate  subdivisions  of  the  tubes  are  generally  highly  convoluted. 
They  are  formed  of  a  basement-membrane,  lined  by  epithelium  of 
various  forms.  The  larger  tubes  may  have  an  outside  coating  of  fibrous, 
areolar,  or  muscular  tissue.  The  kidtiey,  testes,  salivary  glands,  pan- 
creas, Brunner''s  glands,  with  the  lachrymal  and  mammary  glands,  and 
some  mucous  glands  are  examples  of  this  type  but  present  more  or  less 
marked  variations  among  themselves. 

3.  The  aggregate  OY  racemose  glands,  in  which  a  number  of  vesicles  or 
acini  are  arranged  in  groups  or  globules  (c,  fig.  327).  The  meibomicm 
follicles  are  examples  of  this  kind  of  gland.  There  seem  to  be  glands  of 
mixed  character,  combining  some  of  the  characters  of  the  tubular  with 
others  of  the  racemose  type ;  these  are  called  tubulo-racemose  or  tubulo- 
acitious  glands.  These  glands  differ  from  each  other  only  in  secondary 
points  of  structure :  such  as,  chiefly,  the  arrangement  of  their  excretory 
ducts,  the  grouping  of  the  acini  and  lobules,  their  connection  by  areolar 
tissue,  and  supply  of  blood-vessels.  The  acini  commonly  appear  to  be 
formed  by  a  kind  of  fusion  of  the  walls  of  several  vesicles,  which  thus 


METABOLISM    OF   THE   TISSUES. 


459 


combine  to  form  one  cavity  lined  or  filled  with  secreting  cells  which  also 
occupy  recesses  from  the  main  cavity.  The  smallest  branches  of  the 
gland-dncts  sometimes  open  into  the  centres  of  these  cavities;  some- 
times the  acini  are  clustered  round  the  extremities,  or  by  the  sides  of 
the  ducts:  but,  whatever  secondary  arrangement  there  may  be,  all  have 
the  same  essential  character  of  rounded  groups  of  vesicles  containing 


Fig.  327.— Plans  of  extension  of  secreting  membrane  by  inversion  or  recession  in  form  of  cav- 
ities. A,  Simple  glands,  viz.,  </,  straight  tube:  h,  sac;  /,  coiled  tube,  b,  Multilocular  crypts;  fc, 
of  tubular  form  ;  Y,  saccular,  c,  Racemose,  or  saccular  compound  gland ;  wi,  entire  gland,  show- 
ing branched  duct  and  loliular  sti-ucture ;  n,  a  lobule,  detached  with  o,  branch  of  duct  proceed- 
ing from  it.     D,  Compound  tubular  gland  (Sharpey). 

gland-cells,  and  opening  by  a  common  central  cavity  into  minute  ducts, 
which  ducts  in  the  large  glands  converge  and  unite  to  form  larger  and 
larger  branches,  and  at  length  by  one  common  trunk  open  on  a  free 
surface  of  membrane. 

Among  these  varieties  of  structure,  all  the  secreting  glands  are  alike 
in  some  essential  points,  besides  those  which  they  have  in  common  with 


40()  HANDBOOK    OF    PHYSIOLOGY. 

all  truly  secreting  structures.  They  agree  in  presenting  a  large  extent 
of  secreting  surface  within  a  comparatively  small  space;  in  the  circum- 
stance that  while  one  end  of  the  gland-duct  opens  on  a  free  surface,  the 
opposite  end  is  always  closed,  having  no  direct  communication  with 
blood-vessels,  or  any  other  canal;  and  in  a  uniform  arrangement  of 
capillary  blood-vessels,  ramifying  and  forming  a  network  around  the 
walls  and  in  the  interstices  of  the  ducts  and  acini. 

Process  of  Secretion. — In  secretion  two  distinct  processes  are  concerned, 
which  may  be  spoken  of  as  Physical  and  Chemical. 

Physical  Processes. — These,  viz.,  {n)  filtration,  [h)  dialysis,  have 
already  been  discussed. 

Chemical  Processes. — The  chemical  processes  constitute  the  process  of 
secretion.,  properly  so  called,  as  distinguished  from  mere  transudation 
spoken  of  above.  In  the  chemical  2)rocess  of  secretion  various  materials 
which  do  not  exist  as  such  in  the  blood  are  manufactured  by  the  agency 
of  the  gland-cells  from  the  blood,  or  to  speak  more  accurately,  from  the 
plasma  which  exudes  from  the  blood  vessels  into  the  interstices  of  the 
gland-textures. 

The  best  evidence  in  favor  of  this  view  is  :  1st.  That  cells  and  nuclei 
are  constituents  of  all  glands,  however  diverse  their  outer  forms  and  other 
characters,  and  that  they  are  in  all  glands  placed  on  the  surface  or  in 
the  cavity  whence  the  secretion  is  poured.  2d.  That  certain  materials 
of  secretions  are  visible  with  the  microscope  in  the  gland  cells  before 
they  are  discharged.  Thus,  granules  probably  representing  the  fer- 
ments of  the  panci'eas  may  be  discerned  in  the  cells  of  that  gland ; 
spermatozoids  in  the  cells  of  the  tubules  of  the  testicles;  granules  of 
uric  acid  in  those  of  the  kidneys  (of  fish) ;  fatty  particles,  like  those  of 
milk,  in  the  cells  of  the  mammary  gland. 

Secreting  cells,  like  the  cells  of  other  organs,  appear  to  develop,  grow, 
and  attain  their  individual  perfection  by  appropriating  nutriment  from 
the  fluid  exuded  by  adjacent  blood-vessels  and  building  it  up,  so  that 
it  shall  form  part  of  their  own  substance.  In  this  perfected  state  the 
cells  subsist  for  some  brief  time,  and  when  that  period  is  over  they 
appear  to  dissolve,  wholly  or  in  part,  and  yield  their  contents  to  the 
peculiar  material  of  the  secretion.  And  this  appears  to  be  the  case  in 
every  part  of  the  gland  that  contains  the  appropriate  gland-cells;  there- 
fore not  in  the  extremities  of  the  ducts  or  in  the  acini  alone,  but  in  great 
part  of  their  length. 

We  have  described  elsewhere  the  changes  which  have  been  noticed  from 
actual  experiment  in  the  cells  of  the  salivary  glands,  pancreas,  and  peptic 
glands. 

Discharge  of  secretions  from  glands  may  either  take  place  as  soon  as 
they    are  formed ;    or  the  secretion  may  be  long  retained  within  the 


3IETAB0LISM    OF   THE   TISSUES.  461 

gland  or  its  ducts.  The  former  is  the  case  with  the  sweat  glands.  But 
the  secretions  of  those  glands  whose  activity  of  function  is  only  occa- 
sional are  usually  retained  in  the  cells  in  an  undeveloped  form  during 
the  periods  of  the  gland's  inaction.  And  there  are  glands  which  are 
like  both  these  classes,  such  as  the  lachrymal,  which  constantly  secrete 
small  portions  of  fluid,  and  on  occasions  of  greater  excitement  discharge 
it  more  abundantly. 

When  discharged  into  the  ducts,  the  further  course  of  secretions  is 
affected  (1)  partly  by  the  pressure  from  behind;  the  fresh  quantities  of 
secretion  propelling  those  that  were  formed  before.  In  the  larger  ducts, 
its  propulsion  is  (2)  assisted  by  the  contraction  of  their  walls.  All  the 
larger  ducts,  such  as  the  ureter  and  common  bile-duct,  possess  in  their 
coats  plain  muscular  fibres;  they  contract  when  irritated,  and  sometimes 
manifest  peristaltic  movements.  Rhythmic  contractions  in  the  pancreatic 
and  bile-ducts  have  been  observed,  and  also  in  the  ureters  and  vasa 
deferentia.  It  is  probable  that  the  contractile  power  extends  along  the 
ducts  to  a  considerable  distance  within  the  substance  of  the  glands  whose 
secretions  can  be  rapidly  expelled.  Saliva  and  milk,  for  instance,  are 
sometimes  ejected  with  much  force.     • 

Circumstances  Influencing  Secretion. — The  principal  conditions  which 
influence  secretion  are  (1)  variations  in  the  quantity  of  blood,  (2)  varia- 
tions in  the  quantity  of  the  peculiar  materials  for  any  secretion  that  the 
blood  may  contain,  and  (3)  variations  in  the  condition  of  the  nerves  of 
the  glands. 

(1.)  An  increase  i)i  the  quantity  of  blood  traversing  a  gland,  as  in 
nearly  all  the  instances  before  quoted,  coincides  generally  with  an  aug- 
mentation of  its  secretion.  Thus  the  mucous  membrane  of  the  stomach 
becomes  florid  when,  on  the  introduction  of  food,  its  glands  begin  to 
secrete;  the  mammary  gland  becomes  much  more  vascular  during  lacta- 
tion; and  all  circumstances  Avhich  give  rise  to  an  increase  in  the  quan- 
tity of  material  secreted  by  an  organ  produce,  coincideutly,  an  increased 
supply  of  blood;  but  we  have  seen  that  a  discharge  of  saliva  may  occur 
under  extraordinary  circumstances,  without  increase  of  blood-supply, 
and  so  it  may  be  inferred  that  this  condition  of  increased  blood-supply 
is  not  absolutely  essential. 

(2.)  An  increase  in  the  amount  of  the  materials  ivhich  the  glands  are 
designed  to  separate  or  elaborate,  contained  in  the  blood  supplied  to  them, 
increases  the  amount  of  any  secretion.  Thus,  when  an  excess  of  nitro- 
genous waste  is  in  the  blood,  whether  from  excessive  exercise  or  from 
destruction  of  one  kidney,  a  healthy  kidney  will  excrete  more  urea  than 
it  did  before. 

(3.)  Influence  of  the  Nervous  System  on  Secretion. — The  process  of 
secretion  is  largely  influenced  by  the  condition  of  the  nervous  system. 


462  HANDBOOK    OF    PHYSIOLOGY. 

The  exact  mode  in  which  the  influence  is  exhibited  must  still  be  re- 
garded as  somewhat  obscure.  In  part,  it  exerts  its  influence  by  increasing 
or  diminishing  the  quantity  of  blood  supplied  to  the  secreting  gland, 
in  virtue  of  the  power  which  it  exercises  over  the  contractility  of  the 
smaller  blood-vessels;  while  it  also  has  a  more  direct  influence,  as  was 
described  at  length  in  the  case  of  the  submaxillary  gland,  upon  the 
secreting  cells  themselves;  this  may  be  called  trophic  influence.  Its 
influence  over  secretion,  as  well  as  over  other  functions  of  the  body, 
may  be  excited  by  causes  acting  directly  upon  the  nervous  centres,  upon 
the  nerves  going  to  the  secreting  organ,  or  upon  the  nerves  of  other 
parts.  In  the  latter  case,  a  reflex  action  is  produced;  thus  the  impres- 
sion produced  upon  the  nervous  centres  by  the  contact  of  food  in  the 
mouth  is  reflected  upon  the  nerves  supplying  the  salivary  glands,  and 
produces,  through  these,  a  more  abundant  secretion  of  the  saliva. 

Through  the  nerves,  various  conditions  of  the  brain  also  influence  the 
secretions.  Thus,  the  thought  of  food  may  be  sufficient  to  excite  an 
abundant  flow  of  saliva.  And,  probably,  it  is  the  mental  state  which 
excites  the  abundant  secretion  of  urine  in  hysterical  paroxysms,  as  well 
as  the  perspirations,  and  occasionally  diarrhcea,  which  ensue  under  the 
influence  of  terror,  and  the  tears  excited  by  sorrow  or  excess  of  joy. 
The  quality  of  a  secretion  may  also  be  affected  by  mental  conditions,  as 
in  the  cases  in  which,  through  grief  or  passion,  the  secretion  of  milk  is 
altered,  and  is  sometimes  so  changed  as  to  produce  irritation  in  the 
alimentary  canal  of  the  child,  or  even  death. 

Relations  between  the  Secretions. — The  secretions  of  some  of  the  glands 
seem  to  bear  a  certain  relation  or  antagonism  to  each  other,  by  which 
an  increased  activity  of  one  is  usually  followed  by  diminished  activity  of 
one  or  more  of  the  others;  and  a  deranged  condition  of  one  is  apt  to 
entail  a  disordered  state  in  the  others.  Such  relations  appear  to  exist 
among  the  various  mucous  membranes;  and  the  close  relation  between 
the  secretion  of  the  kidney  and  that  of  the  skin  is  a  subject  of  constant 
observation. 

The  Mammary  Glands. 

Structure. — The  mammary  glands  are  composed  of  large  divisions  or 
lobes,  and  these  are  again  divisible  into  lobules — the  lobules  being  com- 
posed of  the  convoluted  and  dilated  subdivisions  of  the  main  ducts 
(alveoli)  held  together  by  connective  tissue.  The  lobes  and  lobules  too 
are  bound  together  by  areolar  tissue;  penetrating  between  the  lobes  and 
covering  the  general  surface  of  the  gland,  with  the  exception  of  the 
nipple,  is  a  considerable  quantity  of  yellow  fat,  itself  lobulated  by 
sheaths  and  processes  of  tough  areolar  tissue  (fig.  328)  connected  both 
with  the  skin  in  front  and  the  gland  behind;  the  same  bond  of  connec- 


METABOLISM    OF   THE   TISSUES.  463 

tion  extending  also  from  the  under  surface  of  the  gland  to  the  sheathing 
connective  tissue  of  the  great  pectoral  muscle  on  which  it  lies.  The 
main  ducts  of  the  gland,  fifteen  to  twenty  in  number,  called  the  lactif- 
erous or  (jaladophorous  ducts,  are  formed  by  the  union  of  the  smaller 
(lobular)  ducts,  and  ojDcn  by  small  separate  orifices  through  the  nipple. 
At  the  points  of  junction  of  lobular  ducts  to  form  lactiferous  ducts,  and 
just  before  these  enter  the  base  of  the  nipple,  the  ducts  are  dilated  (fig. 


Fig.  328.— Dissection  of  the  lower  half  of  the  female  mamma,  during  the  period  of  lactation. 
%. — In  the  left-hand  side  of  the  dissected  part  the  glandular  lobes  are  exposed  and  partially  un- 
ravelled; and  on  the  right-hand  side,  the  glandular  substance  has  been  removed  to  show  the 
reticular  loculi  of  the  connective  tissue  in  which  the  glandular  lobules  are  placed:  1,  Upper  part 
of  the  mamilla  or  nipple:  2,  areola;  3.  subcutaneous  masses  of  fat;  4,  reticular  loculi  of  the 
connective  tissue  which  support  the  glandular  substance  and  contain  the  fatty  masses;  5,  one  of 
three  lactiferous  ducts  shown  passing  toward  the  mamilla  where  they  open;  6,  one  of  tlie  sinus 
lactei  or  reservoirs;  7,  some  of  the  glandular  lobules  which  have  been  unravelled;  7',  others 
massed  together  (Luschka). 

328) ;  and,  during  lactation,  thej^eriod  of  active  secretion  by  the  gland, 
the  dilatations  form  reservoirs  for  the  milk,  which  collects  in  and  dis- 
tends them.  The  walls  of  the  gland -ducts  are  formed  of  areolar  with  some 
unstriped  muscular  tissue,  and  are  lined  internally  by  short  columnar 
and  near  the  nipple  by  squamous  epithelium.  The  alveoli  consist  of  a 
membrana  propria  of  flattened  endothelial  cells  lined  by  low  columnar 
epithelium,  and  are  filled  with  fat  globules. 

The  nipple,  which  contains  the  terminations  of  the  lactiferous  ducts, 
is  composed  also  of  areolar  tissue,  and  contains  unstriped  muscular  fibres. 
Blood-vessels  are  also  freely  supplied  to  it,  so  as  to  give  it  a  species  of 
■erectile  structure.     On  its  surface  are  very  sensitive  papillae;  and  around 


464  HANDBOOK    Ol-     PHYSIOLOGY. 

it  is  a  small  area  or  areola  of  pink  or  dark-tinted  skin,  on  which  are  to 
be  seen  small  projections  formed  by  minute  secreting  glands. 

Blood-vessels,  nerves,  and  lymphatics  are  plentifully  suj)plied  to  the 
mammary  glands;  the  calibre  of  the  blood-vessels,  as  weW  as  the  size  of 
the  glands,  varying  very  greatly  under  certain  conditions,  especially 
those  of  pregnancy  and  lactation. 

The  alveoli  of  the  glands  during  the  secreting  periods  are  found  to  be 
lined  with  very  short  columnar  cells,  with  nuclei  situated  toward  the 


Fig.  329. — Section   of  mammary  gland  of  bitch,  showing  acini,  lined  with  epithelial  cells  of  a 
polyhedral  or  short  columnar  form.     X  200.     (V.  D.Harris.) 

centre.  The  edges  of  the  cells  toward  the  lumen  may  be  irregular  and 
jagged,  and  the  remainder  of  the  alveolus  is  filled  up  with  the  materials 
of  the  milk.  During  the  intervals  between  the  acts  of  discharge,  the 
cells  of  the  alveoli  elongate  toward  the  lumen,  their  nuclei  divide,  and 
in  the  part  of  the  cells  toward  the  lumen  a  collection  of  oil  globules  takes 
place  and  probably  of  other  materials. 

The  next  stage  is  that  tlie  cells  divide  and  the  part  of  each  toward  the 
lumen  containing  a  nucleus  and  the  materials  of  the  secretion  is,  as  it 
were,  broken  off  from  the  outer  part  and  goes  to  form  the  solid  part  of 
the  milk.  The  cells  also  secrete,  from  the  blood  supplied  to  them,  the 
water,  salts,  and  probably  sugar.  In  addition  to  the  actual  casting  off 
parts  of  the  cells  containing  fat  and  the  other  materials,  oil  globules 
appear  to  pass  out  from  the  cells  with  the  other  materials  into  the  lumen 
of  the  alveoli.  The  cast-off  parts  of  the  cells  disintegrate  or  break  down, 
undergoing  a  kind  of  solution  in  the  more  fluid  part  of  the  secretion. 

In  the  earlier  days  of  lactation,  epithehal  cells  partially  transformed 
are  discharged  in  the  secretion :  these  are  termed  colostrum  corjniscles, 
but  later  on  the  cells  are  completely  transformed  into  fat  before  the 
secretion  is  discharged. 

After  the  end  of  lactation,  the  mamma  gradually  returns  to  its  original 
size  (involution).  The  acini,  in  the  early  stages  of  involution,  are  lined 
with  cells  in  all  degrees  of  vacuolation.  As  involution  proceeds  the 
acini  diminish  considerably  in  size,  and  at  length,  instead  of  a  mosaic 


METABOLISM    OF   THE   TISSUES.  465 

of  liuiug  epithelial  cells  (twenty  to  thirty  in  each  acinus),  we  have  five 
or  six  nuclei  (some  with  no  surrounding  protoplasm)  lying  in  an  irregu- 
lar heap  within  the  acinus.  During  the  later  stages  of  involution,  large 
yellow  granular  cells  are  to  be  seen.  As  the  acini  diminish  in  size,  the 
connective  tissue  and  fatty  matter  between  them  increase,  and  in  some 
animals,  when  the  gland  is  completely  inactive,  it  is  found  to  consist  of 
a  thin  film  of  glandular  tissue  overlying  a  thick  cushion  of  fat.  Many 
of  the  products  of  waste  are  carried  off  by  the  lymphatics. 

During  j)regnancy  the  mammary  glands  undergo  changes  {evolution) 
which  are  readily  observable.  They  enlarge,  become  harder  and  more 
distinctly  lobulated:  the  veins  on  the  surface  become  more  prominent. 
The  areola  becomes  enlarged  and  dusky,  with  projecting  papillae;  the 
nipple  too  becomes  more  prominent,  and  milk  can  be  squeezed  from  the 
orifices  of  the  ducts.  This  is  a  very  gradual  process,  which  commences 
about  the  time  of  conception,  and  progresses  steadily  during  the  whole 
period  of  gestation.  In  the  gland  itself  solid  columns  of  cells  bud  off 
from  the  old  alveoli  to  form  new  alveoli.  But  these  solid  columns  after 
a  while  are  converted  into  tubes  by  the  central  cells  becoming  fatty  and 
being  discharged  as  the  colostrum  corpuscles  above  mentioned. 

Milk. 

The  mammary  secretion,  or  milk,  is  a  bluish-white,  opaque  fluid  with 
a  pleasant,  sweet  taste,  of  specific  gravity  of  1028-1034.     It  is  a  true" 

O^        0°o      „Q     ^°    «A 


Fig.  330.— Globules  and  molecules  of  cow's  milk,     x  400. 

emulsion.  Under  the  microscope,  it  is  found  to  contain  a  number  of 
globules  of  various  sizes  (fig.  330),  the  majority  about  y^-g-Q-j  of  an  inch 
(.25,"  )  in  diameter.  They  are  composed  of  oily  matter,  probably  coated 
by  a  fine  layer  of  albuminous  material,  and  are  called  milk-globides; 
while,  accompanying  these,  are  numerous  minute  jjarticles,  both  oily 
and  albuminous,  which  exhibit  ordinary  molecular  movements.  The 
milk  whicli  is  secreted  in  the  first  few  days  after  jmrturition,  called  the 


466  HANDBOOK    OF    PHYSIOLOGY. 

colostrum^  differs  from  ordinary  milk  in  containing  a  larger  quantity  of 
solid  matter;  and  under  the  microscope  are  to  be  seen  certain  granular 
masses  called  colostrum-corpuscles,  already  mentioned. 

Chemical  Composition. — In  addition  to  the  oil  existing  in  numberless 
little  globules,  coated  with  a  thin  layer  of  albuminous  matter,  floating 
in  a  large  quantity  of  water,  milk  contains  certain  proteids,  milk-siic/ar 
(lactose),  and  several  varieties  of  salts.  Its  percentage  composition  has 
been  already  mentioned,  but  may  be  here  repeated.  Its  reaction  is 
alkaline. 

Chemical  Composition  of  Milk 


Water 
Solids 


Fats 
Proteids 
Sugar 
Salts      . 


IF  Milk. 

(After  Foster.) 

Human. 

Cow. 

Mare. 

Bitch. 

90 

87 

90 

76 

10 

13 

10 

24 

2.75 

4 

2. 

10 

2. 

4 

2.5 

10 

5 

4.4 

5 

3.5 

.25 

.6 

.5 

.5 

Constituents  of  Milk. 


(1.)  Wafer-. — The  amount  of  water  varies  in  different  animals,  and  in 
the  same  animal  from  time  to  time.  This  is  seen  from  the  varying  spe- 
cific gravity;  that  of  cow's  milk,  on  the  average,  varies  from  1028  to 
1034  in  unskimmed  milk,  and  from  1033  to  1037  in  skimmed  milk. 
The  amount  secreted  by  a  woman  is  about  700  to  800  cc. ,  or  rather  more 
than  a  pint,  and  by  a  cow  under  favorable  circumstances  about  6  litres 
a  day,  or  about  10  pints. 

(2.)  Proteids. — These  are  of  two  kinds  at  least,  viz.,  caseinogen  and 
lact-alhumin.  Caseinogen  may  be  obtained  from  milk  either  by  the 
addition  of  an  acid,  e.g.^  acetic,  or  by  saturation  with  crystallized  mag- 
nesium sulphate  or  sodium  chloride  in  the  way  already  indicated  (p. 
107).  The  nature  of  caseinogen  is  somewhat  uncertain;  it  in  some  re- 
spects resembles  an  alkali  albumen,  and  in  other  respects,  particularly 
in  its  undergoing  clotting  on  the  addition  of  a  ferment,  it  is  like  a  glob- 
ulin. The  clotting  of  caseinogen  is  seen  when  the  gastric  ferment  ren- 
nin,  or  when  similar  ferments  from  the  pancreas  or  intestinal  juice  are 
added  to  milk;  it  will  take  place  when  the  milk  is  neutral  or  alkaline. 
By  the  clotting,  caseinogen  is  converted  into  a  coagulated  proteid,  casein, 
and  a  proteid  residue  of  the  nature  of  a  proteose.  Casein  carries  down 
with  it  the  fat  and  the  two  materials  form  cheese. 

Lact-aliumin  does  not  differ  in  its  reactions  from  serum-albumin 
(p.  106) ;  it  coagulates  when  milk  is  boiled,  but  this  scum  is  also  partly 
due  to  the  drying  up  of  the  caseinogen  on  the  surface  of  the  milk. 

NucMn,  not  exactly  a  proteid,  but  allied  to  it,  is  also  present  in  small 


METABOLISM    OF   THE   TISSUES.  467 

amoimt  derived  from  the  nuclei  of  tlie  parts  of  the  cells  cast  off  in  the 
secretions.     Its  properties  have  been  already  mentioned  (p.  111.) 

(3.)  Fats. — The  fats  of  milk  are  those  usually  found  in  animal  tissues, 
viz.,  olein,  stearin,  and  palmatin  (p.  111).  There  are  also  others,  es- 
pecially that  of  butyric  acid  in  combination  with  glycerine.  Lecithin 
and  cholesterin  and  a  lipochrome  may  also  be  present.  The  fat  split  up 
into  minute  particles,  which  are  believed  to  be  encased  with  proteid, 
being  lighter  than  the  remainder  of  the  constituents,  rises  to  the  surface 
when  the  milk  stands,  forming  cream ;  and  cream,  when  its  fatty  mole- 
.cules  are  divested  of  their  casing  and  run  together,  forms  butter. 

(4.)  Lactose. — This  sugar,  the  reactions  of  which  are  mentioned  p. 
112,  is  apt  to  undergo  lactic  acid  fermentation  if  the  milk  be  exposed 
to  the  air,  from  the  action  of  the  organized  ferment,  the  bacterium 
lactis.  "When  this  occurs  milk  becomes  sour  and  the  caseinogen  is 
thrown  down. 

(5.)  Salts. — The  chief  salt  of  milk  is  calcium  phosphate.  Without 
its  presence  caseinogen  cannot  form  casein.  Chloride  of  sodium  is  also 
present,  and  phosphates  and  chlorides  of  potassium,  and  traces  of  iron,  of 
sulphocyanate  and  of  silica.     The  gases  are  carbon  dioxide  and  nitrogen. 

Metabolism  in  the  Liver. 

The  changes  which  take  place  in  the  liver  cells  during  life  result  in 
(«)  The  Formation  of  Bile,  the  fluid  which  the  liver  contributes  to  the 
digestive  operations  in  the  small  intestine;  ih)  The  Production  of  Gly- 
cogen ;  and  (c)  The  Formation  of  Urea. 

{a)    The  Formation  of  Bile. 

The  method  of  the  secretion  of  bile  has  been  discussed  at  some  length 
in  a  preceding  chapter  (p.  349  et  scq.),  and  it  will  be  pnly  necessary  here 
to  epitomize  some  of  the  main  observations  upon  the  subject. 

1.  That  bile  is  actually  formed  in  the  liver  by  the  activity  of  its  cells, 
since  no  accumulation  of  it  takes  place  in  the  blood  when  the  liver  is 
extirpated,  as  proved  by  experiments  on  frogs  and  birds. 

2.  That  the  coloring  matter  of  bile  is  derived  from  and  is  closely  re- 
lated to  that  of  blood,  since  the  quantity  of  the  bile  pigment  secreted  is 
markedly  increased  by  the  injection  of  substances  into  the  veins  which 
are  capable  of  setting  free  hffimoglobiu,  e.g.^  water,  ether,  chloroform,  or 
bile  salts,  or  of  blood  containing  free  coloring  matter — bile  pigment 
may  under  such  circumstances  appear  in  the  urine.  Certain  drugs  pro- 
duce the  same  effects,  e.^. ,  toluylendiamine.  The  substances  connecting 
the  blood  and  bile  pigments  are  the  following: 

Htematoporphyrin  (p.  149)  or  iron-free  hoematin — differs  only  slightly 


468  HANDBOOK    OF    PHYSIOLOGY, 

from  bilirubin — and  hreniatoidin  (p.  150)  found  in  old  blood  extravasa- 
tions, probably  identical  or  at  any  rate  isomeric  with  bilirubin.  The 
iron  which  is  obtained  from  the  decomposition  of  haemoglobin  is  notably 
retained  in  the  hepatic  cells  probably  combined  with  some  organic  sub- 
stance. 

The  blood-coloring  matter  which  the  liver  cells  convert  into  haemo- 
globin is  most  likely  brought  to  them  in  such  a  form  as  to  be  easily 
decomposed  (p.  352). 

3.  That  the  bile  acids  are  also  found  in  the  liver  cells,  but  that  to 
some  extent  at  any  rate  the  taurin  and  the  glycin  are  brought  to  them 
ready  formed  in  the  blood,  and  that  the  cells  manufacture  the  cholic 
acid. 

4.  That  there  is  no  support  to  the  idea  that  the  bile  is  formed  from 
the  blood  of  the  hepatic  artery,  and  not  from  that  of  the  portal  vein 
(p.  350). 

(b)   The  Formation  of  Glycogeii  {Glycogeiiesis). 

The  important  fact  that  the  liver  normally  forms  sugar,  or  a  substance 
readily  convertible  into  it,  was  discovered  by  Claude  Bernard  in  the  fol- 
lowing way:  he  fed  a  dog  for  seven  days  with  food  containing  a  large 
quantity  of  sugar  and  starch;  and,  as  might  be  expected,  found  sugar 
in  both  the  portal  and  hepatic  blood.  But  when  this  dog  was  fed  with 
meat  only,  to  his  surprise,  sugar  was  still  found  in  the  blood  of  the 
hepatic  veins.  Eepeated  experiments  gave  invariably  the  same  result; 
no  sugar  being  found,  under  a  meat  diet,  in  the  portal  vein,  if  care  were 
taken,  by  applying  a  ligature  on  it  at  the  transverse  fissure,  to  prevent 
reflux  of  blood  from  the  hepatic  venous  system.  Bernard  found  sugar 
also  in  the  substance  of  the  liver.  It  thus  seemed  certain  that  the  liver 
formed  sugar,  even  when,  from  the  absence  of  saccharine  and  amyloid 
matters  in  the  .food,  none  could  be  brought  directly  to  it  from  the  stom- 
ach or  intestines. 

Bernard  found,  subsequently  to  the  before-mentioned  experiments, 
that  a  liver,  removed  from  the  body,  and  from  which  all  sugar  had  been 
completely  washed  away  by  injecting  a  stream  of  water  through  its 
blood-vessels,  after  the  lapse  of  a  few  hours  contained  sugar  in  abun- 
dance. This  post-mortem  production  of  sugar  was  a  fact  which  could 
only  be  explained  on  the  supposition  that  the  liver  contained  a  substance 
readily  convertible  into  sugar ;  and  this  theory  was  proved  correct  by  the 
discovery  of  a  substance  in  the  liver  allied  to  starch,  and  now  generally 
termed  glycogen.  We  may  believe  that  glycogen  is  first  formed  and 
stored  in  the  liver  cells,  and  that  the  sugar,  when  present,  is  the  result 
of  its  transformation. 

Source  of  Glycogen. — Although,  as  before  mentioned,  the  greatest 


METABOLISM    OF   THE   TISSUES.  469 

amount  of  glycogen  is  produced  by  the  liver  upon  a  diet  of  starch  or 
sugar,  a  certain  quantity  is  produced  upon  a  proteid  diet.  The  glyco- 
gen when  stored  in  the  liver  cells  may  readily  be  demonstrated  in  sec- 
tions of  liver  containing  it  by  its  reaction  (red  or  port-wine  color)  with 
iodine,  and  moreover,  when  the  hardened  sections  are  so  treated  that 
the  glycogen  is  dissolved  out,  the  protoplasm  of  the  cell  is  so  vacuolated 
as  to  appear  little  more  than  a  framework.  There  is  no  doubt  that  in 
the  liver  of  a  hibernating  frog  the  amount  of  glycogen  stored  up  in  the 
outer  parts  of  the  liver  cells  is  very  considerable. 

Average  amount  of  Glycogen  in  the  Liver  of  Dogs  under   Various  Diets 

(Pavy). 

Diet.  Amount  of  Glycogen  in  Liver. 

Animal  food      .          .  .          .          .         .          .          .         7.19  per  cent. 

Animal  food  with  sugar  (about  \  lb.  of  sugar  daily)  14.5         " 

Vegetable  diet  (potatoes,  with  bread  or  barley-meal)  17.23       " 

The  dependence  of  the  formation  of  glycogen  on  the  kind  of  food 
taken  is  also  well  shown  by  the  following  results,  obtained  by  the  same 
■experimenter : 

Average  quantity  of  Glycogen  found  in  the  Liver  of  Babbits  after  Fast- 
ing, and  after  a  diet  of  Starch  and  Sugar  respectively. 

Average  Amoxint  of  Glycogen  in  Liver. 

After  fasting  for  three  days  .          .          .     Practically  absent. 

"       diet  of  starch  and  grape-sugar         .          .     15.4  per  cent, 
cane-sugar  .  .         .         .16.9 

Glycogen  is  also  formed  on  a  gelatin  diet,  but  fats  taken  in  as  food  do 
not  increase  its  amount  in  the  cells.  The  diet  most  favorable  to  the 
production  of  a  large  amount  of  glycogen  is  a  mixed  diet  containing  a 
large  amount  of  carbo-hydrate,  but  with  some  proteid.  Glycerin  injected 
into  the  alimentary  canal  may  also  increase  the  glycogen  of  the  liver. 

Destination  of  Glycogen. — There  are  two  chief  theories  as  to  the  desti- 
nation of  hepatic  glycogen.  (1.)  That  the  glycogen  is  converted  into 
sugar  during  life  by  the  agency  of  a  ferment  {liver  diastase)  also  formed 
in  the  liver;  and  that  the  sugar  is  conveyed  away  by  the  blood  of  the 
hepatic  veins,  to  undergo  combustion  in  the  tissues.  (2.)  That  the 
conversion  into  sugar  only  occurs  after  death,  and  that  during  life  no 
sugar  exists  in  healthy  livers;  glycogen  not  undergoing  this  transforma- 
tion. The  chief  arguments  advanced  in  support  of  this  view  are,  («) 
that  scarcely  a  trace  of  sugar  is  found  in  blood  drawn  during  life  from 
the  right  ventricle,  or  in  blood  collected  from  the  right  side  of  the  heart 
immediately  after  an  animal  has  been  killed;  while  if  the  examination 
be  delayed  for  a  very  short  time  after  death,  sugar  in  abundance  may 


470  HANDBOOK    OF    PHYSIOLOGY. 

be  found  in  such  blood;  (i),  tbat  the  liver,  like  the  venous  blood  in  the 
heart,  is,  at  the  moment  of  death,  completely  free  from  sugar,  although 
afterward  its  tissue  speedily  becomes  saccharine,  unless  the  formation  of 
sugar  be  prevented  by  boiling,  or  other  means  calculated  to  interfere 
with  the  action  of  a  ferment. 

Instead  of  adopting  the  view  that  normally,  during  life,  glycogen 
acts  as  a  store  of  carbo-hydrate  material  to  be  converted,  little  by  little, 
into  sugar  as  occasion  requires,  and  that  it  passes  as  sugar  into  the  he- 
patic venous  blood,  to  be  conveyed  to  the  tissues  to  be  further  disposed 
of,  Pavy  inclines  to  the  belief  that  it  may  represent  an  intermediate 
stage  in  the  formation  of  fat  from  materials  absorbed  from  the  alimen- 
tary canal.  There  is  little  evidence  in  favor  of  this  view,  and  although 
it  is  possible  that  the  liver  cells  may,  in  some  way  or  other  (not  at  pres- 
ent understood),  be  able  to  convert  part  of  its  store  of  glycogen  into  fat, 
the  consensus  of  opinion  inclines  to  the  belief  that  most  of  the  glycogen 
leaves  the  liver  as  sugar. 

Indeed,  wherever  glycogen  is  found,  in  the  muscles,  in  the  placenta, 
or  elsewhere,  it  must  be  looked  upon  as  a  store  of  carbo-hydrate  material 
which  may  be  taken  up  during  the  metabolism  of  the  tissue  and  built  up  in 
its  protoplasm,  to  be  used  up  only  indirectly  when  catabolism  of  the 
I^rotoplasm  takes  place.  Whether  the  glycogen  which  probably  reaches 
the  muscles  as  sugar  is  reconverted  into  glycogen  before  it  is  built  up 
as  it  were  into  the  protoplasmic  molecule  is  not  known. 

The  relation  of  glycogen  to  the  cell  metabolism. — It  is  not  exactly  known 
whether  the  glycogen  is  formed  simply  by  a  process  of  dehydration  of 
the  sugar  which  reaches  the  cells  in  the  portal  blood,  or  whether 
the  cells  by  their  metabolism  are  usually  in  the  habit  of  form- 
ing glycogen  or  sugar  which,  during  fasting  and  other  similar  conditions, 
is  at  once  discharged  into  the  hepatic  blood  to  be  used  up  by  the  tissues, 
but  which  is  stored  up  in  the  cells  as  glycogen  as  long  as  there  is  suffic- 
ient sugar  in  the  blood  without  it,  or  as  long  as  the  tissues  are  so  quiescent 
as  not  to  require  more  than  a  small  quantity  of  the  total  amount  of 
carbo-hydrate  secreted  by  the  hepatic  cells. 

Glycosuria. — Sugar  may  be  present  not  only  in  the  hepatic  veins, 
but  in  the  blood  generally,  and  when  such  is  the  case,  the  sugar  is  ex- 
creted by  the  kidneys,  and  appears  in  variable  quantities  in  the  urine. 
This  condition  is  known  as  glycosuria. 

Influence  of  the  Nervous  System. — Glycosuria  may  be  experimentally 
produced  by  puncture  of  the  medulla  oblongata  in  the  region  of  the 
vaso-motor  centre.  The  better  fed  the  animal  the  larger  is  the  amount 
of  sugar  found  in  the  urine;  in  the  case  of  a  starving  animal  no  sugar 
appears.  It  is,  therefore,  highly  probable  that  the  sugar  comes  from 
the  hepatic  glycogen,  since  in  the  one  case  glycogen  is  in  excess,  and  in 


METABOLISM    OF   THE   TISSUES.  471 

the  other  it  is  almost  absent.  The  nature  of  the  influence  is  uncertain. 
It  may  be  exercised  in  dilating  the  hepatic  vessels,  or  possibly  may  be 
exerted  on  the  liver  cells  themselves.  The  whole  course  of  the  nervous 
stimulus  cannot  be  traced  to  the  liver,  but,  at  any  rate,  it  is  not  con- 
ducted by  the  vagi  or  by  the  splanchnics,  but  at  first  it  passes  from  the 
lower  part  of  the  floor  of  the  fourth  ventricle  and  medulla  down  the 
spinal  cord  as  far  as — in  rabbits — the  fourth  dorsal  vertebra,  and  hence 
to  the  first  thoracic  ganglion.  The  formation  of  sugar  by  the  liver  is 
also  not  a  vaso-dilator  effect,  since  it  will  occur  when  the  vessels  are 
constricted. 

Many  other  circumstances  will  cause  glycosuria.  It  has  been  observed 
after  the  administration  of  various  drugs — e.g.,  strychnine  (in  frogs), 
phloridzin,  a  glucoside,  and  phloretin,  a  derivative  of  phloridzin,  not  a 
glucoside,  morphine,  nitrite  of  amyl,  etc. — after  the  injection  of  urari, 
poisoning  with  carbonic  oxide  gas,  the  inhalation  of  ether,  chloroform, 
etc.,  the  injection  of  oxygenated  blood  into  the  portal  venous  system. 
It  has  been  observed  in  man  after  injuries  to  the  head,  and  in  the  course 
of  various  diseases. 

In  all  such  cases,  at  any  rate,  the  glycosuria  appears  to  be  due  to  some 
abnormal  activity  of  the  liver  cells  themselves  set  up  by  the  direct  action 
of  the  secretory  nerves  uj^on  them. 

The  well-known  disease,  diahetus  mellitns,  in  which  a  large  quantity  of 
sugar  is  persistently  secreted  daily  with  the  urine,  has,  doubtless,  some 
close  relation  to  the  normal  glycogenic  function  of  the  liver;  but  the 
nature  of  the  relationship  is  at  present  quite  unknown. 

(f)   The  Formation  of  Urea. 

It  is  not  strictly  correct  to  include  the  formation  of  urea  under  the 
head  of  metabolic  changes  in  the  liver,  since  although  as  we  shall  see 
directly  there  is  a  considerable  amount  of  evidence  that  some  of  the  urea 
is  formed  by  means  of  the  liver,  yet  we  cannot  go  so  far  as  to  assert  that 
all  of  the  urinary  solids  or  even  all  of  the  urea  is  produced  by  the  hepatic 
cells.  We  can,  however,  state  with  certainty  that  the  urea  is  not  formed 
to  even  the  very  smallest  extent  by  means  of  the  kidney,  since  it  is  not 
only  found  in  the  blood  going  to  the  kidneys,  but  may  also  accumulate 
to  a  very  harmful  degree  if  the  kidneys  are  extensively  diseased,  and  the 
separation  of  the  urine  by  those  organs  is  interfered  with.  This  is  also 
the  case  if  the  kidneys  be  experimentally  removed  from  an  animal. 
Thus  it  seems  reasonable  to  assume  that  the  function  of  the  kidneys,  as 
far  as  the  more  important  solid,  the  urea,  is  concerned,  is  only  one  of 
separation.  This  has  already  been  discussed  under  the  head  of  the 
method  of  secretion  of  urine.      It  becomes  necessary  to  consider  the 


472  HANDBOOK    OP    PHYSIOLOGY. 

question  of  the  sources  of  the  urea  which  is  formed  in  the  hody  and  also 
the  way  by  which  it  is  formed. 

(1.)  In  the  first  place  there  is  evidence  to  connect  the  formation  of 
urea  with  two  of  the  products  of  the  digestion  of  proteid  materials  in 
the  alimentary  canal.  In  treating  of  the  subject  of  pancreatic  digestion 
it  was  shown  that  the  ferment  trypsin  appears  to  have  the  power  of  car- 
rying the  proteid  digestion  a  step  further  than  the  gastric  ferment  pep- 
sin; and  that  when  the  pancreatic  digestion  is  carried  on  to  its  natural 
termination  there  appears  in  tlie  digestion-fluid  two  substances,  nitroge- 
nous and  crystallizable,  which  were  absent  from  the  fluid  in  which  pepsin 
has  acted  as  far  as  it  can.  These  substances  are  leiicin  and  tyrosin.  They 
appear  in  the  majority  of  cases  together,  and  although  they  do  not  be- 
long to  the  same  series  of  chemical  substances,  yet  they  agree  in  this 
that  they  are  both  amidated  acids,  that  is  to  say,  they  both  contain  ami- 
dogen,  NHj,  leucin  being,  as  we  have  seen,  amido-caproic  acid,  and 
tyrosin,  amido-oxy-phenyl-propionic  acid.  It  must  be  confessed  that  it 
is  difficult  to  see  how  the  ferment  trypsin  can  of  itself  perform  the  long 
series  of  changes  which  result  in  the  formation  of  these  two  bodies,  but 
the  view  is  very  generally  held  that  it  not  only  produces  peptones  from 
albumins,  hut  that  part  of  the  peptones  called  hemipeptone  is  further 
converted  into  the  two  substances  in  question. 

Whether  the  conversion  into  leucin  and  trypsin  is  done  by  the  trypsin 
itself,  or  by  some  other  ferment,  organized  or  unorganized,  it  is  un- 
doubted that  these  substances  appear  as  a  result  of  pancreatic  digestion. 
It  should  be  recollected,  however,  that  the  same  bodies  may  arise  outside 
the  body  from  the  splitting  up  of  proteids  by  putrefaction,  ?.e.,by  the 
action  of  micro-organisms,  and  it  is  possible  that  the  leucin  and  tyrosin 
of  intestinal  digestion  are  similarly  produced. 

The  connection  between  leucin  and  tyrosin  and  urea  then  is  supposed 
to  be  the  following:  the  leucin  and  tyrosin  formed  in  the  intestinal 
digestion  are  absorbed  by  the  blood-vessels  and  are  carried  by  the  portal 
vein  into  the  liver.  By  the  action  of  the  hepatic  cells  they,  or  at  any 
rate  the  leucin,  is  converted  into  urea,  which  then  is  taken  up  by  the 
hepatic  veins  into  the  ordinary  systematic  circulation,  and  after  a  time 
reaches  the  kidneys  and  is  eliminated  from  the  body. 

This  view  is  based  upon  the  following  facts: — 

(1.)  Firstly,  that  if  leucin  be  introduced  into  the  alimentary  canal, 
the  amount  of  urea  in  the  urine  is  considerably  increased,  but  that  leucin 
itself  does  not  appear ;  the  same  phenomena  have  been  noticed  if  glycin 
be  administered  instead  of  leucin. 

(2.)  Secondly,  that  in  a  certain  disease  of  the  liver  in  which  the  liver 
cells  are  rapidly  degenerated  and  lose  their  function,  i.e.,  acute  yellow 
atrophy,  the  urea  of  the  urine  is  replaced  by  leucin  and  tyrosin. 


METABOLISM    OF   THE   TISSUES.  473 

(3.)  And  thirdly,  that  the  liver  is  found  to  contain  a  considerable 
amount  of  urea,  contrasting  very  markedly  with  other  glands  and  with 
the  muscles  of  the  body  in  this  respect.  If  blood  be  passed  through  the 
liver  of  a  recently  killed  animal  the  amount  of  urea  which  it  contains  is 
found  to  be  greatly  increased. 

This  evidence  appears  to  show  that  urea  is  produced  by  the  liver  cells 
when  in  normal  condition,  and  also  that  leuciu,  and  possibly,  but  not  so 
certainly,  tyrosin,  is  one  source  from  which  it  is  formed. 

The  exact  way  in  which  the  urea  is  formed  l:)y  the  liver  cells  is  not 
■understood,  but  it  has  been  suggested  that  it  is  done  in  at  least  these 
two  stages,  viz.,  the  reduction  of  the  leucin  into  a  condition  of  ammonia 
<ind  caproic  acid,  and  the  building  up  of  the  urea  from  the  ammonia 
thus  obtained.  There  is  reason  for  thus  concluding  that  the  liver  is 
able  to  construct  urea  from  ammonia  compounds,  since  the  administra- 
tion of  ammonium  salts,  such  as  the  chloride  or  carbonate,  appears  to 
increase  the  amount  of  urea  in  the  urine  in  a  degree  commensurate  with 
the  amount  of  the  nitrogen  contained  in  the  salt  so  introduced  into  the 
body. 

(2.)  The  second  probable  source  of  the  urea  of  the  urine  is  creatin. 
This  substance  is  produced,  as  we  have  before  mentioned,  in  the  ordi- 
nary metabolism  of  muscle;  it  is  always  present  in  muscle,  and  since 
the  chief  part  of  the  metabolism  of  the  body  takes  place  in  muscle  it 
must  be  exceedingly  probable  that  a  considerable  quantity  of  creatin  is 
formed  in  the  twenty-four  hours.  Creatin,  however,  does  not  appear 
in  the  urine,  and  although  its  closely  associated  product,  creatinin,  is  a 
normal  constituent,  \ei  the  amount  of  that  body,  less  than  one  gramme 
in  twenty-four  hours,  is  so  small  as  scarcely  to  represent  the  large  amount 
of  creatin  which  must  be  formed  in  the  course  of  a  day,  and  which  has 
been  calculated  as  upward  of  100  gi'ms.  (as  muscle  contains  .2  to  .4 
per  cent  of  the  substance) .  It  is  also  remarkable  that  there  is  no  urea, 
or  scarcely  any,  produced  by  muscular  metabolism,  whereas  urea  is  the 
largest  solid  constituent  of  the  urine.  It  therefore  seems  almost  certain 
that  muscular  creatin  appears  in  the  urine  as  urea.  This  is  made  more 
likely,  since  creatin  may  so  easily  be  converted  into  urea  in  the  labor- 
atory; e.g.,  by  boiling  with  baryta  water,  creatin  is  split  up  into  urea 
and  sarcosin,  thus  C.H^NgO.+H.O,  CON^H^+CjH^KO,;  again  sarcosin 
is  methyl-glycin,  and  as  we  have  before  jiointed  out,  glvcin  is  amido- 
acetic  acid,  so  that  it  may  be  supposed  that  the  sarcosin  may  also  be 
■converted  into  urea  as  well  as  the  creatin  from  which  it  is  obtained. 
Creatin  appears  to  be  a  substance  which  also  arises  in  nervous  tissue 
■during  its  metabolism,  so  that  nervous  tissue  may  be  another  source  of 
urea.  There  is  no  positive  evidence  as  to  the  locality  in  the  body  in 
which  the   creatin  is  formed  into  urea,  yet  it  is  not  unlikely  that  the 


474  HANDBOOK    OF    PHYSIOLOGY, 

changes  producing  this  body  are  carried  out  more  or  less  completely  in 
the  liver. 

It  was  always  thought  that  in  addition  to  the  two  chief  sources  of 
urea  above  considered  there  might  be  a  more  direct  change  of  some  of 
the  proteid  food  material,  from  that  which  is  absorbed  into  the  portal 
vein  and  brought  to  the  liver,  the  proteid  being  split  up  there  into  a 
glycogen  moiety  and  an  urea  moiety;  and  this  may  really  be  the  case. 
There  appears  to  be  undoubted  evidence  that  the  introduction  of  pro- 
teid into  the  alimentary  canal,  even  in  small  amount,  soon  increases 
the  amount  of  the  urea,  but  although  the  method  of  formation  of  urea 
from  leucin  is  admitted,  yet  there  is  no  very  confident  belief  among 
physiologists  that  the  series  of  changes  resulting  in  the  formation  of 
urea  from  proteid  through  that  substance  is  a  very  extensive  or  a  very 
general  one.  If  it  occurs  in  the  way  above  suggested,  it  is  only  an  alter- 
native course  toward  excretion,  and  is  only  followed  by  the  proteid  food 
when  taken  into  the  body  in  excess.  Further,  even  when  some  of  the 
peptone  is  further  converted  into  the  two  bodies  above  mentioned,  a 
moiety  of  the  peptone,  called  anti-peptone,  in  order  to  signify  its  power 
of  resistance  to  such  action,  is  unchanged. 

Another  way  of  accounting  for  the  undoubted  increase  of  urea  which 
occurs  in  the  urine  on  taking  proteid  food  has  been  suggested,  and  that 
is  this,  that  the  presence  of  such  materials  in  the  blood  stimulates  the 
nitrogenous  metabolism  of  the  tissues,  especially  of  the  muscles,  with 
the  production  of  waste  materials  which  may  be  converted  into  urea. 

From  what  we  have  said  it  will  be  seen  that  we  are  unable  to  make 
any  very  definite  statement  as  to  the  methods  in  which  the  urea  is  formed, 
and  although  it  is  probable  that  a  large  amount  of  the  urea  is  formed  in 
the  liver,  yet  there  is  no  reason  to  think  that  the  whole  of  the  urea  is; 
there  formed,  and  it  has  been  suggested  that  it  may  be  formed  elsewhere, 
e.g.,  in  the  spleen,  and  in  lymphatic  and  other  glands. 

Again,  in  mentioning  the  possible  antecedents  of  urea,  it  must  not  be 
forgotten  that  many  other  substances  have  been  suggested  as  interme- 
diate between  proteid  and  urea,  especially  uric  acid.  Uric  acid  may  be 
split  up  into  urea  in  the  laboratory,  and  from  this  it  was  concluded  that 
urea  was  a  further  oxidized  stage  of  uric  acid;  but  although  this  opinion 
is  still  held  by  some  physicians  it  has  been  almost  entirely  given  up  by 
physiologists.  It  is  now  regarded  as  quite  possible  that  there  are  several 
simpler  bodies  formed  from  the  breaking  up  of  proteids  in  the  body 
which  give  rise  to  urea;  we  have  already  mentioned  ammonium  carbon- 
ate, and  may  add  cyanic  acid  and  ammonium  carbamate  to  the  list. 

We  are  quite  unable  to  explain  how  much,  if  any,  of  the  urea  repre- 
sents the  breakiug  down  of  the  proteid  food  material  supplied  to  the 
tissues,  which  never  is  built  up  into  the  tissues,  and  how  much  to  the. 


METABOLISM    OF   THE   TISSUES.  475 

actual  breaking  down  of  the  protoplasm,  nor  can  we  make  any  definite 
statement  as  to  the  nature  of  the  anabolic  process  beyond  this,  that  it 
is  a  process  which  cannot  go  on  without  having  a  proteid  supply,  and  is 
increased  up  to  a  certain  point,  both  in  extent  and  rapidity,  by  an  in- 
crease in  that  supply.  The  intimate  relations  which  exist  between 
several  of  these  nitrogenous  crystalline  bodies  will  be  seen  by  a  reference 
to  their  f ormulte : — 

Hypoxanthin  or  Carniu   ......     CaHjNiO. 

Xanthin  ....  ...  C5H4N4O2. 

Uric  Acid C5H4N4O3. 

If,  then,  the  view  of  the  chemical  nature  of  proteid,  as  mentioned  in 
Chapter  III.,  is  correct,  viz.,  that  the  nitrogen  in  living  proteid  exists 
in  the  form  of  cyanogen  compounds,  when  proteid  splits  up,  much  energy 
is  set  free,  and  the  nitrogen  is  afterward  found  in  some  of  the  ammonia 
groups. 

Formation  of  Uric  Acid. — Uric  acid  probably  arises  much  in  the  same 
way  as  urea.  The  relation  which  uric  acid  and  urea  bear  to  each  other, 
as  we  have  seen,  is  still  obscure.  The  fact  that  they  often  exist  together 
in  the  same  urine,  makes  it  seem  probable  that  they  have  different  ori- 
gins; but  the  entire  replacement  of  either  by  the  other,  as  of  urea  by 
uric  acid  in  the  urine  of  birds,  serpents,  and  many  insects,  and  of  uric 
acid  by  urea  in  the  urine  of  the  feline  tribe  of  Mammalia,  shows  that 
either  alone  may  take  the  place  of  the  two.  At  any  rate,  although  it  is 
true  that  one  molecule  of  uric  acid  is  capable  of  splitting  uj)  into  two 
molecules  of  urea  and  one  of  mes-oxalic  acid,  this  is  no  evidence  for  be- 
lieving that  uric  acid  is  an  antecedent  of  urea  in  the  nitrogenous 
metabolism  of  the  body. 

Formation  of  Hippuric  Acid. — The  source  of  hippuric  acid  is  not  sat- 
isfactorily determined;  in  part  it  is  probably  derived  from  some  constit- 
uents of  vegetable  diet,  though  man  has  no  hippuric  acid  in  his  food, 
nor,  commonly,  any  benzoic  acid  that  might  be  converted  into  it;  in 
part  from  the  natural  disintegration  of  tissues,  independent  of  vegetable 
food,  for  Weismann  constantly  found  an  appreciable  quantity,  even  when 
living  on  an  exclusively  animal  diet.  Hippuric  acid  arises  from  tho 
union  of  benzoic  acid  with  glycin  (C^H^NO^  +  C,HjO„  =  CgHgNO,  + 
H„0),  which  union  probably  takes  place  in  the  kidneys  themselves.  It  is 
possible  that  the  aromatic  radicle  in  this  reaction  is  obtained  from  the 
splitting  up  of  tyrosin,  which  appears  so  frequently  as  a  result  of  the 
decomposition  of  proteid,  the  ammonia  radicle  with  which  it  is  associ- 
ated going  to  form  urea. 

The  source  of  the  extractives  of  the  urine  is  probably  in  chief  part 
metabolism  of  the  nitrogenous  tissues,  but  we  are  unable  to  say  whether 
these  nitrogenous  bodies  are  merely  accidental,  having  resisted  further 


476  HANDBOOK    OF    PHYSIOLOGY. 

decomposition  into  urea,  or  whether  they  are  the  representatives  of  the 
-decomposition  of  special  tissues,  or  of  special  forms  of  metabolism  of 
the  tissues.  There  is,  however,  one  exception,  and  that  is  in  the  case 
of  creatinin;  it  has  been  suggested  that  this  represents  the  creatin 
which  enters  the  body  in  ordinary  flesh  food. 

Metabolism  in  the  Vascular  Glands. 

In  addition  to  the  various  glands  the  structure  and  functions  of  Avhich 
have  been  considered  in  the  preceding  chapters,  and  which  have  been 
.shown  either  to  secrete  from  the  blood  materials  of  use  in  digestion  or 
to  excrete  from  the  blood  materials  of  no  further  use  in  the  economy, 
there  are  others  which  have  not  to  do  with  secretion  or  excretion,  at  all 
events  directly.  These  are  called  Vascular  glands,  and  comprise  the 
Spleen,  the  Tliymus,  the  Tonsils,  and  the  Solitary  and  Agminated  glands 
cf  Peyei'  in  the  intestines,  all  of  which  are  made  up  chiefly  of  lymphatic 


-  '51 


Fig.  331.— Section  of  injected  dog's  spleen;  c,  capsule;  tr,  trabeculse;  m,  two  Malpighian 
bodies  with  numerous  small  arteries  and  capillaries;  a,  artery;  I,  lymphoid  tissue,  consisting  of 
closely-packed  lymphoid  cells  supported  by  very  delicate  retiform  tissue;  a  light  space  unoc- 
cupied by  cells  is  seen  all  round  the  trabeculse,  which  corresponds  to  the  "lymph  path"  in  lym- 
phatic glands.     (Schofleld.) 

tissue,   resembling  lymphatic  glands,   and  which  are  evidently  closely 
connected  with  the   lymphatic  system;  the  Svjjra-renal  capsnles  or  Ad- 


METABOLISM    OE   THE    TISSUES.  477' 

rena'ls;  the  Thijroid ;  the  Pineal  and  Pituitary  glands  and  the  Carotid 
and  CGccygeal  glands,  about  of  all  of  which  very  little  is  known. 

The  Spleen  is  the  largest  of  these  so-called  vascular  glands;  it  is 
situated  to  the  left  of  the  stomach,  between  it  and  the  diaphragm.  It 
is  of  a  deep  red  color,  of  a  variable  shape,  generally  oval,  somewhat 
concavo-convex.  Vessels  enter  and  leave  the  gland  at  the  inner  side  or 
hilus. 

Structure. — The  spleen  is  covered  externally  almost  completely  by  a 
serous  coat  derived  from  the  peritoneum,  while  within  this  is  the  proper 


Fig.  332. — Reticulum  of  the  spleen  of  a  cat,  shown  bj-  injection  with  gelatine.     (Cadiat.) 

fibrous  coat  or  capsule  of  the  organ.  The  latter,  composed  of  connective- 
tissue,  with  a  large  preponderance  of  elastic  fibres,  and  a  certain  propor- 
tion of  unstriated  muscular  tissue,  forms  the  immediate  investment  of 
the  spleen.  Prolonged  from  its  inner  surface  are  fibrous  processes  or 
trabeculm,  containing  much  unstriated  muscle,  which  enter  the  interior 
of  the  organ,  and,  dividing  and  anastomosing  in  all  parts,  form  a  kind 
of  supporting  framework  or  stroma,  in  the  interstices  of  which  the 
proper  substance  of  the  spleen  (spleen-jmlj))  is  contained  (fig.  332).  At 
the  hilus  of  the  spleen,  the  blood-vessels,  nerves,  and  lymphatics  enter, 
and  the  fibrous  coat  is  prolonged  into  the  spleen-substance  in  the  form 
of  investing  sheaths  for  the  arteries  and  veins,  which  sheaths  again  are^ 
continuous  with  the  trabeculfe  before  referred  to. 

The  sjileen-pulp,  which  is  of  a  dark  red  or  reddish-brown  color,  is 
composed  chiefly  of  cells,  imbedded  in  a  matrix  of  fibres  formed  of  the 
branching  of  large  flattened  nucleated  endotheloid  cells.  The  spaces  of 
the  network  only  partially  occupied  by  cells  form  a  freely  communicat- 
ing system.  Of  the  cells  some  are  granular  corpuscles  resembling  the 
lymph-corpuscles,  more  or  less  connected  with  the  cells  of  the  meshwork, 
both  in  general  appearance  and  in  being  able  to  perform  amoeboid 
movements;  others  are  red  blood-corpuscles  of  normal  appearance  or 
variously  changed ;  while  there  are  also  large  cells  containing  either  a- 
pigment  allied  to  the  coloring  matter  of  the  blood,  or  rounded  corpuscles 
like  red  corpuscles. 

The  splenic  artery,  after  entering  the  spleen  by  its  concave  surface, 
divides  and  subdivides,  with  but  little  anastomosis  between  its  branches;. 


478  HANDBOOK    OF    niYSIOLOGY. 

at  the  same  time  its  brauches  are  sheathed  by  the  prolongations  of  the 
fibrous  coat,  wliich  they,  so  to  speak,  carry  into  the  spleen  with  them. 
The  arteries  send  off  brauches  into  the  spleen-pulp  which  end  in  capil- 
laries, and  these  either  communicate,  as  in  other  parts  of  the  body,  with 
the  radicles  of  the  veins,  or  end  in  lacunar  spaces  in  the  spleen-pulp, 
from  which  veins  arise. 

The  walls  of  the  smaller  veins  are  more  or  less  incomplete,  and  readily 
allow  lymphoid  corpuscles  to  be  swept  into  the  blood-current.  The 
blood  from  the  arterial  capillaries  is  emptied  into  a  system  of  interme- 
diate passages,  which  are  directly  bounded  by  the  cells  and  fibres  of  the 
network  of  the  pulp,  and  from  which  the  smallest  venous  radicles  with 
their  cribriform  walls  take  origin.  The  veins  are  large  and  distensible: 
the  whole  tissue  of  the  spleen  is  highly  vascular  and  becomes  readily 


vR%A^ 


Fig.  333.— Section  of  spleen  of  cat.      a,  a',  Malpighian  corpuscles,  in  case  of  a',  in  connection 
with  small  artery,  b;  b,  6',  small  arteries;  c,  section  of  trabeculee. 

engorged  with  blood :  the  amount  of  distention  is,  however,  limited  by 
the  fibrous  and  muscular  tissue  of  its  capsule  and  trabeculae,  which  forms 
an  investment  and  supjjort  for  the  pulpy  mass  within. 

On  the  face  of  a  section  of  the  spleen  can  be  usually  seen  readily  with 
the  naked  eye,  minute,  scattered  rounded  or  oval  whitish  spots,  mostly 
from  ^  to  6-V  inch  (|  to  |  mm.)  in  diameter.  These  are  the  Malpi- 
ghian  corpuscles  of  the  spleen,  and  are  situated  on  the  sheaths  of  the 


METABOLISM    OF   THE   TISSUES.  479 

minute  splenic  arteries,  of  which,  indeed,  they  ma}'  be  said  to  be  out- 
gro"Wths  (fig.  333),  For  while  the  sheaths  of  the  larger  arteries  are  con- 
structed of  ordinary  connective  tissue,  this  has  become  modified  where  it 
forms  an  investment  for  the  smaller  vessels,  so  as  to  be  composed  of 
adenoid  tissue,  with  abundance  of  corpuscles,  like  lymph-corpuscles, 
contained  in  its  meshes,  and  the  Malpighiau  corpuscles  are  but  small 
outgrowths  of  this  cytogenous  or  cell-bearing  connective  tissue.  They 
are  composed  of  cylindrical  masses  of  corpuscles,  intersected  in  all  parts 
by  a  delicate  fibrillar  tissue,  which,  though  it  invests  the  Malpighian 
bbdies,  does  not  form  a  complete  capsule.  Blood-capillaries  traverse  the 
Malpighian  corpuscles  and  form  a  plexus  in  their  interior.  The  struc- 
ture of  a  Malpighian  corpuscle  of  the  spleen  is,  therefore,  very  similar  to 
that  of  lymphatic-gland  substance. 

Functions. — With  respect  to  the  office  of  the  spleen,  we  have  the  fol- 
lowing data:  (1.)  The  large  size  which  it  gradually  acquires  toward 
the  termination  of  the  digestive  process,  and  the  great  increase  observed 
about  this  period  in  the  amount  of  the  finely-granular  albuminous 
plasma  within  its  parenchyma,  and  the  subsequent  gradual  decrease  of 
this  material,  seem  to  indicate  that  this  organ  is  concerned  in  storing  up 
some  of  the  changed  and  absorbed  proteid  food,  to  be  gradually  intro- 
duced into  the  blood,  according  to  the  demands  of  the  general  system. 

(2.)  It  seems  probable  that  the  spleen,  like  the  lymphatic  glands,  is 
engaged  in  the  formatio7i  of  hlood-corpuscles.  For  it  is  quite  certain, 
that  the  blood  of  the  splenic  vein  contains  an  unusually  large  amount 
of  white  corpuscles;  and  in  the  disease  termed  leucocythsemia,  in  which 
the  pale  corpuscles  of  the  blood  are  remarkably  increased  in  number, 
there  is  almost  always  found  an  hypertrophied  state  of  the  spleen  or  of 
the  lymphatic  glands.  In  Kolliker's  opinion,  the  development  of  color- 
less and  also  colored  corpuscles  of  the  blood  is  one  of  the  essential  func- 
tions of  the  spleen,  into  the  veins  of  which  the  new-formed  corpuscles 
pass,  and  are  thus  conveyed  into  the  general  current  of  the  circulation. 

(3.)  There  is  reason  to  believe,  that  in  the  spleen  many  of  the  red 
corpuscles  of  the  blood,  those  probably  which  have  discharged  their 
office  and  are  worn  out,  undergo  disintegration;  for  in  the  colored  por- 
tions of  the  spleen-pulp  an  abundance  of  such  corpuscles,  in  various 
stages  of  degeneration,  are  found,  while  the  red  corpuscles  in  the  splenic 
venous  blood  are  said  to  be  relatively  diminished.  This  process  appears  to 
be  as  follows:  the  blood-corpuscles,  becoming  smaller  and  darker,  collect 
together  in  roundish  heaps,  which  may  remain  in  this  condition,  or 
become  each  surrounded  by  a  cell-wall.  The  cells  thus  produced  may 
contain  from  one  to  twenty  blood-corpuscles  in  their  interior.  These 
corpuscles  become  smaller  and  smaller;  exchange  their  red  for  a  golden 
yellow,  brown,  or  black  color;  and  at  length  are  converted  into  pigment- 


480  HANDBOOK    OF    PHYSIOLOGY. 

graxiules,  which  by  degrees  become  paler  and  paler,  until  all  color  is  lost. 
The  corpuscles  undergo  these  changes  whether  the  heaps  of  them  are 
enveloped  by  a  cell- wall  or  not;  some  pigment  is  also  to  be  found  in  the. 
cell  of  the  reticulum. 

(4.)  From  the  almost  constant  presence  of  uric  acid,  in  larger  quan- 
tities than  in  other  organs,  as  well  as  of  the  nitrogenous  bodies,  xanthin, 
hypoxanthin,  and  leucin,  in  the  spleen,  some  special  nitrogenous  meta- 
holism  may  be  fairly  inferred  to  occur  in  it.  One  of  the  features  of  the- 
chemical  composition  of  the  Sf)leen  is  the  presence  of  a  special  proteid, 
of  the  nature  of  alkali-albumin,  containing  iron.  The  salts  of  the 
spleen  consist  chiefly  of  sodium  phosphates. 

(5.)  Besides  these,  its  supposed  direct  offices,  the  spleen  is  believed  t& 
fulfil  some  purpose  in  regard  to  the  portal  circulation,  with  which  it  i& 
in  close  connection.  From  the  readiness  with  which  it  admits  of  being 
distended,  and  from  the  fact  that  it  is  generally  small  while  gastrin 
digestion  is  going  on,  and  enlarges  when  that  act  is  concluded,  it  is  sup- 
posed to  act  as  a  kind  of  vascular  reservoir,  or  diverticulum  to  the  portal 
system,  or  more  particularly  to  the  vessels  of  the  stomach.  That  it  may 
serve  such  a  purpose  is  also  made  probable  by  the  enlargement  which  it- 
undergoes  in  certain  alfections  of  the  heart  and  liver,  attended  with  ob- 
struction to  the  passage  of  blood  through  the  latter  organ,  and  by  its. 
diminution  when  the  congestion  of  the  portal  system  is  relieved  by 
discharges  from  the  bowels,  or  by  the  effusion  of  blood  into  the  stomach. 
This  mechanical  influence  on  the  circulation,  however,  can  hardly  be 
supposed  to  be  more  than  a  very  subordinate  function. 

The  spleen  may  be  removed  without  any  obvious  ill  effect. 

Influence  of  the  Nervous  System  iqmi  the  Spleen. — When  the  sjileen  is- 
enlarged  after  digestion,  its  enlargement  is  probably  due  to  tAvo  causes, 
(1)  a  relaxation  of  the  muscular  tissue  which  forms  so  large  a  part  of 
its  framework ;  (2)  a  dilatation  of  the  vessels.  Both  these  phenomena, 
are  doubtless  under  control  of  the  nervous  system.  It  has  been  found 
by  experiment  that  when  the  splenic  nerves  are  cut  the  spleen  enlarges, 
and  that  contraction  can  be  brought  about  (1)  by  stimulation  of  the 
spinal  cord  (or  of  the  divided  nerves) ;  (2)  reflexly  by  stimulation  of  the 
central  stumps  of  certain  divided  nerves,  e.g.^  vagus  and  sciatic;  (3)  by 
local  stimulation  by  an  electric  current;  (4)  the  exliiUtion  of  quinine  and 
some  other  drugs.  It  has  been  shown  by  the  oncometer  of  Eoy  (fig.  294), 
that  the  spleen  undergoes  rhythmical  contractions  and  dilatations,  due 
no  doubt  to  the  contraction  and  relaxation  of  the  muscular  tissue  in  its 
capsule  and  trabeculae.  It  also  shows  the  rhythmical  alteration  of  the- 
general  blood  pressure,  but  to  a  less  extent  than  the  kidney. 

The  Thymus. — This  gland  must  be  looked  upon  as  a  temporary 
organ,  as  it  attains  its   greatest  size  early  after  birth,  and  after  tlie- 


METABOLISM    OF   THE   TISSUES.  481 

secoucl  year  gradually  diminishes,  until  in  adult  life  hardly  a  vestige 
remains.  At  its  greatest  development  it  is  a  long,  narrow  body,  situated 
in  the  front  of  the  chest  behind  the  sternum  and  partly  in  the  lower  part 
of  the  neck.     It  is  of  a  reddish  or  grayish  color,  distinctly  lobulated. 

Structure. — The  gland  is  surrounded  by  a  fibrous  capsule,  which  sends 
in  processes,  forming  trabecule,  which  divide  the  glands  into  lobes,  and 
carry  the  blood  and  lymph-vessels.  The  large  trabeculse  branch  into 
small  ones,  which  divide  the  lobes  into  lobules.  The  lobules  are  further 
subdivided  into  follicles  by  fine  connective  tissue.  A  follicle  (fig=  336) 
is  seen  on  section  to  be  more  or  less  polyhedral  in  shape,  and  consists  of 


Fig.  334.  Fig.  335. 

Fig.  334.— Transverse  section  of  a  lobule  of  an  injected  infantile  thymus  gland,  a.  Capsule 
of  connective-tissue  surrounding  tlie  lobule;  6,  membrane  of  the  glandular  vesicles;  c,  cavity  of 
the  lobule,  from  which  the  larger  blood-vessels  are  seen  to  extend  toward  and  ramify  in  the 
spheroidal  masses  of  the  lobule,     x  30.     (Kolliker.) 

Fig.  .3.35. —Thymus  of  a  calf,  a,  Cortex  of  follicle;  6,  medulla;  c,  interfollicular  tissue, 
magnified  about  twelve  times.     (Watney.) 

cortical  and  medullary  portions,  both  of  which  are  composed  of  adenoid 
tissue,  but  in  the  medullary  portion  the  matrix  is  coarser,  and  is  not  so 
filled  up  with  lymphoid  corpuscles  as  in  the  cortex.  The  adenoid  tissue 
of  the  cortex,  and  to  a  less  marked  extent  that  of  the  medulla,  consists 
of  the  two  elements,  one  with  small  meshes  formed  of  fine  fibres  with 
thickened  nodal  points,  and  the  other  enclosed  within  the  first,  com- 
posed of  branched  connective- tissue  corpuscles  (Watney) .  Scattered  in 
the  adenoid  tissue  of  the  medulla  are  the  concentric  corpiiscles  of  Hctssall, 
which  are  protoplasmic  masses  of  various  sizes,  consisting  of  a  nucleated 
granular  centre,  surrounded  by  flattened  nucleated  endothelial  cells. 
In  the  reticulum,  especially  of  the  medulla,  are  large  transparent  giant 
cells.  In  the  thymus  of  the  dog  and  of  other  animals  are  to  be  found 
31 


482  HANDBOOK    OF    I'lIYSIOLOCJY. 

cysts,  probably  derived  from  the  conceutric  corpuscles,  some  of  which 
are  li^ed  with  ciliated  epithelium,  aud  others  with  short  columnar  cells. 
Haimoglobin  is  found  in  the  thymus  of  all  animals,  either  in  these  cysts, 
or  in  cells  near  to  or  of  the  concentric  corpuscles.  In  the  lymph  issuing 
from  the  thymus  are  cells  containing  colored  blood-corpuscles  and 
licemoglobin  granules,  and  in  the  lymphatics  of  the  thymus  there  are 
more  colorless  cells  than  in  the  lymj^hatics  of  the  neck.  In  the  blood  of 
the  thymic  vein,  there  appears  sometimes  to  be  an  increase  in  the 
colorless  corpuscles,  and  also  masses  of  granular  matter  (corpuscles'  of 
Zimmermann)  (Watney).  The  arteries  radiate  from  the  centre  of  the 
gland.  Lymph  sinuses  may  be  seen  occasionally  surrounding  a  greater 
or  smaller  portion  of  the  periphery  of  the  follicles  (Klein).  Tlie  nerves 
are  very  minute. 

From  the  thymus  various  substances  may  be  extracted,  many  of  them 
similar  to  those  obtained  from  the  spleen,  e.g.,  xanthin,  hypoxanthin, 


Fig.  336.  Fig.  337. 

Fig.  336.- From  a  horizontal  section  tlu-ough  superficial  part  of  the  thymus  of  a  calf ,  slightly 
niaguifled.  Showing  in  the  centre  a  follicle  of  polygonal  shape  with  similarly  shaped  follicles 
round  it.     (Klein  and  Noble  Smith.) 

Fig.  337.— The  reticulum  of  the  Thymus,  a,  Epithelial  elements;  6,  corpuscles  of  Hassall. 
(Cadiat. ) 

and  leucin,  as  well  as  a  certain  proteid  body  of  the  nature  of  globulin  (cell- 
globulin),  which  on  injection  into  the  veins  of  an  animal  produces  intra- 
vascular clotting. 

Fimction.-^The  thymus  appears  to  take  part  in  producing  colored 
corpuscles,  both  from  the  large  corpuscles  containing  haemoglobin,  aud 
also  indirectly  from  the  colorless  corpuscles  (Watney). 

Kespecting  the  thymus  gland  in  the  hybernating  animals,  in  which  it 
exists  throughout  life, as  each  successive  period  of  hybernation  approaches, 
the  thvmus  greatly  enlarges  and  becomes  laden  with  fat,whicli  accumulates 
in  it  and  in  fat  glands  connected  with  it,  in  even  larger  proportions  than 
it  does  in  the  ordinary  seats  of  adipose  tissue.  Hence  it  appears  to 
serve  for  the  storing  up  of  materials  which,  being  re-absorbed  in  inactivity 
of  the  hybernating  period,  may  maintain  the  respiration  and  the  tem- 
perature of  the  body  in  the  reduced  state  to  which  they  fall  during  that 


METABOLISM    OF   THE   TISSUES. 


483 


time.     It  has  been  shown  also  to  be  a  source  of  the  red  blood-corpuscles, 
at  any  rate  in  early  life. 

The  Thyroid. — The  thyroid  gland  is  situated  in  the  neck.  It  con- 
sists of  two  lobes  one  on  each  side  of  the  trachea  extending  upward  to 
the  thyroid  cartilage,  covering  its  inferior  cornu  and  part  of  its  body; 
these  lobes  are  connected  across  the  middle  line  by  a  middle  lobe  or 


Fig.  338.  —Part  of  a  section  of  the  human  thyroid,  a,  Fibrous  capsule ;  b.  th  jToid  vesicles  filled 
with.  e.  colloid  substance ;  c,  supporting:  fibrous  tissue:  rf,  short  columnar  cells  lining  vesicles :  /, 
arteries:  y,  veins  filled  with  blood;  /i,  lymphatic  vessel  filled  with  colloid  substance.  X  CS.  K. 
Alcock.) 

isthmus.     The  tliyroid  is  covered  by  the  muscles  of  the  neck.     It  is 
highly  vascular,  and  varies  in  size  in  different  individuals. 

Structures. — The  gland  incased  in  a  thin  transparent  layer  of  dense 
areolar  tissue,  free  from  fat,  containing  elastic  fibres.  This  capsule  sends 
in  strong  fibrous  trabeculse,  which  inclose  the  thyroid  vesicles — which  are 
rounded  or  oblong  irregular  sacs,  consisting  of  a  wall  of  thin  hyaline 
membrane  lined  by  a  single  layer  of  short  cylindrical  or  cubical  cells. 
These  vesicles  are  filled  with  a  coagulable  fluid  or  transparent  colloid 
material.  The  colloid  substance  increases  with  age,  and  the  cavities 
appear  to  coalesce.  In  the  interstitial  connective  tissue  is  a  round 
meshed  capillary  plexus,  and  a  large  number  of  lymphatics.  The  nerves 
adhere  closelv  to  the  vessels. 


484  HANDBOOK    OF    PHYSIOLOGY. 

In  the  vesicles  there  are  in  iiddition  to  the  yellowish  glassy  colloid 
material,  epithelium  cells,  colorless  blood-corpuscles,  and  also  colored 
corpuscles  undergoing  disintegration. 

Function. — There  is  little  known  definitely  about  the  function  of  the 
thyroid  body.  It,  however,  produces  colloid  material  of  the  vesicle, 
which  is  carried  off  by  the  lymphatics  and  discharged  into  the  blood, 
and  so  may  contribute  its  share  to  the  elaboration  of  that  fluid.  The 
destruction  of  red  blood-corpuscles  is  also  supposed  to  go  on  in  the  gland. 
In  certain  animals  its  removal  appears  to  produce  a  peculiar  condition 
in  which  mucin  is  deposited  in  its  tissues.  A  similar  condition, 
known  as  Myxoedema,  and  Cretinism  are  closely  associated  with  disease 
or  removal  of  the  thyroid  gland  in  the  human  subject.  In  certain 
animals,  too,  peculiar  nervous  symptoms,  such  as  twitchings,  tremors, 
or  convulsions  have  been  noticed  after  the  most  careful  removal  of  the 
gland,  with  more  or  less  paralysis  or  inco-ordination. 

The  Supra-renal  Capsules  or  Adrenals. — These  are  two  flattened, 
more  or  less  triangular  or  cocked-hat  shaped  bodies,  resting  by  their 
lower  border  upon  the  upper  border  of  the  kidneys. 

Structure. — The  gland  is  surrounded  by  an  outer  sheath  of  connective 
tissue,  which  sometimes  consists  of  two  layers,  sending  in  exceedingly 


■■(I 


■Q-J 


Fig.  339.— Vertical  section  through  part  of  the  cortical  portion  of  supra-renal  of  guinea-pig. 
o,  Capsule;  6,  zona  glomerulosa;  c,  zona  fasciculata;  d,  connective  tissue  supporting  the  columns 
of  the  cells  of  the  latter,  and  also  indicating  the  positions  of  the  blood-vessels,    x    (S.  K.  Alcock.) 

fine  prolongations  forming  the  framework  of  the  gland.  The  gland 
tissue  proper  consists  of  an  outside  firmer  cortical  portion,  and  an  inside 
soft  dark  medullary  portion. 


METABOLISM    OF   THE   TISSUES.  485 

(1.)  The  cortical  portion  is  divided  into  (fig.  339)  an  external  nar- 
row layer  of  small  rounded  or  oval  spaces,  the  zona  glomerulosa,  made 
by  the  fibrous  trabecula?,  containing  multinucleated  masses  of  proto- 
plasm, the  differentiation  of  which  into  distinct  cells  cannot  be  made 
out  {!)).  A  layer  of  cells  arranged  radially,  the  zona  fasciculata  (c). 
The  substance  of  this  layer  is  broken  up  into  cylinders,  each  of  which 
is  surrounded  by  the  connective-tissue  framework.  The  cylinders  thus 
produced  are  of  three  kinds — one  containing  an  opaque,  resistant, 
highly  refracting  mass  (probably  of  a  fatty  nature) ;  frequently  a  large 
number  of  nuclei  are  present;  the  individual  cells  can  only  be  made  out 
with  difficulty.  The  second  variety  of  cylinders  is  of  a  brownish  color, 
and  contains  finely  granular  cells,   in  which  are  fat  globules.      The 


Fig.  340.— Section  through  a  portion  of  the  meduUary  part  of  the  supra-renal  of  guinea-pig. 
The  vessels  are  very  numerous,  and  the  fibrous  stroma  more  distinct  than  in  the  cortex,  and  is 
moreover  reticulated.  The  cells  are  irregular  and  larger,  clean,  and  free  from  oil  globules.  X 
(S.  K.  Alcock.) 

third  variety  consists  of  gray  cylinders,  containing  a  number  of  cells 
whose  nuclei  are  filled  with  a  large  number  of  fat  granules.  The  third 
layer  of  the  cortical  portion  is  the  zona  reticularis  (not  shown  in  fig. 
339) .  This  layer  is  apparently  formed  by  the  breaking  up  of  the  cylinders, 
the  elements  being  dispersed  and  isolated.  The  cells  are  finely  granular, 
and  have  no  deposit  of  fat  in  their  interior;  but  in  some  specimens  fat 
may  be  present,  as  well  as  certain  large  yellow  granules,  which  may  be 
called  pigment  granules. 

(2.)  The  medullary  stibstance  consists  of  a  coarse  rounded  or  irregular 
meshwork  of  fibrous  tissue,  in  the  alveoli  of  which  are  masses  of  multi- 
nucleated protoplasm  (fig.  340) ;  numerous  blood-vessels ;  and  an  abun- 
dance of  nervous  elements.  The  cells  are  very  irregular  in  shape  and  size, 
poor  in  fat,  and  occasionally  branched ;  the  nerves  run  through  the  cor- 
tical substance,  and  anastomose  over  the  medullary  portion. 


486  HANDBOOK    OF    PHYSIOLOGY. 

JVerves. — The  adrenals  are  very  abundantly  supplied  with  nerves, 
chiefly  composed  of  medullated  fibres.  These  fibres  are  derived  from 
the  solar  and  renal  plexuses,  vagi  and  phrenics.  Nerve-cells  are  also 
numerous  in  connection  with  these  fibres.  The  fibres  enter  the  hilum  of 
the  gland,  but  the  method  of  their  termination  is  unknown. 

Composition. — In  addition  to  the  ordinary  extractives,  benzoic  acid, 
hippuric  acid,  and  taurin  have  been  found,  and  also  inosite,  as  well  as  a 
peculiar  pigmentary  substance,  soluble  in  water,  becoming  red  on  ex- 
posure to  light,  and  giving  with  ferric  chloride  a  green  or  blue  color. 
Haemochromogen  has  been  found  by  McMunn.  Neurin,  apparently 
from  the  nervous  elements,  has  also  been  shown. 

Function. — Of  the  function  of  the  supra-renal  bodies  nothing  can  be 
definitely  stated,  but  they  are  in  all  probability  connected  with  the 
lymphatic  system. 

Addison's  Disease. — The  collection  of  large  numbers  of  cases  in  which  the 
supra-renal  capsules  have  been  diseased,  has  demonstrated  the  very  close  relation 
subsisting  between  disease  of  those  organs  and  brown  discoloration  of  the  skin 
(Addison's  disease)  ;  but  the  explanation  of  this  relation  is  still  involved  in 
obscurity,  and  consequently  does  not  aid  much  in  determining  the  functions  of 
the  supra-renal  capsules. 

The  Pituitary  Body. — This  body  is  a  small  reddish-gray  mass, 
occupying  the  sella  turcica  of  the  sphenoid  bone. 

Structure. — It  consists  of  two  lobes — a  small  2:)osterior  one,  consist- 
ing of  nervous  tissue;  an  anterior  larger  one,  resembling  the  thyroid  in 
structure.  A  canal  lined  with  flattened  or  with  ciliated  epithelium 
passes  through  the  anterior  lobe;  it  is  connected  with  the  infundi- 
bulum.  The  gland  spaces  are  oval,  nearly  round  at  the  periphery, 
spherical  toward  the  centre  of  the  organ ;  they  are  filled  with  nucleated 
cells  of  various  sizes  and  shapes  not  unlike  ganglion  cells,  collected 
together  into  rounded  masses,  filling  the  vesicles,  and  contained  in  a  semi- 
fluid granular  substance.  The  vesicles  are  inclosed  by  connective  tissue, 
rich  in  capillaries. 

Function. — Nothing  is  known  of  the  function  of  the  pituitary  body. 

The  Pineal  Gland. — This  gland,  which  is  a  small  reddish  body,  is 
placed  beneath  the  back  part  of  the  corpus  callosum,  and  rests  upon  the 
corpora  quadrigemina. 

Structure. — It  contains  a  central  cavity  lined  with  ciliated  epithelium. 
The  gland  substance  proper  is  divisible  into — (1.)  An  outer  cortical 
layer,  analogous  in  structure  to  the  anterior  lobe  of  the  pituitary  body; 
and  (2.)  An  inner  central  layer,  wholly  nervous.  The  cortical  layer 
consists  of  a  number  of  close  follicles,  containing  (a)  cells  of  variable 
shajje,  rounded,  elongated,  or  stellate;  (b)  fusiform  cells.  There  is  also 
present  a  gritty  matter    {acervulus  cerebri),  consisting  of  round   par- 


METABOLISM    OF   THE   TISSUES.  487 

tides  aggregated  into  small  masses.  The  central  substance  consists  of 
white  and  gray  matter.  The  blood-vessels  are  small,  and  form  a  very 
delicate  capillary  plexus. 

Function. — Of  this  there  is  nothing  known. 

The  Coccygeal  and  Carotid  Glands. — These  so-called  glands  are 
situated,  the  one  in  front  of  the  tip  of  the  coccyx,  and  the  other  at  the 
point  of  bifurcation  of  the  common  carotid  artery  on  each  side.  They 
are  made  up  of  a  plexus  of  small  arteries,  are  inclosed  and  supported 
by  a  capsule  of  fibrous  tissue,  which  contains  connective-tissue  corpuscles. 
The  blood-vessels  are  surrounded  by  one  or  more  layers  of  cells  like 
secreting-cells,  which  are  said  to  be  modified  plasma  cells  of  the  con- 
nective tissue.     The  function  of  these  bodies  is  unknown. 

Functions  of  the  Vascular  Glands  in  General. 

The  opinion  that  the  vascular  glands  serve  for  the  higher  organiza- 
tion of  the  blood,  is  supported  by  their  being  all  especially  active  in  the 
discharge  of  their  functions  during  foetal  life  and  childhood,  when,  for 
the  development  and  growth  of  the  body,  the  most  abundant  supply  of 
highly  organized  blood  is  necessary.  The  bulk  of  the  thymus  gland, 
in  proportion  to  that  of  the  body,  appears  to  bear  almost  a  direct 
proportion  to  the  activity  of  the  body's  development  and  growth,  and 
when,  at  the  period  of  j^^^berty,  the  development  of  the  body  may  be 
said  to  be  complete,  the  gland  wastes,  and  finally  disappears.  The 
thyroid  gland  and  supra-renal  capsules,  also,  though  they  probably 
never  cease  to  discharge  some  function,  yet  are  proportionally  much 
smaller  in  childhood  than  in  foetal  life  and  infancy;  and  with  the  years 
advancing  to  the  adult  period,  they  diminish  yet  more  in  proportionate 
size  and  apparent  activity  of  function.  The  spleen  more  nearly  retains 
its  proportionate  size,  and  enlarges  nearly  as  the  whole  body  does. 

Although  the  functions  of  all  the  vascular  glands  may  be  similar,  in 
so  far  as  they  may  all  alike  serve  for  the  elaboration  and  maintenance 
of  the  blood,  yet  each  of  them  probably  discharges  a  peculiar  office,  in 
relation  either  to  the  whole  economy  or  to  that  of  some  other  organ. 
Kespecting  any  special  office  of  the  thyroid  gland,  nothing  reasonable 
has  been  hitherto  suggested;  nor  is  there  any  certain  evidence  concern- 
ing that  of  the  supra-renal  capsules.  Bergman  believed  that  they 
formed  part  of  the  sympathetic  nervous  system  from  the  richness  of 
their  nervous  supply.  Kolliker  looked  upon  tlie  two  parts  as  function- 
ally distinct,  the  cortical  part  belonging  to  the  blood  vascular  system, 
and  the  medullary  to  the  nervous  system. 


CHAPTER   XIII. 

ANIMAL    HEAT. 

One  of  the  most  important  results  of  the  metabolism  of  the  tissues  is 
the  production  of  the  heat  of  the  body.  It  is  by  this  means  that  the 
bodily  temperature  is  raised  to  such  a  point  as  to  make  life  possible. 
In  man  and  in  such  animals  as  are  called  warm-blooded,  including  only 
mammals  and  birds,  it  is  found  on  the  one  hand,  that  there  is  an  aver- 
age temperature  which  is  maintained  with  only  slight  variations  in  spite 
of  changes  in  their  environment,  and  on  the  other  hand,  that  the  pos- 
sible variations  above  and  below  this  average  are  comparatively  slight. 
It  must  not  be  thought,  however,  that  the  average  temperature  in  all 
mammals  and  birds  is  the  same ;  for  example,  as  we  shall  see,  the  average 
temperature  of  man  is  just  37°  C.  (98.  G°  F.),  in  some  birds  it  is  as  high 
as  44°  C.  (111°  F.),  whereas  in  the  wolf  it  is  said  to  beunder  36°  C 
(96°  F.). 

The  average  temperature  of  the  human  body  in  those  internal  parts 
which  are  most  easily  accessible,  as  the  mouth  and  rectum,  is  from  36.9° 
-37.4°  C.  (98.5°  to  99.5°  F.).  In  different  parts  of  the  external  surface 
of  the  human  body  the  temperature  varies  only  to  the  extent  of  one  or 
two  degrees  (C),  when  all  are  alike  protected  from  cooling  influences; 
and  the  difference  which  under  these  circumstances  exists,  depends  chiefly 
upon  the  different  degrees  of  blood-supply.  In  the  axilla — the  most 
convenient  situation,  under  ordinary  circumstances,  for  examination  by 
the  thermometer — the  average  temperature  is  36. 9°  C.  (98.6°  F.).  In 
different  internal  parts,  the  variation  is  one  or  two  degrees;  those  parts 
and  organs  being  warmest  which  contain  most  blood,  and  in  which  tliere 
occurs  the  greatest  amount  of  chemical  change,  e.y.^  the  muscles  and 
the  glands;  and  the  temperature  is  highest,  when  they  are  in  a  condi- 
tion of  activity :  while  those  tissues  which,  subserving  only  a  mechanical 
function,  are  the  seat  of  least  active  circulation  and  chemical  change, 
are  the  coolest.  These  differences  of  temperature,  however,  are  actually 
but  slight,  on  account  of  the  provisions  which  exist  for  maintaining 
uniformity  of  temperature  in  different  parts. 

Circumstances  causing  Variations  in  Temperature. — The  chief  circumstances 
by  vs'hich  the  temperature  of  a  healthy  body  is  influenced  are  the  following  : — 

Age. — The  average  temperature  of  the  new-born  child  is  only  about  half  a 
degree  C.    {V  F.)  above  that  of  the  adult;  and  the  difference  becomes  still 


AXIMAL   HEAT.  489 

more  trifling  during  infancy  and  early  childhood.  The  temperature  falls  to 
the  extent  of  about  .2°  C.  (.5'  F. )  from  early  infancy  to  puberty,  and  by 
about  the  same  amount  from  puberty  to  fifty  or  sixty  years  of  age.  In  old  age 
the  temperature  again  rises,  and  approaches  that  of  infancy. 

Sex. — The  average  temperature  of  the  female  is  slightly  higher  than  that  of 
the  male. 

Period  of  the  Day. — The  temperature  undergoes  a  gradual  alteration,  to  the 
extent  of  about  .54°-. S''  C.  (1'  to  1.5"  F. )  in  the  course  of  the  day  and  night; 
the minmnim  being  at  night  or  in  the  early  morning,  the  7naximum  late  in  the 
afternoon. 

Exercise. — Active  exercise  raises  the  temperature  of  the  body  from  .54°-1.08° 
C.   (1=  to  2"  F.). 

Climate  and  Season. — The  temperature  of  the  human  body  is  practically  the 
same  in  temperate  as  in  tropical  climates.  In  summer  the  temperature  of  the 
body  is  a  little  higher  than  in  winter ;  the  difference  amounting  to  about  a 
fifth  of  a  degree  C. 

Food  and  Drink. — The  effect  of  a  meal  upon  the  temperature  of  a  body  is  but 
small.  A  very  slight  rise  usually  occurs.  Cold  alcoholic  drinks  slightly 
depress  the  temperature  about  half  a  degree  C.  Warm  alcoholic  drinks,  as 
well  as  warm  tea  and  coffee,  raise  the  temperature  about  a  third  of  a  degree  C. 

Disease. — In  disease  the  temperature  of  the  body  deviates  from  the  normal 
standard  to  a  greater  extent  than  ■would  be  anticipated  from  the  slight  effect 
of  external  conditions  during  health.  Tlius,  in  some  disease,  as  pneumonia 
and  typhus,  it  occasionally  rises  as  high  as  41°-41.6°  C.  (106°  or  107°  F.),  and 
considerabh'  higher  temperatures  have  been  noted.  In  Asiatic  cholera,  on  the 
other  hand,  a  thermometer  placed  in  the  mouth  may  sometimes  rise  only  to 
25°-26.2=  C.    (77°  or  79°  F.). 

The  temperature  maintained  by  Mammalia  in  an  active  state  of  life,  accord 
ing  to  the  tables  of  Tiedemann  and  Rudolphi,  averages  38.3°  C.  (101°  F. ). 
The  extremes  recorded  by  them  were  34.6°  C.  (96°  F.)  and  41°  C.  (106°  F.),  the 
former  in  the  narwhal,  the  latter  in  a  bat  (Vespertilio  pipistrella) .  In  Birds, 
the  average  is  as  high  as  41.2°  C.  (107°  F. )  ;  the  highest  temperature,  46.2°  C. 
(111.25°  F. )  being  in  the  small  species,  the  linnets,  etc.  Among  Reptiles,  while 
the  medium  they  were  in  was  23.9°  C.  (75°  F.)  their  average  temperature  was 
31.2°  C.  (82.5°  F. ).  As  a  general  rule,  their  temperature,  though  it  falls  with 
that  of  the  surrounding  medium,  is,  in  temperate  inedia,  tvvo  or  more  degrees 
higher ;  and  though  it  rises  also  with  that  of  the  medium,  yet  at  very  high 
degrees  it  ceases  to  do  so,  and  remains  even  lower  than  that  of  the  medium. 
Fish  and  invertebrata  present,  as  a  general  rule,  the  same  temperature  as  the 
medium  in  which  they  live,  whether  that  be  high  or  low  ;  only  among  fish,  the 
tunny  tribe,  with  strong  hearts  and  red  meat-like  muscles,  and  more  blood 
than  the  average  of  fish  have,  are  generally  3.8'  C.  (7°  F. )  warmer  than  the 
water  around  them. 

The  difference,  therefore,  between  what  are  commonly  called  the  warm  and 
the  cold-blooded  animals,  or  homoiothermal  {bf^otog,  like,  Oepfr;,  heat)  and  poikilo- 
thermal  {■KoiKi7.oQ,  changeful,  6sp^n],  heat,  is  not  one  of  absolutely  higher  or  lower 
temperature ;  for  the  animals  which  to  us  in  a  temperate  climate  feel  cold  (be- 
ing like  the  air  or  water,  colder  than  the  surface  of  our  bodies) ,  would  in  an 
external  temperature  of  37.8°  C.  (100°  F.)  have  nearly  the  same  temperature 
and  feel  hot  to  us.  The  real  difference  is  that  warm-blooded  animals  have  a 
certain  permanent  heat  in  all  atmospheres,  while  the  temperature  of  cold- 
blooded animals  is  variable  with  every  atmosphere. 


490  handbook  of  physiology. 

The   Peoduction   of  the   Body   Heat, 

The  heat  which  is  produced  in  the  body  arises  from  the  metabolic 
changes  of  the  tissues,  the  chief  part  of  which  are  of  the  nature  of  oxida- 
tion, since  it  may  be  supposed  that  the  oxygen  of  the  atmosphere  taken 
into  the  system  is  ultimately  combined  with  carbon  and  hydrogen,  and 
discharged  from  the  body  as  carbonic  acid  and  water.  Any  changes, 
indeed,  which  occur  in  the  protoplasm  of  the  tissues,  resulting  in  an 
exhibition  of  their  function,  are  attended  by  the  evolution  of  heat  and 
the  formation  of  carbonic  acid  and  water.  The  more  active  the 
changes  the  greater  is  the  heat  produced  and  the  greater  is  the  amount 
of  the  carbonic  acid  and  water  formed.  But  in  order  that  the  jjroto- 
plasm  may  perform  its  function,  the  waste  of  its  own  tissue  (destructive 
metabolism),  must  be  repaired  by  the  due  supply  of  food  material  to  be 
built  up  in  some  way  into  the  protoplasmic  molecule.  For  the 
production  of  heat,  therefore,  food  is  necessary.  In  the  tissues, 
as  we  have  several  times  remarked,  two  processes  are  continually 
going  on:  the  building  up  of  the  protoplasm  from  the  food  (constructive 
metabolism)  which  is  not  accompanied  by  the  evolution  of  heat,  possibly 
even  by  its  storing,  and  the  oxidation  of  the  protoplastic  materials 
resulting  in  the  production  of  energy,  by  which  heat  is  set  free  and 
carbonic  acid  and  water  are  evolved. 

It  is  not  necessary  to  assume  that  the  combustion  processes,  indeed, 
are  as  simple  as  the  bare  statement  of  the  fact  might  seem  to  indicate; 
and,  we  have  indicated,  in  treating  of  muscular  metabolism,  the  process, 
appears  to  consist  first  of  all  of  building  up  of  the  oxygen  into  the 
molecule.  But  complicated  as  the  various  stages  may  be,  the  ultimate 
result  is  as  simple  as  in  ordinary  combustion  outside  the  body,  and  the 
products  are  the  same. 

This  theory,  that  the  maintenance  of  the  temperature  of  the  living 
body  depends  on  continual  chemical  change,  chiefly  by  oxidation  of 
combustible  materials  in  the  tissues,  has  long  been  established  by  the 
demonstration  that  the  quantity  of  carbon  and  hydrogen  as  supplied  as 
food,  which,  in  a  given  time,  unites  in  the  body  with  oxygen,  is  sufficient 
to  account  for  the  amount  of  heat  generated  in  the  animal  within  the 
same  period :  an  amount  capable  of  maintaining  the  temperature  of  the 
body  at  from  36.8°-3.87°  C.  (98°-100°  F.),  notwithstanding  a  large 
loss  by  radiation  and  evaporation.  This  estimation  depends  upon  the 
chemical  axiom  that  when  a  body  undergoes  a  chemical  change  the 
amount  of  energy  set  free  is  the  same,  supposing  the  resulting  products 
are  the  same,  whether  the  change  takes  place  suddenly  or  gradually.  If 
a  certain  number  of  grammes  of  different  substances  are  introduced  as 
food,  and  if  they  undergo  complete  oxidation,  the  amount  of   kinetic 


ANIMAL   HEAT.  491 

energy  as  shown  in  the  amount  of  heat,  and  mechanical  work,  is  the 
same  if  the  same  bodies  are  completely  oxidized  outside  the  body;  so 
that  if  1  gramme  of  fat  be  taken  into  the  body  and  the  oxidation 
completely  oxidized,  resulting  in  the  production  of  a  definite  amount 
of  carbon  dioxide  and  water,  it  may  be  supposed  to  have  produced  the 
same  amount  of  heat  as  it  would  have  produced  outside  the  body.  In 
the  caseof  proteidfoodit  is  a  little  different,  since  it  is  never  completely 
oxidized  within  the  body,  but  may  be  supposed  to  give  rise  to  a  definite 
amount  of  urea,  not  a  completely  oxidized  body.  In  this  case  the 
gramme  of  proteid  may  be  considered  to  perform  the  same  amount  of 
heat  as  the  proteid  would  outside  the  body  minus  the  amount  which 
would  be  obtained  from  the  complete  oxidation  of  the  resulting  urea. 

The  actual  amount  of  heat  produced  per  diem  has  been  experimentally 
ascertained  in  the  case  of  small  animals  by  the  aid  of  an  apparatus 
called  a  Calorimeter.  The  animal  is  inclosed  in  a  metal  box  com- 
pletely contained  in  a  second  box  containing  water,  and  air  is  led  into 
and  out  of  the  inner  box  by  means  of  metal  tubes;  the  one  through  which 
the  air  is  led  out  of  the  chamber  has  several  coils  in  it.  The  heat  given 
out  by  the  animal  warms  the  water  in  the  outside  box,  and  may  be 
estimated  by  the  rise  of  its  temperature,  the  amount  of  which  is  known. 

The  amount  of  heat  pToduced  and  of  energy  in  the  form  of  mechanical 
work  set  free  in  a  given  time  arise  from  the  oxidation  of  the  substances 
taken  in  as  food  in  so  far  as  they  are  oxidized.  In  order  that  there  may 
be  correct  data  to  assist  in  the  consideration  of  the  subject,  the  amount 
of  heat  evolved  by  the  oxidation  of  various  food-stuffs  has  been  carefully 
measured.  The  results  may  be  set  downi  in  terms  of  gramme-calories 
(Ca),  a  calorie  being  the  heat  unit,  and  meaning  the  amount  of  heat 
required  to  raise  1  gramme  of  water  1  degree  C. ,  or,  more  strictly,  from 
15°  C.  to  16°  C*  The  number  of  gramme-calories  which  1  gramme 
of  the  following  substances  equals  will  be  seen  in  the  annexed  table. 

Hydrogen     .     3450         Fat         .         .     9000        Urea  .  2200 

Carbon    .      .      8100         Carbohydrate    4000 

Proteid  .     5000—5500 

1  gramme  of  proteid  giving  rise  to  \  gramme  of  urea. 

The  relation  between  the  income  and  expenditure  of  the  body  will  be 
considered  more  in  detail  in  the  next  chapter,  after  the  question  of 
diets  has  been  more  fully  gone  into.  We  may  now  turn  to  the  question 
of  the  chief  heat-producing  tissues. 

Heat-producing  Tissues. — (1.)  The  Muscles. — As  the  muscles 
form  so  large  a  part  of  the  body,  and  as  in  them  metabolism  is  particularly 
active,  it  is  only  reasonable  to  consider  the  muscular  as  the  chief  heat- 

*  Sometimes  the  term  kilogramme- calorie  is  used  ;  one  kilogramme-calorie 
being  equal  to  1000  gramme-calories. 


492  HANDBOOK    OF    PHYSIOLOGY. 

producing  tissue.  It  has  already  been  pointed  out  that  the  manifesta- 
tion of  muscular  energy  is  always  accompanied  by  the  evolution  of  heat 
and  the  jiroduction  of  carbon  dioxide.  This  production  of  carbon 
dioxide  goes  on  while  the  muscles  are  at  rest,  only  in  a  less  degree  to 
that  which  is  noticed  during  muscular  activity,  and  so  it  is  certain  that 
an  active  metabolism  is  going  on  in  resting  as  well  as  in  contracting 
muscles.  This  metabolism  is  a  source  of  much  heat,  and  so  the  total 
amount  of  heat  produced  in  the  muscular  tissues  per  diem  must  be  very 
great.  It  has  been  calculated  that,  even  neglecting  the  heat  produced 
by  the  quiet  metabolism  of  muscular  tissue,  the  amount  of  heat  gener- 
ated by  muscular  activity  would  supjjly  the  principal  part  of  the  total 
heat  produced  within  the  body.  (2.)  The  Secreting  glands,  and  prin- 
cipally the  liver,  as  being  the  largest  and  most  active,  come  next  to  the 
muscles  as  heat-j^roducing  tissue.  It  has  been  found  by  experiment  that 
the  blood  leaving  the  glands  is  considerably  warmer  than  that  entering 
them.  The  metabolism  in  the  glands  is  very  active,  and,  as  we  have 
seen,  the  more  active  the  metabolism  the  greater  the  heat  jiroduced. 
(3.)  The  Brain;  the  venous  blood  has  a  higher  temperature  than  the 
arterial.  It  must  be  remembered,  however,  that  although  the  organs 
above  mentioned  are  the  chief  heat-producing  parts  of  the  body,  all 
living  tissues  contribute  their  quota,  and  this  in  direct  proportion  to 
their  activity.  The  blood  itself  is  also  the  seat  of  metabolism,  and, 
therefore,  of  the  production  of  heat;  but  the  share  which  it  takes  in 
this  respect,  apart  from  the  tissues  in  which  it  circulates,  is  very  incon- 
siderable. There  are  two  other  means  by  which  the  heat  produced  by 
metabolism  of  the  tissues  is  added  to  in  slight  degree,  viz.,  by  friction, 
i.e.,  in  the  movements  of  muscles,  in  the  circulation  of  blood,  and  else- 
where. This  contributes  a  slight  but  undetermined  amount  of  heat, 
and  by  the  taking  in  of  warm  foods,  solid  or  liquid,  a  further  small 
amount  of  heat  is  at  the  same  time  acquired. 

Kegulation   of  the  Temperature   of  the   Human    Body. 

The  average  temperature  of  the  body  is  maintained  under  different 
conditions  of  external  circumstances  by  mechanisms  which  j)ermit  of 
(1)  variation  in  the  loss  of  heat,  and  (2)  variations  in  the  production  of 
heat.  In  healthy  warm-blooded  animals  the  loss  and  gain  of  heat  are  so 
nearly  balanced  one  by  the  other  that,  under  all  ordinary  circumstances, 
an  uniform  temperature,  within  a  degree  or  two,  is  jDreserved. 

Variation  in  the  Loss  of  Heat. — The  loss  of  heat  from  the  human 
body  is  principally  regulated  by  the  amount  given  off  (1)  by  radiation 
and  conduction  from  its  surface,  and  by  means  of  the  (2)  constant  evapo- 
ration of  water  from  the  same  part,  heat  being  thus  rendered  latent,  and 


ANIMAL    HEAT.  493 

to  a  mucli  less  degree  (3)  from  the  air-passages;  in  each  act  of  respira- 
tion, heat  is  lost  to  a  greater  or  less  extent  according  to  the  temperature 
of  the  atmosphere;  unless  indeed  the  temperature  of  the  surrounding 
air  exceed  that  of  the  blood.  We  must  remember  too  that  (4)  all  food 
and  drink  which  enter  the  body  at  a  lower  temperature  than  itself  ab- 
stract a  small  measure  of  heat;  (5)  while  the  urine  and  fgeces  which 
leave  the  body  at  about  its  own  temperature  are  also  means  by  which  a 
small  amount  is  lost. 

(a.)  From  the  Surface  of  the  Body. — By  far  the  most  important  loss 
of  heat  from  the  body, — probably  90  per  cent  and  upward  of  the  whole 
amount,  is  that  which  takes  place  by  radiation,  conduction,  and  evapora- 
tion from  the  skin.  The  actual  figures  are  as  follows: — of  100  calories 
of  heat  produced,  2.6  are  lost  in  heating  food  and  drink;  2.G  in  heating 
air  inspired;  14.7  in  evaporation ;  and  80.1  by  radiation  and  conduction. 
The  means  by  which  the  skin  is  able  to  act  as  one  of  the  most  impor- 
tant organs  for  regulating  the  temperature  of  the  blood,  are — (1),  that 
it  offers  a  large  surface  for  radiation,  conduction,  and  evaporation;  (2), 
that  it  contains  a  large  amount  of  blood;  (3),  that  the  quantity  of 
blood  contained  in  it  is  the  greater  under  those  circumstances  which 
demand  a  loss  of  heat  from  the  body,  and  vice  versa.  For  the  circum- 
stance which  directly  determines  the  quantity  of  blood  in  the  skin,  is 
that  which  governs  the  supply  of  blood  to  all  the  tissues  and  organs  of 
the  body,  namely,  the  power  of  the  vaso-motor  nerves  to  cause  a  greater 
or  less  tension  of  the  muscular  element  in  the  walls  of  the  arteries,  and, 
in  correspondence  with  this,  a  lessening  or  increase  of  the  calibre  of 
the  vessel,  accompanied  by  a  less  or  greater  current  of  blood.  A  warm 
or  hot  atmosphere  so  acts  on  the  nerve  fibres  of  the  skin,  as  to  lead 
them  to  cause  in  turn  a  relaxation  of  the  muscular  fibre  of  the  blood- 
vessels; and,  as  a  result,  the  skin  becomes  full-blooded,  hot,  and  sweat- 
ing; and  much  heat  is  lost.  With  a  low  temperature,  on  the  other 
hand,  the  blood-vessels  shrink,  and  in  accordance  with  the  consequently 
diminished  blood-supply,  the  skin  becomes  pale,  and  cold,  and  dry;  and 
no  doubt  a  similar  effect  may  be  produced  through  the  vaso-motor  cen- 
tre in  the  medulla  and  spinal  cord.  Thus,  by  means  of  a  self-regulating 
apparatus,  the  skin  becomes  the  most  important  of  the  means  by  which 
the  temperature  of  the  body  is  regulated. 

In  connection  with  loss  of  heat  by  the  skin,  reference  has  been  made 
to  that  which  occurs  both  by  radiation  and  conduction,  and  by  evapora- 
tion; and  the  subject  of  animal  heat  has  been  considered  almost  solely 
with  regard  to  the  ordiliary  case  of  man  living  in  a  medium  colder  than 
his  body,  and  therefore  losing  heat  in  all  the  ways  mentioned.  The 
importance  of  the  means  however,  adopted,  so  to  speak,  by  the  skin  for 
regulating  the  temperature  of  the  body,  will  depend  on  the  conditions 


494  HANDBOOK    OF   PHYSIOLOGY. 

by  which  it  is  surrounded ;  an  inverse  proportion  existing  in  most  cases 
between  a  loss  by  radiation  and  conduction  on  the  one  hand,  and  by 
evaporation  on  the  other.  Indeed,  the  small  loss  of  heat  by  evaporation 
in  cold  climates  may  go  far  to  compensate  for  the  greater  loss  by  radia- 
tion; as,  on  the  other  hand,  the  great  amount  of  fluid  evaporated  in 
hot  air  may  remove  nearly  as  much  heat  as  is  commonly  lost  by  both 
radiation  and  evaporation  together  in  ordinary  temperatures;  and  thus, 
it  is  possible  that  the  quantities  of  heat  required  for  the  maintenance  of 
a  uniform  proper  temperature  in  various  climates  and  seasons  are  not 
so  different  as  they,  at  first  sight,  seem. 

Many  examples  may  be  given  of  the  power  which  the  body  possesses  of  resist- 
ing the  effects  of  a  high  temperature,  in  virtue  of  evaporation  from  the  skin. 
Blagden  and  others  supported  a  temperature  varying  between  92'-100°  C. 
(198^-212°  F.)  in  dry  air  for  several  minutes  ;  and  in  a  subsequent  experiment 
he  remained  eight  minutes  in  a  temperature  of  126.5°  C.  (260°  F.).  "The 
workmen  of  Sir  F.  Chantrey  were  accustomed  to  enter  a  furnace,  in  which 
his  moulds  were  dried,  while  the  floor  was  red-hot,  and  a  thermometer  in  the 
air  stood  at  177.8°  C.  (350°  F.),  and  Chabert,  the  fire-king,  was  in  the  habit  of 
entering  an  oven,  the  temperature  of  which  was  from  205°-315°  C.  (400°-600° 
F. ) . "     (Carpenter. ) 

But  such  heats  are  not  tolerable  when  the  air  is  moist  as  well  as  hot,  so 
as  to  prevent  evaporation  from  the  body.  C.  James  states,  that  in  the  vapor 
baths  of  Nero  he  was  almost  suffocated  in  a  temperature  of  44.5°  C.  (112°  F. ), 
while  in  the  caves  of  Testaccio,  in  which  the  air  is  dry,  he  was  but  little 
incommoded  by  a  temperature  of  80°  C.  (1 76°  F. ) .  In  the  former,  evaporation 
from  the  skin  was  impossible ;  in  the  latter  it  was  abundant,  and  the  layer 
of  vapor  which  would  rise  from  all  the  surface  of  the  body  would,  by  its  very 
slowly  conducting  power,  defend  it  for  a  time  from  the  full  action  of  the  ex- 
ternal heat. 

We  are  able  by  suitable  clothing  to  increase  or  to  diminish  the  amount 
of  heat  lost  by  the  skin. 

The  ways  by  which  the  skin  may  be  rendered  more  efficient  as  a  cool- 
ing-apparatus too,  by  exposure,  by  baths,  and  by  other  means  which 
man  instinctively  adopts  for  lowering  his  temperature  when  necessary, 
are  too  well  known  to  need  more  than  passing  mention. 

Although  under  any  ordinary  circumstances  the  external  application  of 
cold  only  temporarily  depresses  the  temperature  to  a  slight  extent,  it  is  other- 
wise in  cases  of  high  temperature  in  fever.  In  these  cases  a  tepid  bath  may 
reduce  the  temperature  several  degrees,  and  the  effect  so  produced  last  in 
some  cases  for  many  hours. 

{!))  From  the  Lungs. — As  a  means  for  lowering  the  temperature,  the 
lungs  and  air-passages  are  very  inferior  to  the  skin;  although,  by  giving 
heat  to  the  air  we  breathe,  they  stand  next  to  the  skin  in  importance. 
2\s  a  regulating  power,  the  inferiority  is  still  more  marked.  The  air 
which  is  expelled  from  the  lungs  leaves  the  body  at  about  the  tempera- 


AXI.MAL    HEAT.  495 

ture  of  the  blood,  and  is  alwa3^s  saturated  with  moisture.  Xo  inverse 
proportion,  tlierefore,  exists,  as  in  the  case  of  the  skin,  between  the  loss 
of  heat  by  radiation  and  conduction  on  the  one  hand,  and  by  evaporation 
on  the  other.  The  colder  the  air,  for  example,  the  greater  will  be  the 
loss  in  all  ways.  Neither  is  the  quantity  of  blood  which  is  exposed  to 
the  cooling  influence  of  the  air  diminished  or  increased,  so  far  as  is 
known,  in  accordance  with  any  need  in  relation  to  temperature.  It  is 
true  that  by  varying  the  number  and  depth  of  the  respirations,  the 
quantity  of  heat  given  off  by  the  lungs  may  be  made,  to  some  extent, 
to  vary  also.  But  the  respiratory  passages,  while  they  must  be  considered 
important  means  by  which  heat  is  lost,  are  altogether  subordinate,  in 
the  power  of  regulating  the  temperature,  to  the  skin. 

(c)  By  Warming  Cold  Foods. — This  is  an  obvious  method  of  expendi- 
ture of  heat  which  may  be  resorted  to,  but  the  loss  of  heat  by  the  excreta 
discharged  from  the  body  at  a  high  temperature,  must  be  of  little  use  as 
a  means  of  regulating  the  temperature,  since  the  amount  so  lost  must  be 
capable  of  little  variation. 

Variation  in  the  Production  of  Heat. — It  may  seem  to  have  been 
assumed,  in  the  foregoing  pages,  that  the  only  regulating  apparatus  for 
temperature  required  by  the  human  body  is  one  that  shall,  more  or  less, 
produce  a  cooling  effect;  and  as  if  the  amount  of  heat  produced  were 
always,  therefore,  in  excess  of  that  which  is  required.  Such  aa  assump- 
tion would  be  incorrect.  We  have  the  power  of  regulating  the  produc- 
tion of  heat,  as  well  as  its  loss.. 

The  regulation  of  the  production  of  heat  in  the  body  is  apparently 
different  for  each  animal,  as  the  absolute  amount  of  heat  set  free  by 
different  animals  in  a  given  period  varies;  in  one  the  production  of  heat 
exceeds  that  in  another.  It  is  even  said  that  each  individual  has  his 
own  coefficient  of  heat  production.  From  all  that  has  been  said  on  the 
subject  it  will  be  seen  that  the  amount  of  heat  for  all  practical  purposes 
depends  upon  the  metabolism  of  the  tissues  of  the  body,  everything 
therefore  which  increases  that  metabolism  will  increase  the  heat  produc- 
tion, so  therefore  the  absolute  amount  of  heat  produced  by  a  large 
^animal,  having  a  larger  amount  of  tissues  in  which  metabolism  may  go 
on,  will  be,  cceteris  paribus^  greater  than  that  of  a  small  animal.  But  of 
course  the  activity  of  the  tissue  change  in  a  small  animal  may  be  greater 
than  in  a  large  one,  and  naturally  no  strict  line  can  be  drawn  between 
the  two. 

The  ingestion  of  food  has  been  jsroved  to  increase  the  metabolism  of 
the  tissues,  and  so,  as  one  would  expect,  the  rate  of  heat  production  is 
found  by  experiment  upon  the  dog  to  be  increased  after  a  meal,  and 
in  this  animal  the  heat  production  reaches  its  height  about  G  to  9  hours 
.after  a  meal. 


496  HANDBOOK    OF    PHYSIOLOGY. 

It  has  also  been  experimentally  ascertained  that  the  rate  of  heat 
production  varies  somewhat  with  the  kind  of  food  taken,  for  example, 
if  sugar  be  added  to  the  meal  of  meat  given  to  the  dog,  the  height  of 
maximum  production  is  reached.  It  was  always  said  that  various  nations 
had  found  by  experience  what  food  was  rnost  suitable  for  the  climate  in 
which  they  lived,  and  that  such  experience  could  be  trusted  to  regulate 
the  quantity  consumed.  Although  there  have  been  no  very  conclusive 
exj)erimentsto  prove  this  view,  yet  it  is  a  matter  of  general  observation 
that  in  northern  climates  and  in  colder  seasons  the  quantity  of  food 
taken  is  greater  than  in  warmer  climates  or  in  warmer  seasons.  Why 
the  inhabitants  of  the  coldest  climates  appear  to  require  a  large  propor- 
tion of  fats  in  their  diet  is  difficult  to  understand,  but  such  is  the  case. 

In  exercise,  we  have  an  important  means  of  raising  the  temperature  of 
our  bodies,  by  it  the  muscular  metabolism  is  increased,  as  is  shown  by 
the  increased  outj^ut  of  carbon  dioxide. 

Influence  of  the  Nervous  System. — The  influence  of  the  nervous 
system  in  modifying  the  production  of  heat  must  be  very  important,  as 
upon  nervous  influence  depends  the  amount  of  the  metabolism  of  the 
tissues.  The  experiments  and  observations  which  best  illustrate  it  are 
those  showing,  first,  that  when  the  supply  of  nervous  infiuence  to  a  part 
is  cut  off,  the  temperature  of  that  part  after  a  time  falls  below  its  ordi- 
nary degree;  and,  secondly,  that  when  death  is  caused  by  severe  injury 
to,  or  removal  of,  the  nervous  centres,  the  temperature  of  the  body 
rapidly  falls,  even  though  artificial  respiration  be  performed,  the  circu- 
lation maintained,  and  to  all  appearance  the  ordinary  chemical  changes 
of  the  body  be  completely  effected.  It  has  been  repeatedly  noticed,  that 
after  division  of  the  nerves  of  a  limb  its  temperature  ultimately  falls; 
and  this  diminution  of  heat  has  been  remarked  still  more  j^lainly  in 
limbs  deprived  of  nervous  influence  by  paralysis. 

With  equal  certainty,  though  less  definitely,  the  influence  of  the 
nervous  system  on  the  production  of  heat  is  siiown  in  the  rapid  and 
momentary  increase  of  temperature,  sometimes,  general,  at  other  times 
quite  local,  which  is  observed  in  states  of  nervous  excitement;  in  the 
general  increase  of  warmth  of  the  body,  excited  by  passions  of  the  mind ; 
in  the  sudden  rush  of  heat  to  the  face,  which  is  not  a  mere  sensation; 
and  in  the  equally  rapid  diminution  of  temperature  in  the  depressing 
passions.  All  of  these  examples,  however,  are  explicable,  on  the  suppo- 
sition that  the  nervous  system  alters,  by  its  power  of  controlling  the 
calibre  of  the  blood-vessels,  the  quantity  of  blood  supplied  to  a  part. 

Apart,  however,  from  this  vaso-motor  power  of  increasing  the  blood- 
supply  to  internal  organs,  and  to  the  tissues  in  general,  by  means  of 
which  it  is  possible  to  increase  their  metabolism  and  so  their  production 
of  heat,  there  is  evidence  to  suppose  that  there  is  another  nervous  appa- 


AXIMAL   HEAT.  497 

ratus  closely  comparable  to  that  which  regulates  the  secretion  of  saliva  or 
of  sweat,  by  means  of  which  the  production  of  heat  in  the  warm- 
blooded animals  is  increased  or  diminished  as  occasion  requires.  This 
apparatus  probably  consists  of  a  centre  which  may  be  reflexly  stimulated, 
as  for  example  by  impulses  from  the  skin,  and  which  acts  through 
special  nerves  supplied  to  the  various  tissues.  The  evidence  upon 
which  the  existence  of  this  regulating  apparatus  depends  is  the  marked 
effect  in  the  increase  of  the  oxygen  taken  in  by  a  warm-blooded  animal 
when  exposed  to  cold  and  the  corresponding  increase  in  the  output  of 
carbon  dioxide,  indicating  that  there  is  an  increase  of  the  metabolism 
and  so  an  increased  production  of  heat,  under  such  circumstances  and 
not  a  mere  diminution  of  the  amount  of  heat  lost  by  the  skin,  etc.  A  cold- 
blooded animal  reacts  very  differently  to  exposure  to  cold ;  instead  of  as  in 
the  case  of  the  warm-blooded  animal,  increasing  the  metabolism,  cold 
diminishes  the  metabolism  of  its  tissues.  It  appears  clear,  therefore, 
that  in  warm-blooded  animals  there  is  some  extra  ajjparatus  which 
counteracts  the  effects  of  cold  which  in  cold-blooded  animals  causes 
diminished  metabolism.  In  warm-blooded  animals  poisoned  by  urari, 
or  in  which  section  of  the  bulb  has  been  done,  it  has  been  found  that 
this  regulating  apparatus  is  no  longer  in  action,  and  under  such  circum- 
stances no  difference  appears  to  exist  between  such  animals  and  those 
which  are  naturally  cold-blooded.  Warmth  increases  their  temperature 
and  cold  lowers  it,  and  with  this  there  is  of  course  evideuce  of  dimin- 
ished metabolism.  The  explanation  of  these  experiments  as  given  by 
modern  physiologists  is  that  in  such  animals  the  connection  which  natu- 
rally exists  between  the  skin  and  the  muscles  through  the  nervous  chain, 
such  as  a  thermotaxic  nervous  apparatus  might  be  supposed  to  afford,  is 
broken  either  at  the  termination  of  the  nerves  in  the  muscles  or  at  the 
section  point  of  the  bulb.  The  position  of  this  hypothetical  centre  is  a 
matter  of  some  difference  of  opinion.  It  has  been  demonstrated  that 
stimulation  of  different  parts  of  the  brain  may,  among  other  symptoms, 
produce  increased  metabolism  of  the  tissues  with  increased  output  of 
carbon  dioxide  and  a  raised  temperature:  the  parts  of  which  this  may  be 
asserted  are  parts  of  the  corpus  striatum  and  of  the  optic  thalamus. 
The  exact  situation  of  the  heat  centre,  however,  is  at  present  not  known 
with  certainty. 

Experimental  observations  such  as  have  been  made  upon  animals 
receive  confirmation  from  the  observations  of  patients  who  suffer  from 
fever  or  pyrexia;  in  them  the  temperature  of  the  body  may  be  raised 
several  degrees,  as  we  have  already  pointed  out  (p.  489.)  This  increase 
of  temperature  might  of  course  be  due  to  diminished  loss  of  heat  from 
the  skin,  but  this  although  in  all  probability  entering  into  its  causation, 
is  not  the  only  cause.  The  amount  of  oxygen  taken  in  and  the  amount 
32 


498  HANDBOOK    OF    PHYSIOLOCtY. 

of  carbon  dioxide  given  out  are  both  increased,  and  with  this  there  must 
be  increased  metabolism  of  the  tissues,  and  particularly  of  the  muscular 
tissues,  since  at  the  same  time  the  amount  of  urea  in  the  urine  is 
increased.  Every  one  is  familiar  with  the  rapid  wasting  which  is  such 
a  characteristic  of  high  fever;  it  must  indicate  not  only  too  rapid 
metabolism  of  the  body,  but  also  insufficient  time  for  the  tissues  to  build 
themselves  up.  In  fever  then  there  may  be  supposed  to  be  some  inter- 
ference in  the  ordinary  channel  by  which  the  skin  is  able  to  communi- 
cate to  the  nervous  system  the  necessity  of  an  increased  or  diminished 
production  of  heat  in  the  muscles  and  other  tissues.  In  consequence  of 
this,  and  in  spite  of  the  condition  of  heat  of  the  surface  of  the  body, 
the  production  of  heat  goes  on  at  an  abnormal  rate.  It  is  not  certain 
in  what  way  the  centre  acts,  whether  it  is  one  which  keeps  the  meta- 
bolism in  check,  and  when  out  of  gear  it  is  no  longer  able  to  do  this,  or 
whether,  on  the  other  hand,  it  is  a  centre  by  means  of  which  the  meta- 
bolism of  the  tissues  may  be  increased  by  stimuli  proceeding  from  it. 
Impulses  from  the  skin  would,  according  to  these  two  possible  modes 
of  action,  act  either  in  the  direction  of  increasing  its  inhibitory  action, 
or  in  the  direction  of  increasing  or  of  diminishing  the  different  stimuli 
causing  increased  production. 

Influence  of  Extreme  Heat  and  Cold. — In  connection  with  the 
regulation  of  animal  temperature,  and  its  maintenance  in  health  at  the 
normal  height,  may  be  noted  the  result  of  circumstances  too  powerful, 
either  in  raising  or  lowering  the  heat  of  the  body,  to  be  controlled  by  the 
proper  regulating  apparatus.  "VValther  found  that  rabbits  and  dogs  kept 
exposed  to  a  hot  sun,  reached  a  temperature  of  46°  C.  (114.8°  F.),  and 
then  died.  Cases  of  sunstroke  furnish  us  with  several  examples  in 
the  case  of  man;  for  it  would  seem  that  here  death  ensues  chiefly  or 
solely  from  elevation  of  the  temperature. 

The  effect  of  mere  loss  of  bodily  temperature  in  man  is  less  well  known 
than  the  effect  of  heat.  Prom  experiments  by  Walther,  it  appears  that 
rabbits  can  be  cooled  down  to  8.9°  C.  (48°  F.),  before  they  die,  if  arti- 
ficial respiration  be  kept  up.  Cooled  down  to  17.8°  C.  (64°  F.),  they 
cannot  recover  unless  external  warmth  be  applied  together  with  the 
employment  of  artifical  respiration.  Eabbits  not  cooled  below  25°  C. 
(77°  F.)  recover  by  external  warmth  alone. 


CHAPTEE  XIV. 

NUTRITION    AND    DIET. 

It  is  not  only  necessary  that  the  animal  body  should  be  supplied  with 
food  in  order  that  its  natural  functions  may  go  on  without  interrup- 
tion, but  it  is  also  equally  requisite  that  the  food  should  consist  of  proper 
materials.  It  may  be  supposed  that  each  kind  of  animal  by  instinct 
keeps  itself  supplied  with  the  substances  which  supjjly  the  needs  of  its 
own  metabolism  the  best,  and  it  is  a  matter  of  every-day  experience  that 
in  the  case  of  man,  each  endeavors  to  supply  himself  with  food  accord- 
ing to  the  circumstances  of  his  surroundings.  We  may  therefore  accept 
such  data  as  we  can  obtain  from  the  observation  of  numerous  examples 
of  such  selection  in  the  way  of  diet  when  we  are  in  the  act  of  drawing 
up  a  diet-scale,  relying  upon  such  empiric  knowledge  alone,  or,  on  the 
•other  hand,  we  may  proceed  more  scientifically,  and  endeavor  to  plan  a 
diet-scale  from  our  experimental  observation  of  the  loss  which  takes 
place  in  the  body  in  the  course  of  the  twenty-four  hours  by  the  excreta. 
If  we  do  this  we  assume  that  the  food  is  taken  in  to  supply  what  is 
generally  called  the  waste  of  the  tissues.  The  term  is  scarcely  an  accu- 
rate one,  but  if  we  take  it  to  mean  in  a  restricted  sense,  what  the  tissues 
and  organs  of  the  body  give  out  to  be  eliminated  by  the  excretory  organs 
in  the  course  of  the  day,  we  may  continue  to  use  it. 

The  food  then  may  be  supposed  as  intended  to  supply  the  place  of 
that  which  is  given  out  by  the  body.  But  in  the  choice  of  a  diet  this  is 
not  enough ;  the  food  should  be  sufficient  to  supply  such  need  without 
waste  and  without  unduly  increasing  the  output  of  excreta,  while  at  the 
•same  time  the  body  should  be  maintained  in  health,  without  increase 
or  loss  of  weight. 

These  requisites  of  a  diet  scale  then  allow  for  wide  alterations  in  the 
.amount  of  different  kinds  of  foods  under  different  circumstances. 

Careful  analyses  of  the  excreta,  many  of  which  we  have  already  had 
occasion  to  call  attention  to,  show  that  they  are  made  up,  besides  water, 
-chiefly  of  the  chemical  elements  carbon,  hydrogen,  oxygen,  and  nitrogen, 
but  that  they  also  contain,  to  a  less  extent,  sulphur,  phosphorus,  chlorine, 
potassium,  sodium,  and  certain  other  of  the  elements.  Since  this  is  the 
■case  it  must  be  evident  that  to  balance  this  waste,  foods  must  be  supplied 
containing  all  these  elements  to  a  certain  degree,  but  some  of  them,  viz., 
those  which  take  a  principal  part  in  forming  the  excreta,  in  large  amount. 


500 


HANDBOOK    OF    PHYSIOLOGY. 


Of  the  excreta  the  carbon  dioxide  and  ammonia,  which  are  made  up 
of  the  elements  carbon,  oxygen,  nitrogen,  hydrogen,  are  given  off 
from  the  lungs.  By  the  urine  many  elements  are  eliminated  from  the 
blood,  especially  nitrogen,  hydrogen,  and  oxygen.  In  the  sweat,  the 
elements  chiefly  represented  are  carbon,  hydrogen,  and  oxygen,  and 
these  are  also  those  of  which  the  faeces  are  made.  By  all  the  excretions 
large  quantities  of  water  are  got  rid  of  daily,  but  chiefly  by  the  urine. 

The  relations  between  the  amounts  of  the  chief  elements  contained 
in  these  various  excreta  in  twenty-four  hours  maybe  thus  summarized: — 


Water. 

C. 

H. 

N. 

0 

By  the  lungs 

330 

660 

1700 

128 

248.8 
2.6 
9.8 
20. 

3.3 
3. 

? 

15.8 
3. 

651.15 

Bv  the  skin 

7.2 

Bv  the  urine 

11.1 

By  the  faeces 

12. 

Grammes 

2818 

281.2 

6.3 

18.8 

681.41 

From  this  should  be  subtracted  the  296  grms.  water,  which  are  pro- 
duced by  the  union  of  hydrogen  and  oxygen  in  the  body  during  the 
process  of  oxidation  {i.  e.,  33  hydrogen  and  262  oxygen).  There  are  26 
grms.  of  salts  got  rid  of  by  the  urine,  and  6  by  the  faeces;  total, 
32  grms. 

The  quantity  of  carbon  daily  lost  from  the  body  amounts  to  about 
281.2  grms.  (nearly  4,500  grains),  and  of  nitrogen  18.8  grms.  (nearly 
300  grains),  and  if  a  man  could  be  fed  by  these  elements,  as  such,  the 
problem  would  be  a  very  simple  one;  a  corresponding  weight  of  char- 
coal and,  allowing  for  the  oxygen  in  it,  of  atmospheric  air,  would  be  all 
that  is  necessary.  But  an  animal  can  live  only  upon  these  elements 
when  they  are  arranged  in  a  particular  manner  with  others,  in  the  form 
of  such  food-stuffs  as  Ave  have  already  enumerated,  p.  285  et  seq. ;  more- 
over, the  relative  proportion  of  carbon  to  nitrogen  in  either  of  these 
compounds  alone  is,  by  no  means,  the  proportion  required  in  the  diet 
of  man.  Thus,  in  proteid,  the  proportion  of  carbon  to  nitrogen 
is  only  as  3.5  to  1.  If,  therefore,  a  man  took  into  his  body,  as  food, 
sufficient  proteid  to  supply  him  with  the  needful  amount  of  carbon,  he 
would  receive  more  than  four  times  as  much  nitrogen  as  he  wanted; 
and  if  he  took  only  sufficient  to  supply  him  w^th  nitrogen,  he  would  be 
starved  for  want  of  carbon.  It  is  plain,  therefore,  that  he  should  take 
with  the  albuminous  part  of  his  food,  which  contains  so  large  a  relative 
amount  of  nitrogen  in  proportion  to  the  carbon  he  needs,  substances  in 
which  the  nitrogen  exists  in  much  smaller  quantities  relatively  to  the 
carbon. 


NUTRITION    AND    DIET, 


501 


It  is  therefore  evident  that  the  diet  must  consist  of  several  substances, 
not  of  one  alone. 

Many  valuable  observations  have  been  made  with  a  view  of  ascertain- 
ing the  effect  upon  the  metabolism  of  a  variation  in  the  amount  and 
nature  of  food.  These  are  of  great  assistance  in  the  consideration  of 
dietetics. 

Ejfeds  of  Deprivation  of  Food. — The  animal  body  deprived  of  all  food 
in  the  course  of  a  variable  time  dies  from  starvation.  The  length  of 
time  that  any  given  animal  will  live  in  such  a  condition  depends  upon 
many  circumstances;  the  chief  may  be  supposed  to  be  the  nature  and 
activity  of  the  metabolism  of  its  tissues. 

The  effect  of  starvation  on  tlie  lower  animals,  as  recorded  by  various 
experimenters  is: — (1.)  One  of  the  most  notable  effects  of  starvation,  as 
might  be  expected,  is  loss  of  iveiglit ;  the  loss  being  greatest  at  first,  as  a 
rule,  but  afterward  not  varying  very  much,  day  by  day,  until  death 
ensues.  Chossat  found  that  the  ultimate  proportional  loss  was,  in  dif- 
ferent animals  experimented  on,  almost  exactly  the  same;  death  occur- 
ring when  the  body  had  lost  two-fifths  (forty  per  cent)  of  its  original 
weight.  Different  parts  of  the  body  lose  weight  in  very  different  pro- 
portions. The  following  most  noteworthy  losses  are  taken,  in  round 
numbers,  from  the  table  given  by  Chossat : — 


Fat      . 

loses  93  per  cent. 

Liver 

.  loses  52  per  cent 

Blood      . 

.     75        " 

Muscles 

43        " 

Spleen 

71 

Nervous  tissues 

.       3 

Pancreas 

.     64 

These  figures  are  in  practical  agreement  with  those  of  later  experi- 
menters. They  show  that  the  chief  losses  are  sustained  by  the  adipose 
tissue,  the  muscles  and  glands. 

(2.)  The  effect  of  starvation  on  the  temperature  oi  the  various  ani- 
mals experimented  on  by  Chossat  was  very  distinct.  For  some  time  the 
variation  in  the  daily  temperature  was  more  marked  than  its  absolute 
and  continuous  diminution,  the  daily  fluctuation  amounting  to  3"  C.  (5°  or 
6'^  F.),  instead  of  5°  to  1°  C.  (1°  or  2'^  F.),  as  in  health.  But  a  short  time 
"before  death,the  temperature  fell  very  rapidly,  and  death  ensued  when  the 
loss  had  amounted  to  about  16.2°  C.  (30°  F.).  It  has  been  often  said, 
and  with  truth,  although  the  statement  requires  some  qualification,  that 
death  by  starvation  is  really  death  from  want  of  heat ;  for  not  only  has  it 
been  found  that  differences  of  time  with  regard  to  the  period  of  the  fatal  re- 
sult are  attended  by  the  same  ultimate  loss  of  heat,  but  the  effect  of  the 
application  of  external  warmth  to  animals  cold  and  dying  from  starvation, 
is  more  effectual  in  reviving  them  than  the  administration  of  food. 

The  symptoms  produced  by  starvation  in  the  human  subject  are  hun- 
ger, accompanied,  or  it  may  be  replaced,  by  pain,  referred  to  the  region 


502  HANDBOOK    OF    PHYSIOLOGY. 

of  the  stomach;  insatiable  thirst;  sleeplessness;  general  weakness  and 
emaciation.  The  exhalations  both  from  the  lungs  and  skin  are  foetid^ 
indicating  the  tendency  to  decomjsosition  which  belongs  to  badly  nour- 
ished tissues ;  and  death  occurs,  sometimes  after  the  additional  exhaustion 
caused  by  diarrhoea,  often  with  symptoms  of  nervous  disorder,  delirium 
or  convulsions. 

In  the  human  subject  death  commonly  occurs  within  six  to  ten  days 
after  total  deprivation  of  food.  But  this  j^eriod  may  be  considerably 
prolonged  by  taking  a  very  small  quantity  of  food,  or  even  water  only. 
The  cases  so  frequently  related  of  survival  after  many  days,  or  even  some 
weeks,  of  abstinence,  have  been  due  either  to  the  last-mentioned  circum- 
stances, or  to  others  no  less  effectual,  which  prevented  the  loss  of  heat 
and  moisture.  Cases  in  which  life  has  continued  after  total  abstinence 
from  food  and  drink  for  many  weeks,  or  months,  exist  only  in  the  imag- 
ination of  the  vulgar. 

(3.)  During  the  starvation  period  the  excreta  diminish.  The  urea, 
as  representing  the  nitrogen,  falls  quickly  in  amount,  reaches  a  mini- 
mum and  remains  constant  at  this  point  for  several  days,  and  then  rises- 
again  and  finally  falls  rapidly  immediately  before  death;  the  sulphates 
and  phosphates  undergo  much  the  same  form  of  reduction.  The  carbon 
dioxide  given  out  and  the  oxygen  taken  in  diminish.  The  fasces  dimin- 
ish, as  well  as  the  bile.  It  has  been  concluded  as  highly  probable  that 
the  greater  part  of  the  urea  represents  the  loss  of  weight  of  the  muscles. 

The  appearances  presented  after  death  from  starvation  are  those  of 
general  wasting  and  bloodlessness,  the  latter  condition  being  least  notice- 
able in  the  brain.  The  stomach  and  intestines  are  empty  and  contracted, 
and  the  walls  of  the  latter  appear  remarkably  thinned  and  almost  trans- 
parent. The  various  secretions  are  scanty  or  absent,  with  the  exception 
of  the  bile,  which,  not  being  discharged,  usually  fills  the  gall-bladder. 
All  parts  of  the  body  readily  decompose. 

In  starvation,  then,  we  see  that  the  only  income  consists  of  the  in- 
spired ox5'gen.  The  whole  of  the  energy  of  the  body  given  out  in  the 
direction  of  heat  and  mechanical  labor  is  obtained  at  the  expense  of  the 
using  up  of  its  own  tissues,  there  being  as  a  result  a  constant  drain  of 
the  nitrogen  and  carbon,  not  to  mention  the  other  elements  of  which 
they  are  made  up.  It  is  obvious  that  such  a  condition  cannot  be  en- 
dured for  any  length  of  time. 

Effect  of  a  Proteid  Diet. — Experiments  have  been  made,  to  a  consider- 
able extent  upon  dogs,  which  demonstrate  the  effect  of  proteid  food. 
After  a  period  without  food,  during  which  the  output  of  nitrogen,  as 
shown  by  the  urea,  had  diminished  to  a  certain  amount,  the  animal  is 
fed  with  a  diet  of  lean  meat  which  would  suffice  to  produce  the  amount 
of  urea,  and  so  of  fiesh,  which  it  had  been  losing  during  its  starvation 


NUTRITION    AND    DIET.  503 

period.  The  effect  of  this,  however,  is  at  once  to  send  up  the  amount 
of  urea  excreted  to  a  point  above  that  which  it  has  been  previous  to  the 
commencement  of  its  flesh  diet,  so  that  again  the  output  of  nitrogen 
would  exceed  its  income,  and  the  weight  of  the  animal  would  continue 
slowly  to  diminish.  It  is  only  after  a  considerable  increase  of  the  flesh 
given  that  a  point  is  reached  where  the  income  and  expenditure  are 
equal,  and  at  which  the  animal  is  not  using  up  quickly  or  slowly  the 
nitrogen  of  his  own  tissue,  and  is  no  longer  losing  flesh.  This  condition 
in  which  the  nitrogen  of  the  egesta  equals  the  nitrogen  of  the  ingesta  is 
known  as  nitrogenous  equilibrium.  In  the  dog,  according  to  Waller,  it 
does  not  occur  until  the  amount  of  flesh  of  the  food  is  over  three  times 
as  great  as  would  be  necessary  to  supply  the  nitrogen  of  the  urea  during 
a  period  of  starvation.  Thus  a  dog  excretes  during  a  starvation  period 
0.5  grms.  of  urea  per  kilo  of  body  weight;  in  order  to  satisfy  this  it 
would  be  necessary  to  administer  1.5  grms.  per  kilo  of  meat;  this  at 
once  increases  urea  excreted  to  about  0.75  grms.  per  kilo  of  body  weight, 
and  nitrogenous  equilibrium  is  not  attained  until  over  three  times — viz., 
5  grms.  per  kilo  of  body  weight  of  meat  is  given.  Foster  gives  even  a 
larger  figure.  The  effect,  therefore,  of  proteid  food  is  largely  to  increase 
the  excretion  of  urea,  which  indicates  increase  of  the  metabolism  of  the 
tissues. 

It  must  not  be  thought  however  that  during  nitrogenous  equilibrium 
there  is,  of  necessity,  equilibrium  of  carbon.  On  the  contrary,  it  is  very 
possible  that  the  carbon,  as  supplied  by  the  large  amount  of  meat,  is  not 
entirely  eliminated,  but  may  be  partially  retained  in  the  body.  If  re- 
tained in  the  body  it  is  probably  retained  in  the  form  of  fat,  although 
possibly  it  might  be  retained  partially  as  some  carbohydrate,  e.g.,  gly- 
cogen ;  but  the  amount  of  glycogen  obtained  from  the  body  is  too  small 
for  the  latter  to  be  appreciable.  The  animal  in  nitrogenous  equilib- 
rium, therefore,  may  gain  weight,  although  not  in  the  form  of  flesh. 
The  converse  may  also  be  the  case,  the  animal  getting  rid  of  more  carbon 
than  the  meat  supplies,  in  which  case  he  would  lose  weight  but  would 
not  lose  flesh. 

The  proteids  of  food  are  described  by  Foster  as  having  two  relations 
to  the  proteid  metabolism  and  to  outgoing  urea;  the  first  part  going  to 
maintain  the  ordinary  and  quiet  metabolism  of  the  tissues,  for  which 
purpose  it  is  actually  built  up  into  their  molecule,  and  the  second  part 
causing  a  more  rapid  formation  of  urea  and  rapid  proteid  metabolism, 
but  never  forming  a  part  of  the  actual  protoplasmic  molecule.  The 
former  proteids  are  called  morphotic  or  tissue  proteids,  the  latter  circu- 
lating or  floating  proteids.  A  method  by  which  the  latter  may  be 
changed  into  urea  has  already  been  suggested,  viz.,  that  they  are  con- 
verted into  leucin  and  tyrosin,  carried  to  the  liver  and  converted  into 


504  HANDBOOK    OF    PHYSIOLOGY. 

urea.  This  use  of  the  proteids  to  form  by  their  oxidation  heat  and  not 
to  produce  tissue,  was  looked  upon  by  the  older  physiologists  as  a  waste- 
ful use  of  good  material,  and  was  called  a  luxus  coyisiimption. 

The  condition  of  nitrogenous  equilibrium  {i.e.,  the  income  and  out- 
put being  equal)  is  one  which  may  be  maintained  even  if  the  amount  of 
proteid  taken  as  diet  far  exceeds  the  necessities  of  the  economy,  the  urea 
being  excreted  in  excessive  amount,  and  the  wasteful  use  of  proteid  food 
which  is  so  common  may  not  be  attended  with  harmful  consequences, 
so  long  as  the  liver  is  able  to  do  its  work  in  the  formation  of  urea.  The 
body  may  or  may  not  increase  in  weight,  but  if  the  liver  strikes  work 
from  any  cause,  a  condition  of  lithiasis,  or  of  gout,  follows. 

We  have  before  had  occasion  to  remark  that  many  physiologists  think 
that  the  quicker  and  shorter  series  of  changes  of  proteid  into  urea,  by 
way  of  leucin  and  tyrosin,  only  comes  into  force  when  the  food  contains 
an  excess  of  proteid. 

It  has  not  actually  been  proved,  but  it  is  not  unlikely,  that  even  in 
the  condition  of  lithiasis,  the  nitrogen  of  the  ingesta  may  not  greatly 
exceed  that  of  the  egesta,  but  that  the  mode  of  elimination  is  different. 
It  is  only  in  cases  of  growth  or  putting  on  of  flesh,  as  in  growing  chil- 
dren, that  nitrogen  is  retained  in  the  body,  except  to  a  very  small  amount, 
in  health. 

According  to  calculations  which  have  been  made,  it  appears  that 
the  body  puts  on  thirty  grammes  of  flesh  for  every  gramme  of  nitrogen 
so  retained. 

As  regards  the  retention  of  carbon  in  the  body,  it  is  calculated  that 
one  gramme  and  a  half  of  weight  is  put  on  for  each  gramme  by  which 
the  ingesta  of  carbon  is  greater  than  the  egesta. 

Ejfects  of  Fats  and  Carbohydrates  as  Food. — Experiments  illustrating 
the  ill-effects  produced  by  feeding  animals  upon  one  or  two  alimentary 
substances  only  have  been  often  performed. 

Dogs  were  fed  exclusively  on  sugar  and  distilled  luater.  During  the 
first  seven  or  eight  days  they  were  brisk  and  active,  and  took  their  food 
and  drink  as  usual ;  but  in  the  course  of  the  second  week  they  began  to 
get  thin,  although  their  appetite  continued  good,  and  they  took  daily 
between  six  and  eight  ounces  of  sugar.  The  emaciation  increased  during 
the  third  week,  and  they  became  feeble,  and  lost  their  activity  and  ap- 
petite. At  the  same  time  an  ulcer  formed  on  each  cornea,  followed  by 
an  escape  of  the  humors  of  the  eye :  this  took  place  in  repeated  experi- 
ments. The  animals  still  continued  to  eat  three  or  four  ounces  of  sugar 
daily ;  but  became  at  length  so  feeble  as  to  be  incapable  of  motion,  and 
died  on  a  day  varying  from  the  thirty-first  to  the  thirty-fourth.  On  dis- 
section their  bodies  presented  all  the  appearances  produced  by  death  from 


NUTRITION    AND    DIET.  505 

starvation;  indeed,  dogs  will  live  almost  the  same  length  of  time  without 
any  food  at  all. 

When  dogs  were  fed  exclusively  on  gnm,  results  almost  similar  to  the 
above  ensued.  When  they  were  kept  on  olive-oil  and  water,  all  the 
phenomena  produced  were  the  same,  except  that  no  ulceration  of  the 
cornea  took  place ;  the  effects  were  also  the  same  with  butter.  The  ex- 
periments of  Chossat  and  Letellier  prove  the  same;  and  in  men,  the 
same  is  shown  by  the  various  diseases  to  which  those  who  consume  but 
little  nitrogenous  food  are  liable,  and  especially  by  the  affection  of  the 
cornea  which  is  observed  in  Hindus  feeding  almost  exclusively  on  rice. 
But  it  is  not  only  the  non-nitrogenous  substances  which,  taken  alone, 
are  insufficient  for  the  maintenance  of  health.  The  experiments  of  the 
Academies  of  France  and  Amsterdam  were  equally  conclusive  that  gelatin 
alone  soon  ceases  to  be  nutritive. 

Effect  of  too  7nuch  Food. — All  the  three  classes  of  food-stuffs  men- 
tioned— fats,  carbohydrates  and  gelatin — have  their  distinct  uses  when 
combined  with  proteids.  A  small  amount  of  fat  or  a  larger  amount  of 
carbohydrate  (starch  or  sugar)  added  to  some  proteid  diminishes  the 
amount  of  proteid  required  before  nitrogenous  equilibrium  is  attained 
(in  a  dog  to  the  extent  of  50  per  cent  or  more),  but  if  either  fat  or 
carbohydrate  exceed  a  certain  minimum  it  is  retained  in  the  body  as  fat. 
If  the  proteid  be  increased,  the  metabolism  is  increased  likewise,  and  so 
fat  may  not  be  deposited,  even  if  the  carbohydrate  of  the  diet  be  exces- 
sive. It  is  even  possible  that  some  of  the  already  stored-up  fat  may  be 
used  up,  and  so  loss  of  weight  (fat)  might  result. 

Persistent  excess  of  carbohydrate  food  produces  an  accumulation  of 
fat,  which  may  not  only  be  an  inconvenience  causing  obesity,  but  may 
interfere  with  the  proper  nutrition  of  muscles,  and  a  feebleness  of  the 
action  of  the  heart,  with  other  troubles.  Starches  when  taken  in  great 
excess  are  almost  certain  to  give  rise  to  dyspepsia,  with  acidity  and  flat- 
ulence. Excess  of  starch  or  of  sugar  in  the  food  may,  however,  be  got 
rid  of  by  the  urine  in  the  form  of  sugar.  There  is  evidently  a  limit  to 
the  absorption  of  fat  as  well  as  of  starch,  since  if  in  excessive  amount 
they  may  appear  in  the  faeces. 

Gelatin  may  in  part  replace  the  proteid  of  food,  and  may  be  econom- 
ically used  with  proteid  to  produce  nitrogenous  equilibrium.  It  has 
been  suggested  that  gelatin  will  take  the  place,  as  it  were,  of  the  floating, 
but  not  of  the  morphotic  proteids. 

Peptones  or  Proteoses  may, according  to  some,  take  the  place  of  proteids 
as  food,  whereas,  according  to  others,  they  act  simply  in  the  same  way 
as  gelatin. 

That  salts  are  necessary  as  food  is  proved  by  the  presence  of  scurvy 


506  HANDBOOK    OF    PHYSIOLOGY, 

when  they  are  not  present,  and  we  know  that  there  is  a  consant  excre- 
tion of  chlorides,  phosphates  and  sulphates  in  the  urine,  so  that  in  order 
to  balance  the  income  and  output,  these  salts  in  combination  with 
sodium,  potassium,  calcium,  etc.,  must  be  taken  in. 

The  necessity  for  the  taking  in  of  water,  in  order  to  balance  the  ex 
cretion,  is  sufficiently  obvious. 

To  summarize  what  has  been  said: — 

Proteid. — i.  If  the  nitrogen  of  the  income  is  less  than  that  of  the 
output,  the  animal  loses  flesh  and  starves,  gradually  or  quickly,  accord- 
ing to  the  extent  of  the  deficiency. 

ii.  If  the  nitrogen  of  the  income  be  evenly  balanced,  the  proteid 
being  only  just  sufficient,  the  animal  does  not  lose  flesh,  but  may  increase 
or  diminish  in  weight  (fat). 

iii.  If  the  nitrogen  of  the  ingesta  exceed  that  of  the  egesta,  the  ex- 
cess is  mainly  retained  in  the  form  of  flesh. 

iv.  If  the  proteid  be  in  great  excess,  although  there  be  a  condition 
of  nitrogenous  equilibrium,  there  may  be  increase  in  weight,  but  also  a 
likelihood  of  gout  and  similar  affections. 

Fatty  and  Carbohydrate  Foods  are  of  no  use  either  together  or  sepa- 
rately without  the  addition  of  the  other  food-stuffs.  In  moderation, 
either  may  diminish  the  amount  of  proteid  necessary  to  produce  nitro- 
genous equilibrium.  If  the  quantity  of  either  be  increased  beyond  a 
certain  amount,  it  is  retained  in  the  body  in  form  of  fat  (and  partly, 
perhaps,  in  the  case  of  the  carbohydrate,  as  glycogen).  If  in  great  ex- 
cess, disorders  of  digestion  occur.  Fats  have  more  potential  energy  than 
carbohydrates,  but  are  less  digestible.  Fatty  foods  need  more  oxygen 
than  carbohydrates  when  they  are  used  up  in  the  body. 

Gelatin  will  not  entirely,  but  will  partly  replace  the  proteid  in  a  diet. 

Peptones  and  Proteoses  will  in  part  replace  proteids. 

8alts  of  sodium,  potassium,  calcium,  etc.,  are  necessary  in  food. 
The  chlorides,  phosphates  and  sulphates,  and  possibly  the  citrates,  being 
the  most  important  of  those  required. 

Water  is  absolutely  essential  to  life — an  animal  will  not  survive 
deprivation  for  longer  than  a  few  days. 

Requisites  of  a  Normal  Diet. 

It  will  have  been  understood  that  it  is  necessary  that  a  normal  diet 
should  be  be  made  up  of  various  articles,  that  they  should  be  well  cooked, 
and  that  they  should  contain  about  the  same  amount  of  carbon  and  ni- 
trogen as  are  got  rid  of  by  the  excreta.  No  doubt  these  desiderata  may 
be  satisfied  in  many  ways,  and  it  would  be  unreasonable  to  expect  the 
diet  of  every  adult  to  be  unvarying.     The  age,  sex,  strength,  and  cir- 


NUTRITIO]S^    AND    DIET.  507 

cnmstances  of  each  individual  must  ultimately  determine  what  he  takes 
as  food.  A  dinner  of  bread  and  cheese  with  an  onion  contains  all  the 
requisites  for  a  meal,  but  such  diet  would  be  suitable  only  for  those  pos- 
sessing strong  digestive  powers.  It  is  a  well-known  fact  that  the  diet 
of  the  continental  nations  differs  from  that  of  our  own  country,  and 
that  of  cold  from  that  of  hot  climates,  but  the  same  principle  underlies 
them  all,  viz.,  the  replacement  of  the  loss  of  the  excreta  in  the  most 
convenient  and  economical  way  possible.  Without  going  into  detail  in 
the  matter  here,  it  may  be  said  that  any  one  in  active  work  requires  more 
food  than  one  at  rest,  and  that  children  and  women  require  less  food 
than  do  adult  men. 

Of  the  various  diet-scales  which  have  been  drawn  out  with  the  object 
of  supplying  the  proximate  principles  in  the  required  proportions,  the 
foregoing  is  slightly  modified  from  Moleschott : — 


Dry  Food — 
Proteid        .     120  grms. 
Fat      .         .       90     " 
Carbohydrate  320     " 

N.                      c. 
(4.232  oz.)   supplying  18.88  grms.  64.18  grms. 
(3.174  oz.)          "                                     70.20       " 
(11.64  oz.)         "                                  146.82       " 

Salts      .         .     30     " 
Water    .    .     2800     " 

N.  18.88       C.  281.2 
(nearly  1  oz.) 

Two  other  diet-scales  may  be  mentioned,  which  are  often  quoted, 
viz: — 

Ranke's   Diet -Scale. 

Proteid       . 100  grms. 

Fats 100     " 

Carbohydrates 250     " 

Salts 25      " 

Water 2600      " 

Pettenkofer  &  VoiT's  Diet-Scale  is  as  follows : — 

Proteids 118  to  137  grms. 

Fats 56  to  117     " 

Carbohydrates 352  to  500     " 

Salts     .         .         , 

Water 2016  grms. 

The  amount  of  the  excreted  carbon  and  nitrogen  is  not,  of  course, 
always  the  same,  it  having  been  unfortunately  proved  possible,  for  example, 
to  subsist  on  9  or  10  grms.  of  nitrogen  and  200  grms.  of  carbon  per 
diem  (the  ordinary  diet  for  needle- women  in  London,  and  the  average  of 
the  cotton  operatives  in  Lancashire  during  the  famine,  18G2),  the 
amount  of  these  elements  excreted  falling  to  figures  corresponding  to 
such  an  income.  Of  course,  upon  such  a  diet  the  metabolism  is  low, 
and  persistent  weakness  must  be  the  result. 

The  9  or  10  grms.  of  N  in  such  a  semi-starvation  diet  would  be 
equivalent  to  58.5  to  65  grms.  of  proteids,  whereas  the  amount  of  pro- 


508 


HANDBOOK    OF    PHYSIOLOGY. 


teids  in  some  diets  may  be  as  high  as  150-159  grms,  per  diem  (English 
navvies),  or  165  gms.  (Munich  brewers'  men).  The  English  and 
Bavarian  soldier  in  time  of  peace  consumes  126  grms.  of  proteid  per 
diem  (4.4  oz.). 

Not  only  the  proteids  but  also  the  fats  may  vary ;  the  amount  may  be 
as  low  as  5(}  grms.  and  as  high  as  117  grms.  The  carbohydrates  may 
vary  from  200  grms.  to  500  grms.  and  upward.  Sometimes,  with  a 
small  proportion  of  fat,  the  carbohydrate  may  be  correspondingly 
increased  to  make  up  the  necessary  carbon.  A  useful  table  after  Payen 
will  help  to  show  in  what  ways  it  is  possible  to  obtain  the  requisite 
amount  of  nitrogen  and  carbon  from  the  most  common  food-stuffs. 

In  100  parts  of  the  following  substances  the  proportion  of  N  and  0 
is  indicated: 


N.             c. 

Beef  (without  bone 

Roast  Beef  . 

Eggs 

Cow's  Milk 

Cheese     . 

Beans  .         .        .         . 

Lentils    . 

3           11 
3.528     17.76 
1.9        13.5 
.66        8 
2  to  7    35  to  71 
4.5        42 
4.1         48 

Oatmeal 
Bread 
Potatoes 
Eels  . 
Mackerel 
Sardines  in  oil 
Butter    . 

In  order  to  obtain 
nitrogen,  multii^ly  by 

the  amount   of 
6.5. 

proteid  present 

N. 

c. 

1.95 

44 

1 

28 

.33 

11 

2 

30 

3.74 

19.26 

6 

29 

.64 

83 

From  these  data  it  is  possible  to  form  various  diet-scales  which  shall 
supply  the  needs  of  different  conditions.  Assuming  that  the  average 
amount  of  carbon  and  nitrogen  required  is  about  300  grms,  and  20  grms. 
respectively,  this  may  be  obtained  as  follows: — 


340  grms.    |  J^j^^"  avoirdupois  i  ^^^^  uncooked  meat  *  10  grms. 
(32  oz.  or  2  lbs.  avoirdupois)  bread    .         .     9    " 


906 


c. 
37  grms. 

252      " 


19  grms.       289  grms. 


But  this  diet  is  not  a  usual  one;  a  certain  proportion  of  the  carbon 
is  usually  supplied  as  butter,  or  bacon,  and  so  if  90  grms.  (3.1  oz.)  of 
butter  or  bacon  be  used  they  would  supply  about  72  grms.  of  carbon,  and 
the  carbohydrate  would  be  diminished  nearly  one- third ;  but  the  nitro- 
gen would  also  be  diminished  from  9  grms.  to  6  grms.  It  would  be 
necessary  to  supply  some  extra  nitrogenous  principle,  and  this  might 
be  done  by  the  addition  of  eggs,  milk,  cheese,  beans,  or  of  any  of  the 
food-stuffs  already  enumerated  at  p.  285  et  seq.,  as  supplying  nitrogenous 
food  chiefly.  For  example,  56  grms.  (2  oz.)  cheese,  would  supply,  on 
an  average,  3  grms.  nitrogen  and  20  grms.  carbon ;  or  28  grms.  cheese, 
supplying    1.5  grms.    nitrogen  and  about    10   grms.    carbon,  and  225 


*  As  meat  loses  23  to  34  per  cent  on  cooking,  the  weight  of    cooked  meat 
would  be  proportionately  be  less. 


NUTRITION    AND    DIET.  509 

grms.  (-J  lb.)  potatoes,  and  225  grms.  (-^  lb.)  carrots,  supplying  together 
about  1  grm.  of  nitrogen  and  35  grms,  of  carbon.  The  diet  would  then 
read  as  follows : — 

340  grms.  lean  uncooked  meat 

600       "       Bread  .         .         ... 

90       "       Butter 

28       "       Cheese  ..... 


225       "       Potatoes 
225       "       Carrots 


[ 


N. 

C. 

10  grms. 
6      " 
.5  " 
1.5  " 

37  grms, 
-  168       " 

72       " 
10      " 

1       " 

35      " 

N    19  C.  332 


The  salts,  over  30  grms.,  would  be  supplied  by  the  meat  16  grms., 
the  bread  12  grms.,  and  vegetables  about  4  grms.  The  fluids  should 
consist  of  about  2,500-2,800  grms.,  and  might  be  given  as  water,  with 
or  without  tea,  coffee,  or  cocoa  (which  are  chiefly  stimulants) ,  together 
with  a  small  proportion  of  alcohol. 

Variations  in  Diet  Tables. 

For  infancy. — Milk  affords  a  natural  and  perfect  diet  for  infants. 
The  amount  which  an  infant  dnring  the  first  month  should  take  is  not 
less  than  1  kilogramme  (2^  lbs.)  per  diem.  In  1,000  grms.  there  would 
be  about  6.6  grms.  nitrogen  and  80  to  90  of  carbon.  This  allows  for  a 
gain  of  weight  of  2  to  5  oz.  in  the  time. 

For  climate. — Very  slight  alteration  is  necessary.  For  warm  climates, 
slightly  increase  the  carbohydrates. 

For  hard  labor. — All  the  articles  of  diet  should  be  increased  to  make 
up  for  the  increased  metabolism. 

Fattening  diet. — In  such  a  diet  an  excess  of  carbohydrates  should  be 
present. 

To  reduce  ohe&ity. — The  fats  and  carbohydrates  should  be  diminished, 
but  the  proteids  should  be  relatively  increased. 

To  increase  muscle. — It  has  been  found  that  a  diet  consisting  largely 
of  proteids  in  considerable  amount  combined  with  such  passive  exercise 
as  that  obtained  by  massage,  will  cause  the  body  to  put  on  flesh. 

For  training. — The  whole  diet  should  be  increased,  possibly  preceded 
by  a  diet  in  which  the  proteid  is  in  excess. 

For  brain  work. — The  chief  essential  is  that  the  diet  should  consist  of 
easily  digestible  materials. 

Income  and  Output  of  Energy. 

The  food  must  be  considered  from  another  point  of  view  in  addition 
to  that  from  which  we  have  been  considering  it.  It  not  only  makes 
up  for  the  substances  eliminated  from    the  body,  but  it  also  supjilies 


510  HANDBOOK    OF   PHYSIOLOGY. 

potential  energy  to  balance  the  energy  set  free  in  the  living  body  as 
heat  and  movement.  The  amount  of  heat  is  measured  in  terms  of 
calories,  as  has  been  already  pointed  out.  The  work  done  may  be  ex- 
pressed in  terms  of  foot-jjounds,  (see  p.  191)  (English  system),  or  metre- 
grammes,  or  metre-kilogrammes  (metric  system).  The  calories  may  also 
be  expressed  in  terms  of  work,  as  heat  is  also,  as  has  been  said,  a  mode 
of  motion.  The  heat-unit  Ca,  may  be  transformed  into  the  metric 
"work-unit  by  multiplying  by  42  and  dividing  by  1000,  and  the  converse. 

Manifestations  of  Force  in  the  form  either  of  Heat  or  Motion. — In  the 
former  case  (Heat), the  combustion  must  be  sufficient  to  maintain  a  tem- 
perature of  about  37.8°  C.  (100°  F.)  throughout  the  whole  substance  of 
the  body,  in  all  varieties  of  external  temperature,  notwithstanding  the 
large  amount  continually  lost  in  the  ways  previously  enumerated.  In 
the  case  of  Motion,  there  is  the  expenditure  involved  in  the  {a)  Ordi- 
nary muscular  movements,  as  in  Prehension,  Mastication,  Locomotion, 
and  numberless  other  ways:  as  well  as  in  {h)  Various  involuntary  move- 
ments^ as  in  Respiration,  Circulation,  Digestion,  etc. 

Manifestation  of  Nerveforce;  as  in  the  general  regulation  of  all 
physiological  processes,  e.g.^  Eespiration,  Circulation,  Digestion;  and 
in  Volition  and  all  other  manifestations  of  cerebral  activity. 

The  &}iergy  expended  in  all  physiological  ^jrocesses,  e.g. ,  Nutrition, 
Secretion,  Growth,  and  the  like. 

The  total  expenditure  or  total  manifestation  of  energy  by  an  animal 
body  can  be  m.easured,  with  fair  accuracy.  All  statements,  however, 
must  be  considered  for  the  present  approximate  only,  and  especially  is 
this  the  case  with  respect  to  the  comparative  share  of  expenditure  to 
be  assigned  to  the  various  objects  just  enumerated. 

The  amount  of  energy  daily  manifested  by  the  adult  human  body 
in  (a)  the  maintenance  of  its  temperature;  (Ij)  in  internal  mechani- 
cal work,  as  in  the  movements  of  the  respiratory  muscles,  the  heart, 
etc. ;  and  (c)  in  external  mechanical  work,  as  in  locomotion,  and  all 
other  voluntary  movements,  is  made  up,  according  to  McKendrick,  as 
follows : — 

Metre-  Gramme- 

kilogrammes,  calories. 

Work  of  heart  per  diem      ...         88, 000 
Work  of  respiratory  muscle  .         .  14,000 

Eight  hours'  active  work  .         .       213,344 


315,334  or  743,000 

Amount  of  heat  produced  in  24  hours    1,583,700  or       3,724,000 


1,898,034  or       4,467,000 

So  that  4,  467  kilogramme  calories  represent  the  total  energy  manifested  in 
24  hours,  8  of  which  were  employed  in  mechanical  work,  one-sixth  of  the 
total  energy  being  work.     This  estimation  considerably  exceeds  those  of  others. 


NUTRITIOlSr    AND    DIET.  511 

and  the  most  general  view  is  that  the  total  energy    exhibited  in   24  hours  by 

the  average  adult  is  rather  under  than  over  1,000, 000  k i log.  metres. 

Taking  the  diet-scale  as  given   above  (modified  from  Moleschott),  we    may 

see  how  this  supplies  the  energy  which  is  given  out,  remembering  that  1  grm. 

proteid  =  5,000  to  5,500  calories;  minus  the  value  of  i  grm.  urea  =  700  or  800 

calories,  =  say  4,500;  1  grm.  fat  =  9,000  calories;  and  1  grm.  carbohydrate  = 

4,000  calories. 

Gramme- 
calories. 

130  grms.  Proteid  at  4, 500  per  grm.  =       544, 500 

90      "        Fat  at  9, 000  per  grm.  =      810, 000 

330      "        Carbohydrate  at  4000  per  grm.    =1,320,000 


2,694,500 


Or  roughly,  2,694  kilog.  calories,  equivalent  to  1,144,950  metre-kilogrammes 
of  energy.  This  shows,  although  the  calculation  is  only  rough,  that  the  diet 
which  from  other  reasons  was  considered  to  be  correct  contains  the  potential 
energy  to  set  free  one  million  metre -kilogrammes  of  kinetic  energy,  and  to 
leave  a  fair  margin  for  errors  of  calculation. 

To  the  foregoing  amounts  of  expenditure  must  be  added  the  quite 
unknown  quantity  expended  in  the  various  manifestations  of  nerve-force, 
and  in  the  work  of  nutrition  and  growth  (using  these  terms  in  their 
widest  sense).  By  comparing  the  amount  of  energy  which  should  be 
produced  in  the  body  from  so  much  food  of  a  given  kind,  with  that 
which  is  actually  manifested  (as  shown  by  the  various  products  of  com- 
bustion, in  the  excretions),  attempts  have  been  made,  indeed,  to  estimate, 
by  a  process  of  exclusion,  these  unknown  quantities;  but  all  such  calcu- 
lations must  be  at  present  considered  only  very  doubtfully  approximate. 

Sources  of  Err-oi'. — Among  the  sources  of  error  in  any  such  calcula- 
tions as  the  one  above  given  must  be  reckoned,  as  a  chief  one,  the, 
at  present,  entirely  unknown  extent  to  which  forces  external  to  the  body 
(mainly  heat)  can  be  utilized  by  the  tissues.  We  are  too  apt  to  think 
that  the  heat  and  light  of  the  sun  are  directly  correlated,  as  far  as  living 
beings  are  concerned,  with  the  chemico-vital  transformations  involved 
in  the  nutrition  and  growth  of  the  members  of  the  vegetable  world  only. 
But  animals,  although  comparatively  independent  of  external  heat  and 
other  forces,  probably  utilize  them,  to  the  degree  occasion  offers.  And 
although  the  correlative  manifestation  of  energy  in  the  body,  due  to  ex- 
ternal heat  and  light,  may  still  be  measured  in  so  far  as  it  may  take 
the  form  of  mechanical  work;  yet,  in  so  far  as  it  takes  the  form  of  ex- 
penditure in  nutrition  or  nerve-force,  it  is  evidently  impossible  to  include 
it  by  any  method  of  estimation  )^et  discovered;  and  all  accounts  of  it 
must  be  matters  of  the  purest  theory.  These  considerations  may  help 
to  explain  the  apparent  discrepancy  between  the  amount  of  energy  which 
is  capable  of  being  produced  by  the  usual  daily  amount  of  food,  with 
that  which  is  actually  manifested  daily  by  the  body;  the  former  leaving 


512  HANDBOOK    OF    PHYSIOLOGY. 

but  a  small  margin  for  anything  beyond  the  maintenance  of  heat,  and 
mechanical  work. 

It  is  of  much  interest  to  consider  the  way  in  Avhich  protoplasm   acts 
in  converting  food  into  energy  plus  decomposition  products.     It  is  certain 
that  the  substance  itself  does  not  undergo  much  change  in  the  process 
except  a  slight  amount  of  wear  and  tear.     We  may  assume  that  it  is  the 
property  of  protoplasm  to  separate  from  the  blood  the  materials  which 
it  may  require  to  produce  secretions,  in  the  case  of  the  protoplasm  of 
secreting  glands,  or  to  enable  it  to  evolve  heat  and  energy,  as  in  the 
case  of  the  protoplasm  of  muscle.     The  properties  of  the  protoplasm  are 
very  possibly  differently  developed  in  each  case,  and  the  decomposition 
products,  too,  may  be  different  in  quality  or  quantity.     Proteid  materials 
appear  to  be  specially  needed,  as  is  shown  by  the  invariable  presence  of 
urea  in  the  urine  even  during  starvation ;  and  as  in  the  latter  case  there 
has  been  no  food  from  which  these  materials  could  have  been  derived, 
the  urea  is  considered  to  be  derived  from  the  disintegration  of  the  nitro- 
genous tissues  themselves.     Which,  if  not  all,  of  the  three  varieties  of 
proteid  of   the  blood,  viz.,  serum-albumin,  serum-globulin,  and  fibrino- 
gen,   is  necessary  for    muscular    metabolism   is  not   certainly  known, 
opinion  appears  to  incline  toward  the  first  as  the  most  important.     The 
removal  of  all  fat  from  the  body  in  a  starvation  period,  as  the  first  appar- 
ent change,  would  lead   to  the  supposition  that  fat  is  also  a  specially 
necessary  pabulum  for  the  production  of  protoplasmic  energy;  and  the 
fact  that,  as  mentioned  above,  with   a  diet  of  lean  meat  an  enormous 
amount  appears  to  be   required,  suggests   that  in  that  case  protoj^lasm 
obtains  the  fat  it  needs  from  the  proteid   food,  which  process  must  be 
evidently  a  source   of   much    waste   of    nitrogen.      The   fat   which    is 
deposited  in  the  tissues  has  for  its  origin,  as  we  have  before  remarked, 
in  great  part  carbohydrate  food,  and  is  looked  upon  as  a  store  of  carbo- 
naceous material;  it  has  been  suggested  that  as  it  leaves  the  tissue  to  be 
used  up,   it   is   reconverted    into  a  carbohydrate,  viz.,  dextrose.      Salts 
appear  to  be  absolutely  essential  for  protoplasmic  life.     The  idea  that 
proteid  food  has  two  destinations  in  the  economy,  viz.,  to  form  organ  or 
tissue  proteid  which  builds  up  organs  and  tissues,  and  circulating  pro- 
teid,  from   which  the  organs  and  tissues  derive  the  materials  of  their 
secretions  or  for  producing  their  energy,  is  a  convenient  one,  but  cannot 
be  said  to  rest  upon  any  very  certain  facts.     Except  in  the  possible  case 
of  the  appearance  of  leucin  and  tyrosin  in  pancreatic  digestion,  already 
fully  discussed,  it  must  not  be  looked  upon  as  more  than  a  convenient 
hypothesis. 

One  question  which  has  been  little  considered  by  physiologists,  is 
what  relationship,  if  any,  there  is  between  each  tissue  and  the  waste  pro- 
ducts of  other  tissues,  or  perhaps  it  should  be  said,  the  products  of  the 


NUTRITION    AXD    DIET.  513 

metabolism  of  other  tissues.  It  is  not  known  whether,  as  the  result  of 
the  katabolism  of  one  tissue,  products,  proteid  or  otherwise,  are  not 
taken  up  by  the  blood  and  carried  to  other  tissues,  supplying  exactly 
what  is  necessary  for  their  complete  anabolism;  whether,  for  example, 
a  proteid  residue  does  not  arise  from  the  metabolism  of  muscle  which 
may  be  used  further  by  glands.  One  step,  at  all  events,  in  this  direction 
has  been  taken;  it  has  been  suggested  that  the  sarco-lactic  acid  contin- 
ually produced  by  muscle  is  carried  to  the  liver,  either  to  be  converted 
itself  into  glycogen,  or  by  its  influence  on  the  hepatic  cells  to  cause 
them  to  store  up  that  substance. 

33 


CHAPTER   XY. 


THE  PRODUCTION  OF  THE  VOICE. 


Before  commencing  the  consideration  of  the  Nervous  system  and 
the  Special  Senses  it  will  be  convenient  to  consider  first  speech,  the 
production  of  the  human  voice,  as  this  is  concerned  with  the  employ- 
ment of  certain  special  muscles,  viz.,  those  of  the  larynx. 

The  Larynx. — In  nearly  all  air-breathing  vertebrate  animals  there 
are  arrangements  for  the  production  of  sound,  or  voice,  ia  some  parts  of 


Comumin:- 

Comumttj 


Comu  supr— -  Js 


Lig:  crico-th>T.  med 

Cart:  cricoidea.- 
Xag:  crico-tracheae. 

Cart:  traclieale, 


(?«.  Stemo-liyoideua 


i''~  -    mj.  Steraorhyoidcasi 


m.  Stemo-hfoideud, 
m.  Crico-thyroideuSi 


Fie   341  —The  Larynx,  as  seen  from  the  front,  showing  the  cartilages  and  ligaments. 
'      cles,  with  the  exception  of  one  crico-thyroid,  are  cut  off  short.     (Stoerk.) 


The  mus- 


the  respiratory  apparatus.  In  many  animals,  the  sound  admits  of  being 
variously  modified  and  altered  during  and  after  its  production;  and,  in 
man,  one  such  modification  occurring  in  obedience  to  dictates  of  the 
cerebrum,  is  speech. 

It  has  been  proved  by  observations  on  living  subjects,  by  means  of 
the  laryngoscope  (p.  519),  as  well  as  by  experiments  on  the  larynx  taken 
from  the  dead  body,  that  the  sound  of  the  human  voice  is  the  result 
of  the  vibration  of  the  inferior  laryngeal  ligaments,   or  the  true  vocal 

514 


THE    PRODUCTIOX    OF   THE    VOICE.  515 

cords  which  bound  the  glottis,  caused  by  currents  of  expired  air  impelled 
over  their  edges.  If  a  free  opening  exists  in  the  trachea,  the  sound  of 
the  voice  ceases,  but  it  returns  if  the  opening  is  closed.  An  opening 
into  the  air-passages  above  the  glottis,  on  the  contrary,  does  not  prevent 
the  voice  being  produced.  By  forcing  a  current  of  air  through  the 
larynx  in  the  dead  subject,  clear  vocal  sounds  are  elicited,  through  the 
epiglottis,  the  upper  ligaments  of  the  larynx  or  false  vocal  cords,  the 
ventricles  between  them  and  the  inferior  ligaments  or  true  vocal  cords, 
and  the  upper  part  of  the  arytenoid  cartilages,  be  all  removed;  provided 
the  true  vocal  cords  remain  entire,  with  their  points  of  attachment, 
and  be  kept  tense  and  so  approximated  that  the  fissure  of  the  glottis  may 
be  narrow. 

The  vocal  ligaments  or  cords,  therefore,  are  regarded  as  the  proper 
organs  for  the  production  of  vocal  sounds:  the  modifications  of  these 
sounds  being  effected,  as  will  be  presently  explained,  by  other  parts, 
viz.,  by  the  tongue,  teeth,  lips,  etc.  The  structure  of  the  vocal  cords 
is  adapted  to  enable  them  to  vibrate  like  tense  membranes,  for  they  are 
essentially  composed  of  elastic  tissue;  and  they  are  so  attached  to  the 
cartilaginous  parts  of  the  larynx  that  their  position  and  tension  can  be 
variously  altered  by  the  contraction  of  the  muscles  which  act  on  these 
parts. 

Thus  it  will  be  seen  that  the  larynx  is  the  organ  of  voice.  It  may 
be  said  to  consist  essentially  of  the  two  vocal  cords  and  the  various  car- 
tilaginous, muscular,  and  other  apparatus  by  means  of  which  not  only 
can  the  ajDcrture  of  the  larynx  (rima  glottidis),  of  which  they  are  the 
lateral  boundaries,  be  closed  against  the  entrance  and  exit  of  air  to  or 
from  the  lungs,  but  also  by  means  of  which  the  cords  themselves  can  be 
stretched  or  relaxed,  brought  together  and  separated  in  accordance  with 
the  conditions  that  may  be  necessary  for  the  air  in  passing  over  them,  to 
set  them  vibrating  to  produce  the  various  sounds.  Their  action  in 
respiration  has  been  already  referred  to. 

Anatomy  of  the  Larynx. — The  principal  parts  entering  into  the  formation  of 
the  larynx  (figs.  342  and  343)  are — the  thyi'oid  cartilage  ;  the  cricoid  cartilage  ; 
the  two  arytenoid  cartilages ;  and  the  two  true  vocal  cords.  The  epiglottis 
(fig.  343) ,  has  but  little  to  do  with  the  voice,  and  is  chiefly  useful  in  protect- 
ing the  vipper  part  of  the  larynx  from  the  entrance  of  food  and  drink  in 
deglutition.  It  also  probably  guides  mucus  or  other  fluids  in  small  amount 
from  the  mouth  around  the  sides  of  the  upper  opening  of  the  glottis  into  the 
pharynx  and  oesophagus :  thus  preventing  them  from  entering  the  larynx. 
The  false  vocal  cords  and  the  ventricle  of  the  larynx,  which  is  a  space  between 
the  false  and  the  true  cord  of  either  side,  need  be  here  only  referred  to. 

Cartilages.  —  (a)  The  thyroid  cartilage  (fig.  342,  1  to  4)  does  not  form  a  com- 
plete ring  around  the  laiynx,  but  only  covers  the  front  portion.  (&)  The 
cricoid  cartilage    (fig.    342,  5,  6) ,  on  the   other  hand,  is  a  complete  ring ;  the 


516 


HANDBOOK    OF    PHYSIOLOGY. 


back  part  of  the  ring  being  much  broader  than  the  front.  On  the  top  of  this 
broad  portion  of  the  cricoid  are  (c)  the  arytenoid  cartilages  (fig.  342,  7) ,  the 
connection  between  the  cricoid  below  and  arytenoid  cartilages  above  being  a  joint 
with  synovial  membrane   and  ligaments,  the  latter  permitting  tolerably  free 


Fig.  342. —Cartilages  of  the  larynx  seen  from  the  front.  1  to  4,  thyroid  cartilage;  1,  verti- 
cal ridge  or  pomuni  Adami ;  2,  right  ala:  .3,  superior,  and  4,  inferior  cornu  of  the  right  side;  5,  6, 
cricoid  cartilage;  5,  inside  of  the  posterior  part;  6,  antei-ior  narrow  part  of  the  ring;  7,  arytenoid 
cartilages.     X  M- 

motion  between  them.  But  although  the  arytenoid  cartilages  can  move  on  the 
cricoid,  they  of  course  accompany  the  latter  in  all  its  movements,  just  as  the 
head  may  nod  or  turn  on  the  top  of  the  spinal  column,  but  must  accompany 
it  in  all  its  movements  as  a  whole. 

Joints  and  Ligaments. — The  thyroid  cartilage  is  also  connected  with  the 
cricoid,  not  only  by  ligaments,  but  also  by  joints  with  synovial  membranes ; 
the  lower  corniia  of  the  thyroid  clasyjing,  or  nipping,  as  it  were,  the  cricoid 
between  them,  but  not  so  tightly  but  that  the  thyroid  can  revolve,    within  a 


Ijf^,  Ary.-ep%Iott. 


Caiti  Wrisberg'ii 
Cart,  Santorinl 


Cart,  an'ten. 
True.  lauscnl. 

TUg.  erico-aiyten. 
Efg,  cfiffltof-crico.  post,  "sup.. 

Cornuinfer. 

Hgj,  carafcsaicoyjost.jnt. 


Cart,  traciiero 


--  Tars  mcmbraa. 


t«^^^ 


Fig.  343.— The  larynx  as  seen  from  behind  after  removal  of  the  muscles.    The  cartilages  and  lig- 
aments only  renaain.     (Stoerk.) 


certain  range,  around  an  axis  passing  transversely  through  the  two  joints  at 
which  the  cricoid  is  clasped.  The  vocal  cords  are  attached  (behind)  to  the 
front  portion  of  the  base  of  the  arytenoid  cartilages,  and  (in  front)  to  the 
re-entering  angle  at  the  back  part  of  the  thyroid  ;  it  is  evident,  therefore,  that  all 


THE    PRODUCTION    OF    THE    VOICE. 


ol7 


movements  of  either  of  these  cartilages  must  produce  an  effect  on  them  of 
some  kind  or  other.  Inasmuch,  too,  as  the  arytenoid  cartilages  rest  on  the 
top  of  the  back  portion  of  the  cricoid  cartilage,  and  are  connected  with  it  by 
capsular  and  other  ligaments,  all  movements  of  the  cricoid  cartilage  must 
move  the  arytenoid  cartilages,  and  also  produce  an  effect  on  the  vocal  cords. 

Intrinsic  31uscles. — The  intrinsic  muscles  of  the  laiynx  are  so  connected 
with  the  laryngeal  cartilages  that  by  their  contraction  alterations  in  the  con- 
dition of  the  vocal  cords  and  glottis  are  produced.  They  are  usually  divided 
into  four  classes  according  to  their  action,  viz.,  into  abductors,  adductors, 
sphinctevs,  and  tensors.  The  Abductors,  the  crico-arytenoidei,  widen  the  glottis, 
by  separating  the  cords ;  the  Adductors,  consisting  of  the  thyro-ary-epiglottici, 
the  arytenoideus posticus  sen  transversus,  the  thyro-arytenoidei  externi,  t\ie  crico- 
arytenoidei  laterales,  and  the  thyro-arytenoidei  interni,  approximate  the  vocal 
cords,  diminish  the  rima  glottidis,  and  act  generally  as  Sphincters  and  sup- 
porters of  the  glottis.  Finally,  the  Tensors  of  the  cords  put  the  cords  on  the 
stretch,  with  or  without  elongating  them  ;  the  tensors  are  the  crico-thyroidei 
and  the  thyro-arytenoidei  interni. 

The  attachments  and  the  action  of  the  muscles  will  be  readily  understood 
from  the  following  table.  All  the  muscles  are  in  pairs  excej^t  the  arytenoideus 
posticus. 

Table  of  the  several  Groups   op  the  Intrinsic  Muscles   of  the   Larynx 
and  their  attachments. 


Group. 

Muscle.                                 Attachments. 

Action. 

I. 
Abductors. 

Crico-aryte- 
noidei pos- 
tici. 

This    pair    of    muscles    arises,     on 
either  side,    from   the    posterior 
surface  of  the  corresponding  half 
of  the  cricoid    cartilage.     From 
this    depression  their  fibres  con- 
verge on  either  side  upward   and 
outward  to    be  inserted    into  the 
outer  angle  of   the  base   of    the 
arytenoid    cartilages  behind   the 
crico-arytenoid  laterales. 

Draw  inward  and 
backward  the 
outer  angle  o  f 
arytenoid  carti- 
lages, and  so  ro- 
tate out  w  a  r  d 
the  processus  vo- 
calis  and  widen 
the  glottis. 

II.  and  III. 
Adductors 

and 
Sphincters. 

In  three  lay- 
ers : 

(a)        Outer 
layer,  Thy- 
r o - ar y  - 
e  p  i  g  1  ot- 
tici. 

A  pair  of  muscles.      Flat  and   nar- 
row, which  arise   on  either  side 
from  the  processus  muscularis  of 
the  arytenoid  cartilage,  then  pass- 
ing   vipward    and    inward    cross 
one  another  in  the  middle  line  to 
be  inserted  into  the  upper  half  of 
the  lateral  border  of  the  opposite 
arytenoid  cartilage  and  the  poste- 
rior   border  of    the    cartilage    of 
Santorini.     The    lower  fibres  run 
forward    and     downward    to    lie 
inserted  into  the    thj-roid    carti- 
lage  near  the  commissure.      The 
fibres  attached  to  the  cartilage  of 
Santorini  are   continvied  forward 
and  upward  into  the  ary-epiglot- 
tic  fold. 

Help  to  narrow  or 
close  the  rima 
glottidis. 

518 


HANDBOOK    OF    PHYSIOLOGY. 


Group. 


II.  and  III. 

Adductors 

and 
Sphincters. 

— continued. 


Muscle. 


(b)  3fiddle 
layer. 

i.  Aryte- 
noid e  us 
posticus. 


ii.  Thyro- 
aryteno  i  - 
d  e  i  e  X  - 
terni. 


ATTACHMENT.S. 


A  single  muscle.  Half-q  u  a  d  r  i- 
lateral,  attached  to  tlie  borders 
of  the  arytenoid  cartilages,  its 
fibres  running  horizontally  be- 
tween the  two. 


Draws  together  the 
arytenoid  carti- 
lages and  also  de- 
presses them. 
When  the  mus- 
cle is  paralj'zed, 
the  inter- carti- 
laginous pa-rt  of 
the  cords  cannot 
come  together. 


A  pair  of  muscles.  Each  of  which 
consists  of  three  chief  portions 
— lower,  middle,  and  upper 
The  lower  and  principal  fibres 
may  be  further  divided  into  two 
layers,  internal  and  external. 
These  fibres  arise  side  by  side 
from  the  lower  half  of  the  inter- 
nal surface  of  the  thyroid  carti- 
lage, close  to  the  angle,  and  from 
the  fibrous  expansion  of  the  crico- 
thyroid ligament,  and  are  insert- 
ed into  the  lateral  border  of  the 
arytenoid  cartilage.  The  inner 
fibres  run  horizontally,  to  be  at- 
tached to  the  lower  half  of  this 
border,  and  the  outer  fibres  pass 
obliquely  ovitwai'd  to  be  inserted 
into  the  upper  half,  while  some 
pass  to  the  cartilage  of  Wrisbvirg 
and  the  ary -epiglottic  fold. 


111.  Crico-  A  pair  of  muscles.  They  arise  on 
aryteno  i  -'  either  side  from  the  middle  third 
of  the  upper  border  of  the  cricoid 
cartilage  and  are  inserted  into  the 
whole  anterior  margin  of  the  base 
of  the  arytenoid  cartilage.  Some 
of  their  fibres  join  the  thyroid- 
ary-epiglottici. 


dei    later- 
ales. 


(c)  Inner- 
most lay 
er,  Thyro- 
ar  ytenoi- 
dei  i  n - 
terni. 


Approximate  the 
vocal  cords 
by  drawing  the 
processus  mus- 
cularis  of  the 
arytenoid  carti- 
lages forward 
and  downward 
and  so  rotate  the 
processus  vocalis 
inward. 


A  pair  of  muscles.  They  arise  on  Render  the  vocal 
either  side,  internally  from  the  cords  tense  and 
angle  of  the  thyroid  cartilage,  i  rotate  the  aryte- 
internal  to  the  last  described;  noid  cai'tilages 
muscle  (  (b),  iii.),  and  running  and  approximate 
parallel  to  and  in  the  substance  of  the  processus 
the  vocal  cords  are  attached  pos-  vocalis. 
teriorly  to  the  processus  vocalis 
along  their  whole  length  and  to 
the  adjacent  part  of  the  outer 
surface  of  the  arytenoid  carti- 
lages. 


THE    PRODUCTION    OF   THE    VOICE. 


519 


Group. 


IV. 
Tensors. 


MUSCL~. 


Crico  - 1  h  y- 
roidei. 


Attachments. 


A  pair  of  fan-shaped  muscles  at- 
tached on  either  side  to  the  cricoid 
cartilage  below  ;  from  the  mesial 
line  in  front  for  nearly  one-half  of 
its  lateral  circumference  back- 
ward the  fibi-es  pass  upward  and 
outward  to  be  attached  to  the  low- 
er border  of  the  thyroid  cartilage 
and  to  the  front  border  of  its 
lower  cornea, 


Action. 


Thyro  -  ary- 
teno  i  d  e  i 
interni. 


The  most  posterior  part  is  almost 
a  distinct  muscle  and  its  fibres 
are  all  but  horizontal :  some- 
times this  muscle  is  described  as 
consisting  of  two  layers,  super- 
ficial with  cortical  fibres,  deep 
with  oblique  fibres,  described 
under  Group  III. 


The  thyroid  carti- 
lage being  fixed 
by  its  extrinsic 
muscles,  the 
front  of  the  cri- 
coid cartilage  is 
drawn  upward, 
and  its  back, 
with  the  aryte- 
noids attached, 
is  drawn  down. 
Hence  the  vocal 
cords  are  elon- 
gated a  n  t  e  r  o  - 
posteriorly  and 
put  upon  the 
stretch.  Paral- 
ysis of  these 
muscles  causes 
an  inability  to 
produce  high 
notes. 


Described  above. 


Nerve  Supply.  —In  the  performance  of  the  functions  of  the  larynx  the  sensory 
filaments  of  the  superior  laryngeal  branch  of  the  vagus  supply  that  acute  sen- 
sibility by  which  the  glottis  is  guarded  against  the  ingress  of  foreign  bodies,  or 
of  irrespirable  gases.  The  contact  of  these  stimulates  the  nerve  filaments ; 
and  the  impression  conveyed  to  the  medulla  oblongata,  whether  it  produce 
sensation  or  not,  is  reflected  to  the  filaments  of  the  recurrent  or  inferior  laryngeal 
branch,  and  excites  contraction  of  the  muscles  that  close  the  glottis.  Both  these 
branches  of  the  vagi  co-operate  also  in  the  production  and  regulation  of  the 
voice ;  the  inferior  laryngeal  determining  the  contraction  of  the  muscles  that 
vary  the  tension  of  the  vocal  cords,  and  the  superior  laryngeal  conveying  to 
the  mind  the  sensation  of  the  state  of  tliese  muscles  necessary  for  their  contin- 
uous guidance.  And  both  the  branches  co-operate  in  the  actions  of  the  larynx 
in  the  ordinary  slight  dilatation  and  contraction  of  the  glottis  in  the  acts  of 
expiration  and  inspiration,  and  more  evidently  in  those  of  coughing  and  other 
forcible  respiratory  movements. 

The  laryngoscope  is  an  instrument  emploj^ed  in  investigating  during  life  the 
condition  of  the  pharynx,  larynx,  and  trachea.  It  consists  of  a  large  concave 
mirror  with  perforated  centre  and  of  a  smaller  mirror  fixed  in  a  long  handle. 
It  is  thus  used  :  the  patient  is  placed  in  a  chair,  a  good  light  (argand  burner,  or 
lamp)  is  arranged  on  one  side  of,  and  a  little  above  his  head.  The  operator 
fixes  the  large  mirror  round  his  head  in  such  a  manner,  that  he  looks  through 


520 


HANDBOOK    OF    PHYSIOLOGY. 


the  central  aperture  with  one  eye.  He  then  seats  himself  opposite  tlie  patient, 
and  so  alters  the  position  of  the  mirror,  which  is  for  this  purpose  provided 
with  a  ball  and  socket  joint,  that  a  beam  of  light  is  reflected  on  the  lips  of  the 
patient. 

The  patient  is  now  directed  to  throw  his  head  slightly  backward,  and  to 
open  his  mouth ;  the  reflection  from  the  mirror  lights  up  the  cavity  of  the 
mouth,  and  by  a  little  alteration  of  the  distance  between  the  operator  and  the 
patient  the  point  at  which  the  greatest  amount  of  light  is  reflected  by  the 
mirror — in  other  words  its  focal  length — is  readily  discovered.  The  small 
mirror  fixed  in  the  handle  is  then  warmed,  either  by  holding  it  over  the  lamp, 
or  by  putting  it  into  a  vessel  of  warm  water ;  this  is  necessary  to  prevent  the 
condensation  of  breath  upon  its  surface.     The  degree  of  heat  is  regulated  by 


ligiBxy  epigloto       - 


Cal•t^'^Vrisbel•gii4- 
Cart.  SanloTini 


ffli  CxicD-aryteflOid.  Tfost,  * 

C'omu  inferior 
Xig.  cerato-cric. 

■Ears-  post.  Inf.  membi-ant  f 

lEars.  cartUag.  '    „  ^ 

WSuB 


Fig.  344.— Tiie  larynx  as  seen  from  behind.    To  show  the  intrinsic  muscles  posteriorly.    (Stoerk.) 


applying  the  back  of  the  mirror  to  the  hand  or  cheek,  when  it  should  feel  warm 
without  being  painful. 

After  these  preliminaries  the  patient  is  directed  to  put  out  his  tongue,  which 
is  held  by  the  left  hand  gently  but  firmly  against  the  lower  teeth  by  means  of 
a  handkerchief.  The  warm  mirror  is  passed  to  the  back  of  the  mouth,  until 
it  rests  upon  and  slightly  raises  the  base  of  the  uvula,  and  at  the  same  time 
the  light  is  directed  upon  it :  an  inverted  image  of  the  larynx  and  trachea 
will  be  seen  in  the  mirror.  If  the  dorsum  of  the  tongue  be  alone  seen,  the 
handle  of  the  mirror  must  be  slightly  lowered  vmtil  the  larynx  comes  into 
view ;  care  should  be  taken,  however,  not  to  move  the  mirror  upon  the  uvula, 
as  it  excites  retching.  The  observation  should  not  be  prolonged,  but  should 
rather  be  repeated  at  short  intervals. 

The  structures  seen  will  vary  somewhat  according  to  the  condition  of  the 
parts  as  to  inspiration,  expiration,  phonation,  etc.  ;  they  are  (figs.  347)  first, 
and  apparently  at  the  posterior  part,  the  base  of  the  tongue,  immediately  below 
which  is  the  accurate  outline  of  the  epiglottis,  with  its  cushion  or  tubercle. 
Then  are  seen  in  the  central  line  the  true  vocal  cords,  white  and  shining  in  their 
normal  condition.     The  cords  approximate  (in  the  inverted  image)  posteriorly ; 


THE    PRODUCTION    OF   THE    VOICE. 


521 


between  them  is  left  a  chink,  narrow  while  a  high  note  is  being  sung,  wide 
during  a  deep  inspiration.  On  each  side  of  the  true  vocal  cords,  and  on  a 
higher  level,    are  the  pink  false  vocal  cords.     Still  more  externally  than  the 


Fig.  345. 


parts  of  the  Laryngoscope. 


false  vocal  cords  is  the  aryteno-epigJottidean  fold,  in  which  are  situated  upon 
■each  side  three  small  elevations :  of  these  the  most  external  is  the  cartilage  of 
Wrisherg,  the  intermediate  is  the  cartilage  of  Santori)ii,  while  the  summit  of 
the  arytenoid  cartilage  is  in  front,  and  somewhat  below  the  preceding,  being 


Fig.  346.  —To  show  the  position  of  the  operator  and  patient  when  using  the  Laryngoscope. 

only  seen  during  deep  inspiration.  The  rings  of  the  trachea,  and  even  the 
bifurcation  of  the  trachea  itself,  if  the  patient  be  directed  to  draw  a  deep  breath, 
may  be  seen  in  the  interval  between  the  true  vocal  cords. 


522 


HAXDBOOK    OF    rHYSIOLOGY. 


Movements  of  the  Vocal  Cords. 

In  Bespiration. — The  position  of  the  vocal  cords  in  ordinary  tran- 
quil breathing  is  so  adapted  by  the  muscles,  that  the  opening  of  the 
glottis  is  wide  and  triangular  (fig.  347,  b)  becoming  a  little  wider  at 


Fig.  347. — Three  laryngoscopic  views  of  the  superior  aperture  of  the  larynx  and  surrounding 
parts.  A,  the  glottis  during  the  emission  of  a  high  note  in  singing;  B,  in  easy  and  quiet  inha- 
lation of  air;  C,  in  the  state  of  the  widest  possible  dilatation,  as  in  inhaling  a  very  deep  breath. 
The  diagrams  A',  B',  and  C,  show  in  horizontal  sections  of  the  glottis  the  position  of  the  vocal 
ligaments  and  arytenoid  cartilages  in  the  three  several  states  represented  in  the  other  figures. 
In  all  the  figm-es,  so  far  as  marked,  the  letters  indicate  the  parts  as  follows,  viz. :  /,  the  base  of 
the  tongue;  e,  the  upper  free  part  of  the  epiglottis;  e'.  the  tubercle  or  cushion  of  the  epiglottis; 
ph,  part  of  the  anterior  wall  of  the  pharynx  behind  the  larynx ;  in  the  margin  of  the  aryteno- 
epiglottidean  fold  iv.  the  swelling  of  the  membrane  caused  by  the  cartilages  of  Wrisberg;  s,  that 
of  the  cartilages  of  Santorini ;  a.  the  tip  or  summit  of  the  "arytenoid  cartilages;  c  r,  the  true 
vocal  cords  or  lips  of  the  rima  glottidis;  c  v  s,  the  superior  or  "false  vocal  cords;  between  them 
the  ventricle  of  the  larynx ;  in  C,  tr  is  placed  on  the  anterior  wall  of  the  receding  trachea, 
and  b  indicates  the  commencement  of  the  two  bronchi  bevond  the  bifurcation  which  may  be 
brought  into  view  in  this  state  of  extreme  dilatation.     (Quain  after  Czermak.) 

each  inspiration,  and  a  little  narrower  at  each  expiration.  On  making 
a  rapid  and  deep  inspiration  the  opening  of  the  glottis  is  widely  dilated 
(fig.  347,  c),  and  somewhat  lozenge-shaped. 

In  Vocalization. — At  the  moment  of  the  emission  of  a  note,  it  is  nar- 
rowed, the  margins  of  the  arytenoid  cartilages  being  brought  into  contact 
and  the  edges  of  the  vocal  cords  approximated  and  made  parallel,  at 
the  same  time  that  their  tension  is  much  increased.  The  higher  the  note 
produced,  the  tenser  do  the  cords  become  (fig.  347,  a);  and  the  range  of 


THE    PRODUCTION    OF   THE    VOICE.  523 

a  voice  dei:)encls,  of  course,  in  the  main,  on  the  extent  to  whicli  the 
degree  of  tension  of  the  vocal  cords  can  be  thus  altered.  In  the  produc- 
tion of  a  high  note  the  vocal  cords  are  brought  well  within  sight,  so  as 
to  be  plainly  visible  with  the  help  of  the  laryngoscope.  In  the  utter- 
ance of  grave  tones,  on  the  other  hand,  the  epiglottis  is  depressed  and 
brought  over  them,  and  the  arytenoid  cartilages  look  as  if  they  were 
trying  to  hide  themselves  under  it  (fig.  34:8).     The  epiglottis,  by  being 


Fig.  348.  —View  of  the  upper  part  of  the  larvnx  as  seen  by  means  of  the  laryngoscope  during 
the  utterance  of  a  grave  note,  c,  Epiglottis:  s",  tubercles  of  the  cartilages  of  Santorini ;  a,  aryt- 
enoid cartilages;  2,  base  of  the  tongue;  ph.the  posterior  wall  of  the  pharynx.     (Czermak.) 

somewhat  pressed  down  so  as  to  cover  the  superior  cavity  of  the  larynx, 
serves  to  render  the  notes  deeper  in  tone  and  at  the  same  time  somewhat 
duller,  just  as  covering  the  end  of  a  short  tube  placed  in  front  of 
caoutchouc  tongues  lowers  the  tone.  In  no  other  respect  does  the 
epiglottis  appear  to  have_any  effect  in  modifying  the  vocal  sounds. 

The  degree  of  approximation  of  the  vocal  cords  also  usually  corre- 
sponds with  the  height  of  the  note  produced ;  but  probably  not  always, 
for  the  width  of  the  aperture  has  no  essential  influence  on  the  height  of 
the  note,  as  long  as  the  vocal  cords  have  the  same  tension :  only  with  a 
wide  aperture  the  tone  is  more  difficult  to  produce  and  is  less  perfect, 
^the  rushing  of  the  air  through  the  aperture  being  heard  at  the  same 
time. 

No  true  vocal  sound  is  produced  at  the  posterior  part  of  the  aperture 
of  the  glottis,  that,  viz.,  which  is  formed  by  the  space  between  the 
arytenoid  cartilages.  For  if  the  arytenoid  cartilages  be  approximated 
in  such  a  manner  that  their  anterior  processes  touch  each  other,  but  yet 
leave  an  opening  behind  them  as  well  as  in  front,  no  second  vocal  tone 
is  produced  by  the  passage  of  the  air  through  the  posterior  opening,  but 
merely  a  rustling  or  bubbling  sound ;  and  the  height  or  pitch  of  the 
note  produced  is  the  same  whether  the  posterior  part  of  the  glottis  be 
open  or  not. 

The  Voice  in  Singing  and  Speaking. 

Varieties  of  Vocal  Sounds. — The  laryngeal  notes  may  observe  three 
different  kinds  x)f  sequence.  The  first  is  the  monotonous,  in  which  the- 
notes  have  nearly  all  the  same  pitch  as  in  ordinary  speaking;  the 
variety  of  the  sounds  of  speech  being  due  to  articulation  in  the  mouth. 


524  HANDBOOK    OF    PHYSIOLOGY. 

In  speaking,  however,  occasional  syllables  generally  receive  a  higher 
intonation  for  the  siike  of  accent.  The  second  mode  of  sequence  is  the 
successive  transition  from  high  to  low  notes,  and  vice  versa,  without 
intervals;  such  as  is  heard  in  the  sounds,  which,  as  expressions  of  pas- 
sion, accompany  crying  in  men,  and  in  the  howling  and  whining  of 
dogs.  The  third  mode  of  sequence  of  the  vocal  sounds  is  the  musical, 
in  which  each  sound  has  a  determinate  number  of  vibrations,  and  the 
numbers  of  the  vibrations  in  the  successive  sounds  have  the  same  relative 
proportions  that  characterize  the  notes  of  the  musical  scale. 

In  different  individuals  this  comprehends  one,  two,  or  three  octaves. 
In  singers — 'that  is,  in  persons  apt  for  singing — it  extends  to  two  or 
three  octaves.  But  the  male  and  female  voices  commence  and  end  at 
•different  points  of  the  musical  scale.  The  lowest  note  of  the  female 
voice  is  about  an  octave  higher  than  the  lowest  of  the  male  voice;  the 
highest  note  of  the  female  voice  about  an  octave  higher  than  the  highest 
•of  the  male.  The  compass  of  the  male  and  female  voices  taken  together, 
or  the  entire  scale  of  the  human  voice,  includes  about  four  octaves. 
The  principal  difference  between  the  male  and  female  voice  is,  therefore, 
in  their  2^ itch;  but  they  are  also  distinguished  by  their  tone, — the  male 
voice  is  not  so  soft.  The  voice  presents  other  varieties  besides  that  of 
male  and  female;  there  are  two  kinds  of  male  voice,  technically  called 
the  bafis  and  tenor,  and  two  kinds  of  female  voice,  the  contralto  and 
soprano,  all  differing  from  each  other  in  tone.  The  bass  voice  usually 
reaches  lower  than  the  tenor,  and  its  strength  lies  in  the  low  notes; 
while  the  tenor  voice  extends  higher  than  the  bass.  The  contralto 
voice  has  generally  lower  notes  than  the  soprano,  and  is  strongest  in  the 
lower  notes  of  the  female  voice;  while  the  soprano  voice  reaches  higlier 
in  the  scale.  But  the  difference  of  compass,  and  of  power  in  different 
parts  of  the  scale,  is  not  the  essential  distinction  between  the  different 
voices;  for  bass  singers  can  sometimes  go  very  high,  and  the  contralto 
frequently  sings  the  high  notes  like  soprano  singers.  The  essential 
difference  between  the  base  and  tenor  voices,  and  between  the  contralto 
and  soprano,  consists  in  their  tone  or  timhre,  which  distinguishes  them 
even  when  they  are  singing  the  same  note.  The  qualities  of  the  bary- 
tone and  mezzo-soprano  voices  are  less  marked;  the  Jr/rt/^owe  being  in- 
termediate between  the  bass  and  tenor,  the  mezzo-soprano  between  the 
contralto  and  soprano.  They  have  also  a  middle  position  as  to  pitch  in 
the  scale  of  the  male  and  female  voices. 

The  differences  in  the  pitch  of  the  male  and  the  female  voices 
depends  on  the  different  length  of  the  vocal  cords  in  the  two  sexes; 
their  relative  length  in  men  and  women  being  as  three  to  two.  The 
difference  of  the  two  voices  in  tone  or  timbre,  is  owing  to  the  different 
nature  a7id  form  of  the  resounding  walls,  which  in   the  male  larynx   are 


THE    PKODUCTIOX    OF    THE    VOICE.  525 

much  more  extensive,  aud  form  a  more  acute  angle  anteriorly.  The 
different  qualities  of  the  tenor  and  bass,  and  of  the  alto  and  soprano 
voices,  probably  dej)end  on  some  peculiarities  of  the  ligaments,  and  the 
membranous  and  cartilaginous  parietes  of  the  laryngeal  cavity,,  which 
are  not  at  jn'esent  understood,  but  of  which  we  may  form  some  idea,, 
by  recollecting  that  musical  instruments  made  of  different  materials, 
e.g.,  metallic  and  gut-strings,  may  be  tuned  to  the  same  note,  but  that 
each  w.'ll  give  it  with  a  peculiar  tone  or  tinihre. 

The  boy's  larynx  resembles  the  female  larynx;  their  vocal  cords 
before  puberty  are  not  two-thirds  the  length  of  the  adult  cords;  and 
the  angle  of  their  thyroid  cartilage  is  as  little  prominent  as  in  the 
female  larynx.  Boys'  voices  are  alto  aud  soprano,  resembling  in  pitch 
those  of  women,  but  louder,  aud  differing  somewhat  from  them  in  tone. 
But,  after  the  larynx  has  undergone  the  change  produced  during  the 
period  of  development  at  puberty,  the  boy's  voice  becomes  bass  or  tenor. 
AVhile  the  change  of  form  is  taking  place,  the  voice  is  said  to  crack;  it- 
becomes  imperfect,  frequently  hoarse  and  crowing,  and  is  unfitted  for 
singing  until  the  new  tones  are  brought  under  command  by  practice. 
In  eunuchs,  who  have  been  deprived  of  the  testes  before  puberty,  the  voice 
does  not  undergo  this  change.  The  voice  of  most  old  people  is  deficient 
in  tone,  unsteady,  and  .more  restricted  in  extent:  the  first  defect  is- 
owing  to  the  ossification  of  the  cartilages  of  the  larynx  and  the  altered 
condition  of  the  vocal  cords ;  the  want  of  steadiness  arises  from  the  loss  of 
nervous  power  and  command  over  the  muscles ;  the  result  of  which  is 
here,  as  in  other  parts,  a  tremulous  movement.  These  two  causes  com- 
bined render  the  voices  of  old  people  void  of  tone,  unsteady,  bleating, 
and  weak. 

In  any  class  of  persons  arranged,  as  in  an  orchestra,  acording  to  the 
character  of  voices,  each  would  possess,  with  the  general  characteristics 
of  a  bass,  or  tenor,  or  any  other  kind  of  voice,  some  peculiar  character 
by  which  his  voice  would  be  recognized  from  all  the  rest.  The  condi- 
tions that  determine  these  distinctions  are,  however,  quite  unknown. 
They  are  probably  inherent  in  the  tissues  of  the  larynx,  and  are  as 
indiscernible  as  the  minute  differences  that  characterize  men's  features; 
one  often  observes,  in  like  manner,  hereditary  and  family  peculiarities 
of  voice,  as  well  marked  as  those  of  the  limbs  or  face. 

Most  persons,  particularly  men,  have  the  power,  if  at  all  capable  of 
singing,  of  modulating  their  voices  through  a  double  series  of  notes  of 
different  character:  namely,  the  notes  of  the  natural  voice,  or  chest- 
notes,  and  the  falsetto  notes.  The  natural  voice,  which  alone  has  been 
hitherto  considered,  is  fuller,  and  excites  a  distinct  sensation  of  much 
stronger  vibration  and  resonance  than  the  falsetto  voice,  which  has 
more  a  flute-like  character.     The  deeper  notes  of  the   male  voice   can 


526  UANDBOOK    OF    I'lIYSIOLOGY. 

be  produced  ouly  with  the  natural  voice,  the  highest  witli  the  falsetto 
only;  the  notes  of  middle  pitch  can  be  jiroduced  either  with  the  natural 
or  falsetto  voice;  the  two  registers  of  the  voice  are  therefore  not  limited 
in  such  a  manner  as  that  one  ends  when  the  other  begins,  but  they  run 
in  part  side  by  side. 

The  natural  or  chest-notes  are,  as  we  have  seen,  produced  by  the  or- 
dinary vibrations  of  the  vocal  cords.  The  mode  of  j)roduction  of  the 
falsetto  notes  is  still  obscure. 

By  Miiller  they  were  thought  to  be  due  to  vibrations  of  only  the  inner 
borders  of  the  vocal  cords.  In  the  opinion  of  Petrequin  and  Diday,  they 
do  not  result  from  vibrations  of  the  vocal  cords  at  all,  but  from  vibra- 
tions of  the  air  j^assing  through  the  aperture  of  the  glottis,  which  they 
believe  assumes,  at  such  times,  the  contour  of  the  emhouchure  of  a  flute. 
Others,  considering  some  degree  of  similarity  which  exists  between  the 
falsetto  notes  and  the  peculiar  tones  called  harmonic,  which  are  pro- 
duced when,  by  touching  or  stopping  a  harp-string  at  a  particular  point, 
only  a  portion  of  its  length  is  allowed  to  vibrate,  have  supposed  that,  in 
the  falsetto  notes,  j)ortions  of  the  cords  are  thus  isolated,  and  made  to 
vibrate  while  the  rest  are  held  still.  The  question  cannot  yet  be  settled; 
but  any  one  in  the  habit  of  singing  may  assure  himself,  both  by  the 
difficulty  of  passing  smoothly  from  one  set  of  notes  to  the  other,  and  by 
the  necessity  of  exercising  himself  in  both  registers,  lest  he  should 
become  very  deficient  in  one,  that  there  must  be  some  great  difference 
in  the  modes  in  which  their  respective  notes  are  produced. 

The  intcli  of  the  note.,  which  depends  upon  the  rajoidity  of  the  vibra- 
tions, is  altered  by  alterations  of  the  vocal  cords,  and  so  the  strength  of 
the  voice  is  in  proportion  {a)  to  the  degree  to  which  the  vocal  cords  can 
be  made  to  vibrate;  and  partly  {b)  to  the  fitness  for  resonance  of  the 
membranes  and  cartilages  of  the  larynx,  of  the  parietes  of  the  thorax, 
lungs,  and  cavities  of  the  mouth,  nostrils,  and  communicating  sinuses. 
It  is  diminished  by  anything  which  interferes  with  such  capability  of 
vibration. 

The  intensity  or  loudness  of  a  given  note  with  maintenance  of  the 
same  pitch,  cannot  be  rendered  greater  by  merely  increasing  the  force 
of  the  current  of  air  through  the  glottis;  for  increase  of  the  force  of  the 
current  of  air,  coeter is  paribus^  raises  the  pitch  both  of  the  natural  and 
the  falsetto  notes.  Yet,  since  a  singer  possesses  the  power  of  increasing 
the  loudness  of  a  note  from  the  faintest  ])iano  to  fortissimo  without  its 
pitch  being  altered,  there  must  be  some  means  of  compensating  the 
tendency  of  the  vocal  cords  to  emit  a  higher  note  when  the  force  of  the 
current  of  air  is  increased.  This  means  evidently  consists  in  modify- 
ing the  tension  of  the  vocal  cords.  When  a  note  is  rendered  louder 
and  more  intense,  the  vocai  cords  must  be  relaxed  by  remission  of  the 


THE    PRODUCTIOX    OF    THE    VOICE.  527 

muscular  action,  in  propoi'tion  as  the  force  of  the  current  of  the  breath 
through  the  glottis  is  increased.  When  a  note  is  rendered  fainter,  the 
reverse  of  this  must  occur. 

The  arches  of  the  palate  and  the  uvula  become  contracted  during  the 
formation  of  the  higher  notes;  but  their  contraction  is  the  same  for  a 
note  of  given  height,  whether  it  be  falsetto  or  not;  and  in  either  case 
the  arches  of  the  palate  may  be  touched  with  the  finger,  without  the 
note  being  altered.  Their  action,  therefore,  in  the  production  of  the 
higher  notes  seems  to  be  merely  the  result  of  involuntary  associate  ner- 
vous action,  excited  by  the  voluntarily  increased  exertion  of  the  muscles 
of  the  larynx.  If  the  palatine  arches  contribute  at  all  to  the  production 
of  the  higher  notes  of  the  natural  voice  and  the  falsetto,  it  can  only  be 
by  their  increased  tension  strengthening  the  resonance. 

The  office  of  the  ventricles  of  the  larynx  is  evidently  to  afford  a  free 
space  for  the  vibrations  of  the  lips  of  the  glottis;  they  may  be  com- 
pared with  the  cavity  at  the  commencement  of  the  mouthpiece  of  trum- 
pets, which  allows  the  free  vibration  of  the  lips. 

Speech. — Besides  the  musical  tones  formed  in  the  larynx,  a  great 
number  of  other  sounds  can  be  produced  in  the  vocal  tubes,  between 
the  glottis  and  the  external  apertures  of  the  air-passages,  the  combination 
of  which  sounds  by  the  agency  of  the  cerebrum  into  different  groups 
to  designate  objects,  properties,  actions,  etc.,  constitutes  language.  The 
languages  do  not  employ  all  the  sounds  which  can  be  produced  in  this 
manner,  the  combination  of  some  with  others  being  often  difficult. 
Those  sounds  which  are  easy  of  combination  enter,  for  the  most  part, 
into  the  formation  of  the  greater  number  of  languages.  Each  language 
contains  a  certain  number  of  such  sounds,  but  in  no  one  are  all  brought 
together.  On  the  contrary,  different  languages  are  characterized  by  the 
prevalence  in  them  of  certain  classes  of  these  sounds,  while  others  are 
less  frequent  or  altogether  absent. 

Articulate  Sounds, — The  sounds  produced  in  speech,  or  the  articu- 
late sounds,  are  commonly  divided  into  vowels  and  consonants:  the  dis- 
tinction between  which  is,  that  the  sounds  for  the  former  are  generated 
by  the  larynx,  while  those  for  the  latter  are  produced  by  interruption 
of  the  Current  of  air  in  some  part  of  the  air-passages  above  the  larynx. 
The  term  consonant  has  been  given  to  these  because  several  of  them  are 
not  properly  sounded,  except  consonantly  with  a  vowel.  Thus,  if  it  be 
attempted  to  pronounce  aloud  the  consonants  b,  d,  and  g,  or  their  modi- 
fications, p,  t,  k,  the  intonation  only  follows  them  in  their  combination 
with  a  vowel.  To  recognize  the  essential  properties  of  the  articulate 
sounds,  it  is  necessary  first  to  examine  them  as  they  are  produced  in 
whispering,  and  then  investigate  which  of  them  can  also  be  uttered  in 
a  modified  character  conjoined  with  vocal  tone.      By  this  procedure  we 


528  HANDBOOK    OF    PHYSIOLOGY. 

lind  two  series  of  sounds:  in  one  the  sounds  are  mute,  and  cannot  be 
uttered  with  a  vocal  tone;  the  sounds  of  the  other  series  can  be  formed 
independent!}'  of  voice,  but  are  also  capable  of  being  uttered  in  con- 
junction with  it. 

All  the  vowels  can  be  expressed  in  a  whisper  without  vocal  tone,  that 
is,  mutely.  These  mute  vowel-sounds  differ,  however,  in  some  meas- 
ure, as  to  their  mode  of  production,  from  the  consonants.  All  the 
mute  consonants  are  formed  in  the  vocal  tube  above  the  glottis,  or  in 
the  cavity  of  the  mouth  or  nose,  by  the  mere  rushing  of  the  air  between 
the  surfaces  differently  modified  in  disposition.  But  the  sound  of  the 
vowels,  even  when  mute,  has  its  source  in  the  glottis,  though  its  vocal 
cords  are  not  thrown  into  the  vibrations  necessary  for  the  production  of 
voice ;  and  the  sound  seems  to  be  jiroduced  by  the  passage  of  the  current 
of  air  between  the  relaxed  vocal  cords.  The  same  vowel-sound  can  be  pro- 
duced in  the  larynx  when  the  mouth  is  closed,  the  nostrils  being  open^ 
and  the  utterance  of  all  vocal  tone  avoided.  The  sound,  when  the  mouth 
is  open,  is  so  modified  by  varied  forms  of  the  oral  cavity,  as  to  assume 
the  characters  of  the  vowels  a,  e,  i,  O,  u,  in  all  their  modifications. 
"  The  cavity  of  the  mouth  assumes  the  same  form  for  the  articulation 
of  each  of  the  mute  vowels  as  for  the  corresponding  vowel  when  vocal- 
ized; the  only  difference  in  the  two  cases  lies  in  the  kind  of  sound 
emitted  by  the  larynx.  It  has  been  pointed  out  that  the  conditions 
necessary  for  changing  one  and  the  same  sound  into  the  different  vowels, 
are  differences  in  the  size  of  two  parts — the  oral  canal  and  the  oral  open- 
ing; and  the  same  is  tlie  case  with  regard  to  the  mute  vowels.  By  oral 
canal,  is  meant  here  the  space  between  the  tongue  and  palate :  for  the 
pronunciation  of  certain  vowels  both  the  opening  of  the  mouth  and  the 
space  just  mentioned  are  widened;  for  the  pronunciation  of  other  vowels 
both  are  contracted ;  and  for  others  one  is  wide,  the  other  contracted. 
Admitting  five  degrees  of  size,  both  of  the  opening  of  the  mouth  and  of 
the  sjDace  between  the  tongue  and  palate,  Kempelen  thus  states  the 
dimensions  of  these  parts  for  the  following  vowel-sounds: — 

Size  of  oral  opening.  Size  of  oral  canal. 

5  ...  3 

4  ...  2 

3  ...  1 

2  ...  4 

1  ...  5 

Another  important  distinction  in  articulate  sounds  is,  that  the  utter- 
ance of  some  is  only  of  momentary  duration,  taking  place  during  a  sud- 
den change  in  the  conformation  of  the  mouth,  and  being  incapable  of 
prolongation  by  a  continued  expiration.  To  this  class  belong  b,  p,  d, 
and  the  hard  g.  In  the  utterance  of  other  consonants  the  sounds  may- 
be continuous;  they  may  be  prolonged,  ad  libitum,  as  long  as  a  particu- 
lar disposition  of  the  mouth  and  a  constant  expiration  are  maintained. 


Vowel. 

Sound. 

a     as 

in 

"  far" 

a        " 

"  name" 

e        " 

"  theme" 

o        " 

"  go" 

oo      " 

"  cool" 

THE    PRODUCTION    OF   THE    VOICE,  529 

Among  these  consonants  are  h,  m,  n,  f,  s,  r,  1.  Corresponding  differences 
in  respect  to  the  time  tliat  may  be  occupied  in  their  utterance  exist 
in  the  vowel  sounds,  and  princi})ally  constitute  the  differences  of  long 
and  short  syllables.  Thus  the  a  as  in  far  and  fate,  the  o  as  in  go  and 
fort,  may  be  indefinitely  prolonged;  but  the  same  vowels  (or  more 
properly  different  vowels  expressed  by  the  same  letters),  as  in  can  and 
fact,  in  dog  and  rotten,  cannot  be  prolonged. 

All  sounds  of  the  first  or  explosive  kind  are  insusceptible  of  com- 
bination with  vocal  tone  (intonation),  and  are  absolutely  mute;  nearly 
all  the  consonants  of  the  second  or  continuous  kind  may  be  attended 
with  intonation. 

Ventriloquism. — The  peculiarity  of  speaking,  to  which  the  term 
ventriloquism  is  applied,  appears  to  consist  merely  in  the  varied  modi- 
fication of  the  sounds  produced  in  the  larynx,  in  imitation  of  the  modi- 
fications which  voice  ordinarily  suffers  from  distance,  etc.  From  the 
observations  of  Miiller  and  Colombat,  it  seems  that  the  essential 
mechanical  parts  of  the  process  of  ventriloquism  consist  in  taking  a  full 
inspiration,  then  keeping  the  muscles  of  the  chest  and  neck  fixed,  and 
speaking  with  the  mouth  almost  closed,  and  the  lips  and  lower  jaw  as 
motionless  as  possible,  while  air  is  very  slowly  expired  through  a  very 
narrow  glottis ;  care  being  taken  also,  that  none  of  the  expired  air  passes 
through  the  nose.  But,  as  observed  by  Miiller,  much  of  the  ventrilo- 
quist's skill  in  imitating  the  voices  coming  from  particular  directions, 
consists  in  deceiving  other  senses  than  hearing.  We  never  distinguish 
very  readily  the  direction  in  which  sounds  reach  our  ear;  and,  when 
our  attention  is  directed  to  a  particular  point,  our  imagination  is  very 
apt  to  refer  to  that  point  whatever  sounds  we  may  hear. 

Action  of  the  Tongue  in  Speech. — The  tongue,  which  is  usually 
credited  with  the  power  of  speech — language  and  speech  being  often 
employed  as  synonymous  terms — -plays  only  a  subordinate,  although  very 
important  part.  This  is  well  shown  by  cases  In  which  nearly  the  whole 
organ  has  been  removed  on  account  of  disease.  Patients  who  recover 
from  this  operation  talk  imperfectly,  and  their  voice  is  considerably 
modified ;  but  the  loss  of  speech  is  confined  to  those  letters  in  the  pro- 
nunciation of  which  the  tongue  is  concerned. 

Stammering  depends  on  a  want  of  harmony  between  the  action  of 
the  muscles  (chiefly  abdominal)  which  expel  air  through  the  larynx,  and 
that  of  the  muscles  which  guard  the  orifice  (rima  glottidis)  by  Avhich  it 
escapes,  and  of  those  (of  tongue,  palate,  etc.)  which  modulate  the  sound 
to  the  form  of  speech. 

Over   either    of  the  groups  of  muscles,  by  itself,  a  stammerer  may 
have   as    much   power  as  other  people.     But  he  cannot  harmoniously 
.irrange  their  conjoint  actions. 
34 


CHAPTER  XVI 

THE    NERVOUS    SYSTEM. 

The  nervous  system  consists  of  the  following  parts:  firstly,  of  large 
masses  of  nervous  matter  situated  within  the  bony  cranium  and  spinal 
column,  and  constituting  the  brain  and  spinal  cord;  secondly,  of 
smaller  masses  of  nervous  matter,  situated  for  the  most  part  in  the 
abdominal  and  thoracic  cavities,  but  also  in  the  neck  and  head,  and 
constituting  what  are  known  as  sympathetic  ganglia;  thirdly,  of  cords 
of  nerve-fibres  which  connect  the  central  nervous  system  with  the 
periphery  and  with  the  so-called  sympathetic  ganglia,  which  are  not  in 
reality  a  system  independent  of  the  brain  and  cord  as  was  formerly 
taught,  but  are  really  part  and  parcel  of  the  same  system ;  and  fourthly, 
of  peripheral  organs  in  connection  with  the  beginnings  or  endings  of  the 
nerves  at  the  periphery  of  the  body. 

It  will  be  necessary  to  consider  these  several  parts  of  the  nervous  system 
seriatim;  it  will  be  most  useful  for  the  understanding  of  the  subject, 
however,  to  proceed  first  of  all  with  the  consideration  of  the  properties 
of  nerve-fibres,  as  this  forms  the  most  elementary  portion  of  the  subject. 

Nerve-fibres. — The  structure  of  the  ditferent  kinds  of  nerve-fibres 
has  been  already  dealt  with  (p.  89,  et  seg.) ;  their  function  remains  to  be 
considered  here. 

Function  of  Nerve -fibres. 

The  office  of  nerve-fibres  is  to  conduct  impressions.  From  the 
account  of  nervous  action  previously  given  (p.  447  et  seq.)  it  will  be 
readily  understood,  that  nerve-fibres  may  be  stimulated  to  act  by  any- 
thing which,  with  sufficient  suddenness,  increases  their  irritability;  but 
tljey  are  incapable  of  originating  of  themselves  the  condition  necessary 
for  the  manifestation  of  their  own  energy.  The  stimulus  produces  its 
effect  upon  the  termination  of  the  nerve  stimulated,  being  conducted  to 
it  by  the  nerve-fibre.  The  efl'ect  of  the  stimulus  upon  a  nerve  therefore 
depends  upon  the  nature  of  its  end-organ.  A  length  of  a  nerve  trunk 
when  freshly  removed  from  the  body,  if  stimulated  midway  between  its 
extremities,  will,  as  shown  by  the  deflection  of  the  needle  of  a  galvanometer' 
at  either  end,  conduct  the  electrical  impressions  in  either  direction,  and 
it  may  be  considered  therefore  only  an  accidental  circumstance  as  i1 
were,  whether  when  in  situ  it  has  conducted  impressions  to  the  central 


THE    NERVOUS    SYSTEM.  531 

nervous  system  from  the  periphery,  or  from  the  central  nervous  system 
to  the  muscles  or  other  tissues.  The  same  fibre  cannot  be  used  for  the 
one  purj)ose  at  one  time,  and  for  the  other  at  another,  simply  because  of 
the  nature  of  its  terminal  organs.  Thus,  when  a  cerebro-spinal  nerve- 
fibre  is  irritated  in  the  living  body  as  by  pinching,  or  by  heat,  or  by 
electrifying  it, there  is,  under  ordinary  circumstances,  one  of  two  effects, 
— either  there  is  pain,  or  there  is  twitching  of  one  or  more  muscles  to 
which  the  nerve  distributes  its  fibres.  From  various  considerations 
it  is  certain  that  pain  is  always  the  result  of  a  change  in  the  nerve- 
cells  of  the  brain.  Therefore,  in  such  an  experiment  as  that  referred 
to,  the  irritation  of  the  nerve-fibre  is  conducted  in  one  of  two  direc- 
tions, i.e.,  either  to  the  brain,  which  is  the  central  termination  of  the 
fibre,  when  there  is  pain, or  to  a  muscle,  which  is  the  peripheral  ter- 
mination, when  there  is  movement. 

The  effect  of  this  simple  experiment  is  a  type  of  what  always  occurs 
when  nerve-fibres  are  engaged  iir  the  performance  of  their  functions. 
The  result  of  stimulating  them,  which  roughly  imitates  what  happens 
naturally  in  the  body,  is  found  to  occur  at  one  or  other  of  their  ex- 
tremities, central  or  peripheral,  never  at  both;  and  in  accordance  with 
this  fact,  and  because,  for  any  given  nerve-fibre,  the  result  is  always  the 
same,  nerve-fibres  have  been  commonly  classed  as  sensory  or  motor. 

This  is  not  altogether  accurate,  and  the  terms  centrifugal  or  afferent 
and  centripetal  or  efferent  are  more  properly  used,  since  the  result  of 
stimulating  a  nerve  of  the  former  kind  is  not  always  the  production  of 
pain  or  other  form  of  sensation,  nor  is  motion  the  invariable  result  of 
stimulating  the  latter. 

The  term  intercentral  is  applied  to  those  nerve-fibres  which  connect 
more  or  less  distinct  nerve-centres,  and  may,  therefore,  be  said  to  have 
Tio  peripheral  distribution,  in  the  ordinary  sense  of  the  term. 

Impressions  made  upon  the  terminations  or  upon  the  trunk  of  a 
centripetal  nerve  may  cause  (a)  pain,  or  some  other  kind  of  sensation ;  {b) 
special  sensation;  or  (c)  reflex  action  of  some  kind;  or  {d)  inhibition, 
restraint  of  action.  Similarly  imiDressions  made  upon  a  centrif- 
ugal nerve  may  cause  {a)  contraction  of  muscle  (motor  nerve) ;  {b)  it 
may  influence  nutrition  (trophic  nerve) ;  or  (c)  may  influence  secretion 
(secretory  nerve) ;  or  [d)  inhibit,  augment,  or  stop  any  other  efferent 
action. 

It  is  a  law  of  action  in  all  nerve-fibres,  and  corresponds  with  the  con- 
tinuity and  simplicity  of  their  course,  that  an  impression  made  on 
any  fibre,  is  simply  and  uninterruptedly  transmitted  along  it,  without 
itself  being  imparted  or  diffused  to  any  of  the  fibres  lying  near  it.  It 
is  possible  that  the  mere  passage  of  a  nerve  impulse  along  a  nerve-fibre, 
Iiowever,   may  produce  some  effect  upon  the  neighboring  nerve-fibres. 


532  HANDBOOK    OF    PHYSIOLOGY. 

Their  adaptation  to  the  purpose  of  simple  conduction  is,  perhaps,  due 
to  the  contents  of  each  fibre  being  completely  isolated  from  those  of  ad- 
jacent fibres  by  the  myelin  sheath  in  which  each  is  inclosed,  and  which 
acts,  it  may  be  supposed,  just  as  silk,  or  other  non-conductors  of  elec- 
tricity do,  which,  when  covering-a  wire,  prevent  the  electric  condition 
of  the  wire  from  being  conducted  into  the  surrounding  medium. 

Velocity  of  a  Nervoiis  Iminihe. — The  change  which  a  stimulus  sets  up  in 
a  nerve,  of  the  exact  nature  of  which  we  are  unacquainted,  appears  to  travel 
along  a  nerve-fibre  in  both  directions  with  considerable  velocity  in  the 
form  of  a  wave.  Helmholtz  and  Baxt  have  estimated  the  average  rate 
of  conduction  in  human  motor  nerves  at  111  feet  (nearly  29  metres)  per 
second ;  this  result  agreeing  very  closely  with  that  previously  obtained. 
It  is  probably  rather  under  than  over  the  average  velocity.  Eutherford's 
observations  agree  with  those  of  Von  Wittich,  that  the  rate  of  transmis- 
sion in  sensory  nerves  is  about  140  feet  (42  metres)  per  second.  The 
velocity  of  the  nerve  impulse  in  motor  nerves  has  been  calculated  by  notic- 
ing the  duration  of  the  interval  between  two  contractions  of  the  same 
muscle  when  stimulated  by  means  of  two  pairs  of  electrodes,  one  placed 
behind  the  nerve  close  to  the  muscle,  and  the  second  placed  at  a  known 
distance  further  away  from  the  muscle.  The  contraction  ensues  when 
the  stimulus  is  applied  further  from  the  muscle  later  than  the  other 
case,  and  the  interval  between  the  two  contractions  is  occupied  by  the 
passage  of  the  impulse  down  the  nerve.  With  these  data  it  is  concluded 
that  the  velocity  of  the  passage  of  the  nerve  impulse  in  a  frog's  motor 
nerve  is  28  to  30  metres  per  second.  In  the  human  motor  nerve,  cal- 
culated by  applying  the  stimulus  through  the  skin  instead  of  directly 
to  the  nerve,  the  velocity  is  greater,  viz.,  about  33  to  50  metres  per 
second.  In  sensory  nerves  the  velocity  is  said  to  be  about  30  to  33 
metres  per  second.  Various  conditions  modify  the  rate  of  transmission, 
of  which  temperature  is  one  of  the  most  important,  a  very  low  or  a  very 
high  temperature  diminishing  it ;  fatigue  of  the  nerve  acting  in  the 
same  direction,  but  increase  of  the  stimulus  up  to  a  certain  point  increas' 
ing  it,  as  does  also  the  catelectrotonic  condition  of  the  nerve. 

Tlie  Gerehro-Sjjinal  Nervous  System, — The  parts  of  which  this  sys- 
tem is  composed  are  the  following:  {a)  the  spinal  cord  and  its  nerves; 
(J)  the  brain  made  up  of  cerebrum,  crura  cerebri  and  the  ganglia  in  con- 
nection with  them,  pons  varolii,  cerebellum,  and  the  medulla  oblongata 
or  bulb  which  connects  the  upper  parts  of  the  system  with  the  spinal 
cord,  or  medulla  spinalis. 

All  of  these  parts  of  the  nervous  system  are  nerve-centres,  in  con- 
tradistinction to  nerve- trunks,  and  differ  from  the  nerves  in  being  made  up 
of  nerve-cells  and  their  branchings  as  well  as  of  nerve-fibres.     There  are 


THE    NERVOUS    SYSTEM.  533 

other  ganglia  besides  these,  distributed  elsewhere  and  not  within  the 
cranium  and  spinal  column,  but  these  are,  for  the  sake  of  convenience, 
considered  apart,  under  the  head  of  the  sympathetic  system,  as  they 
present  some  differences  to  the  more  central  ganglia. 

The  cerebro-spinal  centres  then  are  distinguished  from  mere  nerve- 
trunks  by  the  possession  of  nerve-cells;  these  are,  as  we  have  seen  in  a 
former  chapter  (p.  96  et  seq.),  of  different  kinds;  they  very  possibly 
differ  in  function.  It  is,  however,  to  the  possession  of  ganglion-cells 
that  the  increase  of  the  functions  of  nerve-centres  over  that  of  nerve- 
trunks  is  credited.  Before  turning  to  the  discussion  of  the  functions 
of  the  spinal  cord  it  will  be  as  well  to  devote  a  little  time  therefore  to 
the  question  of  the  functions  of  the  nerve-centres  in  general.  The 
ganglia  of  the  sympathetic  system  also  contain  nerve-cells,  but  to  these 
it  is  supposed  a  different  use  is  to  be  assigned,  and  what  is  said  as  to  the 
functions  of  nerve-ganglia  in  this  place  is  only  to  be  applied  to  those 
of  the  cerebro-spinal  centres. 

Functions  of  Nerve-centres. 

Reflex  action, — One  of  the  chief  functions  o?  nerve-cells  appears 
to  be  the  power  of  sending  out  impulses  to  the  periphery  along  efferent 
nerves  in  response  to  impulses  reaching  them  through  afferent  nerves. 
This  power  is  sometimes  called  the  conversion  of  an  afferent  into  an 
efferent  impulse.  If  may  be  supposed  that  an  impulse  j^assing  to  a 
nerve-cell  may  ]3roduce  such  a  change  in  its  metabolism  that  a  discharge 
of  energy  ensues.  This  discharge  is  in  some  way  passed  down  an  efferent 
nerve  as  stimulus,  and  effects  some  change — motor,  secretory,  or  nutri- 
tive, at  the  peripheral  extremity  of  the  latter — the  difference  in  effect 
depending  on  the  kind  of  peripheral-nerve  termination.  The  reflex  action 
may  be  limited  in  its  effect,  or  it  may  be  extensive.  Reflex  movements,  oc- 
curring quite  independently  of  sensation,  are  generally  called  excito-motor; 
those  which  are  guided  or  acompanied  by  sensation,  but  not  to  the  extent 
of  a  distinct  perception,  or  intellectual  process,  are  termed  sensori-motor. 

{a)  For  the  manifestation  of  every  reflex  action,  these  things  are 
necessary:  (1),  one  or  more  perfect  afferent  fibres,  to  convey  an  impres- 
sion; (2),  a  nervous  centre  for  its  reception,  and  by  which  it  may  be  re- 
flected ;  (3),  one  or  more  efferent  nerve-fibres,  along  which  the  impres- 
sion may  be  conducted  to  (4)  the  muscular  or  other  tissue  by  which  the 
effect  is  manifested.  In  the  absence  of  any  one  of  these  conditions,  a 
proper  reflex  action  cannot  take  jilace. 

{b)  All  reflex  actions  are  essentially  involuntai'i/,  though  most  of 
them  admit  of  being  modified,  controlled,  or  prevented  by  a  voluntary 
effort. 


534  HANDBOOK    OF    PHYSIOLOGY, 

(c)  Eeflex  actions  performed  in  health  have,  for  the  most  part,  a  dis- 
tinct purpose,  and  are  adapted  to  secure  some  end  desirable  for  the  well- 
being  of  the  body;  but,  in  disease,  many  of  them  are  irregular  and 
purposeless. 

(d)  Muscular  contractions  produced  by  reflex  action  are  often  more 
sustained  than  those  produced  by  the  direct  stimulus  of  motor  nerves, 
themselves.  The  irritation  of  a  muscular  organ,  or  its  motor  nerve, 
produces  contraction  lasting  only  so  long  as  the  irritation  continues;, 
but  irritation  applied  to  a  nervous  centre  through  one  of  its  centripetal 
nerves,  may  excite  reflex  and  harmonious  contractions,  which  last  some 
time  after  the  withdrawal  of  the  stimulus. 

Relations  hehveen  the  Stimulus  and  the  Effect  produced. — Certain  rules 
showing  the  relation  between  the  resulting  reflex  action  and  the  stimulus- 
have  been  drawn  up  by  Pflilger,  as  follows : — 

1.  Laiv  of  unilateral  reflection. — A  slight  irritation  of  the  surface 
supplied  by  certain  sensory  nerves  is  reflected  along  the  motor  nerves  of 
the  same  region.  Thus,  if  the  skin  of  a  frog's  foot  be  tickled  on  the 
right  side,  the  right  leg  is  drawn  up. 

2.  Law  of  symvi^trical  reflection. — A  stronger  irritation  is  reflected, 
not  only  on  one  side,  but  also  along  the  corresponding  motor  nerves  of 
the  opposite  side. 

3.  Law  of  intensity. — In  the  above  case,  the  contractions  will  be- 
more  violent  on  the  side  irritated,  but  it  must  not  be  assumed  that  the 
effect  is  always  in  proportion  to  the  strength  of  the  stimulus. 

4.  Laiu  of  radiation. — If  the  irritation  (afferent  impulse)  increases, 
it  is  reflected  along  other  motor  nerves  till  at  length  all  the  muscles  of 
the  body  are  thrown  into  action. 

In  the  simplest  form  of  reflex  action  a  single  nerve-cell  with  an 
afferent  and  an  efferent  fibre  may  be  supposed  to  be  concerned,  but  in  the 
majority  of  actual  actions  many  cells  are  probably  engaged,  the  stimu- 
lus being  distributed,  which  act  in  concert  or  co-ordination. 

The  reflex  effect  produced  by  a  stimulus  applied  to  a  sensory  surface 
depends,  however,  not  only  upon  the  strength  of  the  stimulus,  but  also 
upon  other  circumstances,  the  most  important  of  which  is  the  condi- 
tion of  the  nerve-centre  itself.  Looking  upon  the  effect  produced  as- 
the  result  of  the  discharge  as  it  were  of  energy  from  the  centre,  it  may 
be  supposed  that  sometimes  the  centre  is  in  a  more  explosive  condition 
than  at  another ;  this  is  shown  for  example  in  the  case  of  a  frog  poisoned 
by  strychnine,  when  the  slightest  stimulus  applied  to  the  skin  will  pro- 
duce the  most  violent  and  general  tetanic  spasms,  while  under  ordinary 
circumstances  the  contraction  of  a  few  muscles  only  would  result.  We 
must  also  suppose  that  the  centres  are  particularly  sensitive  to  particu- 
lar kinds  of  stimuli,  sometimes  producing  very  extensive  and  violent 


THE    NERVOUS    SYSTEM.  535 

muscular  actions  in  response  to  a  slight  stimulus  of  a  special  kind. 
Such  a  condition  is  illustrated  in  the  violent  and  general  muscular 
spasms  occurring  when  a  small  particle  of  food  passes  into  the  larynx, 
violent  expiratory  spasms  accompanied  by  contractions  of  other  muscles 
taking  place. 

A  nerve-centre  must  be  considered  as  capable  by  its  connections 
with  efferent  nerves  of  producing  most  extensive  muscular  movements, 
and  when  from  any  reason,  either  by  the  intensity  of  the  afferent 
stimuli  reaching  it,  or  by  the  special  nature,  extent,  or  point  of  appli- 
cation of  the  afferent  stimuli,  or  by  special  changes  in  its  own  metabol- 
ism brought  about  by  poison  or  by  some  other  mean's,  a  maximum  dis- 
charge takes  place,  the  resulting  movements  are  most  extensive.  Under 
ordinary  conditions,  however,  a  slight  stimulus  produces,  as  above  men- 
tioned, only  a  moderate  discharge  from  the  centre,  the  movement  being 
to  a  certain  extent  co-extensive  with  the  strength  of  the  stimulus. 

The  time  taken  in  a  reflex  action  has  been  found  to  be  .066  to  .058 
second,  but  this  is  only  a  rough  and  arbitrary  estimation. 

Automatism. — A  second  function  which  appears  to  be  possessed  by 
certain  nerve-centres  and  not  by  others  is  that  of  automatic  action  or 
autom.atism.  By  this  is  meant  that  it  is  not  dependent  for  its  discharge 
upon  any  afferent  stimuli,  but  that  it  is  capable  of  sending  out  of  itself 
efferent  impulses  of  various  kinds.  The  centre  may  be  supjDosed  to  do 
this  by  the  nature  of  its  own  metabolism,  anabolism  or  building  up  of  the 
explosive  substance  being  followed  by  katabolism  or  its  discharge.  So 
that  the  centre  sends  out  its  impulses  to  muscles  rhythmically.  Such 
a  power  of  nutomatism  we  have  seen  is  attributed  to  the  respiratory  cen- 
tres in  the  bulb. 

Inhibition  and  Augmentation. — Not  only  may  movements  of 
muscles,  discharge  of  secretion  from  gland-cells  and  the  like  be  produced 
by  afferent  impulses  reaching  nerve-centres,  but  also  inhibition  of  action 
which  is  already  taking  place.  This  is  well  seen  in  the  matter  of  the 
inhibitory  action  of  the  vagus  upon  the  cardiac  contractions.  The  vagi 
convey  to  the  heart  impulses  from  the  cardio-inhibitory  centres  which 
have  a  restraining  action  upon  the  contractions  of  the  heart,  as  is  seen 
by  the  increase  in  the  frequency  of  the  heart-beats  when  the  vagi  are 
divided;  but  we  have  seen  that  appropriate  afferent  stimuli,  as,  for 
example,  when  applied  to  the  abdominal  sympathetic,  may  increase  the 
action  of  the  centre  to  such  an  extent  that  the  heart  may  be  altogether 
stopped  in  diastole.  In  such  a  case  the  result  of  the  afferent  stimuli 
upon  the  centre  has  been  to  produce  complete  inhibition  and  not  mus- 
cular contraction.  This  is  not  the  only  example  of  inhibition  which 
might  be  instanced ;  the  action  of  almost  any  centre  may  be  inhibited 
by  impulses  reaching  it;  indeed  the  effect  of  afferent  impulses  upon  a 


536 


HANDBOOK    OF    PHYSIOLOGY. 


centre  may  be  not  only  not  to  set  it  into  activity,  but  to  prevent  or 
8top  an  action  already  going  on.  On  the  other  hand,  the  action  of 
afferent  impulses  upon  a  nerve-centre  may  be  to  augment,  render  more 


of  S/iitud  Cora 


1st  DoAFai 
Vertebra. 


^fSfunulCorA         \     fC%<      \ 


cranium  and  trunk  of  the  body  has  been  rpmov^H  h^'^.^'^T"'.  '^"l?"-  ^he  right  half  of  the 
brain  and  .spinal  eord  have  also  beLremovT«,^i  ^L^  vertical  section:  the  membranes  of  the 
cranial,  ancf  of  all  spinal  nerves  rfffherTX^i'/^*''''  roots  and  first  part  of  the  fifth  and  ninth 
the  wall  of  the  skulfand  on  the  several  v?rt-hr^'  ^^""^  dissected  out  and  laid  separately  on 

the  cranio-spinal  cavity.     (Af tir  Bourglry  )  ^PP^^'^e  to  the  place  of  their  natural  exit  from 

powerful  or  extensive,  and  increase  in  a  certain  direction  an  action 
already  m  course.     Such  may  be  well  illustrated  by  the  action  of  the 


THE    NERVOUS   SYSTEM.  537 

vagi  upon  the  respiratory  centres  to  which  attention  has  been  drawn  in 
the  chapter  ujion  respiration. 

Membranes  of  the  Brain  and  Spinal  Cord. — The  Brain  and  Spinal  Cord  are 
enveloped  in  three  membranes — (1)  the  Dura  Mater,  (3)  the  Arachnoid,  (3) 
the  Pia  Mater. 

(1)  The  Dura  Mater,  or  external  covering,  is  a  tough  membrane  composed  of 
bundles  of  connective-tissue  wiiich  cross  at  various  angles,  and  in  whose  inter- 
stices branched  connective-tissue  corpuscles  lie  :  it  is  lined  by  a  thin  elastic  mem- 
brane, and  on  the  inner  surface  and  where  it  is  not  adherent  to  the  bone,  on  the 
outer  surface  also  is  a  layer  of  endothelial  cells  very  similar  to  those  found 
in  serous  membranes.  (3.)  The  Arachnoid  is  a  much  more  delicate  mem- 
brane, very  similar  in  structure  to  the  dura  mater,  and  lined  on  its  outer  or 
free  surface  by  an  endothelial  membrane. 

(3. )  The  Pia  Mater  consists  of  tw^o  chief  layers,  between  which  numerous  blood- 
vessels ramify.  Between  the  arachnoid  and  pia  mater  is  a  netwoi-k  of  fibrous- 
tissue  trabeculae  sheathed  with  endothelial  cells  :  these  sub-arachnoid  ti-abeculae 
divide  up  the  sub  arachnoid  space  into  a  number  of  irregular  sinuses.  There 
are  some  similar  trabeculae,  but  much  fewer  in  number,  traversing  the  sub-dural 
space,  i.e.,  the  space  between  the  dura  mater  and  arachnoid. 

Pacchionian  bodies  are  growths  from  the  sub-arachnoid  network  of  connec- 
tive-tissue trabeculje  which  project  through  small  holes  in  the  inner  layers  of 
the  dura  mater  into  the  venous  sinuses  of  that  membrane.  The  venous  sinuses 
of  the  dura  mater  liave  been  injected  from  the  sub-arachnoidal  space  through 
the  intermediation  of  these  villous  outgrowths. 

The  Spinal  Cord  and  its  Nerves. 

Tlie  Spinal  cord  is  a  cyliudriform  column  of  nerve-substance  con- 
nected above  with  the  brain  through  the  medium  of  the  bulb,  and  ter- 
minating below,  about  the  lower  border  of  the  first  lumbar  vertebra,  in  a 
slender  filament  of  gray  substance,  the  Jihini  terminale,  which  lies  in  the 
midst  of  the  roots  of  many  nerves  forming  the  cauda  equina. 

Structure. — The  cord  is  composed  of  white  and  gray  nervous  sub- 
stance, of  which  the  former  is  situated  externally,  and  constitutes  its  chief 
portion,  while  the  latter  occupies  its  central  or  axial  portion,  and  is  so 
arranged,  that  on  the  surface  of  a  transverse  section  of  the  cord  it 
appears  like  two  somewhat  crescentic  masses  connected  together  by  a 
narrower  portion  or  isthmus  (fig.  350).  Passing  through  the  centre  of 
this  isthmus  in  a  longitudinal  direction  is  a  minute  canal  (central 
canal),  Avhich  is  continued  through  the  whole  length  of  the  cord,  and 
opens  above  into  the  space  at  the  back  of  medulla  oblongata  and  pons 
Varolii,  called  the  fourth  ventricle.  It  is  lined  by  a  layer  of  columnar 
ciliated  epithelium. 

The  spinal  cord  consists  of  two  exactly  symmetrical  halves,  separated 
anteriorly  and  posteriorly  by  vertical  ^'6\s?<res  (the  posterior  fissure  being 
deeper,  but  less  wide  and  distinct  than  the  anterior),  and  united  in  the 
middle  by  nervous  matter  which  is  usually  described  as  forming   two 


538 


HANDBOOK    OF    PHYSIOLOGY. 


commissures — an  anterior  commissure,  in  front  of  the  central  canal, 
consisting  of  medullated  nerve-fibres,  and  a  jjosterior  commissure 
behind  the  central  canal  consisting  also  of  medullated  nerve-fibres,  but 
with  more  neuroglia,  which  gives  the  gray  aspect  to  this  commissure 
(fig.  350  b).  Each  half  of  the  spinal  cord  is  marked  on  the  sides  (ob- 
scurely at  the  lower  part,  but  distinctly  above)  by  two  longitudinal  fur- 
rows, which  divide  it  into  three  portions,  columns,  or  tracts,  an  anterior, 
lateral,  and  posterior.  From  the  groove  between  the  anterior  and  lateral 
columns  spring  the  atiterior  roots  of  the  spinal  nerves  (b  and  c,  5) ;  and 
just  in  front  of  the  groove  between  the  lateral  and  posterior  column 


Fig.  350. — Different  views  of  a  portion  of  the  spinal  cord  from  the  cervical  region,  with  the 
roots  of  the  nerves  (slightly  enlarged).  In  a,  the  anterior  surface  of  the  specimeu  is  shown;  the 
anterior  nerve-root  of  its  right  side  being  divided;  in  b,  a  view  of  the  right  side  is  given;  in  c, 
the  upper  surface  is  shown;  in  d,  the  nerve-roots  and  ganglion  are  shown  from  below.  1.  The 
anterior  median  fissure;  2.  posterior  median  fissure;  3,  anterior  lateral  depression,  over  which 
the  anterior  nerve-roots  are  seen  to  spread ;  4,  posterior  lateral  groove,  into  which  the  posterior 
roots  are  seen  to  sink;  5,  anterior  roots  passing  the  ganglion;  5',  in  a.  the  anterior  root  divided; 
6,  the  posterior  roots,  the  fibres  of  which  pass  into  the  ganglion  6' ;  7,  the  united  or  compound 
nerve;  7',  the  posterior  primary  branch,  seen  in  a  and  d  to  be  derived  in  part  from  the  anterior 
and  in  part  from  the  posterior  root.     (Allen  Thomson.) 

arise  the  posterior  roots  of  the  same  (b,  6) :  a  pair  of  roots  on  each  side 
corresponding  to  each  vertebra  (fig.  350). 

White  matter. — The  white  matter  of  the  cord  is  seen  to  be  made 
up  of  medullated  nerve-fibres,  of  different  sizes,  and  arranged  longi- 
tudinally, and  of  a  supporting  material  of  two  kinds,  viz. : — (a)  ordinary 
fibrous  connective  tissue  with  elastic  fibres,  which  is  connected  with 
septa  from  the  pia  mater  which  pass  into  the  cord  to  carry  the  blood 
vessels,  {b)  Neuroglia ;  this  material  is  made  up  of  branching  cells  (fig. 
352),  the  bodies  of  which,  in  consecjuence  of  the  high  development  of 


THE    NERYOUS    SYSTEM. 


539 


the  branchings,  are  small.  The  processes  of  the  nenroglia-cells  are 
arranged  so  as  to  support  the  nerve-fibres  which  are  without  the  usual 
external  nerve  sheaths.  Neuroglia  was  formerly  considered  to  be  a 
kind  of  adenoid  tissue,  but  is  now  considered  to  be  a  distinct  material. 
It  is  derived  from  the  neural  epiblast,  and  yields  neuro-keratin. 

The  general  rule  respecting  the  size  of  different  parts  of  the  cord 
appears  to  be,  that  each  part  is  in  direct  proportion  in  this  respect  to  tlie 
size  and  number  of  nerve-roots  given  off  from  it,  and  has  but  little  rela- 
tion to  the  size  or  number  of  those  given  off  below  it.  Thus  the  cord  is 
very  large  in  the  middle  and  lower  part  of  its  cervical  portion,  whence 
arise  the  large  nerve-roots  for  the  formation  of  the  brachial  plexuses  and 
the  supply  of  the  upper  extremities,  and  again  enlarges  at  the  lowest 


Fig.  351. — Section  of  gray  matter  of  anterior  cornu  of  a  calf's  spinal  cord;  rt,  nerve-fibres  of 
white  matter  in  transverse  section,  showing  axis-cylinder  in  centre  of  each;  r,  large  stellate 
nerve-cells  v.-ith  nuclei  and  three  prolongations.     (Cadiat.) 


part  of  its  dorsal  portion  and  the  upper  part  of  its  lumbar,  at  the  origins 
of  the  large  nerves  which,  after  forming  the  lumbar  and  sacral  plexuses, 
are  distributed  to  the  lower  extremities.  The  chief  cause  of  the  greater 
size  at  these  parts  of  the  spinal  cord  is  increase  in  the  quantity  of  gray 
matter;  for  there  seems  reason  to  believe  that  the  white  part  of  the 
cord  becomes  gradually  and  progressively  larger  from  below  upward, 
doubtless  from  the  addition  of  a  certain  number  of  upward  passing 
fibres  from  each  pair  of  nerves. 

From  careful  estimates  of  the  number  of  nerve-fibres  in  a  transverse 
section  of  the  cord  toward  its  upper  end,  and  the  number  entering  or 
issuing  from  it  by  the  anterior  and  posterior  roots  of  each  pair  of  nerves, 
it  has  been  shown  that  in  the  human  spinal  cord  not  more  than  half 
of  the  total  number  of  nerve-fibres  of  all  .the  spinal  nerves  are  contained 
in  a  transverse  section  near  its  upper  end.     It  is  obvious,  therefore,  that 


540  HANDBOOK    OF    PHYSIOLOGY. 

at  least  half  of  the  nerve-fibres  entering  it  must  terminate  somewhere  in 
the  cord  itself. 

Gray  matter. — The  gray  matter  of  the  cord  consists  of  medullated 
fibres,  most  of  which  are  very  fine   and   delicate,    of   nerve-cells   with 


Fig.  352.— A.   Branched  neuroglia-cells.     (After  Stohr.) 

branching  processes,  and  of  an  extremely  delicate  network  of  the  primi- 
tive fibrillse  of  axis-cylinders.  This  fine  plexus  is  called  GerlacWs  net- 
work^ and  is  mingled  with  the  meshes  of  neuroglia,  which  in  some  parts 
is  chiefly  fibrillated,  in  others  mainly  granular  and  punctiform.  The 
neuroglia  of  the  gray  matter  resembles  that  of  the  white,  but  instead  of 
everywhere  forming  a  close  network  to  suj)port  the  nerve-fibres,  here 
and  there  it  is  in  the  form  of  a  more  open  sponge-work  to  support  the 
nerve-cells.  It  is  especially  developed  around  the  central  canal,  which 
is  lined  with  columnar  ciliated  epithelium,  the  cells  of  which  at  their 
outer  end  terminate  in  fine  processes,  which  join  the  neurogliar  network 
surrounding  the  canal,  and  form  the  suhstantia  gelatinosa  centralis.  It 
is  also  developed  at  the  tip  of  the  jaosterior  cornu  of  gray  matter,  form- 
ing what  is  known  as  the  substantia  gelatitiosa  lateralis  of  Eolando, 
through  which  the  posterior  nerve-roots  pass. 

Groiqis  of  cells  in  gray  matter. — The  multipolar  cells  are  either 
scattered  singly  or  arranged  in  groups,  of  which  the  following  are  to  be 
distinguished  on  either  side — certain  of  the  groups  being  more  or  less 
marked  in  all  of  the  regions  of  the  cord,  viz.,  those  {a)  in  the  anterior 
cornu,  and  (i)  those  in  the  posterior  cornu. 

{a)  The  cells  in  the  anterior  cornu  are  large  and  branching,  and 
each  gives  rise  to  an  axis-cylinder  process  which  passes  out  in  the 
anterior  nerve-root.  These  cells  are  everywhere  conspicuous,  but  are 
particularly  numerous  in  the  cervical  and  lumbar  enlargements.  In 
these  districts  they  may  be  divided  into  several  groups — (i.)  a  group  of 


THE    NERVOUS    SYSTEM. 


541 


large  cells  close  to  the  tip  of  the  inner  part  of  the  anterior  cornu — all 
the  cells  of  the  anterior  cornu  in  the  dorsal  or  thoracic  region  are  said 
to  belong  to  this  group;  (ii.)  several  lateral  groups  (2,  a,  b,  and  c,  fig. 
353)  on  the  outer  side  of  the  gray  matter,  and  (iii.)  a  certain  number  of 
cells  at  the  base  of  the  inner  part  of  the  anterior  cornu  particularly  well 
marked  in  the  thoracic  region,  {b)  Cells  of  the  posterior  cornu — these 
are  not  numerous;  they  are  small  and  branched,  and  each  probably  has 
an  axis-cylinder  process  passing  off;  but  these  processes  do  not  pass 
into  the  posterior  nerve-roots.  The  groups  are  two  at  least  in  number, 
viz.,  (i.)  in  connection  with  the  edge  of  the  gray  matter  externally, 
where  it  is  considerably  broken  up  by  the  passage  of  bundles  of  fibres 
through  it,  and  called  the  lateral  reticular  for7nation;  and  (ii.)  in  con- 
nection with  a  similar  reticular  formation,  more  at  the  tip  of  the  gray 
matter  of  the  posterior  cornu;  this  is  known  as  the  posterior  reticular 
formation. 

The  other  groups  of  cells  (not  represented  in  fig.  353)  are  almost,  if 
not  entirely,  confined  to  the  thoracic  region  of  the  cord,  and  are  two 
in  number,  viz. :  one  situated  at  the  base  of  the  posterior  cornu,  formed 


Fig.  353.— Section  of  spinal  cord,  one  half  of  which   (left)  shows  the  tracts  of  the   white 
matter,  and  the  other  half  (riKht)  shows  the  position  of  the  nerve  cells  in  the  gray  matter.     7, 
10,  9  and  3  are  tracts  of  descending  degeneration,  1,  4,  6  and  8,  of  ascending  degenerat 
diagrammatic.     (After  Sherrington.) 


:  degeneration.    Semi- 


of  fairly  large  cells,  generally  fusiform,  and  possibly  of  two  distinct 
kinds,  constitutes  i\\Q  posterior  vesicular  column  of  Lockliart  Clarke,  and 
the  other  situated  on  the  outer  portion  of  the  gray  matter,  about  mid- 
way between  the  anterior  and  posterior  cornua,  constitutes  the  cells  of  the 
tractus  intermedio-lateralis  or  lateral  gray  column.     These  cells  are  small 


542  HANDBOOK    OF    PHYSIOLOGY. 

and  spindle-shaped,  and  are  more  or  less  well  marked  in  the  lumbar 
region  as  well  as  in  the  thoracic  region. 

Columns  and  tracts  in  the  white  matter  of  the  sjyinal  cord. — In  addition 
to  the  columns  of  the  white  matter  which  are  marked  out  by  the  points 
from  which  the  nerve-roots  issue,  and  which  are  the  anterior,  the  lateral 
and  posterior,  the  posterior  is  further  divided  by  a  septum  of  the  pia 
mater  into  two  almost  equal  parts,  constituting  the  postero-external 
column,  or  column  of  Burdach  (fig.  353,  2),  2iU^'(\\Q poster o-median,  ox 
column  of  Goll  (fig.  353,  1).  In  addition  to  these  columns,  however,  it 
has  been  shown  that  the  white  matter  can  be  still  further  subdivided. 
This  subdivision  has  been  accomplished  by  evidence  of  several  kinds, 
that  the  parts  or,  as  they  are  called,  tracts  in  the  white  matter,  perform 
different  functions  in  the  conduction  of  impulses. 

The  methods  of  observation  are  the  following: — 

{a)  The  emhryological  method.  It  has  been  found  that  if  the  develop- 
ment of  the  spinal  cord  be  carefully  observed  at  different  stages  that  cer- 
tain groups  of  the  nerve-fibres  put  on  their  myelin  sheath  at  earlier  peri- 
ods than  others,  and  that  the  different  groups  of  fibres  can  therefore  be 
traced  in  various  directions.      This  is  known  as  the  method  of  Flechsig. 

{b)  Wallerian  or  degeneration  method. — This  method  depends  upon 
the  fact  that  if  a  nerve-fibre  is  separated  from  its  nerve-cell,  it  wastes  or 
degenerates.  It  consists  in  tracing  the  course  of  tracts  of  degenerated 
fibres,  which  result  from  an  injury  to  any  part  of  the  central  nervous 
system.  When  fibres  degenerate  below  a  lesion  the  tract  is  said  to  be 
of  descending  degeneration,  and  when  the  fibres  degenerate  in  the  oppo- 
site direction  the  tract  is  one  of  ascending  degeneration.  By  modern 
methods  of  staining  of  the  central  nervous  system  it  has  proved  com-' 
paratively  easy  to  distinguish  degenerated  parts  in  sections  of  the  cord 
and  of  other  portions  of  the  central  nervous  system.  Degenerated 
fibres  have  a  different  staining  reaction  when  the  sections  are  stained 
by  what  are  called  Weigert's  and  Pal's  methods,  which  consist  of  sub- 
jecting them  to  a  special  solution  of  hsematoxylin,  and  then  to  special 
differentiating  solutions.  The  degenerated  fibres  appear  light  yellow, 
whereas  the  healthy  fibres  are  a  deep  brown  or  black.  Accidents  to  the 
central  nervous  system  in  man  have  given  us  much  information  upon 
this  subject,  but  this  has  of  late  years  been  supplemented  and  largely 
extended  by  the  experiments  on  animals,  particularly  upon  monkeys; 
and  considerable  light  has  been  by  these  means  shed  upon  the  conduc- 
tion of  impulses  to  and  from  the  nervous  system  by  the  study  of  the 
results  of  section  of  different  parts  of  the  central  nervous  system,  and 
of  the  spinal  nerve-roots.  Thus  we  have  not  only  embryological  evi- 
dence mapping  out  different  tracts,  but  also  confirmatory  pathological 
and  experimental  observations. 


THE    XEKVOUS    SYSTEM.         *  54o 

The  tracts  which  have  been  made  out  are  the  following : — 
(a)  Of  descending-  degeneration. 

(i.)  The  crossed  pyramidal  tract  (tig.  353,7). — This  tract  is  situated 
to  the  outer  part  of  the  posterior  coruu  of  gray  matter.  It  is  found 
throughout  the  whole  length  of  the  spinal  cord;  at  the  lower  part  it  ex- 
tends to  the  margin  of  the  cord,  but  higher  up  it  becomes  displaced 
from  this  position  by  the  interpolation  of  another  tract  of  fibres,  to  be 
presently  described,  viz.,  the  direct  cerebellar  tract.  The  crossed 
pyramidal  tract  is  large,  and  may  touch  the  tip  of  gray  matter  of  the 
posterior  cornu,  but  is  separated  from  it  elsewhere.  In  shape  on  cross- 
section  it  is  somewhat  like  a  lens,  but  varies  in  different  regions  of  the 
cord,  and  diminishes  in  size  from  the  cervical  region  downward. 
The  tract  is  particularly  well  marked  out,  both  by  the  degeneration  and 
the  embryological  methods.  The  fibres  are  supposed  to  pass  off  as  they 
descend,  and  to  join  the  various  local  nervous  mechanisms  of  nerve  cells 
and  their  branchings  which  are  represented  in  the  cord.  The  tract  of 
degeneration  may  be  traced  upward  beyond  the  cord,  in  a  way  to  be 
presently  described.  The  fibres  of  which  this  tract  is  composed  are 
moderately  large,  but  are  mixed  with  some  that  are  smaller. 

(ii.)  The  direct  or  uncrossed  jjyj'amidal  tract  (fig.  353,  10). — This 
tract  is  situated  in  the  anterior  column  by  the  sides  of  the  anterior 
fissure.  It  is  smaller  than  (i.),  and  is  not  present  in  all  animals, 
though  conspicuous  in  the  human  cord  and  in  that  of  the  monkey.  It 
can  be  traced  ujjward  to  the  cerebral  cortex,  and  downward  as  far  as 
the  mid  or  lower  thoracic  region,  where  it  ends. 

(iii.)  Antero-lateral  descending  tract  (fig.  353,9). — An  extensive 
tract,  elongated  but  narrow,  and  reaching  from  the  crossed  to  the  direct 
pyramidal  tract.  It  is  a  mixed  tract,  since  not  all  of  its  fibres  degenerate 
below  the  lesions. 

(iv.)  Comma  tract  (fig.  353,  3)  is  a  small  tract  of  fibres  which  degen- 
erate below  section  or  injury  of  the  cord.  Its  presence  has  been  demon- 
strated in  the  cervical  and  thoracic  regions.  It  is  supposed  to  consist  of 
the  longitudinal  fibres  of  the  posterior  nerve-roots  as  they  pass  up  in 
the  postero-external  columns. 

{h)  Of  ascending  degeneration. 

(i.)  Posfero-median  columji  (fig.  353,1). — This  tract  degenerates  up- 
ward on  injury  or  on  section  of  the  cord,  as  well  as  on  section  of  the 
posterior  nerve  roots.  It  exists  throughout  the  whole  of  the  cord  from 
below  up,  and  can  be  traced  into  the  bulb.     It  consists  of  fine  fibres. 

(ii.)  Direct  cerebellar  tract  (fig.  353,  6). — This  tract  is  situated  on  the 
outer  part  of  the  cord  between  the  crossed  pyramidal  tract  and  the  mar- 
gin. It  is  found  in  the  cervical,  thoracic  and  upper  lumbar  regions  of 
the  cord,  and  increases  in  size  from  below  upward.     It  degenerates  on 


544  HANDBOOK    OF    PHYSIOLOGY. 

injury  or  section  of  the  cord  itself,  but  not  on  section  of  the  posterior 
nerve-roots.  As  its  name  implies  it  is  believed  to  j)ass  up  into  the  cere- 
bellum.    Its  fibres  are  coarse. 

(iii.)  Antcro-latend  ascending  tract  {Tract  of  Goivers  and  Tootli) 
(fig.  353,  8). — This  tract  has  been  shown  on  injury  to  the  spinal  cord; 
it  is  situated  at  the  margin  of  the  cord  outside  of  the  corresponding 
descending  tract.  It  is  traceable  throughout  the  Avhole  length  of  the 
cord.     Its  fibres  are  composed  of  mixed,  fine  and  coarse,  elements. 

(iv.)  Tract  of  Lissauer,  or  'posterior  marginal  zone  (fig.  353,  4). — A 
small  tract  of  ascending  fibres  situated  at  the  outer  side  of  the  tip  of 
the  posterior  cornu.     It  is  made  up  of  fibres  of  the  posterior  nerve-roots. 

Spinal  Nerves. — The  spinal  nerves  consist  of  thirty-one  pairs,  issuing 
from  the  sides  of  the  whole  length  of  the  cord,  their  number  correspond- 
ing with  the  intervertebral  foramina  through  which  they  pass.  Each 
nerve  arises  by  two  roots,  an  anterior  and  posterior,  the  latter  being  the 
larger.  The  roots  emerge  through  separate  apertures  of  the  sheath  of 
dura  mater  surrounding  the  cord;  and  directly  after  their  emergence, 
where  the  roots  lie  in  the  intervertebral  foramen,  a  ganglion  is  found 
on  the  posterior  root.  The  anterior  root  lies  in  contact  with  the  anterior 
surface  of  the  ganglion,  but  none  of  its  fibres  intermingle  with  those  in 
the  ganglion  (5,  fig.  350).  But  immediately  beyond  the  ganglion  the 
two  roots  coalesce,  and  by  the  mingling  of  their  fibres  form  a  compound 
or  mixed  spinal  nerve,  which,  after  issuing  from  the  intervertebral 
canal,  gives  off  anterior  and  posterior  or  ventral  and  dorsal  branches, 
each  containing  fibres  from  both  the  roots  (fig.  350) ,  as  well  as  a  third 
or  visceral  branch,  ramus  c^ommunicans,  to  the  sympathetic. 

The  anterior  root  of  each  spinal  nerve  arises  by  numerous  separate 
and  converging  bundles  from  the  anterior  column  of  the  cord ;  the  pos- 
terior root  by  more  numerous  parallel  bundles,  from  the  posterior  col- 
umn, or,  rather,  from  the  j)osterior  part  of  the  lateral  column  (fig.  350), 
for  if  a  fissure  be  directed  inward  from  the  groove  between  the  middle 
and  posterior  columns,  the  roots  will  remain  attached  to  the  former. 
The  anterior  roots  of  each  spinal  nerve  consist  chiefly  of  efferent  fibres; 
the  posterior  exclusively  of  afferent  fibres. 

Course  of  the  Fibres  of  tlie  Spinal  Nerve- Roots.  —  {a)  The  Anterior 
roots  enter  the  cord  in  several  bundles,  which  may  be  called: — (1) 
Internal;  (2)  Middle;  (3)  External;  all  being  more  or  less  connected  with 
the  groups  of  multipolar  cells  in  the  anterior  cornua.  1.  The  internal 
fibres  are  partly  connected  with  internal  group  of  nerve-cells  of  the 
anterior  cornu  of  the  same  side;  but  some  fibres  pass  over,  through 
the  anterior  commissure  to  end  in  the  anterior  cornu  of  opposite  side, 
probably  in  the  internal  group  of  cells.  2.  The  middle  fibres  are  partly 
in  connection  with  the    lateral   group  of  cells  in  anterior  cornu,  and 


THE    NERVOUS    SYSTEM.  545 

iu  part  pass  backward  to  the  posterior  cornii,  having  no  immediiite 
conection  with  cells.  3.  The  external  fibres  are  partly  in  connection 
with  the  lateral  group  of  cells  in  the  anterior  cornu,  but  some  fibres 
proceed  direct  into  the  lateral  column  without  connection  with  cells, 
and  pass  upward  in  it. 

{b)  The  Posterior  roots  enter  the  posterior  cornu  in  two  chief  inner 
and  lateral  bundles.  Of  those  which  enter  by  the  inner  side  of  the 
cornu  the  majority  pass  up  (or  down)  in  the  white  substance  of  the 
posterior  columns,  and  enter  the  gray  matter  at  various  heights  at  the 
base  of  the  posterior  cornu ;  perhaps  some  pass  directly  upward  and 
inward  in  the  posterior  median  column  without  entering  the  gray 
matter.  Those  that  enter  the  gray  matter  pass  in  various  directions,, 
some  to  Join  the  lateral  cells  in  the  anterior  cornu,  some  to  join  the- 
cells  in  the  posterior  vesicular  column,  and  some  pass  across  to  the 
other  side  of  the  cord  in  the  anterior  commissure,  while  others  become 
again  longitudinal  in  the  gray  matter.  The  bundles  of  the  lateral  divi- 
sion may  also  be  further  subdivided  into  intermediate  and  outer  fibres,  the 
former  becoming  longitudinal  in  the  gray  matter,  while  some  pass  to  the 
anterior  cornu,  while  the  outer  become  longitudinal  and  form  the  tract 
of  Lissauer.  Some  of  these  fibres  seem  to  end  in  the  cells  of  the  posterior 
cornu. 

The  Peculiarities  of  different  regions  of  the  Spinal  Cord. — The  outline  of  the 
gray  matter  and  the  relative  proportion  of  the  white  matter  varies  in  different 
regions  of  the  spinal  cord,  and  it  is,  therefore,  possible  to  tell  approximately 
from  what  region  any  given  transverse  section  of  the  spinal  cord  has  been 
taken.  The  white  matter  increases  in  amount  from  below  upward.  The 
amount  of  gray  matter  varies  ;  it  is  greatest  in  the  cervical  and  lumbar  enlarge- 
ments, viz. ,  at  and  about  the  5th  lumbar  and  6th  cervical  nerve,  and  least  in  the 
thoracic  region.  The  greatest  development  of  gray  matter  corresponds  with 
greatest  number  of  nerve-fibres  passing  from  the  cord. 

In  the  cervical  enlargement  tlie  gray  matter  occupies  a  large  proportion  of  the 
section,  the  gray  commissure  is  short  and  thick,  the  anterior  horn  is  blunt,  while 
the  posterior  is  somewhat  tapering.  The  anterior  and  posterior  roots  run  some 
di.stance  through  the  white  matter  before  they  reach  the  periphery. 

In  the  dorsal  region  the  gray  matter  bears  only  a  small  relation  to  the  white, 
and  the  posterior  roots  in  particular  run  a  long  course  through  the  white  matter 
before  they  leave  the  cord  ;  the  gray  commissure  is  thinner  and  narrower  than 
in  the  cervical  region.     The  tractus  intermedio-lateralis  is  here  most  marked. 

In  the  lumbar  enlargement  the  gray  matter  again  bears  a  very  large  propor- 
tion to  the  whole  size  of  the  transverse  section,  but  its  posterior  cornua  are 
shorter  and  blunter  than  they  are  in  the  cervical  region.  The  gray  commis- 
sure is  short  and  extremely  narrow. 

At  the  upper  part  of  the  conus  medallaris,  which  is  the  portion  of  the  cord 
immediately  below  the  lumbar  enlargement,  the  gray  substance  occupies 
nearly  the  whole  of  the  transverse  section,  as  it  is  only  invested  by  a  thin 
layer  of  white  substance.  This  thin  layer  is  wanting  in  the  neighborhood  of 
the  posterior  nerve-roots.     The  great  commissure  is  extremely  thick. 

35 


646  HANDBOOK    OF    PHYSIOLOGY. 

At  the  level  of  the  fifth  sacral  vertebra  the  gray  matter  is  again  in  excess,  and 
the  central  canal  is  enlarged,  appearing  T-shaped  in  section ;  while  in  the 
upper  portion  of  the  fllum  terminale  the  gray  matter  is  uniform  in  shape  without 
any  central  canal. 

The  shape  of  the  cord  changes  from  the  sacral  and  lumbar  region 
where  it  is  circular  to  the  thoracic  where  it  is  oval,  and  to  the  cervical 
where  the  lateral  diameter  considerably  exceeds  the  antero-posterior ; 
the  change  in  shape  is  due  to  a  gradual  increase  of  the  lateral  columns. 

Functions  of  the  Spinal  Nerve-Roots. 

The  anterior  spinal  nerve-roots  are  efferent  in  function:  the  posterior 
:are  afferent.  The  fact  is  proved  in  various  ways.  Division  of  the 
anterior  roots  of  one  or  more  nerves  is  followed  by  complete  loss  of  mo- 
tion in  the  parts  supplied  by  the  fibres  of  such  roots;  but  the  sensation 
of  the  same  parts  remains  perfect.  Division  of  the  posterior  roots 
•destroys  the  sensibility  of  the  parts  supplied  by  their  fibres,  while  the 
power  of  motion  continues  unimpaired.  Moreover,  irritation  of  the 
ends  of  the  distal  portions  of  the  divided  anterior  roots  of  a  nerve  excites 
muscular  movements;  irritation  of  the  ends  of  the  j)roximal  portions, 
which  are  still  in  connection  with  the  cord,  is  followed  by  no  appreciable 
effect.  It  must  be  remembered,  however,  that  in  the  anterior  or  efferent 
nerves  other  besides  motory  are  contained,  e.g.,  vaso-motor,  secretory, 
heat  fibres,  and  it  may  be  supposed  that  when  the  distal  end  of  a  divided 
nerve  is  stimulated,  the  effects  would  be  exercised  not  only  upon  mus- 
cles, but  upon  glands,  blood-vessels,  etc.  Irritation  of  the  distal  portions 
of  the  divided  posterior  roots,  on  the  other  hand,  produces  no  muscular 
movements  and  no  manifestations  of  pain;  for,  as  already  stated,  sen- 
sory nerves  convey  impressions  only  toward  the  nervous  centres:  but 
irritation  of  the  j^roximal  portions  of  these  roots  elicits  signs  of  intense 
suffering.  Occasionally,  under  this  last  irritation,  muscular  movements 
also  ensue;  but  these  are  either  voluntary,  or  the  result  of  the  irritation 
being  reflected  from  the  sensory  to  the  motor  fibres.  Occasionally,  too, 
irritation  of  the  distal  ends  of  divided  anterior  roots  elicits  signs  of  pain, 
as  well  as  producing  muscular  movements:  the  pain  thus  excited  is  prob- 
ably the  result  either  of  cramj)  or  of  so-called  recurrent  sensibility. 

Recurrent  Sensihility. — If  the  anterior  root  of  a  spinal  nerve  be 
divided,  and  the  peripheral  end  be  irritated,  not  only  movements  of  the 
muscles  supplied  by  the  nerve  take  place,  but  also  of  other  muscles,  indic- 
ative of  pain.  If  the  main  trunk  of  the  nerve  (after  the  coalescence  of 
the  roots  beyond  the  ganglion)  be  divided,  and  the  anterior  root  be 
irritated  as  before,  the  general  signs  of  pain  still  remain,  although  the 
contraction  of  the  muscles  does  not  occur.  The  signs  of  pain  disappear 
when  the  posterior  root  is  divided.     From  these  experiments  it  is  be- 


THE    NERVOUS   SYSTEM.  547 

lie^ed  that  the  stimulus  passes  down  the  anterior  root  to  the  mixed  nerve, 
and  returns  to  the  central  nervous  system  through  the  posterior  root 
iDy  means  of  certain  sensory  fibres  from  the  posterior  root,  which  loop 
back  into  the  anterior  root  before  continuing  their  course  into  the  mixed 
nerve-trunk.  These  fibres  degenerate  when  the  posterior  nerve-root  is 
divided  beyond  the  ganglion. 

Functions  of  the  Ganglia  on  Posterior  Boots. — The  ganglia  act  as 
centres  for  the  nutrition  of  the  nerves,  since  when  the  nerves  are  severed 
from  connection  with  the  ganglia,  the  parts  of  the  nerves  so  severed 
degenerate,  while  the  parts  which  remain  in  connection  with  them  do 
not.  Thus  on  section  of  the  posterior  nerve-root  beyond  the  ganglion 
the  peripheral  part  wastes  and  the  central  does  not,  and  on  section  of 
the  root  between  the  ganglion  and  the  cord  the  central  part  to  a  great 
■extent  wastes  and  the  peripheral  remains  unaffected. 

Functions  or  the  Spinal  Cord. 

The  power  of  the  spinal  cord,  as  a  nerve-centre,  may  be  arranged 
nnder  the  heads  of  (1)  Conduction;   (2)  Eefiex  action. 

(1)  Conduction. — The  functions  of  the  spinal  cord  in  relation  to  con- 
duction, may  be  best  remembered  by  considering  its  anatomical  connec- 
tions with  other  parts  of- the  body.  From  these  it  is  evident  that  there 
is  no  way  by  which  nerve-impulses  can  be  conveyed  from  the  trunk  and 
extremities  to  the  brain,  or  vice  versa,  other  than  that  formed  by  the 
spinal  cord.  Through  it,  the  impressions  made  upon  the  peripheral  ex- 
tremities or  other  parts  of  the  spinal  sensory  nerves  are  conducted  to  the 
brain,  where  alone  they  can  hQ  perceived.  Through  it,  also,  the  stimu- 
lus of  the  will,  conducted  from  the  brain,  is  capable  of  exciting  the 
action  of  the  muscles  supplied  from  it  with  motor  nerves.  And  for  all 
these  conductions  of  impressions  to  and  fro  between  the  brain  and  the 
spinal  nerves,  the  perfect  state  of  the  cord  is  necessary ;  for  when  any 
part  of  it  is  destroyed,  and  its  communication  with  the  brain  is  inter- 
rupted, impressions  on  the  sensory  nerves  given  off  from  it  below  the 
seat  of  injury,  cease  to  be  propagated  to  the  brain,  and  the  brain  loses 
the  power  of  voluntarily  exciting  the  motor  nerves  proceeding  from  the 
portion  of  cord  isolated  from  it.  Illustrations  of  this  are  furnished  by 
various  examples  of  paralysis,  but  by  none  better  than  by  the  common 
paraplegia,  or  loss  of  sensation  and  voluntary  motion  in  the  lower  part  of 
the  body,  in  consequence  of  destructive  disease  or  injury  of  a  portion, 
including  the  whole  thickness,  of  the  spinal  cord.  Such  lesions  destroy 
the  communication  between  the  brain  and  all  parts  of  the  spinal  cord 
below  the  seat  of  injury,  and  consequently  cut  off  from  their  connection 
with  the  brain  the  various  organs  supplied  with  nerves  issuing  from 
those  parts  of  the  cord. 


548  HANDBOOK    OF    PHYSIOLOGY. 

It  is  not  probable  that  the  conduction  of  motor,  even  if  it  be  the  case 
with  sensory  impulses  along  the  cord  is  effected  under  ordinary  circum- 
stances (to  any  great  extent),  as  was  formerly  supposed,  through  the  gray 
substance,  i.e.,  through  the  jierve-corpusclcs  and  filaments  connecting 
them.  All  parts  of  the  cord  are  not  alike  able  to  conduct  all  impres- 
sions; and  as  there  are  separate  nerve-fibres  for  motor  and  for  sensory 
imjsressions,  so  in  the  cord,  separate  and  determinate  tracts  serve  to 
conduct  always  the  same  kind  of  impression. 

Experimental  and  other  observations  point  to  the  following  conclu- 
sions regarding  the  conduction  of  sensory  and  motor  impressions  through 
the  spinal  cord.  Many  of  these  conclusions  must,  however,  be  received 
with  considerable  reserve. 

a.  Sensory  Impressions  are  conveyed  to  the  spinal  cord  by  the 
posterior  nerve-roots,  and  it  is  reasonable  to  suppose  that  they  are  then 
carried  upward  to  the  bulb  by  the  postero-external  and  postero-median 
columns,  since  section  of  the  posterior  nerve-roots  on  the  central  side  of 
the  ganglia  produces  a  definite  degeneration  above  the  section  of  the 
postero-external  column  for  some  distance  and  of  the  posterior  median 
column  as  far  as  the  bulb.  The  degeneration  is  limited  to  different 
parts  of  the  posterior  median  column  according  to  Avhat  nerves  are 
divided.  Thus,  on  section  of  the  posterior  roots  in  the  sacral  region, 
the  degeneration  is  confined  to  the  most  internal  portion  of  the  column 
close  to  the  margin,  while  section  of  the  lumbar,  thoracic  and  cervical 
nerve-roots  is  followed  by  tracts  of  degeneration  seen  in  the  column 
more  and  more  central  and  external.  From  the  researches  of  Mott  and 
others  anything  beyond  a  slight  crossing  of  sensory  impulses  in  the  cord 
is  rendered  highly  improbable.  The  fibres  then  of  the  posterior  nerve- 
roots  pass  up  in  the  posterior  median  column,  and  apparently  end  in  the 
representative  of  that  column  in  the  bulb,  viz.,  in  the  processus  gracilis. 
If  there  be  disease  or  section  of  the  posterior  external  column  or  of  the 
roots  as  they  enter  the  cord,  degeneration  of  that  column  for  some 
distance  and  of  the  posterior  median  column  to  the  bulb  in  a  degree 
proportionate  to  the  nerve-fibres  destroyed  is  produced.  With  degen- 
eration of  the  posterior  median  column,  on  section  of  the  posterior 
nerve-roots  there  is  degeneration  of  the  tract  of  Lissauer  for  some  dis- 
tance. 

The  direct  cerebellar  tract  is  believed  to  commence  in  the  cells  of 
the  posterior  vesicular  column  of  Clarke  of  the  same  side ;  it  goes  chiefly 
to  the  cerebellum,  through  the  restiform  body,  but  is  said  also  to  contain 
fibres  which  pass  up  as  far  as  the  corpora  quadrigemina  and  then  turn 
backward  and  lying  near  the  brachium  pass  to  the  cerebellum.  The 
fibres  of  the  antero-lateral  ascending  tract  are  considered  to  arise  from 
the  gray  matter  of   the  posterior  cornu.     In  the  case  of  the  ascending 


THE    NERVOUS    SYSTEM.  549 

tracts,  with  the  exception  of  the  posterior  median  column,  the  connec- 
tion with  the  posterior  nerve-roots  is  not  direct. 

As  regards  the  conduction  of  sensation  the  following  summary  is 
given  by  Mott.  Painful  sensations  are  conducted  up  both  sides,  as  is  also 
the  sensation  of  heat.  Touch  and  pressure  sensations  associated  with 
localization  are  chiefly  conducted  up  the  same  side,  although  after  a  time 
a  collateral  channel  may  be  developed  which  becomes  permanent,  just  as 
collateral  channels  are  formed  for  the  production  of  bilateral  associated 
movements.  Lastly,  there  can  be  little  doubt  that  muscular-sense  im- 
pressions pass  up  the  same  side.  Muscular-sense  impressions  are  proba- 
bly conduced  by  the  posterior  median  column.  Sensations  of  touch, 
heat,  and  cold,  and  painful  sensations  may  be  conducted  upward  by 
the  antero-lateral  ascending  tract. 

b.  Motor  Impressions. — Motor  impressions  are  conveyed  downward 
from  the  brain  along  the  pi/rainidal  tracts,  viz. ^  the  direct  or  anterior, 
{indthe  crossed  or  lateral,  chiefly  in  the  latter.  Generally  speaking,  the 
impressions  pass  down  on  the  side  opposite  to  which  they  originate, 
having  undergone  decussation  in  the  medulla;  but  some  impressions  do 
not  cross  in  the  medulla,  but  lower  down,  in  the  cord,  being  conveyed 
by  the  anterior  or  uncrossed  pyramidal  fibres,  and  decussate  in  the 
anterior  commissure.  TJie  motor  fibres  for  the  legspartiallij  pass  down- 
ward in  the  lateral  columns  of  the  same  side.  This  is  also  probably  the 
case  with  the  bilateral  muscles,  i.e.,  muscles  of  the  two  sides  acting 
together,  such  as  the  intercostal  muscles  and  other  muscles  of  the  trunk, 
as  well  as  the  costo-humeral  muscles. 

It  is  quite  certain,  as  was  just  now  pointed  out,  that  the  fibres  of  the 
anterior  nerve-roots  are  more  numerous  than  the  fibres  jn'oceeding  down- 
ward from  the  brain  in  the  pyramidal  tracts,  or  the  so-called  pyramidal 
fibres.  It  is  therefore  probable  that  each  pyramidal  fibre,  or  set  of 
fibres,  corresponds  with  an  apparatus  of  ganglion  cells  in  the  anterior 
cornu  either  on  the  same  level,  or  above  or  below  it,  that  when  this  fibre, 
or  set  of  fibres,  is  stimulated,  very  complex  co-ordinated  movements 
occur — such  co-ordinated  movements  having  been  set  up  by  impressions 
starting  from  a  connected  system  of  ganglion  cells,  and  sent  out  into  the 
motor  nerve  fibres  which  arise  from  them.  In  other  words,  it  appears 
to  be  probable  that  in  the  gray  matter  of  the  anterior  cornua  of  various 
S3ctions  of  the  cord  are  contained  the  apparatus  for  various  comiDlicated 
co-ordinated  movements.  The  apparatus  of  each  co-ordinated  move- 
ment may  be  set  in  motion  either  by  sensory  impressions  passing  to  the 
cord,  when  the  result  of  movement  would  be  a  reflex  action,  or  by  an 
impression  travelling  downward  from  the  brain,  and  conveyed  by  one 
or  more  pyramidal  fibres. 

Division    of    the    anterior  pyramids  of  the  medulla  at  the  point  of 


550  HANDBOOK    OF    PHYSIOLOGY. 

decussation  is  followed  by  paralysis  of  motion,  never  quite  absolute,  in 
all  parts  below.  Disease  or  division  of  any  part  of  the  cerebro-spinal 
axis  above  the  seat  of  decussation  is  followed  by  impaired  or  lost  power 
of  motion  on  the  opposite  side  of  the  body ;  while  a  like  injury  inflicted 
below  this  part  induces  similar,  never  quite  absolute  no  doubt,  on  the 
corresponding  side. 

When  one  half  of  the  spinal  cord  is  cut  through  in  monkeys,  the 
follovving  results  follow  (Mott) : — Motor  paralysis  of  the  muscles  of  the 
same  side  (never  complete  of  muscles  used  in  bilateral  associated  action), 
followed  by  gradual  recovery  of  muscular  movement,  except  of  the  finer 
movements  of  the  hand  and  foot ;  wasting  and  flabbiness  of  the  muscles ; 
sensory  paralysis  of  the  same  side  (temperature,  touch,  pain  and  pres- 
sure) ;  temporary  vaso-motor  paralysis  on  came  side.  The  temperature  of 
the  affected  side  was  depressed  1  to  3°  (F.). 

Reflex  Action. — In  man  the  spinal  cord  is  so  much  under  the  control 
of  the  higher  nerve-centres,  that  its  own  individual  functions  in  rela- 
tion to  reflex  action  are  apt  to  be  overlooked;  so  that  the  result  of 
injury,  by  which  the  cord  is  cut  off  completely  from  the  influence  of  the 
encephalon,  is  aj)t  to  lessen  rather  than  increase  our  estimate  of  its 
importance  and  individual  endowments.  Thus,  when  the  human 
spinal  cord  is  divided,  the  lower  extremities  fall  into  any  position  that 
their  weight  and  the  resistance  of  surrounding  objects  combine  to  give 
them;  and  if  the  body  is  irritated,  they  do  not  move  toAvard  the  irrita- 
tion; and  if  they  are  touched,  the  consequent  reflex  movements  are 
disorderly  and  purposeless;  all  power  of  voluntary  movement  is  absolutely 
abolished.  In  other  mammals,  however,  e.g.,  in  the  rabbit  or  dog,  after 
recovery  from  the  shock  of  the  operation,  which  takes  some  time,  reflex 
action  will  occur  in  the  parts  below  after  the  spinal  cord  has  been  divided, 
a  very  feeble  irritation  being  followed  by  extensive  and  co-ordinate 
movements.  In  the  case  of  the  frog,  and  many  other  cold-blooded 
animals,  in  which  experimental  and  other  injuries  of  the  nerve-tissues 
are  better  borne,  and  in  which  the  lower  nerve-centres  are  less  subor- 
dinate in  their  action  to  the  higher,  the  reflex  functions  of  the  cord  are 
still  more  clearly  shown.  When,  for  example,  a  frog's  head  is  cut  off, 
its  limbs  remain  in,  or  assume  a  natural  position ;  they  resume  it  when 
disturbed;  and  when  the  abdomen  or  back  is  irritated,  the  feet  are 
moved  with  the  manifest  purpose  of  pushing  away  the  irritation.  The 
main  difference  in  the  cold-blooded  animals  being  that  the  reflex  move- 
ments are  more  definite,  complicated,  and  effective,  although  less  ener- 
getic than  in  the  case  of  mammals.  It  might  indeed  be  thought,  on 
superficial  examination,  that  the  mind  of  the  animal  was  engaged  in 
the  acts;  and  yet  all  analogy  would  lead  us  to  the  belief  that  the  spinal 
cord  of  the  frog  has  no  different  endowment,  in  kind,  from  those  which 


THE    NERVOUS   SYSTEM.  ■  551 

belong  to  the  cord  of  the  higher  vertebrata:  the  difference  is  only  in 
degree.  And  if  this  be  granted,  it  may  be  assumed  that,  in  man  and 
the  higher  animals,  many  actions  are  performed  as  reflex  movements 
occurring  through  and  by  means  of  the  spinal  cord,  although  the  latter 
cannot  by  itself  initiate  or  even  direct  them  independently. 

Cutaneous  and  Muscle  Reflexes. — In  the  human  subject  two  kinds  of 
reflex  actions  dependent  upon  the  spinal  cord  are  usually  distinguished, 
the  alterations  of  which,  either  in  the  direction  of  increase  or  of  diminu- 
tion, are  indications  of  some  abnormality,  and  are  used  as  a  means  of 
diagnosis  in  nervous  and  other  disorders.  They  are  termed  respectively 
{a.)  cutcHieous  reflexes,  and  {h.)  muscle  reflexes,  (a.)  Cutaneous  reflexes 
are  set  up  by  a  gentle  stimulus  applied  to  the  skin.  The  subjacent 
muscle  or  muscles  contract  in  response.  Although  these  cutaneous 
reflex  actions  may  be  demonstrated  almost  anywhere,  yet  certain  of  such 
actions  as  being  most  characteristic  are  distinguished,  e.g.,  plantar 
reflex;  glutear  reflex,  i.e.,  a  contraction  of  the  gluteus  maximus  when 
the  skin  over  it  is  stimulated;  cremaster  reflex,  retraction  of  the 
testicle  when  the  skin  of  the  inside  of  the  thigh  is  stimulated,  and  the 
like.  The  ocular  reflexes,  too,  are  important.  They  are  contraction 
of  the  iris  on  exposure  to  light,  and  its  dilatation  on  stimulating  the  skin 
of  the  cervical  region.  All  of  these  cutaneous  reflexes  are  true  reflex 
actions.  They  differ  in  different  individuals,  and  are  more  easily  elicited 
in  the  young.  Muscle  reflexes,  or  as  they  are  often  termed,  tendon 
reflexes,  consist  of  a  contraction  of  a  muscle  under  conditions  of  more  or 
less  tension,  when  its  tendon  is  sharply  tapped.  The  so-called  patellar- 
tendon-reflex  is  the  most  well-known  of  this  variety  of  reflexes.  If  one 
knee  be  slightly  flexed,  as  by  croscing  it  over  the  other,  so  that  the 
quadriceps  femoris  is  extended  to  a  moderate  degree,  and  the  patella 
tendon  be  tapped  with  the  Angers  or  the  earpiece  of  a  stethoscope,  the 
muscle  contracts  and  the  knee  is  jerked  forward. 

Another  variety  of  the  same  phenomenon  is  seen  if  the  foot  is  flexed  so 
as  to  stretch  the  calf  muscles  and  the  tendo  Achillis  is  tapped;  the 
foot  is  extended  by  the  contraction  of  the  stretched  muscles.  It  appears, 
however,  that  the  tendon  reflexes  are  not  exactly  what  their  name  im- 
plies. The  interval  between  the  tap  and  the  contraction  is  said  to  be 
too  short  for  the  production  of  a  true  reflex  action.  It  is  suggested 
that  the  contraction  is  caused  by  local  stimulation  of  the  muscle,  but 
that  this  would  not  occur  unless  the  muscle  had  been  reflexly  stimulated 
previously  by  the  tension  applied,  and  placed  in  a  condition  of  excessive 
irritability.  It  is  further  probable  that  the  condition  on  which  it 
depends  is  a  reflex  spinal  irritability  of  the  muscle  or  (exaggerated) 
muscular  tone,  which  is  admitted  to  be  a  reflex  phenomenon,  or  an  ex- 
ample of  automatism,  in  the  spinal  cord. 


552  •         HANDBOOK    OF    PHYSIOLOGY. 

Inhibit  mi  of  Reflex  Actiom. — Movements  such  as  are  produced  by 
irritating  the  skin  of  the  lower  extremities  in  tlie  human  subject,  after 
division  or  disorganization  of  a  part  of  the  spinal  cord,  do  not  follow 
the  same  irritation  when  the  cerebrum  is  active  and  the  connection 
between  the  cord  and  the  brain  is  intact.  This  is,  probably,  due  to 
the  fact  that  the  mind  ordinarily  perceives  the  irritation  and  instantly 
inhibits  or  controls  the  action ;  for,  even  when  the  cord  is  perfect,  such 
involuntary  movements  may  follow  an  irritation,  applied  when  the  cere- 
brum is  inactive.  When,  for  example,  one  is  anxiously  thinking,  even 
slight  stimuli  may  produce  involuntary  and  reflex  movements.  So,  also, 
during  sleep,  such  reflex  movements  may  be  observed,  when  the  skin  is 
touched  or  tickled;  for  example,  when  one  touches  with  the  finger  the 
palm  of  the  hand  of  a  sleeping  child,  the  finger  is  grasped — the  im- 
pression on  the  skin  of  the  palm  producing  a  reflex  movement  of  the 
muscles  which  close  the  hand.  But  when  the  child  is  awake,  no  such 
effect  is  produced. 

Further,  many  reflex  actions  are  capable  of  being  more  or  less  con- 
trolled or  even  altogether  prevented  by  the  will :  thus  an  inhibitory  action 
may  be  exercised  by  the  cerebrum  over  reflex  functions  of  the  cord 
and  the  other  nerve-centres.  The  following  may  be  quoted  as  familiar 
examples  of  this  action : — 

To  prevent  the  reflex  action  of  crying  out  when  in  pain,  it  is  often 
sufficient  firmly  to  clench  the  teeth  or  to  grasp  some  object  and  hold  it 
tight.  When  the  feet  are  tickled  we  can,  by  an  effort  of  will,  prevent 
the  reflex  action  of  jerking  them  up.  So,  too,  the  involuntary  closing 
of  the  eyes  and  starting,  when  a  blow  is  aimed  at  the  head,  can  be 
similarly  restrained. 

Darwin  has  mentioned  an  interesting  example  of  the  way  in  which, 
on  the  other  hand,  such  an  instinctive  reflex  act  may  override  the 
strongest  effort  of  the  will.  He  placed  his  face  close  against  the  glass 
of  the  cobra's  cage  in  the  Reptile  House  at  the  Zoological  Gardens,  and 
though,  of  course,  thoroughly  convinced  of  his  perfect  security,  could 
not  by  any  effort  of  the  will  prevent  himself  from  starting  back  when 
the  snake  struck  with  fury  at  the  glass. 

It  has  been  found  by  experiment  that  in  a  frog  the  02)tic  lobes  and 
optic  tJialami  have  a  distinct  action  in  inhibiting  or  delaying  reflex  ac- 
tion, and  also  that  more  generally  any  afferent  stimulus,  if  sufficiently 
strong,  may  inhibit  or  modify  any  reflex  action  even  in  the  absence  of 
these  centres. 

On  the  whole,  therefore,  it  may,  from  these  and  like  facts,  be  con- 
cluded that  reflex  acts,  performed  under  the  influence  of  the  reflecting 
power  of  the  spinal  cord,  are  essentially  independent  of  the  brain  and  may 
be  performed  perfectly  when  the  brain  is  separated  from  the  cord :  that 


THE    NERVOUS    SYSTEM.  553 

these  include  a  much  hirger  number  of  the  natural  and  purposive  move- 
ments of  the  lower  animals  than  of  the  warm-blooded  animals  including 
man:  and  that  over  nearly  all  of  them  the  mind  may  exercise,  through 
the  higher  nerve-centres,  some  control;  determining,  directing,  hinder- 
ing, or  modifying  them,  either  by  direct  action,  or  by  its  power  over 
associated  muscles. 

To  these  instances  of  spinal  reflex  action,  some  add  yet  many  more, 
including  nearly  all  the  acts  which  seem  to  be  pei'formed  unconsciously, 
such  as  those  of  walking,  running,  writing,  and  the  like:  for  these  are 
really  involuntary  acts.  It  is  true  that  at  their  first  performances  they 
are  voluntary,  that  they  require  education  for  their  perfection,  and  are 
at  all  times  so  constantly  performed  in  obedience  to  a  mandate  of  the 
will,  that  it  is  difficult  to  believe  in  their  essentially  involuntary  nature. 
But  the  will  really  has  only  a  controlling  power  over  their  jierformance ; 
it  can  hasten  or  stay  them,  but  it  has  little  or  nothing  to  do  with  the 
actual  carrying  out  of  the  effect.  And  this  is  proved  by  the  circum- 
stance that  these  acts  can  be  performed  during  complete  mental  abstrac- 
tion: and,  more  than  this,  that  the  endeavor  to  carry  them  out  entirely 
by  the  exercise  of  the  will  is  not  only  not  beneficial,  but  positively  in- 
terferes with  their  harmonious  and  perfect  performance.  Any  one  may 
convince  himself  of  this  fact  by  trying  to  take  each  step  as  a  voluntary 
act  in  walking  downstairs,  or  to  form  each  letter  or  word  in  writing  by 
a  distinct  exercise  of  the  will. 

These  actions,  however,  will  be  again  referred  to. 

Morbid  reflex  actions. — The  relation  of  the  reflex  action  to  the  strength 
of  the  stimulus  is  the  same  as  was  shown  generally  to  occur  in  nerve- 
centres,  a  slight  stimulus  producing  a  slight  movement,  and  a  greater, 
a  greater  movement,  and  so  on;  but  in  instances  in  which  we  must 
assume  that  the  cord  is  morlndlg  more  irritaMe,  i.e.,  apt  to  issue  more 
nervous  force  than  is  pro])ortionate  to  the  stimulus  applied  to  it,  a  slight 
impression  on  a  sensory  nerve  produces  extensive  reflex  movements. 
This  appears  to  be  the  condition  in  the  disease  called  tetanus,  in 
which  a  slight  toucli  on  the  skin  may  throw  the  whole  body  into 
convulsions. 

Special  Centres. — It  may  seem  to  have  been  implied  that  the  spinal 
cord  as  a  single  nerve-centre,  reflects  alike  from  all  j^arts  all  the  impres- 
sions conducted  to  it.  This,  however,  is  not  the  case,  and  it  should  be 
regarded  as  we  have  indicated,  as  a  collection  of  nervous  centres  united 
in  a  continuous  column.  This  is  well  illustrated  by  the  fact  that  seg- 
ments of  the  cord  may  act  as  distinct  nerve-centres,  in  which  special 
co-ordinated  muscular  actions  are  represented,  and  excite  muscular  action 
in  the  parts  supplied  with  nerves  given  off  from  them;  as  well  as  by  the 
analogy  of    certain  cases  in  which  the   muscular  movements  of  single 


554  HANDBOOK    OF    PHYSIOLOGY. 

organs  are  under  the  control  of  certain  circumscribed  portions  of  the 
cord.     The  special  centres  are  the  following  (on  each  side  ) : — 

{((.)  The  Defmcation,  or  Ano- Spinal  centre. — The  mode  of  action  of 
the  ano-sjainal  centre  appears  to  be  this.  The  mucous  membrane  of  the 
rectum  is  stimulated  by  the  presence  of  faeces  or  of  gas  in  the  bowel. 
The  stimulus  passes  up  by  the  afferent  nerves  of  the  hsemorrhoidal  and 
inferior  mesenteric  plexus  to  the  centre  in  the  cord,  situated  in  the 
lumbar  enlargement,  and  is  reflected  through  the  pudendal  plexus  to 
the  anal  sphincter  on  the  one  hand,  and  on  the  other  to  the  muscular 
tissue  in  the  wall  of  the  lower  bowel.  In  this  way  is  produced  a  relaxa- 
tion of  the  first  and  a  contraction  of  the  second,  and  expulsion  of  the 
contents  of  the  bowel  follows.  The  centre  in  the  sjDinal  cord  is  par- 
tially under  the  control  of  the  will,  so  that  its  action  may  be  either 
inhibited  or  augmented.  The  action  may  be  helped  by  the  abdominal 
muscles  which  are  under  the  control  of  the  will,  although  under  a  strong 
stimulus  they  may  also  be  compelled  to  contract  by  reflex  action. 

{!).)  The  Micturition,  or  the  Vesico- Spinal  centre. — The  vesico-spinal 
centre  acts  in  a  very  similar  way  to  that  of  the  ano-spinal.  The  centre 
is  also  in  the  lumbar  enlargement  of  the  cord.  It  may  be  stimulated  to 
action  by  impulses  descending  from  the  brain,  or  reflexly  by  the  pres- 
ence of  urine  in  the  bladder.  The  action  of  the  brain  may  be  voluntary, 
or  it  may  be  excited  to  action  by  the  sensation  of  distention  of  the  bladder 
by  the  urine.  The  sensory  fibres  concerned  are  the  posterior  roots  of  the 
lower  sacral  nerves.  The  action  of  the  centre  thus  stimulated  is  double, 
or  it  may  be  supposed  that  the  centre  consists  of  two  parts,  one  which  is 
usually  in  action  and  maintains  the  tone  of  the  sphincter,  and  the  other 
which  causes  contraction  of  the  bladder  and  other  muscles.  When  evacu- 
ation of  the  bladder  is  to  occur,  impulses  are  sent  to  one  part  of  the 
centre  on  the  one  hand,  and  from  it  to  the  bladder  and  to  certain  other 
muscles  which  cause  their  contraction,  and  on  the  other  to  the  other 
part  of  the  centre,  inhibiting  its  action  on  the  sphincter  urethra?  which 
procures  its  relaxation.  The  way  having  been  opened  by  the  relaxation  of 
the  sphincter,  the  urine  is  expelled  by  the  combined  action  of  the  blad- 
der and  accessory  muscles.  The  cerebrum  may  act  not  only  in  the  way  of 
stimulating  the  cenl^-e  to  action,  but  also  in  the  way  of  inhibiting  its 
action.  The  abdominal  muscles  may  be  called  into  action  as  in  defae- 
cation. 

(c.)  The  Emission  of  Semen  or  Genito- Spinal  centre. — The  centre 
situated  in  the  lumbar  enlargement  of  the  sj^inal  cord  is  stimulated  to 
action  by  sensory  impressions  from  the  glans  jjenis.  Efferent  impulses 
from  the  centre  excite  the  successive  and  co-ordinate  contractions  of  the 
musular  fibres  of  the  vasa  deferentia  and  vesiculoe  seminales,  and  of  the 
accelerator  urinas  and  other  muscles  of  the  urethra;  and  a  forcible  expul- 


THE    NERVOUS    SYSTEM.  555 

si  on  of  semen  takes  place,  over  which  the  mind  has  little  or  no  control, 
and  which,  in  cases  of  paraplegia,  may  be  nnfelt. 

(d.)  The  Erection  of  the  Penis  centre. — This  centre  is  also  situated 
in  the  lumbar  region.  It  is  excited  to  action  by  the  sensory  nerves  of 
the  penis.  Efferent  impulses  produce  dilatation  of  the  vessels  of  the  penis, 
which  also  appears  to  be  in  part  the  result  of  a  reflex  contraction  of  the 
muscles  by  which  the  veins  returning  the  blood  from  the  penis  are  com- 
pressed. 

{e.)  Parturition  centre. — The  centre  for  the  exi:)ulsion  of  the  con- 
tents of  the  uterus  in  parturition  is  situated  in  the  lumbar  spinal  cord 
rather  higher  up  than  the  other  centres  already  enumerated.  The 
stimulation  of  the  interior  of  the  uterus  by  its  contents  may,  under 
certain  conditions,  excite  the  centre  to  send  out  impulses  which  produce 
a  contraction  of  the  uterine  walls  and  exj)ulsion  of  the  contents  of  the 
cavity.  The  centre  is  independent  of  the  will  since  delivery  can  take 
place  in  paraplegic  women,  and  also  while  a  patient  is  under  the  influ- 
ence of  chloroform.  Again,  as  in  the  cases  of  defaecation  and  micturi- 
tion, the  abdominal  muscles  assist;  their  action  being  for  the  most 
part  reflex  and  involuntary. 

[f.)  The  Centre  for  the  Movements  of  Lymphatic  Hearts  of  Frog. — - 
Volkmann  has  shown  that  the  rhythmical  movements  of  the  anterior  pair 
of  lympliatic  hearts  in  the  frog  depend  upon  nervous  influence  derived 
from  the  portion  of  spinal  cord  corresponding  to  the  third  vertebra,  and 
those  of  the  posterior  pair  on  influence  supplied  by  the  portion  of  cord 
opposite  the  eighth  vertebra.  The  movements  of  the  heart  continue, 
though  the  whole  of  the  cord,  except  the  above  portions,  be  destroyed ;  but 
on  the  instant  of  destroying  either  of  these  portions,  though  all  the  rest  of 
the  cord  be  untouched,  the  movements  of  the  correspondiug  hearts  cease. 

{g.)  The  Centre  for  the  Tone  of  Muscles. — The  influence  of  the  spinal 
cord  on  the  sphincter  ani  and  sphincter  urethras  has  been  already  men- 
tioned (see  above).  It  maintains  these  muscles  in  permanent  contrac- 
tion. The  condition  of  these  sphincters,  however,  is  not  altogether 
exceptional.  It  is  the  same  in  kind,  though  it  exceeds  in  degree  that 
condition  of  muscles  which  has  been  called  tone,  or  passive  contraction ; 
a  state  in  which  they  always  when  not  active  appear  to  be  during  health, 
and  in  which,  though  called  inactive,  they  are  in  slight  contraction,  and 
certainly  are  not  relaxed,  as  they  are  soon  after  death,  or  when  the  spinal 
cord  is  destroyed.  This  tone  of  all  the  muscles  of  the  trunk  and  limbs 
depends  on  the  spinal  cord,  just  as  the  contraction  of  the  sphincters 
does.  If  an  animal  be  killed  by  injury  or  removal  of  the  brain,  the 
muscles  retain  their  tone;  but  if  the  spinal  cord  be  destroyed,  the 
sphincter  ani  relaxes,  and  all  the  muscles  feel  loose,  flabby,  and  atonic, 
remaining  so  till  rigor  mortis  commences. 


556  HANDBOOK    OF    PHYSIOLOGY. 

This  kind  of  tone  must  be  distinguished  from  that  mere  firmness  and 
tension  which  it  is  customary  to  ascribe,  under  the  name  of  tone,  to 
all  tissues  that  feel  robust  and  not  flabby,  as  well  as  to  muscles.  The 
tone  peculiar  to  muscles  has  in  it  a  degree  of  vital  contraction :  that  of 
other  tissues  is  only  due  to  their  being  well  nourished,  and  therefore  com- 
pact and  tense. 

All  the  foregoing  examples  illustrate  the  fact  that  the  spinal  cord  is 
a  collection  of  reflex  centres,  upon  which  the  higher  centres  act  by  send- 
ing down  impulses  to  set  in  motion,  modify  or  control  them.  The 
movements  or  other  phenomena  of  reflex  action  are,  as  it  were,  the  func- 
tion of  the  ganglion  cells  to  which  an  afferent  impression  is  conveyed  by 
the  posterior  nerve-trunks  in  connection  with  them.  The  extent  of  the 
movement  depends  upon  the  strength  of  the  stimulus,  the  position  in 
which  it  is  applied  as  well  as  the  condition  of  the  nerve-cells;  the  con- 
nection between  the  cells  being  so  intimate  that  a  series  of  co-ordinated 
movements  may  result  from  a  single  stimulation.  Whether  the  cells 
possess  as  well  the  power  of  originating  impulses  (automatism)  is  doubt- 
ful, but  this  is  possible  in  the  case  of  (h)  vaso-motor  centres  which  are 
situated  in  the  cord  (p.  234),  and  of  (i)  sweatmg  centres  which  must  be 
closely  related  to  them,  and  possibly  in  the  case  of  (/)  the  centres  for 
maintaining  the  tone  of  muscles. 

The  Nutrition  (a)  of  the  muscles,  appears  to  be  under  the  control  of 
the  spinal  cord.  When  the  nerve-cells  of  the  anterior  cornu  are  diseased 
the  muscles  atrophy.  In  the  same  way  (b)  the  bones  and  (c)  joints  are 
seriously  affected  when  the  cord  is  diseased.  The  former  when  the 
anterior  nerve-cells  are  implicated,  do  not  grow,  and  the  latter  are  dis- 
organized in  some  cases  when  the  posterior  columns  are  affected,  (d) 
The  skin,  too,  is  evidently  only  maintained  in  a  healthy  condition  as 
long  as  the  cord  and  its  nerves  are  intact.  No  doubt  part  of  this  influ- 
ence which  the  cord  exercises  over  nutrition  is  due  to  the  relationship 
which  it  bears  to  the  vaso-motor  nerves. 

Within  the  cord  are  contained,  for  some  distance,  fibres  (a)  which 
regulate  the  dilatation  of  the  pupil,  (b)  which  have  to  do  with  the  glyco- 
genic function  of  the  liver,  (c)  which  control  the  nerve-supply  of  the 
vessels  of  the  face  and  head,  {d)  which  produce  acceleration  of  the 
heart's  action,  and,  (e)  have  a  termotaxic  action  on  the  muscles,  etc. 

The  Relations  of  the  Different  Paets  of  the  Brain. 

Before  considering  the  parts  of  the  brain  separately,  it  will  be  best  for 
the  comprehension  of  the  plan  of  its  construction  to  take  a  general  survey 
of  the  whole.  The  brain  on  superficial  examination  presents  four 
distinct  parts,  viz.  (a.)   The   large   and   prominent   masses  of   nervous 


THE    NERVOUS   SYSTEM. 


557 


matter  divided  by  fissures  into  convolutions  (fig.  356),  and  covering  to  a 
large  extent  the  other  pai'ts,  separated  from  one  another  by  a  deep 
fissure  running  from  front  to  back.  These  constitute  the  cerebral 
hemispheres  or  cerebrum.,  (b)  On  the  under  or  central  surface  of  the 
brain  can  be  seen  a  broad  mass  rounded  on  the  surface  more  or  less 
quadrilateral  in  shape;  this  is  the  2Jons  Varolii  (fig.   354,  VI.).     An- 


Fig.  354.— Base  of  the  brain.  1,  superior  longitudinal  fissure;  2,  3',  2",  anterior  cerebral 
lobe;  3,  fissure  of  Sylvius,  between  anterior  and  4,  4',  4",  middle  cerebral  lobe;  5,  5',  posterior 
lobe:  6,  medulla  oblongata.  The  figure  is  in  the  right  anterior  pyramid ;  7,  8,  9,  10,  the  cerebellum; 
+.  the  inferior  verimform  process.  The  figures  from  I.  to  IX.  are  placed  against  the  corresponding 
cerebral  nerves;  III.  is  placed  on  the  right  crus  cerebri.  \t:.  and  VII.  on  the  pons  Varolii;  X. 
the  first  cervical  or  suboccipital  nerve.     (Allen  Thomson.)    J^. 

teriorly  it  is  seen  to  branch  off  into  two  strands,  which  are  the  cni7'a 
cerebri;  and  posteriorly  it  joins  with  a  narrower  portion,  which  is  the 
medulla  oblongata  or  bulb.  This  latter  is  continuous  with  the  spinal  cord. 
In  connection  with  the  bulb  and  pons  are  seen  many  nerve-trunks  pass- 
ing off;  these  are  the  chief  part  of  the  cranial  nerves.  Two  of  the 
cranial  nerves,  however,  are  more  interior,  and  one,  the  optic  (fig.  354, 
2),  is  seen  to  send  off  abroad  band  of  fibres  which  apparently  passes 
into  the  substance  of  the  cerebrum.  The  most  anterior  nerve-root  on 
either  side,  viz.,  the  olfactory  (fig.  354,  1),  extends  for  some  distance 
upon  the  under  surface  of  each  cerebral  hemisphere,  {c.)  The  pons  is 
seen  to  be  connected  laterally  with  a  large  mass  of  nervous  matter,  upon 
which  in  the  position  of  the  brain  turned  upward,  the  bulb  also  rests j 


558  HANDBOOK    OF    PHYSIOLOGY. 

this  is  the  cerebellum^  and  {d.)  When  the  brain  is  viewed  in  the  normal 
position  at  the  bottom  of  the  fissure,  between  the  hemispheres  is  seen  a 
broad  band  of  white  matter  connecting  one  hemisphere  with  its  fellow, 
the  main  commissure  or  corpus  callosum  (fig.  357).  Such  parts  of  the 
brain  are  evident  even  on  superficial  examination.  On  dissection,  it  is 
found  that  the  central  nervous  system  is  not  a  solid  mass  of  nerve  mate- 
rial; it  incloses  certain  cavities,  the  cerebral  ventricles.  Forming  the 
walls  and  boundaries  of  these  ventricles  are  very  important  masses  of 
nervous  matter.  The  cerebrum  proper  incloses  a  large  central  cavity, 
the  lateral  ventricle,  but  separated  by  a  median  partition  into  two.  Into 
the  cavity  of  each  lateral  ventricle  (fig.  355)  projects  a  rounded  mass  of 
gray  matter  anteriorly,  whicli  is  the  caudate  nucleus  of  an  important 
structure  known  as  the  corpus  striatum,  the  more  external  part  of  which, 
the  lenticular  nucleus,  is  embedded  in  the  mass  of  the  cerebral  hemi- 
sphere. Below,  or  more  posterior  to  the  caudate  nucleus,  and  also  pro- 
jecting into  the  lateral  ventricle,  is  a  second  mass  of  gray  matter,  called 
the  optic  thalamus;  the  upper  part  of  this  only,  however,  is  seen  in  the 
lateral  ventricle,  the  lower  and  more  internal  part  approaching  its  fellow 
in  the  middle  line  leaves  a  space  which  on  vertical  section  is  more  or  liess 
triangular,  called  the  third  ventricle.  The  lateral  ventricles  are  sepa- 
rated from  one  another  by  means  of  a  partition  made  of  two  layers  of 
white  matter,  the  septum  lucidum.  On  section  the  septum  is  seen  to  be 
more  or  less  triangular,  and  between  the  two  layers  there  is  the  space  of 
the  fifth  ventricle  filled  with  fluid. 

At  the  posterior  part  of  the  septum  lucidum,  and  joining  with  it,  is 
the  fornix.  This  is  a  longitudinal  commissure;  it  is  arched  and  its 
edge  is  seen  in  the  lateral  ventricle  on  either  side.  Between  its  edge 
and  the  upper  part  of  the  optic  thalamus  projects  a  fringe  of  blood- 
vessels, which  is  the  upper  part  of  the  septum  of  the  vascular  pia  mater, 
which  passes  into  the  interior  of  the  brain,  and  which  is  called  the  cho- 
roid plexus  ;  the  whole  ot  the  projection  forming  a  roof  for  the  third 
ventricle  is  called  the  velum  inter jmsitum. 

The  fornix  (fig.  355,  e)  is  made  up  of  two  strands  anteriorly,  called 
the  anterior  pillars,  and  of  two  similar  pillars  j^osteriorly ;  the  middle 
portion  called  the  body  consists  of  the  parts  of  the  two  pillars  which  are 
joined  together  in  the  middle  line.  The  body  of  the  fornix  is  triangular 
in  shape,  broad  and  flat  behind,  where  it  is  connected  with  the  corpus 
callosum,  and  narrow  in  front  where  it  is  connected  to  the  septum  luci- 
dum. The  anterior  pillars  pass  downward,  separated  from  one  another 
on  either  side  of  the  third  ventricle  in  front  of  the  foramen,  by  which 
the  lateral  communicates  with  the  third  ventricle,  called  the  foramen 
of  Monro;  each  pillar  then  passes  forward  and  down,  and  twisting  upon 
itself  forms  the  corpus  albicans,  and  then  passes  in  part  to  join  the  optic 


THE    NERVOUS    SYSTEM.  559 

thalamus.  The  posterior  pillars  pass  down  and  out  and  form  part  of 
the  interior  of  that  part  of  the  lateral  ventricle  which  descends  into  the 
posterior  lobe  of  the  cerebrum.  Thus,  when  the  fornix  is  reflected  from 
the  front,  first  of  all  the  velum  interpositum  is  seen,  and  when  that  is 
removed  the  third  ventricle  comes  into  sight. 

The  third  ventricle  terminates  at  its  posterior  extremity  in  the  pineal 
body.     From  this  ventricle  a  short  narrow  passage,  the  iter  a  tertio  ad 


Fig.  355.— Dissection  of  brain,  from  above,  expobing  the  lateral  fouith  and  fifth  ventricles 
with  tiie  surrounding  parts,  i^.  o.  Anterior  part,  or  genu  of  corpus  callosum;  b,  corpus  stria- 
tum; t)',  the  corpus  striatum  of  left  side,  dissected  so  as  to  expose  its  gray  substance;  c,  points 
by  a  line  to  the  taenia  semicircularis;  d,  optic  thalamus;  e,  anterior  pillars  of  fornix  divided; 
below  they  are  seen  descending  in  front  of  the  third  ventricle,  and  between  them  is  seen  part  of 
the  anterior  commissure;  in  front  of  the  letter  e  is  seen  the  slit-like  fifth  ventricle,  between  the 
two  laminas  of  the  septum  lucidum;  /,  soft  or  middle  commissure;  g  is  placed  in  the  posterior 
part  of  the  third  ventricle;  immediately  behind  the  latter  are  the  posterior  commissure  (just 
visible)  and  the  pineal  gland,  the  two  crura  of  which  extend  forward  along  the  inner  and  up- 
per margins  of  the  optic  thalami;  h  and  i,  the  corpora  quadrigemina;  k,  superior  crus  of  cere- 
bellum; close  to  k  is  the  valve  of  Vieussens,  which  has  been  divided  so  as  to  expose  the  fourth 
ventricle;  /,  hippocampus  major  and  corpus  fimliiiatum,  or  ta?nia  hippocampi;  in.  liipiineampus 
minor:  n,  eminentia  collateraiis;  o,  fourtli  vt-iitriide;  p,  posterior  surface  of  medulla  olilongata; 
r,  section  of  cerebellum;  s,  upper  part  of  left  hemisphere  of  cerebellum  exposed  by  the  removal 
of  part  of  the  posterior  cerebral  lobe.     (Hirschfield  and  Leveill6.) 

quartum  ventriculum,  or  aqueduct  of  Sylvius,  passes  through  the  next 
portion  of  the  brain  called  the  mid-brain.  This  part  is  covered  in  by 
two  pairs  of  nerve-ganglia,  the  anterior  and  the  posterior  corpora  qua- 
drigemina, and  the  floor  is  formed  by  the  crura  cerebri.  The  aqueduct 
of  Sylvius  opens  at  the  upper  angle  of  a  lozenge-shaped  cavity,  the 
fourth  ventricle,  which  is  situated  on  the  dorsal  aspect  of  the  pons  and 
bulb.      The  fourth  ventricle  has  no  roof  of  its  own  beyond  a  layer  of 


560 


HANDBOOK    OF    PHYSIOLOGY. 


epithelium,  but  it  is  covered  in  by  the  cerebellum,  the  superior  pedun- 
cles of  which,  converging  forward,  form  its  anterior  limits,  and  the 
inferior  peduncles  form  its  posterior  boundaries  on  either  side. 

The  lateral,  third  and  fourth  ventricles  communicate,  and  through 
the  last  with  the  central  canal  of  the  spinal  cord.  They  are  all  lined 
with  columnar  ciliated  epithelium,  beneath  which  is  a  development  of 
neuroglia.  This  lining  so  formed  is  called  the  ependyma  of  the  ven- 
tricles. Where  the  superior  peduncles  of  the  cerebellum  are  approach- 
ing each  other  at  the  upper  part  of  the  fourth  ventricle,  the  interval 
between  them  is  bridged  over  by  a  thin  layer  of  gray  matter  called  the 
valve  of  Vieussens. 

The  portions  of  the  central  nervous  system  are  thus  classified : — 

(i.)  Cerebral  hemispheres  with  the  corpora  striata,  developed  from 
the  cerebral  vesicles — ^and  enclosing  the  lateral  ventricles. 

(ii.)  Fore-brain^  formed  of  the  parts,  including  the  optic  thalami, 
which  inclose  the  third  ventricle. 

(iii.)  Mid-lrain,  consisting  of  the  parts  inclosing  the  aqueduct  of 


Fig.  366.— Plan  in  outline  of  the  encephalon,  as  seen  from  the  right  side.  5^.  The  parts  ara 
represented  as  separated  from  one  another  somewhat  more  than  natural,  so  as  to  show  their 
connections.  A,  Cerebrum;  /,  g,  h,  its  anterior,  middle,  and  posterior  lobes;  e,  fissure  of  Syl- 
vius; B,  cerebellum;  C,  pons  Varolii;  D,  medulla  oblongata ;  a.  peduncles  of  the  cerebrum; 
b.  c.  rf,  superior,  middle,  and  inferior  peduncles  of  the  cerebellum.     (From  Quain.) 


Sylvius,  viz.,  the  corpora  quadrigemina,  which  form  the  roof,  and  the 
crura  cerebri  which  form  the  floor. 

(iv.)  Hind-hrain,  the  pons  Varolii  and  the  cerebellum  form  respec- 
tively the  floor  and  roof  of  the  fore-part  of  the  hind-brain,  and  the  bulb 
the  floor  of  the  back  part  of  the  hind-brain,  the  roof  being  practically 
absent. 


THE    NERVOUS   SYSTEM. 


561 


This  division  of  the  brain  into  the  four  parts  is  justified  by  a  consid- 
eration of  its  development.  As  will  be  seen  later  on,  the  brain  consists 
originally  of  three  cerebral  vesicles,  the  dilated  extremity  of  the  neural 


Fig.  357. — View  of  the  Corpus  Callosum  from  above,  i^^.— The  upper  surface  of  the  corpus 
callosum  has  been  fully  exposed  by  separating  the  cerebral  hemispheres  and  throwing  them  to 
the  side ;  the  gyrus  f ornicatus  has  been  detached,  and  the  transverse  fibres  of  the  corpus  callo- 
sum traced  for  some  distance  into  the  cerebral  medullary  substance,  f,  the  upper  surface  of  the 
corpus  callosum;  2,  median  furrow  or  raphe;  3,  longitudinal  striae  bounding  the  furrow;  4, 
swelling  formed  by  the  transverse  bands  as  they  pass  into  the  cerebrum ;  5.  anterior  extremity 
or  knee  of  the  corpus  callosum:  6,  posterior  extremity;  7,  anterior,  and  H,  posterior  part  of  the 
mass  of  fibres  proceeding  from  the  corpus  callosum;  9,  margin  of  the  swelling;  10,  anterior  part 
of  the  convolution  of  the  corpus  callosum;  11,  hem  or  band  of  union  of  this  convolution;  12,  in- 
ternal convolutions  of  the  parietal  lobe ;  13,  upper  surface  of  the  cerebellum.  (Sappey  after 
Foville.) 


canal,  and  these  consist  of  fore-,  mid-,  and  hind-brain.  From  the  fore- 
brain  there  is  first  of  all  budded  ofl:  on  either  side  a  new  vesicle,  the 
optic  vesicle  from  whicli  is  developed  the  optic  nerve  and  retina,  and 
afterward  a  large  vesicle,  the  cerebral  vesicle,  which  grows  rapidly, 
becomes  divided  by  a  central  partition  into  two,  each  of  which  incloses 
the  lateral  ventricle.  The  cerebral  vesicles  grow  so  quickly  as  to  cover 
both  the  fore-  and  the  mid-brain.  The  parts  of  which  the  fore-,  mid-, 
and  hind-brains  are  made  up  are  developed  from  the  corresponding  cere- 
bral vesicles. 

It  will  be  as  well  here  to  indicate  briefly  the  structure  of  the  brain. 
It  consists  of  white  and  gray  matter  differently  arranged  in  different 
districts. 

36 


562  HANDBOOK    OF    PHYSIOLOGY. 

Distribution  of  the  Gray  Matter. 

(i.)  In  the  bulb,  at  the  lower  part  the  distribution  of  gray  matter  fol- 
lows that  which  prevails  in  the  cord.  Higher  up  the  chief  part  is  found 
toward  the  posterior  or  dorsal  aspect,  surrounding  the  central  canal. 
When  the  central  canal  opens  out  into  the  fourth  ventricle  the  gray 
matter  comes  to  that  surface  chiefly,  and  is  found  to  consist  more  par- 
ticularly, on  either  side,  of  the  nuclei  of  origin  of  the  cranial  nerves, 
viz.,  the  12th,  11th,  10th,  9th,  and  8th,  and  more  externally  of  the 
nucleus  gracilis  and  nucleus  cuneatus  {n.g.,  n.c,  figs.  361,  362).  In 
addition  to  these  masses  of  gray  matter,  there  are  the  olivary  bodies  (o, 
figs.  361,  362)  toward  the  ventral  surface  with  the  accessory  olives  (o'), 
and  the  external  arcuate  {n.ar.  in  figs.)  nuclei,  placed  at  the  tip  of  the 
anterior  fissure  on  either  side  on  the  ventral  surface  of  the  anterior 
pyramids. 

(ii.)  In  the  2)ons  Varolii. — In  addition  to  the  origins  of  nerves  in 
the  floor  of  the  fourth  ventricle  on  the  dorsal  aspect  of  the  pons,  viz., 
of  the  7th,  6th,  and  5th  nerves,  there  are  several  masses  of  gray  matter, 
viz.,  in  the  back  part,  the  superior  olive  (fig.  364),  and  in  the  front 
part  the  locus  cceruleus,  as  well  as  small  amounts  of  the  same  material 
mixed  with  fibres  in  the  more  ventral  surface. 

(iii.)  In  the  mid-brain,  the  gray  matter  preponderates  in  the  optic 
thalami,  corpiora  quadrigemina,  and  corpora  geniculata.  It  is  also  found 
surrounding  the  aqueduct  of  Sylvius,  and  in  other  parts  of  the  crura, 
notably  such  masses  as  the  red  nucleus  (fig.  365),  locus  niger  (fig.  365). 

(iv.)  In  the  cerebral  hemispheres,  the  cerebral  cortex  is  made  up  of 
gray  matter  which  incloses  white  matter,  and  the  corpus  striatum  is 
made  up  more  or  less  of  the  same  material. 

(v.)  In  the  cerebellum,  the  gray  matter  forms  the  incasing  material. 
In  the  interior  too  there  are  masses  of  gray  matter  forming  the  corpora 
dentata. 

This  then  roughly  indicates  the  localities  in  which  gray  matter  is 
found ;  the  arrangement  of  the  fibres  and  their  relationship  to  the  gray 
matter  will  be  dealt  with  later  on. 

The  Medulla  Oblongata  or  Bulb. 

The  medulla  oblongata  (figs.  358,  359),  is  a  column  of  gray  and 
white  matter  formed  by  the  prolongation  upward  of  the  spinal  cord  and 
connecting  it  with  the  brain. 

Structure. — The  gray  substance  which  it  contains  is  situated  in  the 
interior  and  variously  divided  into  masses  and  laminae  by  the  white  or 
fibrous  substance  which  is  arranged  partly  in  external  columns,  and 


THE    JfEEVOUS   SYSTEM. 


563 


partly  in  fasciculi  traversing  the  central  gray  matter.  The  medulla 
oblongata  is  larger  than  any  part  of  the  spinal  cord.  Its  columns  are 
pyriform,  enlarging  as  they  proceed  toward  the  brain,  and  are  continu- 
ous with  those  of  the  spinal  cord.  Each  half  of  the  medulla,  therefore, 
may  be  divided  into  three  columns  or  tracts  of  fibres,  continuous  with 
the  three  tracts  of  which  each  half  of  the  spinal  cord  is  made  up, — the 
columns  more  prominent  than  those  of  the  spinal  cord,  and  separated 
from  each  other  by  deeper  grooves.  The  anterior,  continuous  with  the 
anterior  columns  of  the  cord,  are  called  the  anterior  pyramids,  and  the 


Fig.  358. 


FiET.  359. 


Fig.  358.— Ventral  or  anterior  surface  of  the  pons  Varolii,  and  medulla  oblongata,  a,  a,  an- 
terior pyramids;  t>,  their  decussation;  c,  e,  olivary  bodies;  d,  d,  restiform  bodies;  e,  arciform 
fibres;  /,  fibres  passing  from  the  auterior  column  of  the  cord  to  the  cerebellum ;  gr,  anterior  col- 
umn of  the  spinal  cord;  h,  lateral  column;  p,  pons  Varolii;  i,  its  upper  fibres;  5,  5,  roots  of  the 
fifth  pair  of  nerves. 

Fig.  359. — Dorsal  or  posterior  surface  of  the  pons  Varolii,  corpora  quadrigemina,  and  me- 
dulla oblongata.  The  peduncles  of  the  cerebellum  are  cut  short  at  the  side,  a,  o,  the  upper 
pair  of  corpora  quadrigemina ;  6,  6,  the  lower ;  /,  /,  superior  peduncles  of  the  cerebellum ;  c, 
eminence  connected  with  the  nucleus  of  the  hypoglossal  nerve;  e,  that  of  the  glosso-pharyngeal 
nerve;  i,  that  of  the  vagus  nerve;  d,  d,  restiform  bodies;  p,  p,  posterior  pyramids;  i\  v,  groove 
in  the  middle  of  the  fourth  ventricle,  ending  below  in  the  calamus  scriptorius ;  7,  7,  roots  of  the 
auditory  nerves. 

postero-median  and  postero-external  columns  are  also  represented  at  the 
posterior  or  dorsal  aspect  of  the  cord  as  the  fasciculus  gracilis  and  the 
fasciculus  cuneatus.  The  posterior  pyramids  of  the  medulla  which  in- 
clude these  two  columns  of  white  matter  soon  become  much  increased 
in  width  by  the  addition  of  a  new  column  of  white  matter  outside  the 
other  two  which  is  known  as  the  fasciculus  of  Rolando.  The  lateral  col- 
umns of  the  cord  undergo  considerable  change  and  are  scarcely  repre- 
sented as  such  in  the  bulb. 

It  may  be  said  then  that  the  bulb  at  its  commencement  differs  only 
slightly  in  size  from  the  cord  with  which  it  is  continuous.     It  soon 


564 


HANDBOOK    OF    THYSIOLOGY. 


becomes  larger  both  laterally  and  antero-posteriorly,  and  after  a  tinie 
opens  out  on  the  dorsal  surface  into  a  space  which  is  known  as  the  fourth 
ventricle,  and  from  being  a  cylinder  with  a  central  canal,  it  is  flattened 
out  on  one  surface  by  the  gradual  approach  of  the  central  canal  to  that 


Jin 


Fig  360  —Dorsal  or  posterior  view  of  the  medulla,  fourth  ventricle,  and  mesencephalon 
(natural  size),  v-i^--,  line  of  the  posterior  roots  of  the  spinal  nerves;  p.m./.,  posterior  median 
fissure- /.o.,  funiculus  gracilis;  cl.,  its  clava;  /.c,  funiculus  cuneatus;  f.R.,  funiculus  of 
Rolando-  r  b  ,  restiform  body;  c.s.,  calamus  scriptorius:  Z,  section  of  ligula  or  tajnia;  part  of 
choroid  plexus  is  seen  beneath  it;  /.r. ,  lateral  recess  of  the  ventricle;  str.,  striae  acusticae;  t./. , 
inferior  fossa-  s  f  ,  posterior  fossa;  between  it  and  the  median  sulcus  is  the  fasciculus  teres; 
cbl  cut  surface  of  the  cerebellar  hemisphere;  nd.,  central  or  gray  matter;  s.m.v.,  superior 
medullary  velum ;  Ing.,  ligula;  s.c.p.,  superior  cerebellar  peduncle  cut  longitudinally;  «-., 
combined  section  of  the  three  cerebellar  peduncles ;  f.o.s. ,  c.q.L,  corpora  quadrigemina  (su- 
perior and  inferior) ;  fr. ,  f rsenulum ;  /. ,  fibres  of  the  fillet  seen  on  the  surface  of  the  tegmen- 
tum- c,  crusti;  l.g..  lateral  groove;  c.g.i.,  corpus  geniculum  internus;  th.,  posterior  part  of 
thalamus;  p.,  pineal  body.  The  Roman  numbers  indicate  the  corresponding  cranial  nerves. 
(E.  A.  Schafer.) 

surface.     The  central  canal  of  the  cord,  therefore,  is  directly  continuous 
with  the  fourth  ventricle. 

If  the  bulb  be  examined  on  its  anterior  or  ventral  surface  it  is  found 
that  the  anterior  fissure,  which  is  a  continuation  of  the  same  fissure  in 
the  cord,  is  occupied  at  the  most  posterior  part  by  fibres  which  are 
crossing  from  one  side  to  the  other;  the  central  canal  being  pushed  now 
toward  the  posterior  surface.  This  is  what  is  known  as  the  anterior 
decussation  of  the  medulla  oblongata.  It  is  formed  of  the  fibres  which 
in  the  cord  occupy  the  postero-lateral  region  and  are  called  the  crossed 
pyramidal  fibres.  The  lateral  pyramidal  fibres  of  either  side  after  cross- 
ing in  the  middle  line  in  this  way  become  part  of  the  anterior  pyramid 


THE    ISTEKVOUS   SYSTEM.  565 

of  the  opposite  side;  the  rest  of  the  pyramid  being  made  up  of  the  fibres 
from  the  anterior  column  of  the  cord  known  as  the  direct  or  uncrossed 
pyramidal  fibres.  These  two  pyramidal  strands  of  fibres  are  those  which 
degenerate  on  lesions  of  certain  parts  of  the  cerebrum  which  are  known 
as  the  motor  areas  of  the  cortex.  They  can  therefore  be  traced  downward 
on  such  lesions  as  tracts  of  degeneration.  They  are  the  fibres  of  commu- 
nication between  the  cerebral  cortex  and  the  different  segments  of  the 
spinal  cord.  The  anterior  pyramids  of  the  bulb  are  marked  out  by  the 
exit  from  that  part  of  the  nervous  axis  to  the  outside  of  them,  of  a 
nerve,  the  12th  or  hypoglossal.  More  laterally  than  this  nerve,  there 
soon  becomes  very  prominent  on  either  side  a  rounded  elevation  or  col- 
umn which  is  known  as  the  olivary  body.  It  is  not  seen  at  the  begin- 
ning of  the  bulb  at  its  junction  with  the  cord,  bat  begins  at  a  lower 
level  than  the  opening  of  the  fourth  ventricle.  On  the  further  side  of 
the  olivary  body  is  seen  the  line  of  origin  of  fibres  of  the  11th,  10th,  and 
9th  nerves,  and  from  this  to  the  posterior  fissure  is  the  posterior  pyramid. 

The  whole  of  that  part  of  the  medulla  which  is  situated  laterally 
between  the  olivary  body  and  the  posterior  fissure  is  known  as  the  resti- 
form  body;  it  is  continued  forward  on  either  side  as  the  inferior  peduncle 
of  the  cerebellum. 

The  changes  which  are  noticed  by  the  study  of  series  of  sections  of 
the  bulb  from  below  upward  may  be  summarized  thus:  In  the  dorsal  or 
posterior  region,  the  posterior  cornua  are  pushed  more  to  each  side,  and 
the  substance  of  Rolando  is  increased  and  becomes  rounded,  reaching 
almost  to  the  surface  of  the  bulb  on  each  side,  a  small  tract  of  longitu- 
dinal fibres  of  the  ascending  root  of  the  5th  nerve  only  intervening. 
There  is  a  great  increase  of  the  reticular  formation  around  the  central 
canal,  and  the  lateral  approaches  the  anterior  cornu.  Then  at  the  ven- 
tral or  anterior  aspect  the  decussation  of  the  lateral  fibres  begins.  By 
this  crossing  over  of  the  fibres,  the  tip  of  the  gray  anterior  cornu  is  cut 
off  from  the  rest  of  the  gray  matter.  The  central  canal  is  pushed  further 
toward  the  posterior  surface,  first  of  all  by  the  decussation  of  the  anterior 
pyramids  just  mentioned,  and  later  on,  i.e.,  above,  by  another  decussa- 
tion of  fibres  more  dorsal.  These  fibres  of  the  second  decussation  as 
they  cross  form  a  median  raphe  and  also  help  to  break  up  the  remaining 
gray  matter  into  what  is  called  a  reticular  formation.  There  has  been 
some  little  doubt  as  to  the  origin  of  these  descussating  fibres,  but  the 
best  authorities  now  consider  them  to  be,  at  any  rate  in  part,  the  fibres 
from  the  nuclei  of  the  fasciculus  gracilis  and  fasciculus  cuneatus  of 
either  side,  and  look  upon  tliem  as  a  sensory  decussation.  At  the  pos- 
terior part  soon  there  appear  in  the  columns  of  white  matter  of  the 
fasciculus  gracilis  and  fasciculus  cuneatus  new  masses  of  gray  matter. 
The  lateral  horn  approaches  the  anterior ;  but  soon  the  latter  is  pushed 


566 


HANDBOOK    OF    PHYSIOLOGY. 


further  and  further  toward  the  centre,  while  the  lateral  horn  remains 
near  the  lateral  surface.  The  anterior  gray  m.atter  becomes  broken  up 
and  merged  into  the  reticular  formation.  There  is  also  a  similar  reticu- 
lar 'formation  both  toward  the  centre  and  also  laterally  in  the  dorsal 
region.  At  the  level  where  the  central  canal  opens  into  the  4th  ventri- 
cle, the  posterior  pyramids  diverging  to  form  the  lower  and  outside 
boundaries,  and  inclosing  a  space,  the  calamus  scriptorius,  between 
them,  there  are  to  be  made  out  various  masses  of  gray  matter  in  addi- 
tion to  the  reticular  formation,  viz.,  the  nuclei  of  the  fasciculus  gracilis 


'/•   ¥    '"i9      U 


Fig.  361.— Anterior  or  dorsal  section  of  the  medulla  oblongata  in  the  region  of  the  superior 
pyramidal  decussation.  «.»»./.,  anterior  median  fissure;  /.a.,  superficial  arciform  fibres 
emerging  from  the  fissure;  py. ,  V)yramid;  n.ar.,  nuclei  of  arciform  fibres;  /.a.,  deep  arciform 
becoming  superficial;  o,  lower  end  of  olivary  nucleus;  n.l.,  nucleus  lateralis;  /. r.,  formatio 
reticularis;  f.a."^,  arciform  fibres  proceeding  from  the  formatio  reticularis;  t/. ,  substantia  ge- 
latinosa  of  Rolando;  a.  T^  ,  ascending  root  of  fifth  nerve;  71.  c,  nucleus  cuneatus;  n.  c. ',  external 
cuneate  nucleus ;  n.g.,  nucleus  gracilis;  /.fir.,  funiculus  gracilis;  p.m.f.,  posterior  median  fis- 
sure; c.c. ,  central  canal  surrounded  by  gray  matter,  in  which  are  n.XL,  nucleus  of  the  spinal 
accessory,  and  n.XIL,  nucleus  of  the  hypoglossal;  s.d.,  superior  pyramidal  decussation. 
(Modified  from  Schwalbe. ) 


and  fasciculus  cuneatus  (361,  n.g.  and  n.c),  which  are  at  this  level, 
however,  already  diminishing  and  are  lost  at  a  level  of  the  pons  Varolii. 

The  olivary  bodies  extend  forward  almost  to  the  level  of  the  pons. 
They  consist  of  gray  and  white  matter.  The  gray  matter  consists  of  a 
plicated  thinnish  strand  containing  small  nerve-cells,  folded  upon  itself 
in  the  form  of  a  loop,  with  the  ends  turned  inward  and  slightly  dorsal 
(Fig.  362,  o) .  The  gray  loop  is  filled  with  and  covered  by  white  matter, 
part  of  the  fibres  passing  through  the  gray. 

Internal  to  the  olivary  body  on  either  side  are  two  small  masses  of 
gray  matter,  one  more  ventral  to  the  other,  called  accessory  olives,  ex- 
ternal and  internal,  and  on  the  surface  of  the  anterior  pyramid  on  either 


THE    NERVOUS   SYSTEM. 


56^ 


side  a  small  mass  of  gra}'  matter,  external  arcuate  nucleus;  laterally 
another  mass  of  the  same  material,  the  representative  of  the  lateral  nu- 
cleus of  the  cord,  is  seen,  viz.,  the  antero-lateral  nucleus,  which  gives 
origin  to  the  spinal  accessory  nerve. 

It  will  be  necessary  to  follow  as  shortly  as  possible  the  fibres  of  the 
spinal  cord  upward  into  the  bulb  and  beyond: — 

The  crossed  and  direct  pyramidal  tracts  have  already  been  described. 
Nothing  definite  is  known  of  the  antero-lateral  descending  tracts.  The 
cerebellar  tracts  pass  laterally  into  the  restiform  bodies  and  go  to  the 


nX- 


Fig.  362.— Section  of  the  meduHa  oblongata  at  about  the  middle  of  the  olivary  body,  f.l.a., 
anterior  median  fissure;  n.ar.,  nucleus  arciformis;  p.,  pyramid;  XII.,  bundle  of  hypoglossal 
nerve  emerging  from  the  surface;  at  6,  it  is  seen  coursing  between  the  pyramid  and  the  olivary 
nucleus,  o.  ; /.a. e. ,  external  arciform  fibres;  n.l.,  nucleus  lateralis;  a.,  arciform  fibres  passing 
toward  restiform  body,  partly  through  the  substantia  gelatinosa,  g.,  partly  superficial  to  the 
ascending  root  of  the  fifth  nerve,  a,  V. ;  X,  bundle  of  vagus  root  emerging;  /.?-.,  formatio  retic- 
ularis; c.r.,  corpus  restiform,  beginning  to  be  formed,  chiefly  by  arciform  fibres,  superficial 
and  deep;  n.c,  nucleus  cuneatus;  n.g.,  nucleus  gracilis ;  (,  attachment  of  the  ligula;  /.s.,  funi- 
culus solitarius ;  n.  X. ,  n.  X. ',  two  parts  of  the  vagus  nucleus ;  n.  XII. ,  hypoglossal  nucleus ;  n.  t. , 
nucleus  of  the  funiculus  teres;  n.am.,  nucleus  ambiguus;  ?-. ,  raphe;  A.,  continuation  of  the 
anterior  column  of  cord;  o',  o",  accessory  olivary  nucleus;  p.o.,  pedunculus  olivae.  (Modified 
from  Schwalbe.) 

cerebellum.  The  antero-lateral  ascending  tracts  appear  to  have  the 
same  destination  and  pass  directly  or  indirectly  into  the  cerebellum. 
The  fibres  of  the  postero-median  and  postero-external  columns  end  in 
the  nuclei  of  the  fasciculus  gracilis  and  cuneatus  respectively,  either  in 
or  about  the  cells  contained  in  those  nuclei ;  at  any  rate,  ascending  de- 
generation of  these  columns  cannot  be  traced  above  these  nuclei. 

The  rest  of  the  fibres  of  the  cord  appear  to  end  in  the  reticular  for- 
mation of  the  bulb.  The  bundle  of  fibres  constituting  the  ascending 
root  of  the  5th  nerve  appears  to  correspond  with  the  tract  of  Lissauer. 

Connectio7is  of  the  bulb  with  the  cerebrum  and  cerebellum. — In  addition 


568  HANDBOOK    OF    PHYSIOLOGY. 

to  the  pyramidal  tracts  connecting  the  bulb  with  the  cerebrum  and"  the 
direct  cerebellar  and  the  antero-lateral  ascending  tract  connecting  it 
with  the  cerebellum,  there  are  other  connections  of  the  bulb  with  the 
cerebrum,  and  with  the  cerebellum,  not  actually  direct. 

(1.)  Fibres  from  the  nucleus  gracilis  and  nucleus  cuneatus,  which, 
as  we  have  said,  are  the  bulbar  endings  of  the  fibres  of  the  postero- 
median and  postero-external  columns  of  the  cord,  pass  in  sets  as  it  were 
in  the  following  m.anner : — 

(a.)  Internal  arcuate  fibres. — Some  pass  down  and  inward  to  the  other 
side  in  the  reticular  formation,  forming  in  part  the  superior  or  sensory 
decussation,  and  in  the  inter-olivary  region  become  longitudinal  in  a 
band  of  fibres  called  the  fillet,  which  passes  upward.  These  fibres  are 
probably  augmented  by  the  addition  of  fibres  from  the  anterior  columns 
of  the  cord. 

(b.)  External  arcuate  fibres  also  decussate  in  the  same  way,  pass 
down  along  the  anterior  fissure,  and  then  running  outward  superficially 
over  the  anterior  pyramid  and  olivary  body,  reach  the  restiform  body 
and  pass  to  the  side  of  the  cerebellum  opposite  to  their  nuclei  of  origin. 
These  fibres  appear  to  have  some  relation  with  the  external  arcuate  nu- 
clei. They  connect  one  side  of  the  spinal  cord  with  the  opposite  side  of 
the  cerebellum  through  the  gracile  and  cuneate  nuclei. 

(6'.)  Direct  lateral  fibres  pass  to  the  restiform  body  and  so  to  the  same 
side  of  the  cerebellum. 

(2.)  Fibres  from  the  olivary  body  pass  to  the  opposite  side  of  the 
cerebellum  probably  through  the  reticular  formation. 

(3.)  Arciform  fibres. — Fibres  from  the  nucleus  of  the  8th  or  auditory 
nerve  in  the  floor  of  the  4tli  ventricle,  pass  to  the  same  side  of  the  cere- 
bellum. 

Functions  of  the  Medulla  Oblongata  ok  Bulb, 

The  functions  of  the  bulb  are  those  of,  {a.)  conduction;  (i.)  reflex 
action;  and  (c.)  automatism. 

(«.)  Conduction. — x\s  a  conductor  of  impressions,  the  medulla  oblon- 
gata has  a  wider  extent  of  function  than  any  other  part  of  the  nervous 
system,  since  it  is  obvious  that  all  impressions  passing  to  and  fro  be- 
tween the  brain  and  the  spinal  cord  must  be  transmitted  through  it. 

{b.)  Reflex  Action. — As  a  nerve  centre  by  which  impressions  are 
reflected,  the  medulla  oblongata  also  resembles  the  spinal  cord ;  the  only 
difference  between  them  consisting  of  the  fact  that  many  of  the  reflex 
actions  performed  by  the  former  are  much  more  complicated  than  any 
performed  by  the  spinal  cord. 

It  has  been  proved  by  repeated  experiments  on  the  lower  animals 
that  the  entire  brain  may  be  gradually  cut  away  in  successive  portions, 


THE    ]S"ERVOUS   SYSTEM.  569 

and  yet  life  may  continue  for  a  considerable  time,  and  the  respiratory 
movements  be  uninterrupted.  Life  may  also  continue  when  the  spinal 
cord  is  cut  away  in  successive  portions  from  below  upward  as  high  as 
the  point  of  origin  of  the  phrenic  nerve.  In  amphibia,  the  brain  has 
been  all  removed  from  above,  and  the  cord,  as  far  as  the  medulla  oblon- 
gata, from  below;  and  so  long  as  the  medulla  oblongata  was  intact, 
respiration  and  life  were  maintained.  But  if,  in  any  animal,  the  me- 
dulla oblongata  is  wounded,  particularly  if  it  is  wounded  in  its  central 
part,  opposite  the  origin  of  the  vasi,  the  respiratory  movements  cease, 
and  the  animal  dies  asphyxiated.  And  this  effect  ensues  even  when  all 
parts  of  the  nervous  system,  except  the  medulla  oblongata,  are  left  intact. 
Injury  and  disease  in  men  prove  the  same  as  these  experiments  on 
animals.  Numerous  instances  are  recorded  in  Avhich  injury  to  the  me- 
dulla oblongata  has  produced  instantaneous  death;  and,  indeed,  it  is 
through  injury  of  it,  or  of  the  part  of  the  cord  connecting  it  with  the 
origin  of  the  phrenic  nerve,  that  death  is  commonly  produced  in  frac- 
tures attended  by  sudden  displacement  of  the  upper  cervical  vertebrae. 

Special  Centres. 

In  the  medulla  are  contained  a  considerable  number  of  centres  which 
preside  over  many  important  and  complicated  co-ordinated  movements 
of  muscles.  Tl\«  majority  of  these  centres  are  («.)  reflex  centres  simply, 
which  are  stimulated  by  afferent  or  by  voluntary  impressions.  Some  of 
them  are  {b.)  automatic  centres^  being  capable  of  sending  out  efferent 
impulses,  generally  rhythmical,  without  previous  stimulation  by  afferent 
or  by  voluntary  imprevssions.  The  automatic  centres  are,  however,  gen- 
erally influenced  by  reflex  or  by  voluntary  impulses.  Some  again  of  the 
centres,  whether  reflex  or  automatic,  are  (c.)  control  centres,  by  which 
subsidiary  spinal  centres  are  governed.  Finally  the  action  of  some  of  the 
centres  is  {(I.)  tonic,  i.e.,  they  exercise  their  influence  either  directly  or 
through  another  apparatus,  continuously  and  uninterruptedly  in  main- 
taining a  regular  action. 

Simple  Reflex  centres. 

(1.)  Bilateral  centres  for  the  co-ordinated  movements  of  Mastication^ 
the  afferent  and  efferent  nerves  of  which  have  been  already  enumerated 
(p.  291.) 

(2.)  Bilateral  centres  for  the  movements  of  Deglutition.  The  medulla 
oblongata  appears  to  contain  the  centre  whence  are  derived  the  motor 
impulses  enabling  the  muscles  of  the  palate,  pharynx,  and  oesophagus  to 
produce  the  successive  co-ordinate  and  adapted  movements  necessary  to 
the  act  of  deglutition  (p.  310),  This  is  proved  by  the  persistence  of 
swallowing  in  some  of  the  lower  animals  after  destruction  of  the  cerebral 


570  HANDBOOK    OF   PHYSIOLOGY. 

hemispheres  and  cerebelhim;  its  existence  in  anencephalous  monsters; 
the  power  of  swallowing  possessed  by  the  marsupial  embryo  before  the 
brain  is  developed;  and  by  the  complete  arrest  of  the  power  of  swallow- 
ing when  the  medulla  oblongata  is  injured  in  experiments. 

(3.)  Bilateral  centres  for  the  combined  muscular  movements  of 
Sucking,  the  motor  nerves  concerned  being  the  facial  for  the  lips  and 
mouth,  the  hypoglossal  for  the  tongue,  and  the  inferior  maxillary  divi- 
sion of  the  5tli  for  the  muscles  of  the  jaw. 

(4:.)  Bilateral  centres  for  the  Secretion  of  Saliva,  which  have  been 
already  mentioned  (p.  298.) 

(5.)   Bilateral  centres  for  Vomiting  (p.  326). 

(6.)  Bilateral  centres  for  Coughijig,  which  are  said  to  be  independent 
of  the  respiratory  centre,  being  situated  above  the  inspiratory  part  of 
that  centre. 

(7.)  Bilateral  centres  for  Sneezing,  connected  no  doubt  with  the 
resi^iratory  centre. 

(8.)  Bilateral  centres  for  the  Dilatation  of  the  pupil,  the  fibres  from 
which  pass  out  partly  in  the  third  nerve  and  partly  through  the  spinal 
cord  (through  the  last  two  cervical  and  two  upper  dorsal  nerves)  into  the 
cervical  sympathetic. 

(b.)  Automatic  centres. 

(1.)  Resjnratory  centres. — The  action  of  the  respiratory  centre  has 
been  already  discussed.  It  is  only  necessary  to  i-epeat  here  that  although 
it  can  be  influenced  by  afferent  impulses,  it  is  also  automatic  in  its 
action,  being  capable  of  direct  stimulation,  as  by  the  condition  of  the 
blood  circulating  within  it.  It  is  also  bilateral.  It  probably  consists  of 
an  inspiratory  part  and  of  an  expiratory  part.  The  centre  is  capable  of 
being  influenced  both  reflexly  and  to  a  certain  extent  also  by  voluntary 
impulses.  The  vagus  influence  is  j)robably  constant  in  the  direction  of 
stimulating  the  inspiratory  portion  of  the  centre,  whereas  the  influence 
of  the  superior  laryngeal  is  not  always  in  action,  and  is  inhibitory. 

(2.)  Cardio-Inliibitory  centres.  The  action  of  these  centre  in  main- 
taining the  proper  rhythm  of  the  heart  through  the  vagus  fibres,  which 
terminate  in  a  local  intrinsic  mechanism,  has  been  already  discussed. 
The  centre  can  be  directly  stimulated,  as  by  the  condition  of  the  blood 
circulating  within  it,  and  also  indirectly  by  afferent  stimuli,  especially 
by  stimulating  the  abdominal  sympathetic  nerves,  but  also  by  stimulat- 
ing any  sensory  nerve,  including  the  vagus  itself. 

(3.)  ^cceZem^or  centres  for  the  heart.  The  centres  from  which  arise 
the  accelerator  fibres  of  the  heart,  in  the  medulla.  They  are  automatic 
but  not  tonic  in  action. 

(4.)  Vaso-motor  centres,  which  control  the  unstriped  muscle  of  the 
arteries,  are  also  situated  in  the  medulla.     Like  the  respiratory  centre, 


THE    NERVOUS   SYSTEM.  571 

they  are  bilateral.  As  has  already  been  pointed  out,  these  centres  may 
be  directly  or  reflexly  stimulated,  as  well  as  by  impressions  conveyed 
downward  from  the  cerebrum  to  the  medulla.  The  condition  of  the 
blood  circulating  in  them  is  the  direct  stimulus.  Its  influence  is  no 
doubt  a  tonic  or  else  a  rhythmic  one.  It  is  also  supposed  that  there  is 
in  the  medulla  a  special  vaso-dilator  centre  not  acting  tonically,  stimu- 
lation of  which  produces  vascular  dilatation.  The  diabetic  centre  is 
probably  a  part  of  the  vaso-motor  centre,  at  any  rate  stimulation  of  it 
causes  dilatation  of  the  vessels  of  the  liver. 

(5.)  Bilateral  chief  centres  for  the  secretion  of  Sweat  exist  in  the 
medulla.  The  centres  on  either  side  control  the  subsidiary  spinal  sweat 
centres.  They  may  be  excited  unequally  so  as  to  produce  unilateral 
sweating.     They  are  probably  automatic  and  reflex. 

(6.)  Bilateral  Spasm  centres  are  said  to  be  present  in  the  medulla, 
on  the  stimulation  of  which,  as  by  suddenly  produced  excessive  venosity 
of  the  blood,  general  spasms  of  the  muscles  of  the  body  are  produced. 

{c.)  Control  centres.  These  are  centres  whose  influence  may  be 
directed  to  controlling  the  action  of  subsidiary  centres.     They  are — 

(1.)  The  Respiratory  centres,  which  probably  control  the  action  of 
other  subordinate  centres  in  the  spinal  cord. 

(2.)  The  Cardio-Inhibitory  centres,  which  act  upon  a  local  ganglionic 
mechanism  in  the  heart. 

(3.)  The  Accelerator  centres,  if  they  exist,  probably  act  through  a 
local  mechanism  in  the  heart. 

(4.)  The  Vaso-motor  centres  control  spinal  as  well  as  local  tonic 
centres. 

(5.)   The  medullary  Sweat  centres  control  the  spinal  sweat  centres. 

{d.)  Tonic  centres.  Of  the  centres  whose  action  is  tonic  or  con- 
tinuous up  to  a  certain  degree,  may  be  cited  the  vaso-motor  and  the  car- 
dio-inhibitory . 

It  should  not  be  forgotten  that  in  the  medulla  are  the  centres  for 
the  special  senses.  Hearing  and  Taste,  and  that  other  special  centres  are 
supposed  to  be  localized  there,  of  which  may  be  mentioned  one,  the 
hypothetical  Inhibitory  heat  centre,  which  controls  the  production  of 
heat  by  the  tissues,  independently  of  the  vaso-motor  centre. 

The  Cranial  Nerves. 

The  cranial  nerves  consist  of  twelve  pairs;  they  appear  to  arise  (su- 
perficial origin)  from  the  base  of  the  brain  in  a  double  series,  which 
extends  from  the  under  surface  of  the  anterior  jiart  of  the  cerebrum  to 
the  lower  end  of  the  medulla  oblongata.  Traced  into  the  substance  of 
the  brain  and  medulla,  the  roots  of  the  nerves  are  found  to  take  origin 
from  various  masses  of  gray  matter. 


572 


HANDBOOK    OF    PHYSIOLOGY. 


The  roots  of  the  first  or  olfactory  and  of  the  second  or  optic  nerves 
will  be  mentioned  elsewhere.  The  third  and  fourth  nerves  arise  from 
gray  matter  beneath  the  corpora  quadrigemina;  and  the  roots  of  origin 
of  the  remainder  of  the  cranial  nerves  can  be  traced  to  gray  matter  in 
the  floor  of  the  fourth  ventricle,  and  in  the  more  central  jiart  of  the 
medulla,  around  its  central  canal,  as  low  down  as  the  decussation  of  the 
pyramids. 

According  to  their  several  functions  the  cranial  nerves  may  be  thus 
arranged : — • 
a.  Nerves  of  special  sense 


b.  Nerves  of  common  sensation 

c.  Nerves  of  motion 

d.  Mixed  nerves 


Olfactory,  Optic,  Auditory,  part  of  the 

Glosso- pharyngeal,    and    part    of    the 

Fifth. 
The  greater  portion  of  the  Fifth. 
Third,    Fourth,    lesser  division  of    the 

Fifth,  Sixth,  Facial,  and  Hypoglossal. 
Glosso- pharyngeal.   Vagus,    and    Spinal 

accessory. 

The  physiology  of  the  First,  Second,  and  Eighth  will  be  considered 
with  the  organs  of  Special  sense. 

The  Ilird  Nerve  {Motor  Oculi). 

Origin. — The  third  nerve  arises  in  three  distinct  bands  of  fibres  from 
the  gray  matter  surrounding  the  aqueduct  of  Sylvius  near  the  middle 
line  ventral  to  the  canal.     The  nucleus  of  origin  consists  of  large  multi- 


Fig.  363.— Section  through  anterior  corpus  quadrigeminum  and  part  of  optic  thalamus,  s., 
Aqueduct  of  Sylvius ;  gr. ,  gray  matter  of  the  aqueduct ;  c.  q.  s. ,  quadrigeminal  eminence ;  I. , 
stratum  lemnisci;  o. ,  stratum  opticum ;  c. ,  stratum  cinereum;  Th.,  pulvinate  of  optic  thala- 
mus; c.g.e.,  c.g.i.,  lateral  and  median  corpora  geniculata;  br.s.,  br.i.,  superior  and  inferior 
brachia;/.,  fillet;  p. i.,  posterior  longitudinal  bundle:  r.,  raphe;  III.,  third  nerve,  and  ?i. 7/7., 
its  nucleus;  I. p. p.,  posterior  perforated  space;  s.n.,  substantia  nigra,  above  this  is  the  tegmen- 
tum with  the  circular  area  of  the  red  nucleus;  cr.,  crusta;  77.,  optic  tract;  M. ,  medullary  centre 
of  hemisphere ;  n.c,  nucleus  caudatus;  st.,  stria  terminalis.     (After  Quain,  from  Meynert.) 

polar  ganglion-cells,  and  extends  to  the  back  part  of  the  third  ventricle 
as  far  as  the  level  of  the  anterior  corpus  quadrigeminum.  The  fibres 
pass  from  their  origin  partly  through  the  red  nucleus  to  their  superficial 


THE    NERVOUS   SYSTEM, 


573 


origin  iu  front  of  the  pons,  at  the  median  side  of  each  crus.  They  de- 
cussate with  their  fellows  in  the  middle  raphe.  The  nerve  is  connected 
with  the  optic  nerve. 

Function. — It  supplies  the  levator  palpebrae  superioris  muscle,  and 
all  of  the  muscles  of  the  eyeball,  excejDt  the  superior'  oblique  to  which 


Fig.  364. —Diagram  of  a  longitudinal  section  through  the  pons,  showing  the  relation  of  the 
nuclei  for  the  ocular  muscles.  CQ,  corpora  quadrigemina;  3,  third  nerve;  iii,  its  nucleus;  4, 
fourth  nerve;  iv,  its  nucleus,  the  posterior  part  of  the  third;  6,  sixth  nerve.  The  probable 
position  of  the  centre  and  nerve  fibres  for  accommodation  is  shown  at  a  and  o',  for  the  reflex 
action  of  iris,  at  6,  and  6' ;  for  the  external  rectus  muscles,  at  c,  c'.  The  lines  beneath  the 
floor  of  the  fourth  ventricle  indicate  fibres,  which  connect  the  nuclei.     (Gowers.) 

the  fourth  nerve  is  appropriated,  and  the  rectus  externus  which  receives 
the  sixth  nerve.  Through  the  medium  of  the  ophthalmic  or  lenticular 
ganglion,  of  which  it  forms  what  is  called  the  short  root,  it  also  supj^lies 
motor  filaments  to  the  iris  and  ciliary  muscle.  The  fibres  which  sub- 
serve the  three  functions,  accommodation,  contraction  of  the  pupil,  and 
nerve-supply  to  the  external  ocular  muscles,  arise  from  three  distinct 
groups  of  cells. 

When  the  third  nerve  is  irritated  within  the  skull,  all  those  muscles 
to  which  it  is  distributed  are  convulsed.  When  it  is  paralijzed  or  divided 
the  following  effects  ensue: — (1)  the  up23er  eyelid  can  be  no  longer 
raised  by  the  levator  palpebral,  but  droops  (ptosis)  and  remains  gently 
clos^l  over  the  eye,  under  the  unbalanced  influence  of  the  orbicularis 
palpebrarum,  which  is  supplied  by  the  facial  nerve :  (2)  the  eye  is  turned 
outward  and  downward  (external  strahismus)  by  the  unbalanced  action 
of  the  rectus  externus  and  superior  oblique  to  which  the  sixth  nerve  is 
appropriated;  and  hence,  from  the  irregularity  of  the  axes  of  the  eyes, 
double  sight,  diplopia,  is  often  experienced  when  a  single  object  is  within 
view  of  both  the  eyes:  (3)  the  eye  cannot  be  moved  either  upward,  down- 
ivard,  or  inward:  (4)  the  pupil  I)ecomes  dilated  (mydriasis):  (5)  the  eye 
cannot  accommodate  for  short  distances. 


The  IVth  Nerve  (Trochlearis) . 

Or  if/ in. — The  IVth  nerve  arises  from  a  nucleus  consisting  of  large 
multipolar  ganglion  cells  situated  below,  i.e.,  ventral  to  the  aqueductus 
of  Sylvius,  which  extends  from  the  back  part  of  the  nucleus  of  the 
third  nerve  to  the  hind  level  of  the  posterior  corpus  quadrigeminum. 
The  fibres  from  either  side  sweep  round  the  central  gray  matter,  and 


574 


HANDBOOK    OF    PHYSIOLOGY. 


reach  the  valve  of  Vieusseus,  where  they  decussate  in  the  middle  line 
and  appear  at  the  front  of  the  pons  at  the  lateral  edge  of  the  crus.     The 


Fig.  365.  —Fourth  ventricle  with  the  medulla  oblongata  and  the  corpora  quadrigemina.  The 
reman  numbers  indicate  superficial  origins  of  the  cranial  nerves,  while  the  otlier  numbers  in- 
dicate their  deep  origins,  or  the  position  of  their  central  nuclei.  8,  8',  8",  8'",  auditory  nuclei 
nerves;  t,  funiculus  teres;  A.,  B,  corpora  quadrigemina ;  eg,  corpus  geniculatum;  p,  c,  pedun- 
culus  cerebri ;  m,  c,  p,  middle  cerebellar  peduncle ;  s,  c,  p,  superior  cerebellar  peduncle ;  i,  c,  p, 
inferior  cerebellar  peduncle;  /,  c,  locus  caeruleus;  e,  t,  eminentia  teres;  o,  c,  ala  cinerea;  a,  n, 
accessory  nucleus;  o,  obex;  c,  clava;  /,  c,  funiculus  cuneatus;  /,  g,  funiculus  gracilis. 

nucleus  of  the  fourth  nerve  on  either  side  is  connected  with  those  of  the 
third  and  sixth  nerves. 

Functions. — The  IV th  nerve  is  exclusivel}^  motor,  and  supj)lies  only 
the  trochlearis  or  obliquus  superior  muscle  of  the  eyeball. 


The  Vth  Nerve  (Trigeminus). 

Origin. — The  Vth  or  Trigeminal  nerve  resembles,  as  already  stated, 
the  spinal  nerves,  in  that  its  branches  are  derived  through  two  roots; 
namely,  the  larger  or  sensory,  in  connection  with  which  is  the  Gasserian 
ganglion,  and  the  smaller  or  motor  root  which  has  no  ganglion,  and 
which  passes  under  the  ganglion  of  the  sensory  root  to  join  the  third 
branch  or  division  which  ensues  from  it.  The  fibres  of  origin  of  the 
fifth  nerve  come  from  the  floor  of  the  fourth  ventricle.  The  motor  root 
to  the  inside  of  the  sensory,  about  the  middle  of  each  lateral  half.  The 
sensory  fibres,  however,  can  be  traced  down  in  the  medulla  oblongata  as 
far  as  the  upper  part  of  the  cord.  From  the  motor  nucleus  there 
stretches  forward  as  far  as  the  anterior  corpus  quadrigeminum  a  bundle 
of  long  fibres  termed  the  descending  root,  which  has  attached  to  it  sparse 
spheroidal  nerve-cells.  It  is  also  connected  with  the  locus  caeruleus. 
The  sensory  nucleus  outside  the  motor  has  connected  with  it  a  tract  of 


THE    NERVOUS    SYSTEM. 


575 


fibres  from  the  cord  as  low  as  the  second  cervical  nerve,  and  this  forms 
a  tract  at  the  tip  of  the  posterior  cornu,  between  it  and  the  restiform 
body.  No  nerve  cells  are  connected  with  it.  The  roots  can  be  traced 
obliquely  through  the  pons  Varolii,  beneath  the  floor  of  the  front  part 
of  the  fourth  ventricle.  The  motor  root  is  in  a  position  median  to 
sensory.  The  nerve  appears  at  the  ventral  surface  of  .the  pons  near  its 
front  edge,  at  some  distance  from  the  middle  line. 

Function. — The  first  and  second  divisions  of  the  nerve,  which  arise 
wholly  from  the  larger  root,  are  purely  sensory.  The  third  division 
being  joined,  as  before  said,  by  the  motor  root  of  the  nerve,  is  of  course 
•both  motor  and  sensory. 

(a.)  Motor. — Through  branches  of  the  lesser  or  non-ganglionic  j)or- 
tion  of  the  fifth,  the  muscles  of  mastication,  namely,  the  temporal,  mas- 
seter,  two  pterygoid,  anterior  part  of  the  digastric,  and  mylohyoid, 
derive  their  motor  nerves.  Filaments  are  also  supplied  to  the  tensor 
tynipani  and  tensor  palati.  The  motor  function  of  these  branches  is 
proved  by  the  violent  contraction  of  all  the  muscles  of  mastication  in 
experimental  irritation  of  the  third  or  inferior  maxillary  division  of  the 
nerve;  by  paralysis  of  the  same  muscle,  when  it  is  divided  or  disorgan- 


nvm 


Fig:.  366.  —Section  across  the  pons,  about  tlie  middle  of  the  fourth  ventricle,  pxj. ,  pyramidal 
bundles;  po.,  transverse  fibres  passing  jjOj,  behind,  andpoj,  in  front  ot  py.  ;  r.,  raphe;  o.s.,  su- 
perior olive;  a.  I'.,  bundles  of  ascending  root  of  V.  nerve  inclosed  in  a  prolongation  of  the  sub- 
stance of  Rolando;  F/. ,  the  sixth  nerve,  nVL,  its  nucleus;  VII.,  facial  nerve;  VII. a.,  in- 
termediate portion,  n.VII,  itsnuclevis;  VIII.,  auditory  nerve,  nVIIL,  lateral  nucleus  of  the 
auditory.     (After  Quain.) 


ized,  or  from  any  reason  deprived  of  power;  and  by  the  retention  of  the 
power  of  these  muscles,  when  all  those  supplied  by  the  facial  nerve  lose 
their  power  through  paralysis  of  that  nerve.  The  last  instance  proves 
best,  that  though  the  buccinator  muscle  gives  passage  to,  and  receives 


)76 


HANDBOOK    OF    PIIYSIOLOGT. 


some  filaments  from,  a  buccal  branch  of  the  inferior  division  of  the  fifth 
nerve,  yet  it  derives  its  motor  power  from  the  facial,  for  it  is  paralyzed 
together  with  the  other  muscles  that  are  supplied  by  the  facial,  but 
retains  its  power  when  the  other  muscles  of  mastication  are  paralyzed. 
Whether,  however,  the  branch  of  the  fifth  nerve  which  is  supplied  to 
the  buccinator  muscle  is  entirely  sensory,  or  in  j)art  motor  also,  must 
remain  for  the  present  doubtful.  From  the  fact  that  this  muscle,  be- 
sides its  other  functions,  acts  in  concert  or  harmony  with  the  muscles  of 


Fig.  367.  — Greneral  plan  of  the  branches  of  the  fifth  pair.  J^.— 1,  lesser  root  of  the  fifth 
pair;  2,  greater  root  passing  forward  into  the  Gasserian  ganglion;  3,  placed  on  the  bone  above 
the  ophthalmic  nerve,  which  is  seen  dividing  into  the  supra-orbital,  lachrymal,  and  nasal 
branches,  the  latter  connected  with  the  ophthalmic  ganglion ;  4,  placed  on  the  bone  close  to  the 
foramen  rotundum,  marks  tlic  sujifiidr  maxillary  division,  which  is  connected  below  with  the 
spheno-palatine  ganglion,  and  passes  forward  to  the  infra-orbital  foramen;  5,  placed  on  the  bone 
over  the  foramen  ovale,  marks  tlie  inferior  maxillary  nerve,  giving  off  the  anterior  auricular 
and  muscular  branches,  and  continued  by  the  inferior  dental  to  tlie  lower  jaw,  and  by  the  gus- 
tatory to  the  tongue;  a,  the  submaxillary  gland,  the  sulimaxillary  ganglion  placed  above  it  in 
connection  with  the  gustatory  nerve;  6,  the  chorda  tympaui ;  7,  the  facial  nerve  issuing  from 
the  stylomastoid  foramen.     (Charles  Bell.) 


mastication,  in  keeping  the  food  between  the  teeth,  it  might  be  sup- 
posed from  analogy,  that  it  would  have  a  motor  branch  from  the  same 
nerve  that  supplies  them.  There  can  be  no  doubt,  however,  that  the 
so-called  buccal  branch  of  the  fifth  is,  in  the  main,  sensory ;  although 
it  is  not  quite  certain  that  it  does  not  give  a  few  motor  filaments  to  the 
buccinator  muscle. 

(b.)   Sensory. — Through  the  branches  of  the  greater  or  ganglionic 
portion  of  the  fifth  nerve,  all  the  anterior  and  antero-lateral  parts  of  the 


THE    NERVOUS   SYSTEM.  577 

face  and  head,  with  the  exception  of  the  skin  of  the  parotid  region 
(which  derives  branches  from  the  cervical  spinal  nerves) ,  acquire  com- 
mon sensibility;  and  among  these  parts  may  be  included  the  organs  of 
special  sense,  from  which  common  sensations  are  conveyed  through  the 
fifth  nerve,  and  their  special  sensations  through  their  several  nerves  of 
special  sense.  The  muscles,  also,  of  the  face  and  lower  jaw  acquire 
muscular  sensibility,  through  the  filaments  of  the  ganglionic  portion  of 
the  fifth  nerve  distributed  to  them  with  their  proper  motor  nerves.  The 
sensory  function  of  the  branches  of  the  greater  division  of  the  fifth  nerve^ 
is  proved,  by  all  the  usual  evidences,  such  as  their  distribution  in  parts 
that  are  sensitive  and  not  capable  of  muscular  contraction,  the  exceeding 
sensibility  of  some  of  these  parts,  their  loss  of  sensation  when  the  nerve 
is  paralyzed  or  divided,  the  pain  without  convulsions  produced  by  mor- 
bid or  experimental  irritation  of  the  trunk  or  branches  of  the  nerve, 
and  the  analogy  of  this  portion  of  the  fifth  to  the  posterior  root  of  the 
spinal  nerve. 

Other  Functions. — In  relation  to  muscular  movements,  the  branches 
of  the  greater  or  ganglionic  portion  of  the  fifth  nerve  exercise  a  mani- 
fold influence  on  the  movements  of  the  muscles  of  the  head  and  face 
and  other  parts  in  which  they  are  distributed.  They  do  so,  in  the  first 
place  (a),  by  providing  the  muscles  themselves  with  that  sensibility 
without  which  the  mind,  being  unconscious  of  their  position  and  state, 
cannot  voluntarily  exercise  them.  It  is,  probably,  for  conferring  this 
sensibility  on  the  muscles,  that  the  branches  of  the  fifth  nerve  commu- 
nicate so  frequently  with  those  of  the  facial  and  hypoglossal,  and  the 
nerves  of  the  muscles  of  the  eye;  and  it  is  because  of  the  loss  of  this 
sensibility  that  when  the  fifth  nerve  is  divided,  animals  are  always  slow 
and  awkward  in  the  movement  of  the  muscles  of  the  face  and  head,  or 
hold  them  still,  or  guide  their  movements  by  the  sight  of  the  objects 
toward  which  they  wish  to  move. 

(b.)  Again,  the  fifth  nerve  has  an  indirect  influence  on  the  muscular 
movements,  by  conveying  sensations  of  the  state  and  position  of  the  skin 
and  other  parts:  which  the  mind  perceiving,  is  enabled  to  determine 
appropriate  acts.  Thus,  when  the  fifth  nerve  or  the  infra-orbital  branch 
is  divided,  the  movement  of  the  lips  in  feeding  may  cease,  or  be  imper- 
fect. 

(c.)  An  intimate  connection  with  muscular  movements  through  the 
many  reflex  acts  of  muscles  of  which  it  is  the  necessary  excitant.  Hence, 
when  it  is  divided  and  can  no  longer  convey  impressions  to  the  nervous 
centres  to  be  thence  reflected,  the  irritation  of  the  conjunctiva  produces 
no  closure  of  the  eye,  the  mechanical  irritation  of  the  nose  excites  no 
sneezing. 

(d.)   Through  its  ciliary  branches  and  the  branch  which  forms  the 
37 


578  HANDBOOK    OF    PHYSIOLOGY. 

long  root  of  the  ciliary  or  ophthalmic  ganglion,  it  exercises  also  some 
influence  on  the  movements  of  the  iris.  When  the  trunk  of  the  oph- 
thalmic portion  is  divided,  the  pupil  becomes,  according  to  Valentin, 
contracted  in  men  and  rabbits,  and  dilated  in  cats  and  dogs;  but  in  all 
cases,  becomes  immovable  even  under  all  the  varieties  of  the  stimulus  of 
light.  How  the  fifth  nerve  thus  affects  the  iris  is  unexplained ;  it  has 
been  ingeniously  suggested  the  influence  of  the  fifth  nerve  on  the  move- 
ments of  the  iris  may  be  ascribed  to  the  affection  of  vision  in  consequence 
of  the  disturbed  circulation  or  nutrition  in  the  retina,  when  the  normal 
influence  of  the  fifth  nerve  is  disturbed.  In  such  disturbance,  increased 
•circulation  making  the  retina  more  irritable  might  induce  extreme  con- 
traction of  the  iris. 

Trophic  influence. — The  morbid  effects  which  division  of  the  fifth 
nerve  produces  in  the  organs  of  special  sense,  make  it  probable  that,  in 
the  normal  state,  the  fifth  nerve  exercises  some  special  or  troi)liic  influ- 
ence on  the  nutrition  of  all  these  organs;  although,  in  part,  the  effect 
of  the  section  of  the  nerve  is  only  indirectly  destructive  by  abolishing 
sensation,  and  therefore  the  natural  safeguard  which  leads  to  the  pro- 
tection of  parts  from  external  injury.  Thus,  after  such  division,  within 
a  period  varying  from  twenty-four  hours  to  a  week,  the  cornea  begins  to 
be  opaque;  then  it  grows  completely  white;  a  low  destructive  inflamma- 
tory process  ensues  in  the  conjunctiva,  sclerotica,  and  interior  parts  of 
the  eye;  and  within  one  or  a  few  weeks,  the  whole  eye  may  be  quite 
disorganized,  and  the  cornea  may  slough  or  be  penetrated  by  a  large 
ulcer.  The  sense  of  smell  (and  not  merely  that  of  mechanical  irritation 
of  the  nose),  may  be  at  the  same  time  lost  or  gravely  impaired ;  so  may 
the  hearing,  and  commonly,  whenever  the  fifth  nerve  is  paralyzed,  the 
tongue  loses  the  sense  of  taste  in  its  anterior  and  lateral  parts,  and  ac- 
cording to  Gowers  in  the  posterior  part  as  well. 

In  relation  to  Taste. — The  loss  of  tactile  sensibility  as  well  as  the 
sense  of  taste,  is  no  doubt  due  {a)  to  the  lingual  branch  of  the  fifth  nerve 
being  a  nerve  of  tactile  sense,  and  also  because  with  it  runs  the  chorda 
tympani,  which  is  one  of  the  nerves  of  taste;  partly,  also,  it  is  due  {h), 
to  the  fact  that  this  branch  supplies,  in  the  anterior  and  lateral  parts  of 
the  tongue,  a  necessary  condition  for  the  proper  nutrition  of  that  part; 
while  {c),  it  forms  also  one  chief  link  in  the  nervous  circle  for  reflex 
action,  in  the  secretion  of  saliva.  But,  deferring  this  question  until 
the  glosso-pharyngeal  nerve  is  to  be  considered,  it  may  be  observed  that 
in  some  brief  time  after  complete  paralysis  or  division  of  the  fifth  nerve, 
the  power  of  all  the  organs  of  the  special  senses  may  be  lost ;  they  may 
lose  not  merely  their  sensibility  to  common  impressions,  for  which  they 
all  depend  directly  on  the  fifth  nerve,  but  also  their  sensibility  to  their 
several  peculiar  impressions  for  the  reception  and  conduction  of  which 


THE    NERVOUS   SYSTEM.  579 

they  are  purposely  constructed  and  supplied  with  special  nerves  besides 
the  fifth.  The  facts  observed  in  these  cases  can,  perhaps,  be  only  ex- 
plained by  the  influence  which  the  fifth  nerve  exercises  on  the  nutritive 
processes  in  the  organs  of  the  special  senses.  It  is  not  unreasonable  to 
believe,  that,  in  paralysis  of  the  fifth  nerve,  their  tissues  may  be  the 
seats  of  such  changes  as  are  seen  in  the  laxity,  the  vascular  congestion, 
oedema,  and  other  affections  of  the  skin  of  the  face  and  other  tegumen- 
tary  parts  which  also  accompany  the  paralysis;  and  that  these  changes, 
which  may  appear  unimportant  when  they  affect  external  parts,  are 
suflBcient  to  destroy  that  refinement  of  structure  by  which  the  organs  of 
the  special  senses  are  adapted  to  their  functions. 

The  VI th  Nerve  {AMucens). 

Origin. — The  Vlth  nerve  arises  from  a  compact  oval  nucleus,  situ- 
ated somewhat  deeply  at  the  back  part  of  the  pons  near  the  middle  of 
the  floor  of  the  fourth  ventricle.  The  eminentia  teres  marks  its  posi- 
tion. It  contains  moderately  large  nerve-cells  with  distinct  axis  cylin- 
der processes.  It  is  connected  (fig.  3G4)  with  the  nuclei  of  the  third, 
fourth,  and  seventh  nerves.  It  is  nearer  the  middle  line  than  the  nuclei 
of  the  fifth  and  seventh.  The  root  is  thin,  and  passes  ventrally  and 
laterally  through  the  reticular  formation,  to  the  surface,  which  it  reaches 
at  the  hind  end  of  the  pons  opposite  the  front  end  of  anterior  pyramid. 

Functions. — The  sixth  nerve  is  exclusively  motor,  and  supplies  only 
the  rectus  externus  muscle  of  the  eye. 

The  rectus  externus  is  convulsed,  and  the  eye  is  turned  outward, 
when  the  sixth  nerve  is  irritated;  and  the  muscle  is  paralyzed  when  the 
nerve  is  divided.  In  all  such  cases  of  paralysis,  the  eye  squints  inward, 
and  cannot  be  moved  outward. 

In  its  course  through  the  cavernous  sinus,  the  sixth  nerve  forms 
larger  communications  with  the  sympathetic  nerve  than  any  other  nerve 
within  the  cavity  of  the  skull  does.  But  the  imjDort  of  these  communi- 
cations with  the  sympathetic,  and  the  subsequent  distribution  of  its 
filaments  after  joining  the  sixth  nerve,  are  quite  unknown. 

The  Vllth  Nerve  {Facial). 

Origin. — The  faciat,  or  portio  dura  of  the  seventh  pair  of  nerves, 
arises  from  the  floor  of  the  central  part  of  the  fourth  ventricle  behind 
and  in  line  with  the  motor  nucleus  of  the  fifth,  to  the  outside  of  and 
deeper  down  than  the  nucleus  of  the  sixth.  The  nucleus  is  narrower  in 
front  than  behind,  and  consists  of  large  cells  with  well  marked  axis 
cylinder-processes,  which  are  gathered  up  at  the  dorsal  surface  of  the 
nucleus  to  form  a  root.     The  root  describes  a  loop  round  the  nucleus  of 


580  HANDBOOK    OF    PHYSIOLOGY. 

the  sixth  nerve,  running  forward  for  some  little  distance  dorsal  to  the 
nucleus,  then  descending  vertically,  passing  to  outside  of  its  own  nucleus 
between  it  and  the  ascending  root  of  fifth  nerve.  It  emerges  at  the 
hinder  margin  of  the  pons  lateral  to  the  sixth  nerve,  opposite  the  front 
edge  of  the  groove  between  the  olivary  and  restiform  bodies.  It  may  be 
connected  with  the  hypoglossal  nucleus.  There  are  two  roots;  the  lower 
and  smaller  is  called  the  portio  intermedia. 

Functions. — The  seventh  nerve  is  the  motor  nerve  of  all  the  muscles 
of  the  face,  including  the  platysma,  bat  not  including  any  of  the  mus- 
cles of  mastication  already  enumerated;  it  supjilies,  also,  the  parotid 
gland,  and  through  the  connection  of  its  trunk  with  the  Vidian  nerve, 
by  the  petrosal  nerves,  some  of  the  muscles  of  the  soft  palate,  probably 
the  levator  palati  and  azygos  uvulae.  By  its  tympanic  branches  it  sup- 
plies the  stapedius  and  laxator  tympani ;  and  through  the  optic  ganglion, 
the  tensor  tympani ;  through  the  chorda  tympani  it  sends  branches  to 
the  submaxillary  gland  and  to  the  lingualis  and  some  other  muscular 
fibres  of  the  tongue,  and  to  the  mucous  membrane  of  its  anterior  two- 
thirds;  and  by  branches  given  off  before  it  comes  upon  the  face,  it  sup- 
plies the  muscles  of  the  external  ear,  the  posterior  part  of  the  digas- 
tricus,  and  the  stylo-hyoideus. 

Beside  its  motor  influence,  the  facial  is  also,  by  means  of  the  fibres 
which  are  supplied  to  the  submaxillary  and  parotid  glands,  a  secretory 
nerve.  For,  through  the  last-named  branches,  impressions  may  be  con- 
veyed which  excite  increased  secretion  of  saliva. 

Paralysis  of  Facial  Nerve. — When  the  facial  nerve  is  divided,  or  in 
any  other  way  paralyzed,  the  loss  of  power  in  the  muscles  which  it  sup- 
plies, while  proving  the  nature  and  extent  of  its  functions,  displays  also 
the  necessity  of  its  perfection  for  the  perfect  exercise  of  all  the  organs 
of  the  special  senses.  Thus,  in  paralysis  of  the  facial  nerve,  the  orbicu- 
laris palpebrarum  being  powerless,  the  eye  remains  open  through  the 
unbalanced  action  of  the  levator  palpebrae;  and  the  conjunctiva,  thus 
continually  exposed  to  the  air  and  the  contact  of  dust,  is  liable  to  re- 
peated inflammation,  which  may  end  in  thickening  and  opacity  of  the 
cornea.  These  changes,  however,  ensue  much  more  slowly  than  those 
which  follow  paralysis  of  the  fifth  nerve,  and  never  bear  the  same  de- 
structive character. 

The  sense  of  hearing,  also,  is  impaired  in  many  cases  of  paralysis  of 
the  facial  nerve;  not  only  in  such  as  are  instances  of  simultaneous  dis- 
ease in  the  auditory  nerves,  but  in  such  as  may  be  explained  by  the  loss 
of  power  in  the  muscles  of  the  internal  ear.  The  sense  of  smell  is  com- 
monly at  the  same  time  impaired  through  the  inability  to  draw  air 
briskly  toward  the  upper  part  of  the  nasal  cavities  in  which  part  alone 
the  olfactory  nerve  is  distributed;  because,  to  draw  the  air  perfectly  in 


THE    NERVOUS   SYSTEM,  581 

this  direction,  the  action  of  the  dilators  and  compressors  of  the  nos- 
trils should  be  perfect. 

Lastly,  the  sense  of  taste  is  impaired,  or  may  be  wholly  lost  in  paral- 
ysis of  the  facial  nerve,  provided  the  source  of  the  paralysis  be  in  some 
part  of  the  nerve  between  its  origin  and  the  giving  off  of  the  chorda  tym- 
pani.  This  result,  which  has  been  observed  in  many  instances  of  disease 
of  the  facial  nerve  in  man,  appears  explicable  on  the  supposition  that  the 
chorda  tympani  is  the  nerve  of  taste  to  the  anterior  two-thirds  of  the 
tongue,  its  fibres  being  distributed  with  the  so-called  gustatory  or  lingual 
branch  of  the  fifth.  Some  look  upon  the  chorda  as  partly  or  entirely 
made  up  of  fibres  from  the  fifth  nerve,  and  not  strictly  speaking  as  a 
branch  of  the  facial;  others  consider  that  it  receives  its  taste  fibres  from 
communications  with  the  glosso-2:)haryngeal. 

Together  with  these  effects  of  paralysis  of  the  facial  nerve,  the  mus- 
cles of  the  face  being  all  powerless,  the  countenance  acquires  on  the 
paralyzed  side  a  characteristic,  vacant  look,  from  the  absence  of  all  ex- 
pression :  the  angle  of  the  mouth  is  lower,  and  the  paralyzed  half  of  the 
mouth  looks  longer  than  that  on  the  other  side;  the  eye  has  an  unmean- 
ing stare.  All  these  peculiarities  increase,  the  longer  the  paralysis 
lasts;  and  their  appearance  is  exaggerated  when  at  any  time  the  muscles 
of  the  opposite  side  of  the  face  are  made  active  in  any  expression,  or  in 
any  of  their  ordinary  functions.  In  an  attempt  to  blow  or  whistle,  one 
side  of  the  mouth  and  cheeks  acts  properly,  but  the  other  side  is  mo- 
tionless, or  flaps  loosely  at  the  impulse  of  the  expired  air ;  so  in  trying 
to  suck,  one  side  only  of  the  mouth  acts;  in  feeding,  the  lips  and  cheeks 
Are  f)Owerless,  and  on  account  of  paralysis  of  the  buccinator  muscle  food 
lodges  between  the  cheek  and  gums. 

The  Vlllth  Nerve  (Auditory). 

Origin. — The  Vlllth  iierve  arises  from  two  nuclei,  median  and  lat- 
eral^ in  the  floor  of  the  fourth  ventricle,  in  the  anterior  part  of  the 
bulb  in  front  and  to  the  side  of  the  twelfth  nerve;  it  extends  from  the 
middle  line  to  the  outside  margin  of  the  ventricle.  There  is  also  an 
accessory  nucleus  situated  on  the  ventral  surface  of  the  restiform  body. 
The  nerve  leaves  the  surface  of  the  brain  from  the  ventral  surface  of  the 
fore-part  of  the  restiform  body  at  the  hind  margin  of  the  pons  in  two 
roots.  One  winds  round  the  restiform  body  dorsal  to  it  and  the  other 
passes  median  to  it.  The  former  is  called  the  dorsal  root.  The  latter 
is  called  the  ventral  root.  Most  of  the  fibres  of  the  dorsal  root  {cochlear) 
•end  in  cells  of  the  accessory  nucleus,  but  fibres  emerging  from  this  nu- 
cleus pass  inward  to  the  bulb,  superficially,  forming  the  stria}  acusticm 
in  the  floor  of  the  fourth  ventricle  and  end  in  the  median  nucleus.     Most 


582  HANDBOOK    OF   PHYSIOLOGY. 

of  the  fibres  of  the  veutral  root  {vestihular)  end  in  cells  of  the  lateral 
nucleus.  The  cells  of  the  median  nucleus  are  small,  those  of  the  lateral 
nucleus  large. 

Functions. — The  cochlear  branch  is  the  auditory  nerve  proper,  and 
the  vestibular  is  distributed  to  the  semicircular  canals,  the  utricule  and 
saccule,  parts  of  the  internal  ear  not  directly  concerned  with  hearing. 

The  IXth  Nerve  {Glosso-Pharyiigeal). 

Origin. — The  glosso-j^haryngeal  nerves  (ix. ,  fig.  364),  in  the  enume- 
ration of  the  cerebral  nerves  by  numbers  according  to  the  position  in 
which  they  leave  the  cranium,  ai'e  considered  as  divisions  of  the  eighth- 
pair  of  nerves^  the  vagus  and  spinal  accessory  nerves  being  included  with 
them.  The  union  of  the  nuclei  is  indeed  so  intimate  that  it  will  be  a». 
well  to  take  the  origins  of  the  ninth,  tenth,  and  eleventh  nerves  together. 

These  three  nerves  emerge  from  the  bulb  and  spinal  cord  in  their 
numerical  order  from  above  downward,  the  huTbar  portion  from  the  lat- 
eral aspect  of  the  bulb  in  a  line  between  the  olivary  and  restiform  bodies;, 
and  the  spinal  portion  from  a  line  intermediate  between  the  anterior  and 
posterior  nerve  roots  as  far  down  as  the  sixth  or  seventh  cervical. 

The  combined  glosso-pharyngeal-accessory- vagus  nucleus  appears  tO' 
consist  of  two  parts,  viz.,  one  median  or  common  origin,  having  con- 
spicuous nerve-cells  of  moderate  size,  and  three  lateral  origins,  having 
but  few  cells  of  small  size.  These  are— i.  the  nucleus  ambiguus,  which 
lies  on  the  lateral  side  of  the  reticular  formation  and  is  the  origin  of  the' 
vagus;  ii.  the  fasciculus  solitarius,  situated  in  the  bulb,  ventral  and  a. 
little  lateral  to  the  combined  nucleus,  is  also  called  the  ascending  root, 
of  the  glosso-pharyngeal  nerve  or  the  respiratory  bundle ;  and  iii.  the- 
spinal  jjortion  which  takes  origin  from  a  group  of  cells  lying  in  the  ex- 
treme lateral  margin  of  the  anterior  cornu.  This  is  the  origin  of  the 
spinal  accessory ;  it  corresponds  to  the  antero-lateral  nucleus  of  the  bulb, 
and  the  lateral  part  of  tlie  gray  matter  of  the  spinal  cord. 

The  fibres  of  the  spinal  origin  of  the  nerve  pass  from  these  cells, 
through  the  lateral  column  to  the  surface  of  the  cord. 

The  fibres  from  the  combined  nucleus,  chiefly  from  the  median  piart,. 
pass  in  a  ventral  and  lateral  direction  through  the  reticular  formation, 
then  ventral  to  or  through  the  gelatinous  substance  and  strand  of  fibres- 
connected  with  the  fifth  nerve,  to  the  surface  of  bulb. 

The  fibres  from  the  nucleus  amMguiis  join  the  combined  nerve,  but 
especially  the  vagus. 

The  bundles  of  fibres  of  the  fasciculus  solitarius  start  in  the  lateral 
gray  matter  of  the  cervical  cord  and  higher  in  the  reticular  formation* 
of  the  bulb,  run  longitudinally  forward  to  pass  into  the  roots  of  the  ninth 
nerve. 


THE    NERVOUS    SYSTEM.  583 

IXth  Xerve. — Distrihution. — Tlie  glosso-pharyngeal  nerve  gives  fila- 
ments through  its  tympanic  branch  (Jacobson's  nerve),  to  the  fenestra 
ovalis  and  fenestra  rotunda,  and  the  Eustachian  tube,  parts  of  the  mid- 
dle ear;  also,  to  the  carotid  plexus,  and  through  the  petrosal  nerve,  to 
the  spheno-palatine  ganglion.  After  communicating,  either  within  or 
without  the  cranium,  with  the  vagus,  and  soon  after  it  leaves  the  cra- 
nium, with  the  sympathetic,  digastric  branch  of  the  facial,  and  the 
accessory  nerve,  the  glosso-pharyngeal  nerve  parts  into  the  two  principal 
divisions  indicated  by  its  name,  and  supplies  the  mucous  membrane  of 
the  posterior  and  lateral  walls  of  the  upper  part  of  the  pharynx,  the 
Eustachian  tube,  the  arches  of  the  palate,  the  tonsils  and  their  mucous 
membrane,  and  the  tongue  as  far  forward  as  the  foramen  csecum  in  the 
middle  line,  and  to  near  the  tip  at  the  sides  and  inferior  part. 

Functions. — The  glosso-pharyngeal  nerve  contains  some  motor  fibres, 
together  with  those  of  common  sensation  and  the  sense  of  taste. 

1.  Motor  fibres  are  distributed  to  the  j)alato-pharyngeus,  the  stylo- 
pharyngeus,  palato-giossus,  and  constrictors  of  the  pharynx. 

2.  Sensory  fibres  in  the  parts  which  it  supplies,  and  a  centripetal 
nerve  through  which  impressions  are  conveyed  to  be  reflected  to  the  ad- 
jacent muscles. 

3.  Fibres  for  the  nerve  of  taste  (from  its  fibres  derived  from  the 
fifth,  Gowers),  in  all  the  parts  of  the  tongue  and  palate  to  which  it  is 
distributed.  After  many  discussions,  the  question.  Which  is  the  nerve 
of  taste? — the  chorda  tympani,  the  gustatory,  or  the  glosso-pharyngeal? 
— may  be  most  probably  answered  by  stating  that  they  are  not  them- 
selves, strictly  speaking,  nerves  of  this  special  function,  but  through 
their  connection  with  the  fifth  nerve.  For  very  numerous  experiments 
and  cases  have  shown  that  when  the  trunk  of  the  fifth  nerve  is  paralyzed 
or  divided,  the  sense  of  taste  is  completely  lost  in  the  superior  surface 
of  the  anterior  and  lateral  parts  of  the  tongue,  at  the  back  of  the  tongue, 
and  on  the  soft  palate  and  palatine  arches.  The  loss  is  instantaneous 
after  division  of  the  nerve,  and,  therefore,  cannot  be  ascribed  wholly  to 
the  defective  nutrition  of  the  part,  though  to  this,  perhaps,  may  be 
ascribed  the  more  complete  and  general  loss  of  the  sense  of  taste  when 
the  whole  of  the  fifth  nerve  has  been  paralyzed. 

The  Xth  Nerve  ( Vagus  or  Pneumogastric) . 

The  origin  of  the  Vagus  nerve  is,  as  we  have  Just  seen,  situated  in 
the  lower  half  of  the  calamus  scriptorius  in  the  ala  cinerea  (fig.  365). 
Its  nucleus  is  said  to  represent  the  cells  of  Clarke's  (posterior  vesicular) 
column  of  the  spinal  cord.  In  origin  it  is  closely  connected  with  the 
ninth,    eleventh,   and  the  twelfth.      The  combined   glosso-pharyngeal- 


584  HANDBOOK    OF    PHYSIOLOGY, 

vago-accessory  nuclei  lie  outside  of,  close  to,  and  parallel  with  the  nucleus 
of  the  twelfth. 

Distributioti. — It  supplies  sensory  branches,  which  accompany  the 
sympathetic  on  the  middle  meningeal  artery,  and  others  which  supply 
the  back  part  of  the  meatus  and  the  adjoining  part  of  the  external  ear. 
It  is  connected  with  the  petrous  ganglion  of  the  glosso-pharyngeal,  by 
means  of  fibres  to  its  jugular  ganglion;  with  the  sjiinal  accessory  which 
supplies  it  with  its  motor  fibres  for  the  larger  and  upper  portion  of  the 
cBsophagus,  and  with  its  inhibitory  fibres  for  the  heart;  also  with  the 
twelfth;  with  the  superior  cervical  ganglion  of  the  sympathetic;  and 
with  the  cervical  plexus.  It  has,  of  all  the  nerves,  the  most  varied  dis- 
tribution and  functions,  either  through  its  own  filaments,  or  through 
those  which,  derived  from  other  nerves,  are  mingled  in  its  branches. 
The  parts  supplied  by  the  branches  of  the  vagus  are  as  follows: — 

(1.)  By  its  pharyngeal  branches,  which  enter  the  pharyngeal  plexus, 
a  large  portion  of  the  mucous  membrane,  and,  jjrobably,  all  the  muscles 
of  the  pharynx. 

(2.)  By  the  sujyerior  laryngeal  nerve,  the  mucous  membrane  of  the 
under  service  of  the  epiglottis,  the  glottis,  and  the  greater  part  of  the 
larynx,  and  the  crico-thyroid  muscle. 

(3.)  By  the  inferior  laryngeal  nerve,  the  mucous  membrane  and  mus- 
cular fibres  of  the  trachea,  the  lower  part  of  the  pharynx  and  larynx, 
and  all  the  muscles  of  the  larynx  except  the  crico-thyroid. 

(4.)  By  its  (esophageal  branches,  the  mucous  membrane  and  muscular 
coats  of  the  oesophagus. 

(5.)  Through  the  cardiac  tierves,  moreover,  the  branches  of  the  vagus 
form  a  large  portion  of  the  supply  of  nerves  to  the  heart  and  the  great 
arteries. 

(G.)  Through  the  anterior  and  the  posterior  pulmonary  plexuses  to  the 
lungs. 

(7.)  Through  its  gastric  branches  to  the  stomach;  and  to  the  intes- 
tines, and  kidneys,  by  its  terminal  branches. 

(8.)  Through  its  he2)atic  and  splenic  branches,  the  liver  and  the  spleen 
are  partly  supplied  with  nerves. 

Fimctions. — Throughout  its  whole  course,  the  vagus  contains  both 
sensory  and  motor  fibres.  To  summarize  the  many  functions  of  this 
nerve,  which  have  been  for  the  most  part  considered  in  the  preceding 
chapters,  it  may  be  said  that  it  supplies  (1)  motor  influence  to  the 
pharynx  and  oesophagus,  stomach  and  intestines,  to  the  larynx,  trachea, 
bronchi,  and  lung;  (2)  sensory  and,  in  part,  (3)  vaso-motor  influence, 
to  the  same  regions;  (4)  inhibitory  influence  to  the  heart;  (5)  inhibi- 


THE    NERVOUS   SYSTEM. 


585 


tory  afferent  impulses  to  the  vaso-motor  centre ;  (6)  excito-secretory 

to  the  salivary  glands;  (7)  excito-motor  in  coughing,  vomiting,  etc. 
Effects  of  Section. — Division  of  both  vagi,  or  of  both  their  recurrent 


Fig.  368.— View  of  the  nerves  IX,  X,  and  XI,  their  distribution  and  connections  on  the  left 
side.  2-5. — 1,  Pneumogastric  nerve  in  the  neck:  2,  ganglion  of  its  tninli :  8,  its  union  with  the 
spinal  accessory ;  4,  its  union  with  the  hypoglossal ;  5,  pharyngeal  branch ;  (i,  superior  laryn- 
geal nerve;  7,  external  laryngeal ;  8,  laryngeal  plexus;  9,  inferior  or  recurrent  laryngeal ;  10, 
superior  cardiac  branch;  11,  middle  cardiac;  12,  plexiform  part  of  the  nerve  in  the  thorax;  13, 
posterior  pulmonary  plexus;  14,  lingual  or  gustatory  nerve  of  the  inferior  maxillary;  15,  hypo- 
glossal, pa.ssing  into  the  muscles  of  the  tongue,  giving  its  thyro-hyoid  branch,  and  uniting  with 
twigs  of  the  lingual;  16,  glosso-pharyngeal  nerve;  17,  spinal  accessory  nerve,  uniting  by  its 
inner  branch  with  the  pneumograstric.  and  by  its  outer,  passing  into  the  sterno-mastoid  muscle; 
18,  second  cervical  nerve;  19,  third;  20.  fourth;  21.  origin  of  the  phrenic  nerve,  22,  23,  fifth,  sixth, 
seventh,  and  eighth  cervical  nerves,  forming  with  the  first  dorsal  the  brachial  plexus;  24,  su- 
perior cervical  ganglion  of  the  sympathetic;  25,  middle  cervical  ganglion;  26,  inferior  cervical 
ganglion  united  with  the  first  dorsal  ganglion;  27,  28,  29,  30,  second,  third,  fourth,  and  fifth 
dorsal  ganglia.     (From  Sappey  after  Hirschfeld  and  Leveill6.) 

branches,  is  often  very  quickly  fatal  in  young  animals;  but  in  old  ani- 
mals the  division  of  the  recurrent  nerve  is  not  generally,  and  that  of 
both  the  vagi  is  not  always,  fatal,  and,  when  it  is  so,  death  ensues  slowly. 


586  HANDBOOK    OF    PHYSIOLOGY. 

This  difierence  is,  that  the  yiekliug  of  the  cartilages  of  the  larynx  in 
young  animals  permits  the  glottis  to  be  closed  by  the  atmospheric  pres- 
sure in  inspiration,  and  so  they  are  quickly  suffocated  unless  tracheotomy 
be  performed.  In  old  animals,  the  rigidity  and  prominence  of  the  aryt- 
enoid cartilages  prevent  the  glottis  from  being  completely  closed  by  the 
atmospheric  pressure;  even  when  all  the  muscles  are  paralyzed,  a  por- 
tion at  its  posterior  part  remains  open,  and  through  this  the  animal 
continues  to  breathe. 

In  the  case  of  slower  death,  after  division  of  both  the  vagi,  the  lungs 
are  commonly  found  gorged  with  blood,  oedematous,  or  nearly  solid, 
from  a  kind  of  low  pneumonia,  and  the  bronchial  tubes  full  of  frothy 
bloody  fluid  and  mucus,  to  which,  in  general,  the  death  may  be  ascribed. 
These  changes  are  due,  in  part,  to  the  passage  of  food  and  of  the  various 
secretions  of  the  mouth  and  fauces  through  the  glottis,  which,  being 
deprived  of  its  sensibility,  is  no  longer  stimulated  or  closed  in  conse- 
quence of  their  contact. 

The  Xlth   Nerve  {Spinal  Accessory). 

Origiti  and  Connections. — The  nerve  arises  by  two  distinct  origins — 
one  from  a  centre  in  the  floor  of  the  fourth  ventricle,  partly  but  chiefly 
in  the  medulla,  and  connected  with  the  glosso-jiharyngeal- vagus-nucleus; 
the  other,  from  the  outer  side  of  the  anterior  cornu  of  the  spinal  cord 
as  low  down  as  the  fifth  or  sixth  cervical  nerve.  The  fibres  from  the 
two  origins  come  together  at  the  jugular  foramen,  but  separate  again 
into  two  branches,  the  inner  of  which,  arising  from  the  medulla,  joins 
the  vagus,  to  which  it  supplies  its  motor  fibres,  consisting  of  small  me- 
dullated  or  visceral  nerve-fibres,  while  the  outer  consisting  of  large 
medullated  fibres,  supplies  the  trapezius  and  sterno-mastoid  muscles. 
The  small-fibred  branch  is  said  to  arise  from  a  nucleus  corresponding  to 
the  posterior  vesicular  column  of  Clarke. 

The  principal  branch  of  the  accessory  nerve,  its  external  branch, 
then  suj^plies  the  sterno-mastoid  and  trapezius  muscles;  and,  though 
pain  is  produced  by  irritating  it,  is  composed  almost  exclusively  of 
motor  fibres.  The  internal  branch  of  the  accessory  nerve  supplies  chiefly 
viscero-motor  filaments  to  the  vagus.  The  muscles  of  the  larynx,  all  of 
which,  as  already  stated,  are  supplied,  apparently,  by  branches  of  the 
vagus,  are  said  to  derive  their  motor  nerves  from  the  accessory;  and 
(which  is  a  very  significant  fact)  Vrolik  states  that  in  the  chimpanzee 
the  internal  branch  of  the  accessory  does  not  join  the  vagus  at  all,  but 
goes  direct  to  the  larynx. 

Among  the  roots  of  the  accessory  nerve,  the  lower  or  external,  aris- 
ing from  the  spinal  cord,  appears  to  be  composed  exclusively  of  motor 


THE    XERVOUS    SYSTEM.  587 

fibres,  and  to  be  destined  entirely  to  the  trapezius  and  extending  from 
the  back  of  the  fourth  ventricle  to  the  level  of  the  olivary  bodies  close 
to  the  middle  line,  inside  the  combined  nucleus  of  the  ninth,  tenth,  and 
eleventh  nerves. 

The  Xllth  Nerve  {Hypoglossal). 

Origin  and  Connections. — The  nerve  arises  from  a  large-celled  and 
very  long  nucleus  in  the  bulb,  extending  from  the  back  of  the  fourth 
ventricle  to  the  level  of  the  olivary  bodies  close  to  the  middle  line,  inside 
the  combined  nucleus  of  the  ninth,  tenth,  and  eleventh  nerves.  Fibres 
■from  this  nucleus  run  from  the  ventral  surface  through  the  reticular 
formation  in  a  series  of  bundles  passing  between  the  olivary  nucleus  lat- 
erally and  the  anterior  pyramid  and  accessory  olive  medially,  to  gain 
the  surface.  The  nerve  emerges  from  a  groove  between  the  anterior 
pyramid  and  olivary  body.  The  fibres  of  origin  are  continuous  with 
the  anterior  roots  of  the  spinal  nerves.  It  is  connected  with  the  vagus, 
the  superior  cervical  ganglion  of  the  sympathetic  and  with  the  upper 
cervical  nerves. 

Distrihution. — This  nerve  is  the  motor  nerve  to  the  muscles  con- 
nected with  the  hyoid  bone,  including  those  of  the  tongue.  It  supplies 
through  its  descending  branch  [descendens  noni),  the  sterno-hyoid, 
sterno-thyroid,  and  omo-hyoid;  through  a  special  branch,  the  thyro- 
hyoid, and  through  its  lingual  branches,  the  genio-hyoid,  stylo-glossus, 
hyo-glossus,  and  genio-hyo-glossus  and  linguales. 

Functions. — The  function  of  the  hypoglossal  is  exclusively  motor. 
As  a  motor  nerve,  its  influence  on  all  the  muscles  enumerated  above  is 
shown  by  their  convulsions  when  it  is  irritated,  and  by  their  loss  of 
power  when  it  is  paralyzed.  The  effects  of  the  paralysis  of  one  hypo- 
glossal nerve  are,  however,  not  very  striking.  Often,  in  cases  of  hemi- 
plegia involving  the  functions  of  the  hypoglossal  nerve,  it  is  not  possible 
to  observe  any  deviation  in  the  direction  of  the  protruded  tongue;  prob- 
ably because  the  tongue  is  so  compact  and  firm  that  the  muscles  on  either 
side,  their  insertion  being  nearly  parallel  to  the  median  line,  can  push 
it  straight  forward  or  turn  it  for  some  distance  toward  either  side. 

The  Pons  Varolii. 

The  pons  Varolii  is  generally  spoken  of  as  a  great  commissure  of 
fibres;  of  fibres  which  connect  the  two  halves  of  the  cerebellum  and  of 
fibres  which  connect  the  bulb  and  spinal  cord  with  the  upper  part  of  the 
brain.  Although  this  is  true  it  must  not  be  forgotten  that  the  pons 
contains  several  masses  of  gray  matter,  and  also  in  addition  smaller  col- 
lections of  nerve-cells.     It  is  found  that  on  section  the  following  parts 


588  HANDBOOK    OF    PHYSIOLOGY. 

may  l)o  made  out  in  its  structure,  begiuning  from  the  anterior  or  ven- 
tral surface. 

(a.)  Transverse  or  commissural  fibres  connecting  the  one  side  of  the 
cerebellum  with  the  other,  forming  the  middle  peduncle.  These  fibres 
emerge  from  the  lateral  parts  of  the  white  substance  of  the  hemispheres, 
having  come  from  the  superficial  gray  matter  of  the  whole  surface,  from 
the  median  vermis,  and  from  the  lateral  hemispheres.  Some  of  these 
fibres  are  truly  commissural  and  j^robably  connect  the  same  points  on 
the  surfaces  of  the  two  halves;  some  end  in  the  gray  matter  of  the  same 
side  of  the  pons  on  the  ventral  surface,  and  others  cross  to  the  oj)posite 
side  of  the  pons  and  then  become  longitudinal,  passing  on  to  the  teg- 
mentum, a  system  of  fibres  and  gray  matter  to  be  immediately  described. 

(b.)  Fibres  longitudinal  in  direction  which  are  arranged  in  larger  or 
smaller  bundles  separated  by  gray  matter;  some  of  these  fibres  are  what 
are  called  the  pyramidal  fibres,  which  pass  down  to  the  anterior  pyra- 
mids of  the  bulb. 

(c.)  The  dorsal  portion  of  the  pons  is  made  up  to  a  considerable  ex- 
tent of  the  reticular  formation  of  the  tegmental  region  together  with 
one  or  two  distinct  bundles  of  longitudinal  fibres:  i.,  the  chief,  situated 
toward  the  junction  of  the  ventral  two  thirds  with  the  dorsal  third,  is 
the Jillet,  which  consists  of  two  portions,  outer  and  median;  and  ii.,  the 
second,  a  bundle  of  similar  fibres,  jmsterior  longittidinal  himdles,  is  situ- 
ated between  the  two  divisions  of  the  fillet  below  the  lateral  and  to  the 
outer  side  of  the  median. 

{d.)  In  the  fore  part  of  the  pons,  a  mass  of  gray  matter  containing 
pigment,  the  locus  cmruleus,  possibly  forming  the  origin  of  the  fifth  nerve, 
and  in  the  back  part  a  second  mass  of  gray  matter,  the  siq)erior  olive. 

The  Crura  Cerebri. 

The  crura  cerebri  (iii,  fig.  354)  diverge  from  the  anterior  edge  of 
the  pons  Varolii  and  pass  upward  on  either  side  toward  the  cerebral 
hemispheres.  At  their  anterior  termination  each  of  them  appears  to 
have  upon  its  dorsal  surface,  to  the  inner  and  outer  sides  respectively, 
two  large  masses  of  gray  matter  which  have  been  already  spoken  of,  viz., 
the  optic  thalamus  and  the  corpus  striatum.  These  bodies  are  not  only 
as  it  were  placed  upon  the  surface  of  each  crus,  but  are  also  deeply  em- 
bedded in  its  substance. 

The  crus  is  found  to  be  made  up  of  two  principal  parts : — 

[a.)  The  one,  the  tegmentum,  situated  for  the  most  j)art  on  the  dorsal 
aspect,  is  composed  chiefly  of  gray  matter  and  some  longitudinal  fibres. 

And  ib.)  the  other,  the  crusta,  situated  toward  the  other  surface,  is 
composed  almost  entirely  of  longitudinal  fibres.     It  is  known  also  as  the 


THE    NERVOUS    SYSTEM.  589 

pes.     Separating  these  two  parts,  is  a  mass  of  gray  matter  of  the  shape 
of  a  lens,  called  the  locus  or  nucleus  niger  or  suhstantia  nigra. 

The  tegmentum  situated  dorsally  ends  for  the  most  part  in  the 
neighborhood  of  the  optic  thalamus  and  the  j)arts  beneath.  In  conse- 
quence of  this  the  fibres  of  the  pes  are  allowed  to  come  dorsally  and  to 
proceed  between  the  optic  thalamus  and  the  more  posterior  part  (the 
lenticular  nucleus)  of  the  corpus  striatum,  on  their  course  to  the  cere- 
bral cortex.  "When  in  this  situation  they  form  a  compact  mass  of  fibres. 
As  they  pass  more  dorsally  the  fibres  spread  out  in  the  form  of  a  fan, 
and  this  arrangement  is  called  the  corona  radiata.     The  fibres  of  the  pes 


^<in'.Oy 


f^'?'^-        '  ^  \^  Ark 


r 


Fig:.  369. —Diagram  of  the  motor  tract  as  shown  in  a  diagrrammatic  horizontal  section 
through  the  cerebral  hemispheres,  Crura.  Pons,  and  Medulla.  Fr. ,  Frontal  lobe;  Oc. ,  occipital 
lobe;  AF. ,  ascending  frontal.  AP. ,  ascending  parietal  convolutions;  PCF. ,  pre-central  fissure, 
in  front  of  the  ascending  frontal  convolution;  FR. ,  fissure  of  Rolando;  IPF. ,  inter-parietal  fis- 
sure, a  section  of  crus  is  lettered  on  the  left  side.  SN. ,  Substantia  nigra;  Py. ,  pyramidal  motor 
fibre,  which  on  the  right  is  shown  as  continuous  lines  converging  to  pass  through  the  posterior 
limb  of  IC.  internal  capsule  (the  knee  or  elbow  of  which  is  shown  thus  *)  upward  into  the 
hemisphere  and  downward  through  the  pons  to  cross  the  medulla  in  the  anterior  pyramids. 
(Gowers. ) 

are  found  to  stretch  not  only  between  the  optic  thalamus  and  the  len- 
ticular nucleus,  but  also  more  anteriorly  between  the  former  and  the 
caudate  nucleus  of  the  corpus  striatum  which,  as  we  have  seen,  is  to  be 
seen  in  the  floor  of  the  lateral  ventricle.  The  fibres  of  the  pes  thus 
spread  out,  have  the  form  of  a  fan  bent  upon  itself  as  they  rise  to  pass 
into  the  cerebral  hemisphere.  This  constitutes  the  internal  ccqisule,  and 
that  portion  of  it  which  forms  the  angle  at  which  the  fibres  are  bent  is 
called  the  genu  of  the  capsule,  that  in  front  of  it  being  the  front,  and 
that  behind,  the  hind  limb.  The  fibres  constituting  the  internal  cap- 
sule are  distributed  to  different  districts  of  the  cerebral  cortex.  They 
are  made  up  of  fibres  not  only  constituting  the  pyramidal  system,  but 


590  HANDBOOK    OF    PHYSIOLOGY. 

also  of  others  which  end  in  the  masses  of  gray  matter  in  the  pons  or  crus 
itself;  but  the  function  of  all  of  the  fibres  is  believed  to  be  to  carry  im- 
pulses downward  from  the  cerebrum  either  to  the  spinal  cord  and  so  to 
the  cranial  nerves,  or  to  the  cerebellum. 

The  tegmentum  of  either  side,  on  the  other  hand,  is  supposed  to  be 
concerned,  for  the  most  part  at  any  rate,  with  afferent  impulses.  It  is 
made  up  to  a  very  considerable  extent  of  collections  of  gray  matter,  the 
most  important  of  which  are  (a)  the  loctis  or  nucleus  niger,  separating 
the  pes  and  tegmentum;  {b)  the  nucleus  ruber,  which  is  a  rounded  mass 
situated  more  toward  the  aqueduct  of  Sylvius;  this  extends  from  the 
third  ventricle  to  the  anterior  corpus  quadrigeminum.  The  locus  niger 
extends  back  as  far  as  the  posterior  corpus  quadrigeminum.  (c)  A  third 
mass  of  gray  matter  is  situated  beneath  the  optic  thalamus,  and  is  the 
corpus  subthalamicum.  Posteriorly  the  tegmentum  is  made  up  chiefly 
of  the  reticular  material  so  often  spoken  of,  and  in  the  pons  consists 
almost  entirely  of  that  kind  of  structure,  but  with  the  two  additional 
masess  of  gray  matter  already  indicated,  viz.,  the  locus  coeruleus  and 
superior  olive. 

It  will  be  as  well  here  to  indicate  briefly  the  other  collections  of  gray 
matter  in  the  neighborhood  of  the  crura,  viz.,  the  corpus  striata,  optic 
thalami,  corpora  quadrigemina,  corpora  geniculata,  and  the  corpora 
dentata  of  the  cerebellum. 

Corpora  Striata. — The  corpora  striata  are  situated  in  front  and  to 
the  outside  of  the  optic  thalami,  partly  within  and  partly  without  the 
lateral  ventricle. 

Each  corpus  striatum  consists  of  two  parts : — 

(a.)  An  intraventricular  portion  {cmidate  nucleus)  which  is  conical  in 
shape,  with  the  base  of  the  cone  forward;  it  consists  of  gray  matter, 
with  white  substance  in  its  centre,  {h.)  An  extraventricular  portion 
{lenticular  nucleus),  which  is  separated  from  the  other  portion  by  a  layer 
of  white  material,  which  forms  a  portion  of  the  internal  capsule, — the 
anterior  limb.  The  lenticular  nucleus  is  seen,  on  a  horizontal  section  of 
the  hemisphere,  to  consist  of  three  parts  (the  two  internal  called  globus 
pallidus,  major  and  minor,  and  the  outer  called  the  ^mta^n en),  separated 
from  one  another  by  white  matter,  of  which  the  smallest  of  the  three  is 
inside.  Each  part  somewhat  resembles  a  wedge  in  shape.  The  upper 
and  internal  surface  is  in  relation  with  the  caudate  nucleus,  being  sepa- 
rated from  it  by  the  anterior  limb  of  the  internal  capsule.  The  remain- 
der of  the  internal  surface  is  in  relation  to  the  optic  thalamus,  being 
separated  from  it  by  the  posterior  limb  of  the  internal  capsule.  The 
horizontal  section  is  wider  in  the  centre  than  at  the  ends.  On  the  out- 
side is  the  gray  lamina  (claustrum)  separated  by  a  thin  white  layer — • 
external  capsule — from  the  lenticular  nucleus. 


THE    NEKVOUS    SYSTEM.  591 

Optic  Thalami. — The  optic  thalami  are  oval  in  shape,  and  rest 
upon  the  inner  and  dorsal  surfaces  of  the  crura  cerebri.  The  uj)per 
surface  of  each  thalamus  is  free,  and  of  white  substance,  it  projects  into 
the  lateral  ventricle.  The  posterior  surface  is  also  white.  The  inner 
sides  of  the  two  optic  thalami  form  the  outer  borders  of  the  third  ven- 
tricle, are  in  partial  contact,  and  are  composed  of  gray  material  uncov- 
ered by  white,  and  are,  as  a  rule,  connected  together  by  a  transverse 
portion. 

The  parts  of  which  each  optic  thalamus  is  composed  are  median, 
lateral,  and  anterior  nuclei  in  front,  and  the  ^mlvinar  behind.  The 
extreme  end  of  the  pulvinar  lies  somewhat  dorsal  to  the  corpora  genicu- 
lata  (fig.  363). 

Corpora  Quadrigemina. — There  are  two  on  each  side,  anterior 
and  posterior;  they  form  prominences  on  the  dorsal  surface  of  the  pons 
and  crura  above  the  aqueduct  of  Sylvius.  The  anterior  corpus  qiiadri- 
geminum  is  connected  with  the  optic  tluilamus  and  with  the  lateral  cor- 
pus geniculatum,  and  the  posterior  is  connected  with  the  median  corpus 
geniculatum. 

Corpora  Geniculata. — These  are  two  on  either  side,  lateral  or  outer 
and  median  or  inner ;  the  former  is  developed  from  the  fore-brain,  the 
latter  from  the  mid-brain.  The  lateral  corpus  geniculatum  is  at  the 
side  of  the  crus  and  appears  to  be  a  swelling  on  the  lateral  division  of 
the  optic  tract.  Similarly  the  median  appears  to  be  the  termination  of 
the  median  division  of  the  optic  tract.  They  both  contain  gray  matter 
(fig.  363). 

Corpora  Dentata  are  plicated  areas  of  gray  matter  in  the  interior 
of  the  cerebellum,  not  unlike  the  olivary  body  of  the  bulb.  The  fibres 
from  each  pass  chiefly  to  the  superior  peduncle  of  its  own  side. 

The  Cerebrum. — For  convenience  of  descrijotion,  the  surface  of 
the  brain  has  been  divided  '\\\io  jive  lobes  (Gratiolet). 

1.  Frontal  (F.  fig.  370),  limited  behind  by  the  fissure  of  Rolando 
(central  fissure),  and  beneath  by  the  fissure  of  Sylvius.  Its  surface  con- 
sists of  three  main  convolutions,  which  are  approximately  horizontal  in 
direction,  and  are  broken  up  into  numerous  secondary  gyri.  They  are 
termed  the  superior,  middle,  and  inferior  frontal  convolutions.  In  ad- 
dition, the  frontal  lobe  contains,  at  its  posterior  part,  a  convolution  which 
runs  upward  almost  vertically  {ascending  frontal),  and  is  bounded  in 
front  by  a  fissure  termed  the  prsecentral,  behind  by  that  of  Rolando. 

2.  Parietal  (P.).  This  lobe  is  bounded  in  front  by  the  fissure  of 
Rolando,  behind  by  the  external  perpendicular  Assure  (parieto-occipital), 
and  below  by  the  fissure  of  Sylvius.  Behind  the  fissure  of  Rolando  is 
the  ascending  parietal  convolution,  which  swells  out  at  its  upper  end 
into  what  is  termed  the  superior  parietal  lobule.     The  superior  parietal 


592 


HANDBOOK    OF    PHYSIOLOCtY. 


lobule  is  separated  from  the  inferior  parietal  lobule  by  the  intra-parietal 
sulcus.  The  inferior  parietal  lobule  (pli  courbe)  is  situated  at  the  pos- 
terior and  upper  end  of  the  fissure  of  Sylvius;  it  consists  of  (a)  an 
anterior  part  {supra-marginal  convolution)  which  hooks  round  the  end 
of  the  fissure  of  Sylvius,  and  joins  the  superior  temporal  convolution, 
and  a  posterior  part  {h)  (angular  gyrus)  which  hooks  round  into  the 
middle  temporal  convolution. 

3.   Temporal  (T. ),  contains  three  well-marked  convolutions,  parallel 


Fig.  370.— Lateral  view  of  the  brain  (semi-diagrammatic).  F,  Frontal  lobe;  P,  parietal  lobe; 
O,  occipital  lobe;  T.  temporal  lobe;  S,  flssm-e  of  Sylvius;  S'.  horizontal;  S",  ascending  ramus 
of  the  same ;  c,  sulcus  centralis  (fissure  of  Rolando)  :  A,  ascending  frontal ;  B,  ascending  parietal 
convolution;  Fl,  superior;  Y2,  middle;  F3,  inferior  frontal  convolutions;  fl.  superior,  f2,  in- 
ferior sulcus;  f3,  pHe-central  sulcus;  PI,  superior  parietal  lobule;  P2,  inferior  parietal  lobule 
consisting  of  P2,  supramarginal  gyrus,  and  P2'  angular  gyrus;  ip,  interparietal  sulcus;  cm, 
termination  of  calloso-marginal  fissure;  Ol,  first,  02,  second,  03,  third  occipital  convolutions; 
po,  parieto-occipital  fissure;  o,  transverse  occipital  fissure;  o2,  sulcus  occipitalis  inferior;  Tl, 
first,  T2,  second,  T3,  third  temporal  convolutions;  tl,  first,  t2,  second  temporal  fissures. 
(Ecker. ) 

to  each  other,  termed  the  superior,  middle,  and  inferior  temporal.     The 
superior  and  middle  are  separated  by  the  parallel  fissure. 

4.  Occipital  {0.).  This  lobe  lies  behind  the  external  perpendicular 
or  parieto-occipital  fissure,  and  contains  three  convolutions,  termed  the 
superior,  middle,  and  inferior  occipital.  They  are  often  not  well  marked. 
In  man,  the  external  parieto-occipital  fissure  is  only  to  be  distinguished 
as  a  notch  in  the  inner  edge  of  the  hemisphere;  below  this  it  is  quite 
obliterated  by  the  four  annectant  gyri  (plis  de  passage)  which  run  nearly 
horizontally.  The  upper  two  connect  the  parietal,  and  the  lower  two 
the  temporal  with  the  occipital  lobe. 


THE    NERVOUS    SYSTEM. 


593 


5.    Central  lobe,  or  island  of  Reil,  which  contains  a  number  of  radiat- 
ing convolutions  (gyri  operti). 

The  fig.  372  shows  the  following  gi/ri  and  stdci: — 

Gyrus  fornicatus,  a  long  curved  convolution,  parallel  to  and  curving 


Fig.  371.— View  of  the  brain  from  above  (semi -diagrammatic).     SI,  end  of  horizontal  ramus  of 
fissure  of  Sylvius.     The  other  letters  refer  to  the  same  parts  as  in  Fig.  370.     (Ecker.) 

round  the  corpus  callosum,  and  swelling  out  at  its  hinder  and  upper  end 
into  the  quadrate  lobule  (prfBcuneus),  which  is  continuous  with  the 
superior  parietal  lobule  on  the  external  surface.  Marginal  convolution 
runs  parallel  to  the  preceding,  and  occupies  the  space  between  it  and 
the  edge  of  the  longitudinal  fissure.  The  two  convolutions  are  separated 
by  the  calloso-marginal  fissure.  The  internal  ])erpendicular  fissure  is  well 
marked,  and  runs  downward  to  its  junction  with  the  calcarine  fissure: 
the  wedge-shaped  mass  intervening  between  these  two  is  termed  the 
cuneiis.  The  calcarine  fissure  corresponds  to  the  projection  into  the  pos- 
terior cornu  of  the  lateral  ventricle,  termed  the  Bippocanijjas  minor. 
The  temporal  lohe  on  its  internal  aspect  is  seen  to  end  in  a  hook  (unci- 
nate gyrus).  The  notch  round  which  it  curves  is  continued  up  and 
back  as  the  dentate  or  hippocampal  sulcus:  this  fissure  underlies  the 
projection  of  the  hippocampus  major  within  the  brain.  There  are  three 
internal  temporo-occipital  convolutions,  of  which  the  superior  and  infe- 
rior ones  are  usually  well  marked,  the  middle  one  generally  less  so. 

The  collateral  fissure   (corresponding  to  the  eminentia  collateralis) 
forms  the  lower  boundary  of  the  superior  temporo-occipital  convolution. 
38 


594 


HANDBOOK    OP    PHYSIOLOGY. 


All  the  above  details  will  be  found  indicated  in  the  diagrams  (figs. 
371,  372). 

Structure. — The  cerebrum  is  constructed,  like  the  other  chief  divi- 
sions of  the  cerebro-spinal  system,  of  gray  and  white  matter;  and,  as  in 
the  case  of  the  Cerebellum  (and  unlike  the  spinal  cord  and  medulla  ob- 
longata), the  gray  matter  {cortex)  is  external,  and  forms  a  capsule  or 
covering  for  the  white  substance.  For  the  evident  purpose  of  increasing 
its  amount  without  undue  occupation  of  space,  the  gray  matter  is  vari- 
ously infolded  so  as  to  form  the  cerebral  convolutions. 

The  cortical  gray  matter  of  the  cerebral  cortex  has  an  average 
thickness  of  about  \  inch  (3mm.),  being  thin  in  the  occipital  lobe,  -^ 
inch  (2mm.),  and  thick  in  the  pre-ceutral,  ^  inch  (4  mm.).  The  cells 
■of  which  the  substance  is  composed  are  of  different  kinds:  {a)  The 
most  conspicuous  are  certain  large  triangular  or  pyramidal  cells,  granu- 
lar or  fibrillated,  with  large  and  distinct  nuclei,  arranged  with  their 
apices  toward  the  surface.  All  the  angles  have  branching  processes,  but 
the  axis-cylinder-process  is  prolonged  from  about  the  middle  of  the  base. 
(J)  Small  pyramidal  cells  are  also  numerous,  and  irregular  or  angular 


Fig.  372. —View  of  the  right  hemisphere  in  the  median  aspect  (semi-diagrammatic).  CC, 
Corpus  callosum  longitudinaUy divided ;  Gf,  gyrus  fornicatus;  H,  gyrus  hippocampi;  h,  sulcus 
hippocampi;  U,  uncinate  gyrus;  cm,  calloso-marginal  fissure;  Fl,  median  aspect  of  first  frontal 
convolution ;  c.  terminal  portion  of  sulcus  centralis  (fissure  of  Rolando) ;  A,  ascending  frontal ; 
B,  ascending  parietal  convolution ;  PI',  prsecuneus;  Oz,  cuneus;  po,  parieto-occipital  fissure;  o, 
sulcus  occipitalis  transversus;  oc,  calcarine  fissure;  oc',  superior;  oc",  inferior  ramus  of  the 
same;  D,  gyrus  descendens  gyrus;  T4,  occipito-temporalis  lateralis  (lobulus  fusiformis) ;  T5, 
gyrus  occipito-temporalis  medialis  (lobulus  lingualis).     (Ecker.) 


cells  with  nuclei,  without  distinct  axis-cylinder  processes.  Again  (c) 
there  are  fusiform  cells  arranged  horizontally ;  {d)  certain  granule  cells, 
very  small,  with  large  nuclei,  and  not  unlike  lymphoid  corpuscles,  and 
finally  (e)  cells,  small  and  irregular,  which  may  possibly  be  neuroglia- 
cells.     Nerve-fibres  pass  up  almost  to  the  surface  of  the  cortex — some  of 


THE    NERVOUS   SYSTEM. 


595 


^> 


A' 


which  are  medullated.  The  general  arrangement  of  the  layers  in  the 
cortex  is  as  follows: — It  is  described  as  consisting  of  five  layers  (Mey- 
nert)  (fig.  373). 

1.  Superficial  layer  with  abundance  of  neuroglia  and  a  few  small 
multipolar  ganglion-cells.  2.  A  thin  layer  of  a  large  number  of  closely 
packed  small  ganglion-cells  of  pyramidal 
shape.  3.  The  most  important  layer,  and 
the  thickest  of  all :  it  contains  many  large 
pyramidal  ganglion  cells,  each  with  a  pro- 
cess running  off  from  the  apex  vertically 
toward  the  free  surface,  and  lateral  processes 
at  the  base  which  are  always  branched.  Also 
a  median  process  from  the  base  of  each  cell 
which  is  unbranched  and  becomes  continu- 
ous with  the  axis-cylinder  of  a  nerve-fibre. 
The  bundles  of  fibres  spread  ont  in  this 
layer.  4.  Numerous  ganglion-cells,  some 
large  and  others  small,  forming  the  granular 
formation  of  Meynert.  5.  Spindle-shaped 
and  branched  ganglion-cells  of  moderate  size 
arranged  chiefly  parallel  to  the  free  surface 
{vide  fig.  373).  This  layer  is  remarkable  in 
heing  broken  up  by  fibres  arranged  in  groups 
passing  to  the  outer  layers. 

It  is  a  noticeable  fact  that  the  different 
layers  do  not  bear  the  same  relation  to  one 
another  in  thickness  in  different  regions. 
In  the  area  about  the  fissnre  of  Rolando, 
which  we  shall  presently  see  is  called  the 
motor  area,  the  large  pyramidal  cells  are  con- 
spicuous in  size  and  number,  and  numerous 
large  cells  are  found  in  the  fourth  layer. 
These  latter  attain  their  greatest  develop- 
ment in  the  pre-ceutral  and  post-central 
convolutions.  The  granular  layer  is  very 
marked  in  the  occipital  region,  forming  a 
distinct  and  broad  division  of  the  fourth 
layer,  and  being  present  elsewhere.  The  large  cells  are  scarce.  In  the 
frontal  region,  the  pyramidal  and  fourth  layers  are  well  marked,  but  the 
cells  are  less  numerous;  the  nuclear  layer  is  very  distinct.  The  pyra- 
midal cells  are  those  from  which  motor  or  efferent  fibres  originate. 

Chemical  Composition. — The  chemistry  of  nerves  and  nerve-cells  has 
been  chiefly  studied  in  the  brain  and  spinal  cord.     Nerve  matter  con- 


Fig.  373.— The  layers  of  the 
cortical  s''a.v  matter  of  the  cere- 
brum.    (Meynert. ) 


596 


HANDBOOK    OF   PHYSIOLOGY. 


tains  several  albuminous  and  fatty  bodies  (cerebrin,  lecithin,  and  some 
others),  also  fat  matter  which  can  be  extracted  by  ether  (including  cho- 
lesterin)  and  various  salts,  especially  Potassium  and  Magnesium  phos- 
phates, which  exist  in  larger  quantity  than  those  of  Sodium  and  Calcium. 
Arrangement  of  f/ie  parts  of  the  cerebrum. — The  great  relative  and 
absolute  size  of  the  Cerebral  hemispheres  in  the  adult  man,  masks  to  a 


f^'i'll. 


Process  of  cell  of  .- 
Purkinj6  passing 
into      molecular  ' 
layer. 


A  chief  process 
of  cell  of  Pur- 
kinj6. 

Body  of  the  same  'hlTv 
cell.  W^ 

A  X  i  s  -  c  y  Under  Vg^^ 
process.  "'"""! ... 


Fig.  374. 


Fig.  37.5. 


Fig.  374.— Diagrammatic  horizontal  section  of  a  vertebrate  brain.  The  figures  serve  both 
for  this  and  the  next  diagram.  Mb,  mid-brain:  what  lies  in  front  of  this  is  the  fore-,  and  what 
lies  behind,  the  hind-brain;  Li,  lamina  terminalis;  Olf,  olfactory  lobes;  Hmp,  hemispheres; 
Th.  E.  thalamencephalon ;  Pw,  pineal  gland;  Pi/,  pituitary  body ;  F.M,  foramen  of  Munro ;  cs, 
corpus  striatum;  Th,  optic  thalamus;  CC,  crura  cerebri :  the  mass  lying  above  the  canal  rep- 
resents the  corpora  quadrigemina ;  Cb,  cerebellum;  I^IX,  the  nine  pairs  of  cranial  nerves;  1, 
olfactory  ventricle ;  2,  lateral  ventricle ;  3,  third  ventricle ;  4,  fourth  ventricle ;  -f,  iter  a  tertio 
ad  quartum  ventriculum.     (Huxley.) 

Fig.  375.— Section  through  the  gray  matter  of  the  human  cerebellum,  treated  according  to 
Golgi's  method  (Stohr). 

great  extent  the  real  arrangement  of  the  several  parts  of  the  brain,  which 
is  illustrated  in  the  two  accompanying  diagrams. 

From  these  it  is  apparent  that  the  parts  of  the  brain' are  disposed  in 
a  linear  series,  as  follows  (from  before  backward) :  olfactory  lobes,  cere- 
bral hemispheres,  optic  thalami,  and  third  ventricle,  corpora  quadri- 
gemina, or  optic  lobes,  cerebellum  medulla  oblongata. 

This  linear  arrangement  of  parts  actually  occurs  in  the  human  foetus; 


THE    NERVOUS   SYSTEM. 


597 


and  it  is  permanent  in  some  of  tlie  lower  Vertebrata,  e.g.,  Fishes,  in 
which  the  cerebral  hemispheres  are  represented  by  a  pair  of  ganglia 
intervening  between  the  olfactory  and  the  optic  lobes,  and  considerably 
smaller  than  the  latter.  In  Amphibia  the  cerebral  lobes  are  further 
developed,  and  are  larger  than  any  of  the  other  ganglia. 

In  reptiles  and  birds  the  cerebral  ganglia  attain  a  still  further  devel- 
opment, and  in  mammalia  the  cerebral  hemispheres  exceed  in  weight 
all  the  rest  of  the  brain.  As  we  ascend  the  scale,  the  relative  size  of  the 
cerebrum  increases,  till  in  the  higher  apes  and  man  the  hemispheres, 
which  commenced  as  two  little  lateral  buds  from  the  anterior  cerebral 
vesicle,  have  grown  upward  and  backward,  completely  covering  in  and 
hiding  from  view  all  the  rest  of  the  brain.     At  the  same  time  the  smooth 


Fig.  376. — Longitudinal  and  vertical  diagrammatic  section  of  a  vertebrate  brain.  Letters 
as  before.  Lamina  terminalis  is  represented  by  the  strong  black  line  joining  Pn  and  Py. 
(Huxley. ) 

surface  of  the  brain,  in  many  lower  mammalia,  such  as  the  rabbit,  is 
replaced  by  the  labyrinth  of  convolutions  of  the  human  brain. 

Weight  of  the  Brain. — The  braiu  of  an  adult  man  weighs  from  48  to  50  oz. — 
or  about  3  lbs.  (about  1550  grms.) .  It  exceeds  in  absolute  weight  that  of  all  the 
lower  animals  except  the  elephant  and  whale.  Its  weight,  relatively  to  that  of 
the  body,  is  only  exceeded  by  that  of  a  few  small  birds,  and  some  of  the 
smaller  monkeys.     In  the  adult  man  it  ranges  from  -^^ — gL  of  the  body  weight. 

Variations.  Age. — In  a  new-born  child  the  brain  (weighing  10  to  14  oz. )  is 
•j\j  of  the  body  weight.  At  the  age  of  7  years  the  weight  of  the  brain  already 
averages  40  oz.,  and  about  14  j'ears  the  brain  not  infrequently  reaches  the 
weight  of  48  oz.  Beyond  the  age  of  forty  years  the  weight  slowh'  but  steadily 
declines  at  the  rate  of  about  1  oz.  in  10  years. 

Sex.  — The  average  weight  of  the  female  brain  is  less  than  the  male  :  and  this 
difference  persists  from  birth  throughout  life.  In  the  adult  it  amounts  to 
about  5  oz.     Thus  the  average  weight  of  an  adult  woman's  brain  is  about  44  oz. 

Intelligence. — The  brains  of  idiots  are  generally  much  below  the  average, 
some  weighing  less  than  16  oz.  Still  the  facts  at  present  collected  do  not  war- 
rant more  than  a  very  general  statement,  to  which  there  are  numerous  excep- 
tions, that  the  brain  weight  corresponds  to  some  extent  with  the  degree  of 
intelligence.  There  can  be  little  doubt  that  the  complexity  and  depth  of  the 
convolutions,  which  indicate  the  area  of  the  gray  matter  of  the  cortex,  corre- 
spond with  the  degree  of  intelligence. 


598 


HANDBOOK    OF    PHYSIOLOGY. 


Weight  of  the  Sj^inal  Cord. — The  spinal  cord  of  man  weighs  from  1 — 1^  oz.  ; 
its  weight  relatively  to  the  brain  is  about  1  :  36.  As  we  descend  the  scale, 
this  ratio  constantly  increases  till  in  the  mouse  it  is  1  :  4.  In  cold-blooded 
animals  the  relation  is  reversed,  the  spinal  cord  is  the  heavier  and  the  more 
important  organ.     In  the  newt,  2:1;    and  in  the  lamprey,  75  :  1. 

Distinctive  Characters  of  the  Human  Brain. — The  following  characters  dis- 
tinguish tlte  brain  of  man  and  apes  from  those  of  all  other  animals,  (a.)  The 
rudimentary  condition  of  the  olfactory  lobes,  {h. )  A  perfectly  defined  fissure 
of  Sylvius,  (c. )  A  posterior  lobe  completely  covering  the  cerebellum,  (d.) 
The  presence  of  posterior  cornua  in  the  lateral  ventricles. 

The  most  distinctive  points  in  the  human  hrain,  as  contrasted  with  that  of 
apes,  are: — (1.)  The  much  greater  size  and  weight  of  the  whole  brain.  The 
brain  of  a  full-grown  gorilla  weighs  only  about  15  oz.  (450  grms.),  which  is 
less  than  \  the  weight  of  the  human  adult  male  brain,  and  barely  exceeds  that 
of  the  human  infant  at  birth.  (2. )  The  much  greater  complexity  of  the  con- 
volutions, especially  the  existence  in  the  human  brain  of  tertiary  convolutions 


Fig.  377.— Brain  of  the  Orang,  %  natural  size,  showing  the  arrangement  of  the  convolutions. 
Sy,  fissure  of  Sylvius;  R,  fissure  of  Rolando;  E P,  external  perpendicular  fissure;  Olf,  olfactory 
lobe;  Cb,  cerebellum;  PV.  pons  Varolii;  MO,  medulla  oblongata.  As  contrasted  with  the 
human  brain,  the  frontal  lobe  is  short  and  small  relatively,  the  fissure  of  Sylvius  is  oblique, 
the  temporo-sphenoidal  lobe  very  prominent,  and  the  external  perpendicular  fissure  very  well 
marked.     (Gratiolet. ) 


in  the  sides  of  the  fissures.  (3.)  The  greater  relative  size  and  complexity,  and 
the  blunted  quadrangular  contour  of  the  frontal  lobes  in  man,  which  are 
relativelj'  both  broader,  longer,  and  higher,  than  in  apes.  In  apes  the  frontal 
lobes  j)roject  keel -like  (rostrum)  between  the  olfactory  bulbs.  (4.)  The  much 
greater  prominence  of  the  temporo-sphenoidal  lobes  in  apes.  (5.)  The  fissure 
of  Sylvius  is  nearly  horizontal  in  man,  while  in  apes  it  slants  considerably  up- 
ward. (6.)  The  distinctness  of  the  external  perpendicular  fissure,  which  in 
apes  is  a  well-defined  almost  vertical  "slash,"  while  in  man  it  is  almost 
obscured  by  the  annectent  gyri. 

Most  of  the  above  points  are  shown  in  the  accompanying  figure  of  the  brain 
of  the  Orang. 


THE    NERVOUS   SYSTEM. 


599 


The  Motor  areas  of  the  Cerebral  Cortex. 

The  experiments  upon  the  brains  of  various  animals  by  means  of 
electrical   stimulation   have  demonstrated  that   there   are   definite  re- 


Fig.  379. 
Fies  378  and  379.— Brain  of  dog,  viewed  from  above  and  in  profile.  F,  frontal  fissure  some- 
times termed  crucial  sulcus,  corresponding  to  the  fissure  of  Rolando  in  man.  S,  Assure  of 
Sylvius,  around  which  the  four  longitudinal  convolutions  are  concentrically  arranged ;  1,  tlexion 
of  head  on  the  neck,  in  the  median  line;  2,  flexion  of  head  on  the  neck  with  rotation  toward 
the  side  of  the  stimulus;  3,  4,  flexion  and  extension  of  anterior  limb;  5,  6,  flexion  and  extension 
of  posterior  limb;  7,  8.  9,  contraction  of  orbicularis  oculi.  and  the  facial  muscles  in  general. 
The  unshaded  part  is  that  exposed  by  opening  the  skull.     (Dal ton.) 

gions  of  the  cerebral  cortex  the  stimulation  of  which  produces  definite 
movements  of  co-ordinated  groups  of  muscle  of  the  opposite  side  of 
the  body.     Fritsch  and  Hitzig  were  the  first  to  show  that  the  cere- 


GOO  HANDBOOK    OF    PHYSIOLOGY. 

bral  cortex  responded  to  electric  irritation.  They  employed  a  weak  con- 
stant current  in  their  experiments,  applying  a  pair  of  fine  electrodes  not 
more  than  -^^  in.  apart  to  different  parts  of  the  cerebral  cortex.  The 
results  thus  obtained  have  been  confirmed  and  extended  by  Ferrier  and 
many  others,  chiefly  with  induction  currents. 

The  fundamental  phenomena  observed  in  all  these  cases  may  be  thus 
epitomized : — 

(1).  Excitation  of  the  same  spot  is  always  followed  by  the  same 
movement  in  the  same  animal.  (2).  The  area  of  excitability  for  any 
given  movement  is  extremely  small,  and  admits  of  very  accurate  defini- 
tion. (3).  In  different  animals  excitations  of  anatomically  corresponding 
spots  produce  similar  or  corresponding  results. 

The  various  definite  movements  resulting  from  the  electric  stimulation 
of  circumscribed  areas  of  the  cerebral  cortex,  are  enumerated  in  the  de- 
scription of  the  accompanying  figures  of  the  dog  and  monkey's  brain. 

In  the  case  of  the  dog,  the  results  obtained  are  summed  up  as  fol- 
lows, by  Hitzig: — 

{a.)  One  portion  (anterior)  of  the  convexity  of  the  cerebrum  is 
motor;  another  portion  (posterior)  is  non-motor,  {h.)  Electric  stimu- 
lation of  the  motor  portion  produces  co-ordinated  muscular  contraction 
on  the  opposite  side  of  the  body.  (c. )  With  very  weak  currents,  the 
contractions  produced  are  distinctly  limited  to  particular  groups  of 
muscles;  with  stronger  currents  the  stimulus  is  communicated  to  other 
muscles  of  the  same  or  neighboring  parts,  {d.)  The  portions  of  the 
brain  intervening  between  these  motor  centres  are  inexcitable  by  similar 
means. 

Motor ial  area  of  the  Monkey'' s  Brain.  — According  to  the  observations 
of  Ferrier,  confirmed  and  extended  by  later  experimenters,  stimulation 
of  various  parts  of  the  monkey's  brain,  as  indicated  by  the  numbers  in 
figs.  380,  381,  produces  movements  of  definite  muscles,  thus: — 

Stimulation  of  the  district  marked  1,  causes  movement  of  hind 
foot:  of  2,  chiefly  adduction  of  the  foot;  of  3,  movements  of  hind  foot 
and  tail;  of  4,  of  latissimus  dorsi ;  of  5,  extension  forward  of  arm;  a, 
i,  c,  d,  movements  of  hand  and  wrist;  of  6,  supination  and  flexion  of 
forearm;  of  7,  elevation  of  the  upper  lip;  of  8,  conjoint  action  of  eleva- 
tion of  upper  lip  and  depression  of  lower;  of  9,  opening  of  mouth  and 
protrusion  of  tongue;  of  10,  retraction  of  tongue;  of  11,  action  of 
platysma;  of  12,  elevation  of  eyebrows  and  eyelids,  dilatation  of  pupils, 
and  turning  head  to  opposite  side;  of  13,  eyes  directed  to  opposite  side 
and  upward,  with  usually  contraction  of  the  pupils;  of  13',  similar 
action,  but  eyes  usually  directed  downward;  of  14,  retraction  of  oppo- 
site ear,  head  turns  to  the  opposite  side,  the  eyes  widely  opened,  and 
pupils  dilated;  of  15,  stimulation  of  this  region,  which  corresponds  to 


THE    NEKVOUS   SYSTEM, 


601 


the  tip  of  the  uncinate  couvoh^tiou,  causes  torsion  of  the  lip  and  nostril 
of  the  same  side. 

It  is  thus  seen  that  the  motor  areas  chiefly  correspond  with  the 
ascending  frontal  and  ascending  parietal  convolutions,  and  that  the 
movements  of  the  leg  are  represented  at  the  upper  part  of  these  con- 
volutions, then  follow  from  above  downward  the  centres  for  the  arms, 
the  face,  the  lips,  and  the  tongue. 

According  to  the  further  researches  of  Schiifer  and  Horsley,  electrical 
stimulation  of  the  marginal  convolution  internally  at  the  parts  cori-e- 
sponding  with  the  ascending  frontal  and  parietal  convolutions,   from 


Fig.  380. 


Fig.  381. 


Figs.  380  and  381.— Diagrams  of  monkey's  brain  to  show  the  effects  of  electric  stimulation  of  cer- 
tain spots.     (According  to  Ferrier.) 

before  backward,  produces  movements  of  the  arm,  of  the  trunk,  and 
of  the  leg. 

A  good  deal  of  doubt  was  thrown  upon  the  experiments  of  Ferrier 
by  Goltz  and  other  observers,  from  the  results  of  excising  the  so-called 
motor  areas  of  the  dog's  brain.  It  was  found  that  the  part  might  be 
sliced  away  or  washed  away  with  a  stream  of  water,  but  that  no  perma- 
nent parah'sis  ensued. 

More  extensive  observations  however,  have  confirmed  Ferrier's  original 
statement,  at  any  rate  with  regard  to  the  monkey's  brain.  Destruction 
of  the  motor  areas  for  the  arm  produces  at  any  rate  some  permanent 
paralysis  of  the  arm  of  the  opposite  side,  and  similarly  of  that  for  the 
leg,  paralysis  of  the  opposite  leg.  If  both  areas  are  destroyed  permanent 
hemiplegia  ensues.     Paralysis  of  so  extensive  and  permanent  character 


G02 


HANDBOOK    OF    PHYSIOLOGY. 


does  not,  however,  appear  tlie  rule  when  the  bram  of  a  dog  is  used 
instead  of  that  of  the  monkey.  It  is  suggested  that  in  the  animal  lower 
in  the  scale,  the  functions  which  in  the  monkey  are  discharged  by  the 
cortical  centres  may  be  subserved  by  the  basal  ganglia. 

Motorial  Areas  of  the  Human  Brain. — It  is  naturally  of  great  impor- 
tance to  discover  how  far  the  result  of  experiments  upon  the  dog  and 
monkey  hold  good  with  regard  to  the  human  brain.  Evidence  furnished 
by  diseased  conditions  is  not  wanting  to  supjiort  the  general  idea  of  the 
existence  of  cortical  motorial  centres  in  the  human  brain  (fig.  382). 

Parietal  lobe  (line  indicates 
fissure  of  Rolando). 


Occipital 
lobe. 


Fissure  of  Sylvius.        Temporal  lobe. 

Fig.  382. — Diagram  to   indicate  position  of  centres  on  the  external  surface  of  the   brain, 
exact  position  of  the  centres  may  be  seen  on  comparison  with  fig.  370. 


The 


So  far,  however,  it  has  been  possible  to  localize  motor  functions  in 
the  frontal  and  ascending  parietal  convolutions  only,  to  the  convolutions 
which  bound  the  fissure  of  Eolando,  and  to  those  on  the  inner  side  of 
the  hemispheres  which  correspond  thereto,  and  j^ossibly  to  the  frontal 
lobe  in  front  of  the  ascending  convolution. 

The  position  of  the  centres  is  probably  much  the  same  as  in  the  mon- 
key's brain — those  for  the  leg  above,  those  for  the  arm,  face,  lips,  and 
tongue  from  above  downward.  Destruction  of  these  parts  causes  pa- 
ralysis, corresponding  to  the  district  affected,  and  irritation  causes  con- 
vulsions of  the  muscles  of  the  same  part.  Again,  a  number  of  cases 
are  on  record  in  which  aphasia,  or  the  loss  of  power  of  expressing  ideas 
in  words,  has  been  associated  with  disease  of  the  posterior  part  of  the 
lower  or  third  frontal  convolution  on  the  left  side.  This  condition  is 
usually  associated  with  paralysis  of  the  right  side  (right  hemiplegia). 

This  district  of  the  brain  is  now  generally  known  as  the  motor  area; 
and  there  seems  no  doubt  whatever  that  from  this  area  pass  the  nerve- 


THE    NERVOUS   SYSTEM. 


6oa 


fibres  which  proceed  to  the  spinal  cord,  and  are  there  represented  as 
the  pyramidal  tracts. 

This  is  the  reason,  no  doubt,  that  movements  are  produced  on  stimu- 
lation of  the  white  matter  after  the  superficial  gray  matter  of  the 
animal's  brain  has  been  sliced  off. 

Moto}'  tracts  in  the  hrain. — These  motor  fibres  are  connected  with  the 
pyramidal  cells  of  the  cortex,  and  are  indeed  their  continuations. 

It  will  be  necessary,  therefore,  to  trace  them  from  the  cortex  down- 
ward.    From  the  motor  area  of  the  cortex  they  converge  to  the  inter- 


Tig.  383. —Diagram  to  show  the  connecting  of  the  Frontal  Occipital  Lobes  with  the  Cere- 
bellum, etc.  The  dotted  lines  passing  in  the  crusta  (too),  outside  the  motor  fibres,  indicate  the 
connection  between  the  temporo-occipital  lobe  and  the  cerebellum,  f.c.  ,  the  fronto-cerebellar 
fibres,  which  pass  internally  to  the  motor  tract  in  the  crusta;  i.f.  ,  fibres  from  the  caudate 
nucleus  to  the  pons,  fr.,  frontal  lobe;  Oc,  occipital  lobe;  af. ,  ascending  frontal;  ap. ,  ascend- 
ing parietal  convolutions;  pcf. ,  precentral  fissure  in  front  of  the  ascending  frontal  convolution; 
PR.,  fissure  of  Rolando;  ipp. ,  interparietal  fissure,  a  section  of  crus  is  lettered  on  the  left  side. 
SN. ,  substantia  nigra;  py. ,  pyramidal  motor  fibre,  which  on  the  right  is  shown  as  continuous 
lines  converging  to  pass  through  the  posterior  limb  of  ic.  internal  capsule  (the  knee  or  elbow 
of  which  is  shown  thus  *)  upward  into  the  hemisphere  and  downward  through  the  pons  to  cross 
at  the  medulla  in  the  anterior  pyramids.     (Gowers.) 


nal  capsules,  and  pass  down  to  the  crusta  of  the  crus  in  the  way  already 
indicated. 

In  the  internal  capsule  the  fibres  which  pass  onward  and  downward 
to  the  pyramidal  tracts  of  the  spinal  cord  do  not  occupy  more  than  a 
small  section,  namely,  that  part  known  as  the  knee,  and  the  anterior 
two-thirds  of  the  posterior  segment  (fig.  384).  In  this  district  the 
fibres  for  the  face,  arm,  and  leg,  are  in  this  relation :  those  for  the  face 
and  tongue  are  just  at  the  knee,  and  below  or  behind  them  come  first 
the  fibres  for  the  arm  and  then  those  for  the  leg. 

The  more  accurate  arrangement  of  these  fibres  in  the  monkey's  brain 
from  above  down  are  those  for  the  eye,  head,  tongue,  mouth,  shoulder. 


604 


HANDBOOK    OF    PHYSIOLOGY. 


elbow,  digits,  abdomen,  lip,  knee,  digits.  These  fibres  come  for  the 
most  part  from  the  part  of  the  cortex  on  either  side  of  the  fissure  of 
Kolando,  hence  called  the  Rolandic  area  on  either  side.     But  the  areas 


Fig.  384.— Diagram  to  show  the  relative  positions  of  the  several  motor  tracts  in  their  course 
from  the  cortex  to  the  crus.  The  section  through  the  convolution  is  vertical;  that  through  the 
internal  capsule,  I,  C,  horizontal;  that  thi-ough  the  crus  again  vertical.  C,  N,  caudate  nucleus; 
O,  TH,  optic  thalamus;  L3  and  L3,  middle  and  outer  part  of  lenticular  nucleus;  /,  a,  I,  face, 
arm,  and  legfiljres.    The  words  in  italic  indicate  corresponding  cortical  centres.     (Gowers.) 

for  the  liead  and  eyes  lie  more  anterior  in  the  frontal  lobe,  to  the  front 
of  the  precentral  sulcus,  that  for  the  head  above  that  for  the  e3^es,  and 
an  area  for  the  trunk  (not  indicated  in  the  fig.  383),  is  situated  more 
toward  the  middle  line  of  the  hemisphere,  internal  to  that  for  the  leg. 

But  there  are  other  fibres  which  are  arranged  in  front  of  the 
pyramidal  fibres  in  the  front  limb  of  the  capsule,  as  well  as  others  behind 
them  in  the  hind  limb  of  the  capsule.  Those  in  front  are  from  the 
anterior  part  of  the  frontal  lobe,  and  these  in  passing  into  the  crus  are 
found  on  the  median  side  of  the  pyramidal  fibres  (fig.  383).  They 
appear  to  end  in  the  gray  matter  of  the  pons,  and  there  to  be  connected 
with  fibres  from  the  middle  peduncle  of  the  opposite  side  of  the  cere- 
bellum. Those  behind  the  pyramidal  fibres  in  the  hind  limb  of  the  cap- 
sule are  from  the  temfporal-occipital  lobe.  These  fibres  pass  into  the  crus 
to  the  outer  side  of  the  pyramidal  fibres  (fig.  383),  they  probably  also 
end  in  the  gray  matter  in  the  same  way.  There  are  other  fibres  from  the 
corpus  striatum,  from  both  nuclei,  but  particularly  from  the  caudate 
nucleus,  which  pass  to  the  crus,  and  are  situated  between  the  pyramidal 
tract  and  the  locus  niger  (fig.  383),  some  of  which  terminate  in  that 
nucleus,  while  others  terminate  in  the  pons.  Besides  the  above  fibres, 
all  of  which  are  believed  to  be  efferent  fibres,  and  are  at  any  rate  fibres 
of  descending  degeneration,  there  are  fibres  which  pass  from  the  cortex 
to  the  optic  thalamus  and  tegmentum,  fibres  of  ascending  degeneration 


THE    NERVOUS    SYSTEM.  605 

found  in  the  internal  capsule,  viz.,  those  from  the  frontal  lobes  are 
situated  at  the  extreme  tip  of  the  front  limb,  in  front  of  the  motor  fibres 
from  the  same  district,  and  others  from  the  temporal-occipital  district 
converge  to  the  posterior  part  of  the  hind  limb.  Those  passing  between 
the  occipital  lobe  and  the  optic  thalamus  are  believed  to  be  concerned 
with  vision,  and  are  called  fibres  of  the  ojJtic  radiation. 

It  may  be  as  well  to  mention  here  that  some  other  fibres  from  the 
temporo-occipital  lobe  pass  into  the  optic  thalamus,  without  forming  a 
part  of  the  internal  capsule. 

The  optic  thalamus  then  receives  fibres  from  nearly  all  parts  of  the 
■cerebral  cortex,  some  of  which  are  not  found  in  the  internal  capsule. 
The  tegmentum,  the  afferent  or  sensory  tract  of  the  crus  to  a  great  ex- 
tent ends  in  the  optic  thalamus,  and  is,  therefore,  connected  through  it 
with  nearly  all  parts  of  the  cortex,  indirectly.  It  is  also  more  directly 
connected  with  cortex  {a)  by  fibres  of  the  optic  radiation  which  do  not 
go  to  the  optic  thalamus,  {h)  by  fibres  from  the  frontal  and  parietal 
lobes,  which  pass  through  the  lenticular  nucleus,  and  {c)  by  fibres  from 
both  the  lenticular  and  caudate  nuclei  of  the  corpus  striatum. 

In  the  tegmentum  the  longitudinal  fibres  may  be  thus  enumerated : — 

(«.)  The  fillet,  which  consists  of  fibres  from  the  sensory  decussation  of 


Fig.  385.— Vertical  section  througii  the  cerebrum  and  basic  ganglia  to  show  the  relations  of 
the  latter,  co,  cerebral  convolutions ;  c.c,  cori)us  callosum;  v. I.,  lateral  ventricle;  f,  fornix; 
vlIL,  third  ventricle;  n.c,  caudate  nucleus;  tl(.  ojitic  thalamus;  n.L,  lenticular  nucleus;  c.i., 
internal  capsule;  c.L,  claustrum;  c.e.,  external  capsule;  m,  corpus  mammillare;  t.o.,  optic 
tract;  s.t.t.,  stria  terminalis;  7f.«.,  nucleus  amygdalae ;  cm,  soft  commissure.     (Schwalbe.) 

the  bulb,  which  becomes  longitudinal  in  the  inter-olivary  region,  and  in 
its  course  upward,  from  masses  of  gray  matter,  such  as  the  superior 
olive;  it  divides  into  two  bundles,  (i.)  Lateral,  ends  in  gray  matter 
of  posterior  corpus  quadrigeminum  and  in  white  matter  beneath  the 
anterior,  and  (ii.)  median,  ends  in  anterior  corpus  quadrigeminum  and 


606  HANDBOOK    OF    PHYSIOLOGY. 

in  the  corpus  subthalamicum,  thence  to  the  optic  thalamus  and  the  cere- 
bral cortex, 

{b.)  Posterior  longitudinal  bundles. — A  bundle  of  fibres  which  appear 
to  begin  the  bulb  as  certain  fibres  of  the  anterior  column  of  the  cord, 
which  are  the  short  longitudinal  commissures  between  segments  of  the 
cord.  It  is  traceable  upward  as  far  as  the  nucleus  of  the  third  nerve. 
It  is  supposed  to  connect  the  nuclei  of  the  fourth  and  sixth  nerves  with 
the  third,  and  with  the  anterior  corpus  quadrigeminum. 

(c.)  Superior  peduncle  of  the  cerebellum.  This  arises  on  either  side 
from  the  superficial  gray  matter,  but  chiefly  from  the  corpus  dentatum, 
and  passes  forward  outward  beneath  the  posterior  corpus  quadrigeminum, 
and  beneath  it  and  the  anterior  corpus  quadrigeminum  decussates  with 
its  fellow;  the  fibres  then  pass  forward  in  the  anterior  district  of  the 
tegmentum  and  end  in  the  red  nucleus. 

(fZ.)  Fibres  from  the  corpora  quadrigemina.  From  each  corpus  quad- 
rigeminum passes  forward  and  downward  a  tract  called  the  brachium. 
The  anterior  brachium  goes  to  the  lateral  corpus  geniculatum,  and  then 
to  the  optic  tract,  other  fibres  pass  into  the  tegmentum,  and  thence 
directly  to  the  occipital  cortex.  The  posterior  brachium  goes  to  the 
median  corpus  geniculatum,  thence  to  the  tegmentum,  and  through  it 
possibly  to  the  temporal  region  of  the  cerebral  cortex. 

Commissural  fibres. — In  addition  to  the  fibres  of  the  corpus  callosum, 
which  connect  all  parts  of  the  hemispheres,  and  fornix,  there  are  three 
other  commissures,  the  anterior  white  commissure,  and  the  posterior 
white  commissure  in  the  third  ventricle  connect  by  white  fibres  the  two 
sides  of  the  brain.  The  fibres  in  the  anterior  come  from  the  temporo- 
sphenoidal  convolution  chiefly,  but  a  few  are  part  of  the  olfactory  tract. 
The  posterior  connects  the  optic  thalami  and  tegmenta.  The  middle 
is  chiefly  composed  of  gray  matter,  but  also  contains  some  transverse 
fibres. 

Functions  of  the  Cerebrum. 

Speaking  in  the  most  general  way,  and  for  the  present  omitting 
the  accumulating  evidence  in  favor  of  the  direct  representation  of  the 
various  co-ordinated  movements  of  the  muscles  of  the  body  in  ganglia 
situated  in  different  parts  of  the  cerebral  cortex,  it  may  be  said  that: — 
(1.)  The  cerebral  hemispheres  are  the  organs  by  which  are  perceived 
those  clear  and  more  impressive  sensations  which  can  be  retained,  and 
regarding  which  we  can  judge.  (2.)  The  cerebrum  is  the  organ  of  the 
will,  in  so  far  at  least  as  each  act  of  the  will  requires  a  deliberate,  how- 
ever quick  determination.  (,3.)  It  is  the  means  of  retaining  impressions 
of  sensible  things,  and  reproducing  them  in  subjective  sensations  and 
ideas.     (4.)  It  is  the  medium  of  all  the  higher  emotions  and  feelings,  and 


THE    NERVOUS    SYSTEM.  607 

of  the  faculties  of  judgment,  understandiug,  memory,  reflection,  induc- 
tion, imagination  and  the  like. 

Evidence  regarding  the  jahysiology  of  the  cerebral  hemispheres,  has 
been  obtained,  as  in  the  case  of  other  parts  of  the  nervous  system,  from 
the  study  of  Comparative  Anatomy,  from  Pathology,  and  from  Experi- 
ments on  the  lower  animals.  The  chief  evidences  regarding  the  func- 
tions of  the  cerebral  hemispheres  derived  from  these  various  sources,  are 
briefly  these: — 1.  Any  severe  injury  of  them,  such  as  a  general  concus- 
sion, or  sudden  pressure  by  apoplexy,  may  instantly  deprive  a  man  of  all 
power  of  manifesting  externally  any  mental  faculty.  2.  In  the  same 
■general  proportion  as  the  higher  mental  faculties  are  developed  in  the 
Vertebrate  animals,  and  in  man  at  different  ages  and  in  different  indi- 
viduals, the  more  is  the  size  of  the  cerebral  hemispheres  developed  in 
comparison  Avith  the  rest  of  the  cerebro-spinal  system.  3.  No  other  part 
of  the  nervous  system  bears  a  corresponding  proportion  to  the  develop- 
ment of  the  mental  faculties.  4.  Congenital  and  other  morbid  defects 
of  the  cerebral  hemisphere  are,  in  general,  accompanied  by  correspond- 
ing deficiency  in  the  range  or  power  of  the  intellectual  faculties  and  the 
higher  instincts.  5.  Eemoval  of  the  cerebral  hemispheres  in  one  of  the 
lower  animals  produces  effects  corresponding  with  what  might  be  antici- 
pated from  the  foregoing  facts. 

Effects  of  the  Bemoval  of  the  Cerebrum. — The  removal  of  the  cere- 
brum in  the  lower  animals  apjaears  to  reduce  them  to  the  condition  of  a 
mechanism  v/ithout  spontaneity. 

In  the  case  of  the  frog,  when  the  cerebral  lobes  have  been  removed, 
the  animal  appears  similarly  deprived  of  all  power  of  spontaneous  move- 
ment. But  it  sits  up  in  a  natural  attitude,  breathing  quietly;  when 
pricked  it  jumps  away;  wlien  thrown  into  the  water  it  swims;  when 
placed  upon  the  palm  of  the  hand  it  remains  motionless,  although,  if 
the  hand  be  gradually  tilted  over  till  the  frog  is  on  the  point  of  losing 
his  balance,  he  will  crawl  up  till  he  regains  his  equilibrium,  and  comes 
to  be  perched  quite  on  the  edge  of  the  hand.  This  condition  contrasts 
with  that  resulting  from  the  removal  of  the  entire  brain,  leaving  only 
the  spinal  cord ;  in  this  case  only  the  simpler  reflex  actions  can  take 
place.  The  frog  does  not  breathe,  he  lies  flat  on  the  table  instead  of 
sitting  up;  when  thrown  into  a  vessel  of  water  he  sinks  to  the  bottom; 
when  his  legs  are  pinched  he  kicks  out,  but  does  not  leap  away. 

A  pigeo)i  from  which  the  cerebrum  has  been  removed  will  remain 
motionless  and  apparently  unconscious  unless  disturbed.  When  dis- 
turbed in  any  way  it  soon  recovers  its  former  position;  when  thrown 
into  the  air  it  flies. 

In  mammals  it  is  difficult  to  remove  the  cerebral  hemispheres,  but  in 
those  animals  in  which  the  operation  has  been  carried  ou.t,  as  for  example 


COS  HANDBOOK    OF    PHYSIOLOGY. 

in  the  rabbit  and  rat,  a  result  very  similar  to  those  observed  in  the  case  of 
the  frog  and  pigeon  has  been  obtained.  The  animal  is  able  to  maintain  its 
equilibrium,  to  run  or  jump,  and  in  fact  carry  out  all  the  most  compli- 
cated co-ordinated  movements,  but  it  is  unable  to  originate  them  without 
stimulation.  In  the  case  of  the  dog,  however,  it  has  been  found  impos- 
sible to  remove  the  whole  brain,  but  when  it  has  been  removed  piece- 
meal the  animal  may  be  kept  alive  for  some  time,  and  can  carry  out  co- 
ordinated movements  well,  and  even  manifest  intelligence. 

It  is  quite  evident,  therefore,  that  the  apparatus  for  carrying  out  co- 
ordinated movements  is  in  these  animals  not  localized  either  in  the  cere- 
brum or  in  the  spinal  cord,  and  must  therefore  be  connected  in  some 
way  with  the  parts  of  the  brain  below  the  cerebrum  and  above  the 
cord.  There  is  no  reason  why  such  an  arrangement  may  not  be  supposed 
to  exist  in  the  human  brain. 

We  must  look  upon  the  cerebrum,  however,  for  the  originator  of  vol- 
untary movements. 

As  regards  the  theory,  of  the  localization  of  different  movements  in 
different  parts  of  the  cerebral  cortex  which  as  we  have  seen  has  received 
so  much  support  from  observation  on  animals  such  as  the  dog  and  the 
monkey,  at  any  rate,  we  may  say  that  certain  parts  of  the  cerebral  cortex 
appear  to  be  highly  sensitive  to  electrical  stimuli,  particularly  the 
Rolandic  area  and  the  frontal  lobe  in  front  of  it.  Stimulation  of  cer- 
tain other  regions,  viz.,  of  the  occipital  region,  of  the  parietal  and  tem- 
poral region,  and  of  the  gyrus  fornicatus  and  the  frontal  region  in  front 
of  the  motor  area,  does  not  give  rise  to  such  movements.  Such  observa- 
tions as  it  has  been  jiossible  to  make  on  man  show  that  the  localization 
of  movement  on  the  human  cerebral  cortex  is,  if  anything,  superior 
to  that  observed  in  monkeys.  We  have,  of  course,  but  few  data  upon 
Avhich  to  base  our  conclusion,  except  such  as  have  been,  obtained  from 
the  observation  of  the  symptoms  of  disease,  but  with  the  hel])  of  these 
we  may  assume  that  in  the  cerebral  cortex  the  co-ordinated  movements 
of  the  body  in  some  way  are  represented.  The  cases  which  have  given 
us  most  of  our  knowledge  upon  the  subject  are  those  in  which  haemorrhages 
have  occurred  in  different  parts  of  the  brain,  followed  by  paralysis  of 
the  opposite  side  of  the  body.  These  hgemorrhages  chiefly  occur  in 
the  neighborhood  of  the  corpus  striatum.  The  paralysis  of  the  extremities 
is  practically  permanent,  although,  as  a  rule,  the  muscles  connected  with 
the  trunk  are  not  paralyzed.  This  means  that  some  interruption  has 
taken  place  between  the  cerebral  cortex  and  the  paralyzed  muscles,  and  if 
the  lesion  is  a  destroying  one, the  connection  is  never  re-established.  In  the 
case  of  the  animals,  such  as  the  dog,  this  is  not  the  case,  as  the  paralysis 
is  temporary.  It  is  supposed  that  in  man  not  only  the  more  highly 
skilled   movements  but  all    voluntary  movements  of    the  muscles  are 


THE    XERVOUS   SYSTEM.  609 

actually  represented  in  the  cortical  areas,  and  that  the  pyramidal  tracts 
are  actually  essential  for  voluntary  movements.  If  the  pyramidal 
tracts  be  partially  or  wholly  destroyed,  anywhere  in  their  course,  a 
paralysis  corresponding  with  the  amount  destroyed  invariably  follows. 
In  the  dog  experiments  have  shown  that  this  is  not  the  case,  and  the 
conduction  of  voluntary  impulse  to  muscles  may  take  place,  for  example, 
in  other  parts  of  the  cord  besides  the  pyramidal  tract,  after  hemisection. 

The  pyramidal  tracts  in  man,  however,  must  be  considered  also  as 
the  only  path  connecting  the  cortical  centres  with  the  co-ordinated 
centres  lower  down  in  the  brain,  as,  for  example,  in  the  bulb.  The 
impulses  which  pass  down  from  the  cortex,  whatever  they  may  be,  are 
not  however  of  necessity  connected  with  consciousness,  and  many  volun- 
tary movements  of  a  complicated  nature  may  take  place  really  better  with- 
out consciousness  than  with  it.  This  is  shown  in  such  co-ordinated 
movements  as  writing,  walking,  marching,  and  the  like,  all  of  which  are 
acquired  with  time  and  much  labor,  but  when  once  perfect  in  the 
individual,  can  best  be  performed  without  voluntary  effort.  Such  move- 
ments must  be  represented  by  impulses  passing  in  the  pyramidal  tracts, 
for  if  they  are  interrupted,  the  movements  are  no  longer  performed. 
What  is  the  actual  meaning  of  the  origination  of  a  voluntary  action 
performed  by  what  is  actually  an  effort  of  the  will,  we  are  unable  to  say. 
Hso  doubt  imj^ulses  from  the  periphery  conducted  to  the  cerebral  cortex 
along  all  kinds  of  afferent  channels  must  have  something  to  do  with  it; 
directly  or  indirectly,  sooner  or  later.  In  the  human  cortex  it  would 
seem  that  the  apparatus  for  j^erforming  all  manner  of  possible  co-ordi- 
nated movements  which  may  result  in  speech  or  action,  are  stored.  This 
apparatus  is  capable  of  being  set  in  action  either  in  the  absence  of  con- 
sciousness by  afferent  stimuli  of  some  kind  directly,  or  by  what  may  be, 
indirectly  or  remotely,  in  some  way  the  result  of  afferent  stimuli,  viz., 
the  will.  It  is  also  probable  that  the  will  of  another  may  take  the  place 
of  the  man's  own  will,  and  may  call  forth  movements,  actions,  and 
speech,  all  of  which  are,  as  it  were,  ready  to  be  called  forth  by  a  stimu- 
lus of  some  kind.  It  may  be  supposed  that  the  condition  of  develop- 
ment of  the  brain  inherited  by  the  individual  has  something  to  do  both 
with  the  potentialities  of  the  apparatus  for  co-ordinated  acts,  which  he 
receives  at  birth,  and  with  the  way  in  which  the  apparatus  is  set  in 
motion. 

Unilateral  Action. — Respecting  the  mode  in  which  the  brain  dis- 
charges its  functions,  there  is  no  evidence  whatever.  But  it  appears 
that,  for  all  but  its  highest  intellectual  acts,  one  of  the  cerebral  hemi- 
spheres is  sufficient.  For  numerous  cases  are  recorded  in  which  no 
mental  defect  was  observed,  although  one  cerebral  hemisphere  was  so 
disorganized  or  atrophied  that  it  could  not  be  supposed  capable  of  dis- 

39 


610  HANDBOOK    OF    PHYSIOLOGY. 

charging  its  functions.  The  remaining  hemisphere  was,  in  these  cases, 
adequate  to  the  functions  generally  discharged  by  both;  but  the  mind 
does  not  seem  in  any  of  these  cases  to  have  been  tested  in  very  high 
intellectual  exercises;  so  that  it  is  not  certain  that  one  hemisphere  will 
suffice  for  these.  In  general,  the  brain  combines,  as  one  sensation,  the 
impressions  which  it  derives  from  one  object  through  both  hemispheres, 
and  the  ideas  to  which  the  two  such  impressions  give  rise  are  single.  In 
relation  to  common  sensation  and  the  efforts  of  the  will,  it  must  always 
be  remembered  that  the  impressions  to  and  from  the  hemispheres  of  the 
brain  are  carried  across  the  middle  line;  so  that  in  destruction  or  com- 
pression of  either  hemisphere,  whatever  effects  are  produced  in  loss  of 
sensation  or  voluntary  motion,  are  observed  on  the  side  of  the  body 
■opposite  to  that  on  which  the  brain  is  injured. 

Sleep. — All  parts  of  the  body  which  are  the  seat  of  active  change  require 
periods  of  rest.  The  alternation  of  work  and  rest  is  a  necessary  condition  of 
their  maintenance,  and  of  the  healthy  performance  of  their  functions.  These 
alternating  periods,  however,  differ  much  in  duration  in  different  cases ;  but, 
for  any  individual  instance,  they  preserve  a  general  and  rather  close  uniformity. 
Thus,  as  before  mentioned,  the  periods  of  rest  and  work,  in  the  case  of  the 
heart,  occupy,  each  of  them,  about  half  a  second  ;  in  the  case  of  tlie  ordinary 
respiratory  muscles  the  periods  are  about  four  or  five  times  as  long.  In  many 
cases,  again  (as  of  the  voluntary  muscles  during  violent  exercise) ,  while  the 
periods  during  active  exertion  alternate  very  frequently,  yet  the  expenditure 
goes  far  ahead  of  the  repair,  and.  to  compensate  for  this,  an  after  repose  of 
some  hours  becomes  necessary  ;  the  rhythm  being  less  perfect  as  to  time,  than 
in  the  case  of  the  mu.scles  concerned  in  circulation  and  respiration. 

Obviously,  it  would  be  impossible  that,  in  the  case  of  the  brain,  there 
should  be  short  periods  of  activity  and  repose,  or  in  other  words,  of  conscious- 
ness and  unconsciousness.  The  repose  must  occur  at  long  intervals ;  and  it 
must  therefore  be  proportionately  long.  Hence  the  necessity  for  that  condition 
which  we  call  Sleep;  a  condition  which  seeming  at  first  sight  exceptional,  is 
only  an  unusually  perfect  example  of  what  occurs,  at  varying  intervals,  in 
every  actively  working  portion  of  our  bodies. 

A  temporary  abrogation  of  the  functions  of  the  cerebrum  imitating  sleep, 
may  occur,  in  the  ease  of  injury  or  disease,  as  the  consequence  of  two  appar- 
ently widely  different  conditions.  Insensibility  is  equally  produced  bj^  a 
deficient  and  an  excessive  quantity  of  blood  within  the  cranium  (coma)  ;  but  it 
was  once  svipposed  that  the  latter  offered  the  truest  analogy  to  the  normal  con- 
dition of  the  brain  in  sleep,  and  in  the  absence  of  any  proof  to  the  contrary, 
the  brain  was  said  to  be  during  sleep  congested.  Direct  experimental  inquiry 
has  led,  however,  to  the  opposite  conclusion. 

By  exposing,  at  a  circumscribed  spot,  the  surface  of  the  brain  of  living 
animals,  and  protecting  the  exposed  part  by  a  watch-glass,  Durham  was  able 
to  prove  that  the  brain  becomes  visibly  paler  (anaemic)  during  sleep  ;  and  the 
anaemia  of  the  optic  disc  during  sleep,  observed  by  Hughlings  Jackson,  may 
be  taken  as  a  strong  confirmation,  by  analogy,  of  the  same  fact. 

A  very  little  consideration  will  show  that  these  experimental  results  corre- 
spond exactly  with  what  might  have  been  foretold  from  the  analogy  of  other 


THE    NEKVOUS    SYSTEM.  611 

physiological  conditions.  Blood  is  svipplied  to  the  brain  for  two  partly  dis- 
tinct purposes.  (1.)  It  is  supplied  for  mere  nutrition's  sake.  (2.)  It  is  neces- 
sary for  bringing  supplies  of  potential  or  active  energy  {i.e. ,  combustible  matter 
or  heat)  which  may  be  transformed  by  the  cerebral  corpuscles  into  the  various 
manifestations  of  nerve-force.  During  sleep  blood  is  requisite  for  only  the  first 
of  these  purposes ;  and  its  supply  in  greater  quantity  would  be  not  only 
useless,  but  by  supplying  au  excitement  to  work,  when  rest  is  needed,  would  be 
positively  harmful.  In  this  respect  the  varying  circulation  of  blood  in  the 
brain  exactly  resembles  that  which  occurs  in  all  other  energy -transforming 
parts  of  the  body  ;  e.g.,  glands  or  muscles. 

At  the  same  time,  it  is  necessary  to  remember  that  the  normal  angemia  of 
the  brain  which  accompanies  sleep  is  probably  a  result,  and  not  a  cause  of  the 
■quiescence  of  the  cerebral  functions.  What  the  immediate  cause  of  this 
periodical  partial  abrogation  of  functions  is,  however,  we  do  not  know. 

Somnambulism  and  Dreams. — What  we  term  sleep  occvirs  often  in  very  differ- 
ent degrees  in  different  parts  of  the  nervous  system  ;  and  in  some  parts  the 
expression  cannot  be  used  in  the  ordinary  sense. 

The  phenomena  of  di^eams  and  somnambtdism  are  examples  of  differing 
degrees  of  sleep  in  different  parts  of  the  cerebro-spinal  nervous  system.  In  the 
former  case  the  cerebrum  is  still  partially  active ;  but  the  mind-products  of  its 
action  are  no  longer  corrected  by  the  reception,  on  the  part  of  the  sleeping 
sensorium,  of  impressions  of  objects  belonging  to  the  outer  world  ;  neither  can 
the  cerebrum,  in  this  half-awake  condition,  act  on  the  centres  of  reflex  action 
of  the  voluntary  muscles,  so  as  to  cause  the  latter  to  contract — a  fact  within 
the  painful  experience  of  all -who  have  suffered  from  nightmare. 

In  somnambulism  the  cerebrum  is  capable  of  exciting  that  train  of  reflex 
nervous  action  which  is  necessary  for  progression,  while  the  nerve-centre  of 
muscular  se7ise  (in  the  cerebellum?)  is,  presumably,  fully  awake ;  but  the  .sen - 
sorium  is  still  asleep,  and  impressions  made  on  it  are  not  sufiiciently /eZf  to 
rouse  the  cerebrum  to  a  comparison  of  the  difference  between  mere  ideas  or 
memories  and  sensations  derived  from  external  objects. 

The  centres  for  muscular  co-ordmations. — In  asserting  that  the  co- 
ordination of  complicated  muscular  movements  is  connected  with  the 
middle  parts  of  the  brain  below  the  cerebrum  and  above  the  bulb,  we 
were  stating  a  fact  deduced  from  experiments  upon  animals.  The  exact 
way  in  which  these  parts  of  the  brain  are  concerned  it  is  difficult  to 
understand.  It  appears,  however,  that  co-ordinated  movements  such  as 
standing,  walking,  and  the  maintenance  of  the  equilibrium  generally, 
require  to  be  guided  and  governed  by  afEerent  impulses,  which  tell  of 
the  condition  of  the  body  and  of  its  relations  to  its  environment  ("  its 
position  in  space").  The  afferent  impulses  are  firstly  visual  and  tactile 
sensations,  secondly  sensations  by  which  we  appreciate  the  condition  of 
our  muscles  (muscular  sense),  and  thirdly^  as  appears  from  experiments 
on  pigeons  and  other  animals,  sensations  produced  by  the  pressure,  in 
different  directions,  of  the  fluid  in  the  semicircular  canals  of  the  in- 
ternal ear. 

Experiments  show  that  when    the   horizontal  semicircular  canal  ii 


G12  HANDBOOK    OF    PHYSIOLOGY. 

divided  in  a  pigeon,  inco-ordination  occurs,  with  a  constant  movement 
of  the  head  from  side  to  side,  and  similarly,  when  one  of  the  vertical 
canals  is  operated  upon,  up  and  down  movements  of  the  head  are  ob- 
served. The  bird  is  unable  to  fly  in  an  orderly  manner,  flutters  and 
falls  when  thrown  into  the  air,  and,  moreover,  is  able  to  feed  with 
difficulty.  Hearing  remains  unimpaired.  So  that  inco-ordination 
depends  upon  deficiency  or  disorder  of  normal  ampullar  influences.  It 
will  be  recollected  that  the  semicircular  canals  are  supplied  with  a 
nerve,  the  vestibular  branch  of  the  auditory,  which  is  connected  with  the 
bulb. 

It  is  probable  that  the  various  afferent  impulses  upon  which  co-ordina- 
tion and  the  maintenance  of  the  equilibrium  depend  are  gathered  up,  as 
it  were,  in  the  tegmental  system  from  the  bulb  ujDward,  since  this 
region  is  so  intimately  connected  with  the  bulb  and  cord  posteriorly, 
and  with  the  optic  thalamus  and  corpora  quadrigemina  anteriorly.  In 
addition  to  the  tegmentum,  however,  the  cerebellum  and  pons  are  in 
some  way  concerned,  because  of  their  intimate  connection  with  the 
spinal  cord  and  bulb,  the  cerebellum  being  further  connected  with  the 
auditory  nerve  on  the  one  hand,  and  with  the  gray  matter  in  connection 
with  the  tegmentum  on  the  other  hand. 

Sensory  Centres. 

There  is  evidence  that  fibres  from  the  nerves  of  special  sense  are 
specially  connected  with  definite  and  distinct  parts  of  the  cerebrum. 

Visual  or  Optic  Centre. — The  termination  of  the  optic  nerve  in  each 
eye,  the  retina,  to  the  structure  of  which  we  shall  return  when  treating 
of  the  eye,  is  so  arranged  that  when  we  look  at  an  object  with  both 
eyes  symmetrical  parts  of  each  retina  are  used.  For  example,  if  we  look 
at  an  object  to  the  left,  an  image  of  that  object  is  focussed  upon  the 
right  half  of  both  retinae,  viz.,  upon  the  temporal  side  of  the  right 
retina,  and  upon  the  nasal  side  of  the  left  retina.  The  optic  nerve- 
fibres  of  these  symmetrical  parts  of  the  retina  are  gathered  together 
behind  where  the  optic  nerves  decussate,  viz.,  in  the  optic  chiasma. 
The  fibres  which  come  from  the  right  side  of  both  eyes  are  contained  in 
the  optic  tract  of  the  same  side,  viz. ,  the  right,  those  from  the  right  eye 
being  outside  of  the  others.  In  the  same  w\ay  the  left  optic  tract  con- 
tains internally  fibres  from  the  left  side  of  the  right  eye  and  externally 
those  from  the  left  side  of  the  left  eye.  On  the  inner  border  of  the  optic 
chiasma  and  tract  there  are  also  commissural  fibres  which  pass  from  one 
side  of  the  brain  to  the  other;  these  are  fibres  which  connect  one  median 
corpus  geniculatum  with  the  other.  They  are  called  the  inferior  or 
arcuate  commissure.     The  optic  tract  thus  formed  then  passes  back- 


THE    XERVOUS   SYSTEM.  613 

ward  and  terminates  in  three  distinct  nuclei,  viz. ,  the  pulvinar  of  the 
optic  thalamus,  the  median  corpus  quadrigemiuum  and  the  lateral 
corpus  geniculatum.  These  nuclei  waste  if  the  ej'es  are  removed  from 
an  adult  animal ;  and  if  from  a  newly  born  animal  they  do  not  develop. 
The  optic  chiasma  in  its  course  gives  off  fibres  which  are  connected  with 
the  nucleus  of  the  third  nerve. 

It  appears  that  some  of  the  fibres  of  the  optic  tract  pass  directly  into 
the  cerebral  cortex  without  joining  with  the  optic  thalamus,  corpus  quad- 
rigemiuum or  corpus  geniculatum. 

It  was  shown  above  that  the  fibres  of  the  cerebral  cortex,  known  as 
the  optic  radiation,  pass  from  the  occipital  region  to  the  three  nuclei 
about  which  we  are  speaking,  viz.,  into  the  pulvinar  of  the  optic  thala- 
mus, the  anterior  corpus  quadrigemiuum  and  lateral  corpus  geniculatum. 


Tig.  386.— Mesial   aspect   of  human  cerebral   hemisphere  to  indicate  position  of  centres.     The 
exact  position  of  the  centres  will  be  seen  by  comparing  this  figure  with  figure  372. 

and  it  is  known  that  when  the  occipital  cortex  is  removed,  these  three 
waste.  It  has  been  further  sliown  that  in  a  newly  born  auimal  the 
removal  of  such  a  region  is  followed  by  imperfect  development  of  the 
parts  in  question. 

If  one  optic  nerve  be  divided  blindness  of  the  corresponding  eye 
results,  but  if  one  optic  tract  be  divided  there  is  a  half  blindness, 
which  is  called  hemianopsia,  hemianojna,  or  hemiopia,  right  or  left, 
according  as  the  right  or  left  field  of  vision  is  cut  off.  It  is  highly 
probable  that  the  occipital  lobe  (figs.  382,  386),  and  particularly 
the  cuneus,  is  concerned  as  a  so-called  visual  centre,  since  not  only  is 
it  connected  with  the  optic  nerves,  as  we  have  seen,  but  also  because  the 
removal  of  the  right  occipital  lobe  in  an  animal  (monkey),  is  followed 
by  left  hemiopia,  removal  of  the  left  by  right  hemiopia,  and  removal  of 
both  occipital  lobes  by  total  blindness.   Some  have  connected  the  angular 


614  HANDBOOK    OF    PHYSIOLOGY. 

gyrus  also  with  vision  as  the  centre,  while  others  look  upon  it  merely 
as  an  accessory  centre. 

Olfactory  centre.— The  olfactory  nerve  differs  from  the  other  cranial 
nerves.  In  reality  it  is  a  representative  of  the  olfactory  lobes  of  other 
animals,  which  are  part  of  the  cerebrum.  It  originates  as  an  off-shoot 
from  the  cerebral  vesicle,  the  front  part  of  which  is  developed  into  the 
bulb  of  the  olfactory  nerve,  while  the  back  forms  its  peduncle.  The 
nerve,  the  cavity  of  which  is  filled  up  in  the  fully  developed  condition 
with  neurogliar  substance,  lies  upon  the  cribriform  plate  of  the  ethmoid 
bone,  and  is  contained  in  a  groove  of  the  frontal  lobe  on  its  under  sur- 
face. On  examination  of  the  bulb  it  is  found  to  be  thus  made  up. 
Beneath  the  neurogliar  layer  is  a  layer  of  longitudinal  fibres  and  a  few 
nerve-cells,  next  to  this  is  a  layer  of  small  cells  (nuclear  layer),  fibres; 
from  the  layer  of  nerve-fibres  passing  through  it. 

The  nuclear  layer  is  also  separated  into  groujos  of  cells  by  an  inter- 
lacing of  the  fibres.  The  next  layer  is  thick  and  is  composed  of  neuroglia, 
and  some  fibres,  some  of  which  are  medullated,  as  well  as  of  cells  more 
or  less  pyramidal  in  shape.  Below  this  layer  is  the  layer  of  olfactory 
glomeruli.  These  glomeruli  are  small  coils  of  olfactory  fibres  inclosing 
small  cells  and  granular  matter. 

Fibres  of  the  olfactory  nerve  proper  are  found  below  this  layer  and 
pass  to  be  distributed  to  the  olfactory  mucous  membrane.  They  are 
thought  to  have  origin  in  the  glomeruli.  The  peduncle  of  the  nerve 
or  the  olfactory  tract  as  it  is  sometimes  called,  is  made  up  of  longitudinal 
fibres  originating  in  the  bulb,  with  neuroglia  and  some  nerve-cells. 

The  fibres  of  the  olfactory  tract  have  been  traced  into  the  nucleus, 
amygdala?  and  its  junction  with  the  hippocampal  gyrus  in  the  temporal 
lobe  (fig.  386).  The  hippocampus  must  be  in  some  way  connected  with 
smell,  since  a  lesion  of  it,  leaving  the  olfactory  tract  uninjured,  seriously 
interferes  with  that  sense. 

Taste  centre. — It  is  very  uncertain  where  the  taste  centre  is  situated, 
if  such  exist.  It  has  been  placed  in  the  temjjoral  lobe,  not  far  from  that 
of  smell  (fig.  386). 

Anditory  centre. — The  position  of  this  centre  is  uncertain.  It  has 
been  localized  in  the  superior  temporal  convolution  (fig.  382).  Experi- 
ments have  been  made  which  connect  auditory  impulses  on  either  side 
with  the  posterior  corpus  quadrigeminum  and  the  median  corpus  genicu- 
latum,  for  when  the  internal  ear  is  destroyed  there  results  atrophy  of 
these  bodies  as  well  as  of  the  lateral  fillet  of  the  opposite  side ;  and  on  the 
other  hand,  destruction  of  the  part  of  the  temporal  lobe  above  indicated 
is  similarly  followed  by  atrophy  of  the  nuclei  of  the  same  side.  If  these 
results  be  confirmed  by  additional  experiments,  it  would  make  it  plain 
that  these  nuclei  bear  much  the  same  relation  to  the  sense  of  hearing 


THE    XERVOUS    SYSTEM.  615 

as  do  the  anterior  corpus  qnadrigeminum  and  the  lateral  corpus  geni- 
culatum  to  the  sense  ot  sight. 

FuxcTiONS  OF  Corpora  striata  and  Optic  Thalami. 

llie  corpora  striata. — The  idea  formerly  held  that  the  corpora  striata 
are  concerned  in  the  transmission  of  motor  impulses,  or  that  they  are 
the  great  motor  ganglia  at  the  base  of  the  brain,  rests  upon  insufficient 
evidence.  Lesions  of  the  corpora  striata  produce  hemiplegia  only 
because  of  the  pressure-effects  tliey  exercise  upon  the  internal  capsule 
close  by. 

The  caudate  nucleus  is  connected  with  the  opposite  side  of  the  cere- 
bellum by  fibres  which  conduct  downward,  and  the  lenticular  nucleus 
is  connected  Avith  the  cerebellum  by  fibres  from  the  tegmentum  and 
superior  cerebellar  peduncles  which  conduct  upward.  It  is  suggested 
that  the  corpora  striata  are  central  organs  analogous  to  the  cerebral  cortex 
itself.  "  The  analogy  to  those  parts  of  the  cortex  that  are  connected 
with  the  cerebellum  is  rendered  still  greater  by  the  fact  that  a  lesion, 
even  an  extensive  lesion,  may  exist  in  either  the  caudate  or  lenticular 
nucleus,  and  so  long  as  it  does  not  interfere  with  the  functions  of  the 
motor  or  sensory  parts  of  the  internal  capsules  it  causes  no  persistent 
symptoms."      (Gowers. ) 

The  optic  thalami. — That  the  optic  thalami  are  the  great  sensory 
centres  at  the  base  of  the  brain — Avhich  was  a  view  held  by  many  until 
recently — does  not  seem  to  be  based  upon  sufficiently  accurate  observa- 
tions. The  important  relation  to  the  tegmentum  of  its  own  side  would 
make  it  appear  as  being  specially  concerned  with  the  sensory  fibres  pass- 
ing to  the  cerebrum,  for  which  it  probably  forms  a  relay. 

Its  connection  with  the  optic  nerves  has  been  commented  upon  above. 
Fibres  connect  the  optic  thalamus  too  with  the  superior  peduncle  of  the 
cerebellum  of  the  ojiposite  side. 

Lesions  of  the  optic  thalamus  do  not  of  themselves  produce  entire 
loss  of  sensation.  If  such  a  symptom  follows,  it  is  due  to  pressure  upon, 
or  injury  to,  the  posterior  limb  of  the  internal  capsule.  The  optic 
thalamus  is  connected  with  visual  sensations,  and  may  be  a  reflex-centre 
for  some  of  the  higher  reflex  actions. 

Of  the  functions  of  the  external  capsule  and  of  the  clatistrum  nothing 
definite  is  known. 

The  Cerebellum. 

The  Cerebellum  (7,  8,  9,  10,  fig.  354)  is  composed  of  an  elongated 
central  portion  or  lobe,  called  the  vermiform  processes,  and  two  hemi- 
spheres.    Each  hemisphere  is  connected  with  its  fellow,  not  only  by 


616 


HANDBOOK    OF    PHYSIOLOGY. 


means  of  the  vermiform  processes,  but  also  by  a  bundle  of  fibres  called  the 
middle  cms  or  peduncle  (the  latter  forming  the  greater  part  of  the  pons 
Varolii),  while  the  superior  crura  with  the  valve  of  Vieussens  connect  it 
with  the  cerebrum  (5,  fig.  387),  and  the  inferior  crura  (formed  by  the 
prolonged  restiform  bodies)  connect  it  with  the  medulla  oblongata  (3, 
fig.  387). 

SlrncUire. — The  cerebellum  is  composed  of  white  and  gray  matter, 
the  latter  being  external,  like  that  of  the  cerebrum,  and  like  it,  infolded, 
so  that  a  larger  area  may  be  contained  in  a  given  space.  The  convolu- 
tions of  the  gray  matter,  however,  are  arranged  after  a  different  pattern, 
as  shown  in  fig.  387.     Besides  the  gray  substance  on  the  surface,  there 


Fig.  387.— CerebeUum  in  section  and  fourth  ventricle,  with  the  neighboring  parts.  1, 
Median  groove  of  fourtli  ventricle,  ending  below  in  the  calamus  scriptorius,  with  the  longitu- 
dinal eminences  formed  by  the  fasciculi  teretes,  one  on  each  side;  2,  the  same  groove,  at  the 
place  where  the  white  streaks  of  the  auditory  nerve  emerge  from  it  to  cross  the  floor  of  the  ven- 
tricle; 3,  inferior  crus  or  peduncle  of  the  cerebellum,  formed  by  the  restiform  body;  4,  posterior 
pyramid;  above  this  is  the  calamus  scriptorius;  5,  superior  crus  of  cerebellum,  or  processus  e 
cerebello  ad  cerebrum  Cor  ad  testes) ;  6,  6,  fillet  to  the  side  of  the  crura  cerebri ;  7,  7,  lateral 
grooves  of  the  crura  cerebri ;  8,  corpora  quadrigemina.  (From  Sappey  after  Hirschfeld  and 
Leveillfi.) 

is,  near  the  centre  of  the  white  substance  of  each  hemisphere,  a  small 
capsule  of  gray  matter  called  the  corpus  dentahim  (fig.  388,  cc?),  resem- 
bling very  closely  the  corpus  deyitatum  of  the  olivary  body  of  the  medulla 
oblongata  (figs.  362,  388,  o). 

If  a  section  be  taken  through  the  cortical  portion  of  the  cerebellum, 
the  following  distinct  layers  can  be  seen  (fig.  389)  by  microscopic  ex- 
amination. 

(1.)  Immediately  beneath  the  pia  mater  [p  m)  is  a  layer  of  consid- 
erable thickness,  which  consists  of  a  delicate  connective  tissue,  in  which 
are  scattered  several  spherical  corpuscles  like  those  of  the  granular  layer 
of  the  retina,  and  also  an  immense  number  of  delicate  fibres  passing  up 
toward  the  free  surface  and  branching  as  they  go.     These  fibres  are 


THE    NERVOUS    SYSTEM.  617 

chiefly  the  processes  of  the  cells  of  Piirkinje.  (2.)  The  cells  of  PurMnje 
(fig.  375  and  389).  These  are  a  single  layer  of  very  large  (40/i  X  30,y,) 
branched  nerve-ceils,  with  large  round  nuclei,  each  of  which  gives  off  a 


Fig.  388. — Outline  sketch  of  a  section  of  the  cerebeUum,  showing:  the  corpus  dentatum.  The 
section  has  been  carried  through  tixe  left  lateral  part  of  the  pon.s,  so  as  to  divide  the  superior  pe- 
duncle and  pass  nearly  through  the  middle  of  the  left  cerebellar  hemisphere.  The  olivary  body 
has  also  been  divided  longitudinally  so  as  to  expose  in  section  its  corpus  dentatum.  c  r,  crus 
cerebri;  /,  flUet;  q.  corpora  quadrigemina;  s  p,  superior  peduncle  of  the  cerebellum  divided; 
m  p,  middle  peduncle  or  lateral  part  of  the  pons  Varolii,  with  fibres  passing  from  it  into  the 
white  stem;  a  v,  continuation  of  the  white  stem  radiating  toward  the  arbor  vitae  of  the  folia; 
c  d,  corpus  dentatum ;  o,  olivary  body  with  its  corpus  dentatum ;  p,  anterior  pyramid.  (Allen 
Thomson.)    %. 

single  unbranched  process  downward,  and  numerous  processes  upward 
into  the  external  layer,  some  becoming  continuous  with  the  scattered 
corpuscles  of  that  layer.  (3.)  The  nuclear  or  granular  layer  (g),  con- 
sisting of  immense  numbei's  of  corpuscles  closely  resembling  those  of  the 
nuclear  layers  of  the  retina.  Some  of  these  corpuscles  belong  to  the 
neuroglia,  but  others  are  small  nerve  cells  which  terminate  in  processes 
"which  end  in  minute  branchings.  One  of  the  processes  sends  a  branch 
outward  to  the  molecular  layer.  (4. )  Nerve-fihre  layer  (/. )  Bundles  of 
nerve-fibres  forming  the  white  matter  of  the  cerebellum,  which,  from 
its  branched  appearance,  has  been  named  the  ai'hor  vitce.  Some  of 
these  fibres  pass  out  to  join  with  the  cells  of  Purkinje,  and  others 
pass  further  outward  into  the  molecular  layer,  where  losing  their  me- 
dullas, they  divide  into  fibres  which  form  part  of  the  layer.  In  the 
molecular  layer,  then,  there  are  four  sets  of  fibres,  those  passing  ofi^  from 
the  cell  proper  to  the  layer,  those  from  the  nuclear  layer,  those  from  the 
cells  of  Purkinje,  and  the  fibres  from  the  central  gray  matter. 

Functions  of  the  Cerebellum. 

(1.)  With  the  exception  of  its  middle  lobe,  the  cerehellum  is  itself  in- 
sensible  to  irritation  and  may  be  all  cut  away  without  eliciting  signs  of 
pain  (Longet).  Its  removal  or  disorganization  by  disease  is  also  generally 
unaccompanied  by  loss  or  disorder  of  sensibility;  animals  from  which  it 
is  removed  can  smell,  see,  hear,  and  feel  pain,  to  all  ajjpearances,  as  per- 
fectly as  before  (Flourens;  Magendie).  It  cannot,  therefore,  be 
regarded   as  a  principal  organ  of  sensation.     Yet,  if  any  of  its  crura  be 


618 


HANDBOOK    OF    PHYSIOLOGY. 


touched,  pain  is  indicated;  and,  if  tlie  restiform  tracts  of  the  medulla 
oblongata  be  irritated,  the  most  acute  suffering  apjoears  to  be  produced. 
(2.)   Co-ordination  of  Movements. — In  reference  to  motion,  the  experi- 
ments of  Longet  and  many  others  agree  that  no  irritation  of  the  cerebel- 


.    pa 


Fig.  389.— Vertical  section  of  dog's  cerebellum;  p  w,  pia  mater;  p,  corpuscles  of  Purkinj§ 
which  are  branched  nerve-cells  lying  in  a  single  layer  and  sending  single  processes  downward 
and  more  numerous  ones  upward,  which  branch  continuously  and  extend  through  the  deep 
"molecular  layer"  toward  the  free  surface;  g,  dense  layer  of  ganglionic  corpuscles,  closely  re- 
sembling nuclear  layers  of  retina;  /,  layer  of  nerve-fibres,  with  a  few  scattered  ganglionic  cor- 
puscles, This  last  layer  (//)  constitutes  part  of  the  ichUe  matter  of  the  cerebellum,  while  the 
layers  between  it  and  the  free  surface  are  gray  matter.     (Klein  and  Noble  Smith.) 

lum  produces  movement  of  any  kind.  Remarkable  results,  however,  are 
produced  by  removing  parts  of  its  substance,  Flourens  (whose  experi- 
ments have  been  confirmed  by  those  of  Bouillaud,  Longet,  and  others) 
extirpated  the  cerebellum  in  birds  by  successive  layers.     Feebleness  and 


THE    ISTERYOUS   SYSTEM.  61& 

want  of  harmony  of  muscular  movements  were  the  consequence  of  remov- 
ing the  superficial  layers.  When  he  reached  the  middle  layers,  the  ani- 
mals became  restless  without  being  convulsed;  their  movements  were 
violent  and  irregular,  but  their  sight  and  hearing  were  perfect.  By  the 
time  that  the  last  i^ortion  of  the  organ  was  cut  away,  the  animals  had 
entirely  lost  the  powers  of  springing,  flying,  walking,  standing,  and 
preserving  their  equilibrium.  When  an  animal  in  this  state  was  laid  upon 
its  back,  it  could  not  recover  its  former  posture,  but  it  fluttered  its. 
wings,  and  did  not  lie  in  a  state  of  stupor ;  it  saw  the  blow  that  threatened 
it,  and  endeavored  to  avoid  it.  Volition  and  sensation,  therefore,  were 
not  lost,  but  merely  the  faculty  of  combining  the  actions  of  the  muscles;, 
and  the  endeavors  of  the  animal  to  maintain  its  balance  were  like  those 
of  a  drunken  man. 

The  experiments  afforded  the  same  results  when  repeated  on  all  classes 
of  animals;  and  from  them  and  the  others  before  referred  to,  Flourens 
inferred  that  the  cerebellum  belongs  neither  to  the  sensory  nor  the  intel- 
lectual apparatus;  and  that  it  is  not  the  source  of  voluntary  movements, 
although  it  belongs  to  the  motor  apparatus;  but  is  the  organ  for  the  co- 
ordination of  the  voluntary  movements,  or  for  the  excitement  of  the  com- 
bined action  of  muscles. 

Such  evidence  as  can  be  obtained  from  cases  of  disease  of  this  organ, 
conflrms  the  view  taken  by  Flourens:  and,  on  the  whole,  it  gains  sup- 
port from  comparative  anatomy:  animals  whose  natural  movements- 
require  most  frequent  and  exact  combinations  of  muscular  actions  being- 
those  whose  cerebella  are  most  developed  in  proportion  to  the  spinal 
cord. 

We  must  remember,  too,  that  the  cerebellum  is  connected  with  the 
posterior  columns  of  the  cord  as  well  as  with  the  direct  cerebellar  tract, 
both  of  which  probably  convey  to  the  middle  lobe  muscular  sensations. 
It  is  also  connected  with  the  auditory  nerves  and  bulb  by  the  internal  and 
external  acute  fibres;  and  with  the  tegmentum  through  the  red  nuclei. 
Its  connection  with  the  efl'erent  tracts  from  the  difl'erent  cerebral  lobes 
through  the  pons  is  also  highly  important.  Movements  of  the  eyes  also 
occur  on  direct  stimulation  of  the  middle  lobe.  It  seems,  therefore,  to 
be  connected  in  some  way  with  all  of  the  chief  sensory  impulses  which 
have  to  do  with  the  maintenance  of  the  equilibrium,  and  is  generally 
included  in  the  nervous  apparatus  which  is  supposed  to  govern  this  func- 
tion of  our  bodies. 

Foville  supposed  that  the  cerebellum  is  the  organ  of  vmscidar  sense,  i.  e. ,  the 
organ  by  which  the  mind  acquires  that  knowledge  of  the  actual  state  and 
position  of  the  muscles  which  is  essential  to  the  exercise  of  the  will  upon  them  ; 
and  it  must  be  admitted  that  all  the  facts  just  referred  to  are  as  well  explained 
on  this  hypothesis  as  on  that  of  the  cerebellum  being  the  organ  for  combining 


630  HANDBOOK    OF    PHYSIOLOGY. 

moTements.  A  harmonious  combination  of  muscular  actions  must  depend  as 
much  on  the  capability  of  appreciating  the  condition  of  the  muscles  with  regard 
to  their  tension,  and  to  the  force  with  which  they  are  contracting,  as  on  the 
power  which  any  special  nerve-centre  may  possess  of  exciting  them  to  contrac- 
tion. And  it  is  because  the  power  of  such  harmonious  movement  would  be 
equally  lost,  whether  the  injury  to  the  cerebellum  involved  injury  to  the  seat 
of  muscular  sense,  or  to  the  centre  for  combining  muscular  actions,  that  ex- 
periments on  the  subject  afford  no  proof  in  one  direction  more  than  the  other. 

Forced  Movements. — The  influence  of  each  half  of  the  cerebellum 
is  directed  to  muscles  on  the  opposite  side  of  the  body;  and  it  would 
appear  that  for  the  right  ordering  of  movements,  the  actions  of  its  two 
halves  must  be  always  mutually  balanced  and  adjusted.  For  if  one  of  its 
crura,  or  if  the  pons  on  either  side  of  the  middle  line,  be  divided,  so  as 
to  cut  off  from  the  medulla  oblongata  and  spinal  cord  the  influence  of  one 
of  the  hemispheres  of  the  cerebellum,  strangely  disordered  movements 
ensue  (forced  movements).  The  animals  fall  down  on  the  side  opposite 
to  that  on  which  the  crus  cerebelli  has  been  divided,  and  then  roll  over 
continuously  and  repeatedly;  the  rotation  being  always  round  the  long 
axis  of  their  bodies,  and  generally  from  the  side  on  which  the  injury  has 
been  inflicted.  The  rotations  sometimes  take  place  with  much  rapidity; 
as  often,  according  to  Magendie,  as  sixty  times  in  a  minute,  and  may  last 
for  several  days.  Similar  movements  have  been  observed  in  men;  as  by 
Serres  in  a  man  in  whom  there  was  apoplectic  effusion  in  the  right  crus 
cerebelli ;  and  by  Belhomme  in  a  woman,  in  whom  an  exostosis  pressed 
on  the  left  crus.  They  may,  perhaps,  be  explained  by  assuming  that 
the  division  or  injury  of  the  crus  cerebelli  produces  paralysis  or  imper- 
fect and  disorderly  movements  of  the  opposite  side  of  the  body;  the 
animal  falls,  and  then,  struggling  with  the  disordered  side  on  the 
ground,  and  striving  to  rise  with  the  other,  pushes  itself  over;  and  so 
again  and  again,  with  the  same  act,  rotates  itself.  Such  movements  cease 
when  the  other  crus  cerebelli  is  divided ;  but  probably  only  because  the 
paralysis  of  the  body  is  thus  made  almost  complete.  Other  varieties  of 
forced  movements  have  been  observed,  especially  those  named  "  circus 
movements,"  when  the  animal  operated  upon  moves  round  and  round  in 
a  circle ;  and  again  those  in  which  the  animal  turns  over  and  over  in  a 
series  of  somersaults.  Nearly  all  these  movements  may  result  on  section 
of  one  or  other  of  the  following  parts;  viz.,  crura  cerebri,  medulla, 
pons,  cerebellum,  corpora  quadrigemina,  corpora  striata,  optic  thalami, 
and  even,  it  is  said,  of  the  cerebral  hemispheres. 

Functions  of  the  Corpora  Quadrigemina  and  Geniculata. 

The  corpora  quadrigemina  are  the  homologues  of  the  optic  lobes  in 
birds,  amphibia,  and  fishes.     The  anterior  pair  may  be  regarded  as  the 


THE    KERVOUS   SYSTEM.  621 

principal  nerve-centres  for  visual  sensations,  the  posterior  possibly  with 
auditory  sensation. 

Functions. — (1)  The  experiments  show  that  removal  of  the  anterior 
corpora  quadrigemina  wholly  destroys  the  power  of  seeing;  and  diseases 
in  which  they  are  disorganized  are  usually  accompanied  by  blindness. 
Atrophy  of  them  is  also  often  a  consequence  of  removal  of  the  eyes. 
Destruction  of  one  of  the  anterior  corpora  quadrigemina  (or  of  one  optic 
lobe  in  birds)  produces  hemiopia  of  opposite  field  of  vision.  This  loss  of 
sight  is  the  only  apparent  injury  of  sensibility  sustained  by  the  removal 
of  the  corpora  quadrigemina. 

The  (2)  removal  of  one  of  them  affects  the  movements  of  the  body, 
so  that  animals  rotate,  as  after  division  of  the  crus  cerebri,  only  more 
slowly:  but  this  may  be  due  to  giddiness  and  partial  loss  of  sight. 

(3)  The  more  evident  and  direct  influence  is  that  produced  on  the 
iris.  It  contracts  when  the  anterior  corpora  quadrigemina  are  irritated: 
it  is  always  dilated  when  they  are  removed :  so  that  they  may  be  regarded, 
in  some  measure  at  least,  as  the  nervous  centres  governing  its  move- 
ments, and  adapting  them  to  the  impressions  derived  from  the  retina 
through  the  optic  nerves  and  tracts. 

(4)  The  centre  for  the  co-ordination  of  the  movements  of  the  eyes  is 
also  contained  in  them.  This  centre  is  closely  associated  with  that  for 
contraction  of  the  pupil,  and  so  it  follows  that  contraction  or  dilatation 
follows  upon  certain  definite  ocular  movements. 

As  we  have  seen,  the  lateral  corpus  geniculatum  is  associated  on 
either  side  with  the  anterior  corpus  quadrigeminum,  and  the  median 
corpus  geniculatum  with  the  posterior  corpus  quadrigeminum. 

TJie  iSi/nijjafhetic  System. — Having  in  the  preceding  chapters  com- 
pleted the  description  of  the  Cerebro-spinal  nervous  system  proper,  there 
remains  to  be  considered  the  structure  and  functions  of  the  so-called 
Sympathetic  nervous  system,  and  to  this  it  is  now  necessary  to  direct 
attention. 

It  should,  however,  be  distinctly  borne  in  mind  that  the  cerebro- 
spinal and  sympathetic  systems  are  not  distinct  from  one  another.  The 
separation  of  the  one  from  the  other  may  be  considered  to  be  purely  for 
the  sake  of  convenience. 

Distribution. — It  consists  of:  (1)  A  double  chain  of  ganglia  and 
fibres,  which  extends  from  the  cranium  to  the  pelvis,  along  each  side  of 
the  vertebral  column,  and  from  which  branches  are  distributed  both  to 
the  cerebro-spinal  system,  and  to  other  parts  of  the  sympathetic  system. 
With  these  may  be  included  the  small  ganglia  in  connection  with  those 
branches  of  the  fifth  cerebral  nerve  which  are  distributed  in  the  neigh- 
borhood of  the  organs  of  special  sense :  namely,  the    Oplitlialmic^  Otic, 


622 


HANDBOOK    OF    PnYSIOLOGT. 


Fig.  390.— Diaerammatic  view  of  the 
Sympathetic  cord  of  the  right  side,  show- 
ing Its  connections  with  the  principal 
cerebro-spinal  nerves  and  the  main  prae- 
aortic  plexuses.  K-  CFrom  Quain's 
Anatomy.  J) 

Cerehro-spinal  nerves.— Vl.,  a  portion 
of  the  sixth  cranial  as  it  passes  through 
the  cavernous  sinus,  receiving  two  twigs 
from  the  carotid  plexus  of  the  sympathe- 
tic nerve;  O,  ophthalmic  ganglion  con- 
nected by  a  twig  with  the  carotid  plexus; 
M,  connection  of  the  sphenopalatine 
ganglion  by  the  Vidian  nerve  with  the 
carotid  plexus;  C,  cervical  plexus;  Br, 
brachial  plexus;  D  6.  sixth  intercostal 
nerve;  D  12,  twelfth;  L  3,  third  lumbar 
nerve;  S  1,  first  sacral  nerve;  S3,  third; 
S  5,  fifth;  Cr,  anterior  crural  nerve;  CV, 
great  sciatic ;  pn,  vagus  in  the  lower  part 
of  the  neck;  r,  recurrent  nerve  winding 
round  the  subclavian  artery. 

Symjwthetic  Cord -c,  superior  cervi- 
cal ganglion;  c',  second,  or  middle;  c",  in- 
ferior: from  each  of  these  ganglia  cardiac 
nerves  (all  deep  on  this  side )  are  seen  de- 
scending to  the  cardiac  plexus;  d  1, 
placed  immediately  below  the  first  dorsal 
sympathetic  ganglion;  d  6,  is  opposite 
thesi.xth;  1 1,  first  lumbar  ganglion;  c  g, 
the  terminal  or  coccygeal  ganglion. 

Prcnaorticand  Visceral  Plexuses.— pp, 
pharyngeal,  and,  lower  down,  laryngeal 
plexus;     pU     post-pulmonary      plexus 
spreading  from  the  vagus  on  the  back  of 
the  right  bronchus;  co,  on  the  aorta,  the 
cardiac  plexus,  towardswhieh,  inaddition 
to  the  cardiac  nerves  from  the  three  cer- 
vical sympathetic  gangha,  other  branch- 
are  seen  descending  from  the  vagus 
I  recurrent  nerves;  co,  right  or  poste- 
-  and  CO',  left  or  ant.  coronary  plexus; 
esophageal  plexus  in  long  meshes  on 
gullet:   sp,  great  splanchnic  nerve 
Ml  med  by  branches  from  the  fifth,  sixth, 
seventh, eighth.and ninth  dorsal  ganglia; 
-f,  small  splanchnic  from  the  ninth  and 
tenth;  -\-  -f ,  smallest  or  thu'il  splanchnic 
from  the  eleventh;  the  first  and  second  of 
these  are  shown  joining  the  solar  plexus, 
s  o;  the  third  descending  to  the  renal 
plexus,  re;  connecting  branches  between 
the  solar  plexus  and  the  vagi  are  also  rep- 
resented; pn',  above  the  place  where  the 
right  vagus  passes  to  the  lower  or  pos- 
terior surface  of  the  stomach;  pn",  the 
left  distributed  on  the  anterior  or  upper 
surface  of  the  cardiac  portion  of  the  or- 
gan: from  the  solar  plexus  large  branch- 
es are  seen  sm-rounding  the  arteries  of 
the  cceliac  axis,  and  descending  to  m  s, 
the  sup.  mesenteric  plexus;  opposite  to 
this  is  an  indication  of  the  suprarenal 
plexus;  below  r  e  (the  renal  plexus),  the 
spermatic  plexus  is  also  indicated ;  a  o,  on 
the  front  of  the  aorta,  marks  the  aortic 
plexus,  formed   by  nerves   descending 
from  the  solar  and  sup.  mesenteric  plex- 
uses and  from  the  lumbar  gangha;  mi, 
the  inf.  mesenteric  plexus  surroimding 
thecorrespondingartery;/i2/,  hypogastric 
plexus  placed  between  the  common  iliac 
vessels,  connected  above  with  the  aortic 
plexus,  receiving  nerves  from  the  lower 
lumbar  ganglia,  and  dividing  below  into 
the  right  and  left  pelvic  or  inf.  hypogas- 
tric plexuses;  pi,  the  right  pelvic  plexus; 
from  this  the  nerves  descending  are  join- 
ed by  those  from  the  plexus  on  the  sup. 
hemorrhoidal  vessels,  vii',  by  nerves  from 
the    sacral   ganglia,    and    by    visceral 
nerves  from  the  tliird  and  fourth  sacral 

^MiMj^i.       spinal  nerves,  and  there  are  thus  formed 

the  rectal,  vesical,  and  other  plexuses,  which  ramify  upon  the  viscera,  as  towards  ir,  and  v,  the 
rectum  and  bladder. 


THE    NERVOUS    SYSTEM.  623 

SpJieno-paJatine  and  Suhnaxillary  ganglia.  (2)  Various  ganglia  and 
plexuses  of  nerve-fibres  which  give  off  branches  to  the  thoracic  and  ab- 
dominal viscera,  the  chief  of  such  plexuses  being  the  Cardiac,  Solar, 
and  Ui/jjogastricj  but  inintimate  connection  with  these  are  many  second- 
ary plexuses,  as  the  Aortic,  Spermatic,  and  Renal.  To  these  plexuses, 
fibres  pass  from  the  praevertebral  chain  of  ganglia,  as  well  as  from  cerebro- 
spinal nerves.  (3)  Various  ganglia  and  plexuses  in  the  substance  of 
many  of  the  viscera,  as  in  the  Stomach,  Intestines,  and  Urinary  l)ladder. 
These,  which  are,  for  the  most  part,  microscopic,  also  freely  communi- 
cate with  other  parts  of  the  sympathetic  system,  as  well  as,  to  some  ex- 
tent, with  the  cerebro-spinal.  (I)  By  many,  the  ganglia  on  the  Pos- 
terior roots  of  the  spinal  nerves,  on  the  Glossopharyngeal  and  Vagus,  and 
on  the  Sensory  root  of  the  Fifth  cerebral  nerve  (Gasserian  ganglion) ,  are 
also  included  as  sympathetic-nerve  structures. 

Class  if  cation. — Gaskell's  researches  have  suggested  a  convenient 
classification  for  the  sympathetic  ganglia  into:  (1.)  The  main  sympa- 
thetic chain,  extending  from  above  downward,  in  the  form  of  connected 
ganglia  lying  upon  the  bodies  of  the  vertebrae,  which  may  be  called 
lateral  or  vertebral  ganglia.  (2).  A  more  or  less  distinct  chain,  prever- 
tebral in  position,  consisting  of  the  semi-lunar,  inferior  mesenteric  and 
similar  plexuses,  which  may  be  called  collateral  ganglia.  (3.)  Ganglia 
situated  in  the  organs  and  tissues  themselves,  called  terminal  ganglia. 
(4.)  The  ganglia  of  the  posterior  roots  of  the  spinal  nerves. 

The  connection  between  these  parts  is  as  follows :  the  visceral  branch 
or  ramus  communicaus  of  each  spinal  nerve,  which  is  one  of  the  divi- 
sions of  a  typical  spinal  nerve — the  others  being  the  dorsal  and  ventral 
— passes  first  of  all  into  the  lateral  chain;  from  this  chain  branches, 
rami  efferentes,  pass  into  the  collateral  ganglia,  and  from  these  again 
other  branches  pass  off  into  the  organs  to  end  in  the  terminal  ganglia. 
In  the  thoracic  region  the  rami  communicantes  are  composed  of  two  parts, 
white  and  gray.  The  former  can  be  traced  backward  into  both  spinal 
nerve-roots  of  their  corresponding  spinal  nerve ;  and  in  the  other  direc- 
tion partly  into  the  lateral  sympathetic  chain,  and  partly  into  the  great 
splanchnic  nerves  and  so  into  the  collateral  ganglia  without  entering 
the  lateral  chain  at  all.  The  upper  white  rami  (from  the  2nd  to  the 
5th),  however,  proceed  upward  and  join  the  superior  cervical  ganglion 
instead  of  passing  downward  into  the  sj)lanchnics.  Other  branches  go 
downward  into  the  lumbar  and  sacral  plexuses.  The  gray  rami  of  all 
the  spinal  nerves  are  the  only  apparent  representatives  of  the  visceral 
branches  in  the  regions  above  the  2nd  thoracic  nerve-root,  and  below 
the  2nd  lumbar  nerve-root,  with  the  exception  of  the  roots  of  the  2nd 
and  3rd  sacral  nerves,  which  have  also  white  rami,  and  consist  of  non- 
medullated  fibres,  and  pass  from  the  ganglia  to  be  distributed  chiefly  to 


624  HANDBOOK    OF    PHYSIOLOGY. 

the  spinal  column,  to  the  spinal  membranes  and  to  the  spinal  nerve-roots 
themselves.  We  must  look  upon  the  white  rami  then  as  the  visceral 
branches  proper. 

A  peculiarity  in  the  structure  of  these  white  medullated  visceral 
nerves  is  the  fineness  of  their  fibres.  They  are  a  third  or  a  fourth  of  the 
diameter  of  ordinary  medullated  fibres,  measuring  1.8//  to  2.7/^  instead 
of  14.4/z  to  19//.  Such  fibres  are  a  peculiarity  of  the  spinal  nerve-roots, 
chiefly  in  the  thoracic  region,  but  they  are  also  found  in  the  second  and 
third  sacral  nerves,  and  constitute  there  the  nervi  erigentes  which  pass, 
directly  to  the  hypogastric  ^olexus,  and  not  first  of  all  into  the  lateral 
chain.  From  this  plexus  branches  pass  upward  into  the  inferior 
mesenteric  ganglia  and  downward  to  the  bladder,  rectum  and  generative 
organs.  These  nerves,  called  by  Graskell^;e/y('c  splanchnic  nerves,  differ 
from  the  rami  viscerales  of  the  thoracic  region  only  in  not  communicat- 
ing with  the  lateral  ganglia;  the  branches  which  pass  upward  from  the 
thoracic  region  to  the  neck,  he  calls  cervical  splancJmics,  and  the 
splanchnics  proper  abdominal  splanchnics.  The  white  rami  viscerales  of 
the  upper  cervical  and  cervico-cranial  regions  do  not  run  with  their 
corresponding  gray  rami,  but  form,  Gaskell  thinks,  the  internal  branch 
of  the  spinal  accessory  nerve,  which  contains  small  medullated  fibres 
similar  to  those  of  the  visceral  branches  in  the  thoracic  region.  This 
branch  passes  into  the  ganglion  of  the  trunk  of  the  vagus.  Small  visceral 
fibres  exist  too  in  the  roots  of  the  vagus,  and  in  those  of  the  glosso-pharyn- 
geal  in  connection  with  the  ganglion  of  the  trunk  and  ganglion  petrosum, 
as  well  as  in  the  chorda  tympani,  in  the  small  petrosal  and  in  other 
cranial  visceral  nerves. 

Functions. — The  researches  of  Gaskell  have,  however,  done  much  to 
clear  up  the  former  confusion  as  to  the  functions  of  the  sympathetic; 
and  in  the  following  account  the  description  of  the  functions,  as  given 
by  that  observer,  is  followed. 

The  efferent  iierve  fibres  of  the  sympathetic  system  supply  {a)  the 
muscles  of  the  vascular  system,  to  which  they  send  vaso-motor  fibres, 
i.e.,  vaso-constrictor  and  cardiac  augmentor  or  accelerator.,  and  vaso-in- 
hibitory  fibres,  i.e..,  vaso-dilator  and  cardiac  inhibitory;  (b)  the  visceral 
muscles,  to  which  they  send  both  viscero-motor  and  viscero-inhibitorg 
fibres,     (c)  The  secretory  gland-cells. 

(a)  i.  Vaso-motor  or  Vaso-constrictor  and  Cardio-augmentor  Fibres. — 
The  vaso-motor  nerves  for  all  parts  of  the  body  come  from  the  central  ner- 
vous system,  and  pass  out  from  the  spinal  cord  in  the  white  rami  viscerales 
of  the  thoracic  region  from  the  second  thoracic  to  the  second  lumbar  nerve- 
roots  inclusive,  as  fine  medullated  fibres ;  they  then  pass  to  the  lateral  or 
main  sympathetic  chain,  become  non-medullated,  and  are  distributed  to 
their  muscles  either  directly  or  through  terminal  ganglia.     Thus  the  aug- 


THE    NERVOUS   SYSTEM.  625 

mentor  nerves  of  the  heart  arise  in  the  thoracic  rami,  pass  upward 
through  tlie  ganglion  stellatum  (first  thoracic  ganglion),  the  anuulus  of 
Yieussens  and  the  inferior  cervical  ganglion,  and  are  distributed  to  the 
heart ;  the  vaso-motor  roots  of  the  brachial  plexus,  in  the  anterior  roots 
of  the  second  and  lower  thoracic  nerves,  and  reach  that  plexus  by  the 
same  ganglion ;  the  vaso-motor  nerves  of  the  foot  leave  the  spinal  cord 
high  up,  and  reach  the  sympathetic  lateral  ganglia  above  the  origin  of 
the  sciatic  nerve,  into  which  they  pass  through  the  abdominal  sympa- 
thetic. In  all  cases  the  nerves  lose  their  medulla  in  the  ganglia. 
Similiirly  the  vaso-motor  nerve  supply  for  the  blood-vessels  of  the  head 
and  neck  and  of  the  abdomen  is  derived  from  the  cervical  and  abdominal 
splanchnics  respectively,  or  from  the  corresponding  rami  efPerentes  of 
the  upper  lumbar  ganglia. 

The  lateral  sympathetic  chain  Gaskell  proposes  to  call  the  chain  of 
vaso-motor  ganglia. 

ii.  Vaso-inhibitory  or  Vaso-dilator,  and  Cardio-inhihitory  Fibres. — 
Of  these,  which  are  doubtless  as  widely  distributed  as  the  vaso-motor 
fibres,  we  have  distinct  proof  in  the  existence  of  fibres  separate  from 
vaso-motor,  e.g..,  in  the  inhibitory  nerve  of  the  heart,  the  cardio-vagus; 
in  the  chorda  tympani;  in  the  small  petrosal,  and  inthenervi  erigentes. 

These  nerve-fibres,  as  far  as  we  know  at  present,  leave  the  central 
nervous  system  among  the  fine  medullated  nerves  of  the  cervico-crania"! 
and  sacral  rami  communicantes,  do  not  enter  the  lateral  ganglia,  but 
pass  without  losing  their  medulla  into  the  collateral  or  terminal 
ganglia. 

{b.)  i.  Viscero-motor  Fibres. — These  fibres,  upon  which  depend  the 
peristaltic  movements  of  the  thoracic  portion  of  the  oesophagus,  and  of 
the  stomach  and  intestines,  arise  from  the  central  nervous  system,  as 
the  fine  medullated  fibres  of  the  upper  portion  of  the  cervical  region,  not 
in  the  spinal  nerve-roots  of  that  region,  but  as  the  bundles  of  fibres 
which  may  be  called  the  rami  viscerales  of  the  vagus  and  accessory  nerves. 
They  pass  to  the  ganglion  of  the  trunk  of  the  vagus,  where  they  lose 
their  medulla. 

ii.  Yi.icero-Inliibitory  Fibres. — It  appears  that  the  nerve  supply  to 
the  circular  muscles  of  the  alimentary  canal  and  its  ap^iendages,  is  con- 
tained in  the  abdominal  splanchnics,  and  consists  of  those  fibres  which 
have  not  passed  through  the  lateral  chain,  and  which  therefore  retain 
their  medulla  until  they  reach  the  proximal  or  collateral  chain, 

(c.)  Glandular  Nerve-Fibres. — A  double  nerve  supply,  in  all  proba- 
bility coinciding  with  the  supply  to  the  visceral  muscles,  has  been 
demonstrated  in  the  cases  of  the  submaxillary,  parotid,  and  lachrymal 
glands,  and  in  these  cases  the  course  of  the  fibres  is  very  similar  to 
that  of  the  corresponding  fibres  for  the  vaso-muscular  supply.  Thus 
40 


626  HANDBOOK    OF    PHYSIOLOGY. 

the  sympathetic  suj)ply  for  these  glands  passes  along  with  the  vjiso- 
motor  fibres  from  the  cervical  splanchnic  (or  sympathetic  trunk),  and 
superior  cervical  ganglion;  while  the  cerebro-spinal  supply  comes  from 
the  rami  viscerales  of  the  cranial  nerves  in  conjunction  with  the  vaso- 
dilator fibres. 

Central  Oriffm  of  the  Rami  Viscerales. — There  appears  to  be  the 
strongest  presumption  that  the  white  rami  of  the  thoracic  region  arise 
in  the  spinal  cord  in,  or  are  connected  with,  the  cells  of  the  posterior 
vesicular  column  of  Clarke.  This  conclusion  is  based  upon  the  fact  that 
these  special  cells  are  found  in  the  three  regions  already  mentioned,  and 
in  those  only  where  the  white  rami  of  fine  medullated  fibres  exist,  viz., 
in  the  cervico-cranial  regions,  in  the  spinal  accessory,  in  the  thoracic 
region,  and  in  the  sacral  region.  But  it  is  probable  that  the  fibres  are 
also  connected  with  the  cells  of  the  lateral  horn  of  the  gray  matter  of 
the  spinal  cord,  and  its  representative  in  the  medulla,  the  antero-lateral 
nucleus  of  Clarke. 

In  a  paper  supplementary  to  his  first  account  of  the  sympathetic 
system,  Gaskell  traced  the  nerve  fibres  of  the  anterior  nerve  roots  to  the 
various  groups  of  nerve  cells  in  the  spinal  cord  thus:  (i.)  Efferent 
nerves  to  somatic  muscles  arise  from  group  of  cells  of  anterior  cornua ; 
(ii.)  efferent  nerves  to  striated  splanchnic  muscles  from  cells  of  the  trac- 
tus  intermedio-lateralis.  (iii-)  Anabolic  or  inhibitory  nerves  to  glands, 
muscles  of  viscera,  and  vessels  of  splanchnic  system  from  cells  of  Clarke's 
column;  (iv. )  motor  nerves  to  visceral  muscles  from  solitary  cells  at  the 
base  of  the  posterior  cornu ;  and  (v.)  motor  or  catabolic  nerves  to  glands 
and  vascular  muscles  from  small  cells  of  the  lateral  cornu. 

Structure  and  Functions  of  the  Ganglia.— The  sympathetic 
ganglia  all  contain— (1.)  nerve-fibres  traversing  them;  (3.)  nerve-fibres 
originating  in  them,  (3.)  nerve  or  ganglion -cor  j)uscles,  giving  origin  to 
these  fibres;  and  (4.)  other  corpuscles  that  appear  free.  In  the  sym- 
pathetic ganglia  of  the  frog,  ganglion-cells  of  a  very  complicated  struc- 
ture have  been  described  by  Beale,  and  subsequently  by  Arnold.  The 
cells  are  inclosed  each  in  a  nucleated  capsule :  they  are  pyriform  in  shape, 
and  from  the  pointed  end  two  fibres  are  given  off,  which  gradually 
acquire  the  characters  of  nerve-fibres,  one  of  them  is  straight,  and  the 
other  (which  sometimes  arises  from  the  cell  by  two  roots)  is  spirally 
coiled  around  it. 

According  to  Gaskell  the  functions  of  the  main  sympathetic  ganglia 
are  the  following : — (1.)  They  effect  the  conversion  of  medullated  into 
non-medullated  fibres;  (2.)  They  possess  a  nutritive  influence  over  the 
nerves  which  pass  from  them  to  the  periphery;  (3.)  They  increase  the 
number  of  fibres  at  the  same  time  as  they  cause  the  removal  of  the 
medulla.     As  regards  their  possession  of  the  usual  properties  of  nerve- 


THE    NERVOUS   SYSTEM.  627 

centres  little  or  nothing  is  certainly  known.  It  appears  unlikely  that 
they  possess  the  reflex  functions  of  the  spinal  centres. 

As  a  contribution  toward  the  explanation  of  the  nervous  mechanism 
of  nutrition  comes  in  Gaskell's  theory  of  cataholic  and  anabolic  nerves. 
He  supposes  that  every  tissue  is  supplied  with  two  sets  of  nerves,  the 
former  of  which  corresponds  with  the  motor  nerve,  the  viscero-motor 
and  the  cardio^augmentor,  by  the  stimulation  of  which  an  increase  of 
the  metabolism  takes  place,  and  which  is  followed  by  exhaustion.  It 
may  be  accompanied  either  by  contraction  of  a  muscle  or  by  an  increase 
of  contraction.  Such  a  nerve  is  excellently  illustrated  by  the  sympa- 
thetic augmentor  or  accelerator  nerve  of  the  heart,  on  stimulation  of 
which  an  increase  in  the  force  and  frequency  of  the  heart  takes  place, 
followed  after  a  time  by  exhaustion.  A  catabolic  nerve  stimulates  the 
destructive  metabolism  which  is  always  going  on  in  a  tissue.  The 
anabolic  nerve  is  the  exact  opposite  of  the  catabolic  nerve  in  function. 
It  subserves  constructive  metabolism.  Stimulation  of  the  nerve  pro- 
duces diminished  activity,  repair  of  tissue  and  building  up.  An  exam- 
l^le  of  this  kind  of  nerve  is  seen  in  the  cardiac  vagus,  stimulation  of 
which  produces  inhibition.  Inhibition  must  generally  be  looked  upon 
as  an  anabolic  process. 

It  will  be  seen  that  the  results  of  stimulation  of  the  nerves  to  the 
salivary  glands,  discussed  in  a  former  chapter,  appear  to  support  the 
theory,  that  the  processes  of  constructive  and  destructive  metabolism 
are  under  the  control  of  separate  nerve-fibres.  In  the  case  of  the  sub- 
maxillary gland  for  example,  if  the  sympathetic  fibres  be  stimulated,  a 
catabolic  efEect  is  produced,  and  the  materials  of  secretion  are  formed  at 
the  expense  of  the  protoplasm  (this  action  in  the  case  of  the  gland 
Heidenhain  calls  trophic) ;  if  on  the  other  hand  the  chorda  tympani  or 
the  secretory  nerve  be  stimulated,  two  things  happen,  one  being  the 
discharge  of  water  and  the  materials  of  secretion  from  the  gland  cells, 
and  the  other  the  building  up  or  reconstruction  of  the  protoplasm  of  the 
cells.  A  part  of  this  action  at  any  rate  is  anabolic,  and  similar  to  the 
action  of  inhibitory  nerves. 


CHAPTER    XVII. 

THE    SENSES. 

General  Co?isiderafions. — Through  the  medium  of  the  nervous  sys- 
tem the  mind  obtains  a  knowledge  of  the  existence  both  of  the  various 
parts  of  the  body,  and  of  the  external  world.  This  knowledge  is  based 
upon  sensatiofis  resulting  from  the  stimulation  of  certain  centres  in  the 
brain,  by  irritations  conveyed  to  them  by  afferent  nerves.  Under  normal 
circumstances,  the  following  structures  are  necessary  for  sensation:  (a) 
A  peripheral  organ  for  the  reception  of  the  impression ;  (b)  a  nerve  for 
conducting  it;  (c)  a  nerve-centre  for  feeling  or  perceiving  it. 

Classiiication  of  Sensations. — Sensations  may  be  conveniently  classed 
as  (1)  common  and  (3)  special. 

(1.)  Common  Sensations. — Under  this  head  fall  all  those  general 
sensations  which  cannot  be  distinctly  localized  in  any  particular  part  of 
the  body,  such  as  fatigue,  discomfort,  faintness,  satiety,  together  with 
Imnger  and  thirst,  in  which,  in  addition  to  a  general  discomfort,  there  is 
in  many  persons  a  distinct  sensation  referred  to  the  stomach  or  fauces. 
In  this  class  must  also  be  placed  the  various  irritations  of  the  mucous 
membrane  of  the  bronchi,  which  give  rise  to  coughing,  and  also  the 
sensations  derived  from  various  viscera  indicating  the  necessity  of  ex- 
pelling their  contents;  e.g.,  the  desire  to  defecate,  to  urinate,  and,  in 
the  female,  the  sensations  which  precede  the  expulsion  of  the  foetus. 
We  must  also  include  such  sensations  as  itching,  creeping,  tickling, 
tingling,  burning,  aching,  etc.,  some  of  which  come  under  the  head  of 
2)ain:  they  will  be  again  referred  to  in  describing  the  tactile  sense.  It 
is  impossible  to  draw  a  very  clear  line  of  demarcation  between  many  of 
the  common  sensations  above  mentioned,  and  the  sense  of  touch,  which 
forms  the  connecting  link  between  the  general  and  special  sensations. 
Touch  is,  indeed,  usually  classed  with  the  special  senses,  and  will  be 
considered  in  the  same  group  with  them;  yet  it  differs  from  them  in 
being  common  to  many  nerves.  Among  common  sensations  some  would 
rank  the  muscular  sense,  which  has  been  already  alluded  to.  It  is  by 
means  of  this  sense  that  we  become  aware  of  the  condition  of  the  mus- 
cles, and  thus  obtain  the  information  necessary  for  their  adjustment  to 
various  purposes — standing,  walking,  grasping,  etc.  This  muscular 
sensibility  (to  which  we  shall  again  refer)  is  shown  in  our  power  to  esti- 


THE    SENSES.  629 

mate  the  difEerences  between  weights  by  the  different  muscular  efforts 
necessary  to  raise  them.  It  must  be  carefully  distinguished  from  the 
sense  of  contact  and  of  pressure,  of  which  the  skin  is  the  organ.  When 
standing  erect,  we  can  feel  the  ground  (contact) ,  and  further  there  is  a 
sense  of  pressure,  due  to  our  feet  being  pressed  against  the  ground  by 
the  weight  of  the  body.  Both  these  are  derived  from  the  skin  of  the 
sole  of  the  foot.  If  now  we  raise  the  body  on  the  toes,  we  are  conscious 
(muscular  sense)  of  a  muscular  effort  made  by  the  muscles  of  the  calf, 
which  overcomes  a  certain  resistance. 

(2.)  Special  Sensations. — Including  the  sense  of  touch,  the  special 
senses  are  five  in  number — Touch,  Taste,  Smell,  Hearing,  Sight. 

The  most  important  distinction  between  common  and  special  sensa- 
tions is  that  by  the  former  we  are  made  aware  of  certain  conditions  of 
various  jiarts  of  our  bodies,  while  from  the  latter  we  gain  our  knowledge 
of  the  external  world  also.  This  difference  will  be  clear  if  we  compare 
the  sensations  of  pain  and  touch,  the  former  of  which  is  a  common,  the 
latter  a  special  sensation.  "  If  we  place  the  edge  of  a  sharp  knife  on 
the  skin,  we  feel  the  edge  by  means  of  our  sense  of  touch;  we  perceive 
a  sensation,  and  refer  it  to  the  object  which  has  caused  it.  But  as  soon 
as  we  cut  the  skin  with  the  knife,  we  feel  pain,  a  feeling  which  we  no 
longer  refer  to  the  cutting  knife,  but  which  we  feel  within  ourselves, 
and  which  communicates  to  us  the  fact  of  a  change  of  condition  in  our 
own  body.  By  the  sensation  of  pain  we  are  neither  able  to  recognize 
the  object  which  caused  it,  nor  its  nature." 

In  studying  the  phenomena  of  sensation,  it  is  important  clearly  to 
understand  that  the  sevsorium,  or  seat  of  sensation,  is  in  the  brain,  and 
not  in  the  particular  organ  through  which  the  sensory  impression  is  re- 
ceived. In  common  parlance  we  are  said  to  see  with  the  eye,  hear  with 
the  ear,  etc.,  but  in  reality  these  organs  are  only  adapted  to  receive 
impressions  which,  being  conducted  to  the  sensorium,  through  their  re- 
spective nerves  give  rise  to  sensation. 

Hence,  if  the  optic  nerve  is  severed,  vision  is  no  longer  possible: 
since,  although  the  image  falls  on  the  retina  as  before,  the  sensory  im- 
pression can  no  longer  be  conveyed  to  the  sensorium.  When  any  given 
sensation  is  felt,  all  that  we  can  with  certainty  affirm  is  that  some  part 
of  the  brain  is  excited.  The  exciting  cause  may  be  some  object  of  the 
external  world,  j^roducing  an  objective  sensation;  or  the  condition  of  the 
sensorium  may  be  due  to  some  excitement  Avithin  the  brain  itself,  in 
which  case  the  sensation  is  termed  subjective.  The  mind  habitually  re- 
fers sensations  to  external  causes;  and  hence,  whenever  they  are  subjec- 
tive we  can  hardly  divest  ourselves  of  the  idea  of  an  external  cause,  and 
an  illusion  is  the  result. 

Xumberless  examples  of  such  illusions  might  be  quoted.     As  familial 


630  HANDBOOK    OF    PHYSIOLOGY. 

cases  may  be  mentioned,  humming  and  buzzing  in  the  ears  caused  by 
some  irritation  of  the  auditory  nerve  or  centre,  and  even  musical  sounds 
and  voices  (sometimes  termed  auditory  spectra) ;  also  so-called  optical 
illusions:  objects  are  described  as  seen,  although  not  present.  Such 
illusions  are  most  strikingly  exemplified  in  cases  of  delirium  tremens  or 
other  forms  of  delirium,  and  may  take  the  form  of  cats,  rats,  creeping 
loathsome  forms,  etc. 

Causes  of  Illusions. — One  uniform  internal  cause,  whicli  may  act  on 
all  the  nerves  of  the  senses  in  the  same  manner,  is  capillary  congestion. 
This  one  cause  excites  in  the  retina,  while  the  eyes  are  closed,  the  sensa- 
ions  of  light  and  luminous  flashes;  in  the  auditory  nerve,  the  sensation 
of  humming  and  ringing  sounds;  in  the  olfactory  nerve,  the  sense  of 
odors;  and  in  the  nerves  of  feeling,  the  sensation  of  pain.  In  the  same 
way,  also,  a  narcotic  substance  introduced  into  the  blood,  excites  in  the 
nerves  of  each  sense  peculiar  symptoms:  in  the  optic  nerves,  the  appear- 
ance of  luminous  sparks  before  the  eyes ;  in  the  auditory  nerves,  tinnitus 
aurimn;  and  in  the  common  sensory  nerves,  the  sensations  of  creeping 
over  the  surface.  So,  also,  among  external  causes,  the  stimulus  of  elec- 
tricity, or  the  mechanical  influence  of  a  blow,  concussion,  or  pressure, 
excites  in  the  eye  the  sensation  of  light  and  colors;  in  the  ear,  a  sense 
of  aloud  sound  or  of  ringing;  in  the  tongue,  a  saline  or  acid  taste;  and 
in  the  other  parts  of  the  body,  a  perception  of  peculiar  jarring  or  of  the 
mechanical  impression,  or  a  shock  like  it. 

Experiments  seem  to  have  proved,  however,  that  none  of  the  nerves 
of  special  sense  possess  the  faculty  of  common  sensibility. 

Perceptions. — The  habit  of  constantly  referring  our  sensations  to  ex- 
ternal causes,  leads  us  to  interpret  the  various  modifications  which 
external  objects  produce  in  our  sensations,  ?is,  properties  of  the  external 
bodies  themselves.  Thus  we  speak  of  certain  substances  as  possessing  a 
disagreeable  taste  and  smell;  whereas,  the  fact  is,  their  taste  and  smell 
are  only  disagreeable  to  us.  It  is  evident,  however,  that  on  this  habit 
of  referring  our  sensations  to  causes  outside  ourselves  (perception),  de- 
pends the  reality  of  the  external  world  to  us ;  and  more  especially  is  this 
the  case  with  the  senses  of  touch  and  sight.  By  the  co-operation  of 
these  two  senses,  aided  by  the  others,  we  are  enabled  gradually  to  at- 
tain a  knowledge  of  external  objects  which  daily  experience  confirms, 
until  we  come  to  place  unbounded  confidence  in  what  is  termed  the 
evidence  of  the  senses. 

Judgments. — We  must  draw  a  distinction  between  mere  sensations, 
and  the  judgments  based,  often  unconsciously,  upon  them.  Thus,  in 
looking  at  a  near  object,  we  unconsciously  estimate  its  distance  and  say 
it  seems  to  be  ten  or  twelve  feet  off:  but  the  estimate  of  its  distance  is 
in  reality  a  judgment  based  on  many  things  besides  the  appearance  of 


THE    SENSES,  631 

the  object  itself;  among  which  may  be  mentioned  the  number  of  inter- 
vening objects,  the  number  of  steps  which  from  jjast  experience  we 
know  we  must  take  before  we  could  touch  it,  and  many  others. 

The  Special  Senses. 
I.  Touch. 

Seat. — The  sense  of  touch  is  not  confined  to  particular  parts  of  the 
body  of  small  extent,  like  the  other  senses;  on  the  contrary,  all  parts 
capable  of  perceiving  the  presence  of  a  stimulus  by  ordinary  sensation 
are,  in  a  certain  degrees,  the  seat  of  this  sense ;  but  touch  should  not  be 
considered  as  a  mere  modification  or  exaltation  of  common  sensation  or 
sensibility.  For  although  the  nerves  on  which  the  sense  of  touch  de- 
pends, are  the  same  as  those  which  confer  ordinary  sensation  on  the 
different  parts  of  the  body,  viz.,  those  derived  from  the  posterior  roots 
of  the  nerves  of  the  spinal  cord,  and  the  sensory  cerebral  nerves,  yet  it 
seems  jirobable  that  the  nerve-fibres  which  subserve  the  special  sense  of 
touch  are  provided  with  special  end  organs. 

All  parts  of  the  body  supplied  with  sensory  nerves  are  thus,  in  some 
degree,  organs  of  touch,  yet  the  sense  is  exercised  in  perfection  only  in 
those  parts  the  sensibility  of  which  is  extremely  delicate,  e.g.,  the  skin, 
the  tongue,  and  the  lips,  which  are  provided  with  abundant  papillae. 
A  peculiar  and,  of  its  own  kind  in  each  case,  a  very  acute  sense  of  touch 
is  exercised  through  the  medium  of  the  nails  and  teeth.  To  a  less  extent 
the  hair  may  be  reckoned  an  organ  of  touch ;  as  in  the  case  of  the  eye- 
lashes. The  sense  of  touch  renders  us  conscious  of  the  presence  of  a 
stimulus,  from  the  slightest  to  tlie  most  intense  degree  of  its  action,  by 
that  indescribable  something  which  we  call  feeling,  or  common  sensa- 
tion. The  modifications  of  this  sense  often  depend  on  the  extent  of  the 
I)arts  affected.  The  sensation  of  pricking,  for  example,  informs  us  that 
the  sensitive  fibres  are  intensely  affected  in  a  small  extent ;  the  sensation 
of  pressure  indicates  a  slighter  affection  of  the  parts  in  the  greater  ex- 
tent, and  to  a  greater  dejith.  It  is  by  the  depth  to  which  the  parts  are 
affected  that  the  feeling  of  pressure  is  distinguished  from  that  of  mere 
contact. 

Varieties. — {a)  The  sense  of  touch  proper,  tactile  sensibility  or  pres- 
sure, {b)  temperature.  These  when  carried  beyond  a  certain  degree  are 
merged  in  the  sensation  of  (c)  pain. 

Touch  proper. — In  almost  all  parts  of  the  body  which  have  deli- 
cate tactile  sensibility  the  epidermis,  immediately  over  the  papilla,  is 
moderately  thin.  When  its  thickness  is  much  increased,  as  over  the 
heel,  the  sense  of  touch  is  very  much  dulled.  On  the  other  hand,  when 
it  is  altogether  removed,  and  the  cutis  laid  bare,  the  sensation  of  con- 


632  HANDBOOK    OF    PHYSIOLOGY. 

tact  is  replaced  by  one  of  pain.  Further,  in  all  highly  sensitive  parts, 
the  papilliB  are  numerous  and  highly  vascular,  and  the  sensory  nerves 
are  connected  with  special  end-organs  which  have  been  described  p.  97 
et  seq. 

The  special  endings  of  the  nerves  which  have  to  do  with  touch  may, 
however,  be  here  again  mentioned.  They  are  of  two  kinds,  viz.,  (a) 
touch  corjmscles,  which  are  found  chiefly  in  the  hands  and  feet,  particu- 
larly on  the  palmar  surface  of  the  hands  and  fingers,  but  also  on  the 
under  surface  of  the  forearm,  nipple,  eyelids,  lips,  and  genital  organs. 
Touch  corpuscles  are  situated  in  the  cutis  vera,  (b)  end  hulbs,  which 
are  found  in  conjunctivee  and  other  mucous  membranes,  the  lijis,  genital 
organs,  tongue,  rectum,  and  elsewhere,  but  not  in  the  skin  proper.  As 
regards  the  Pacinian  corpuscles  and  similar  end-organs,  which  are  so 
widely  distributed,  and  which  may  be  in  some  way  connected  with  the 
sensation,  when  they  are  found  in  the  skin  they  are  situated  very  deeply 
in  the  cutis  vera  or  in  the  subcutaneous  tissue.  They  are  extremely 
numerous  on  the  nerves  of  the  palmar  surface  of  the  fingers.  In  all  of 
these  endings,  and  in  similar  ones  found  in  other  animals,  the  nerve 
ends,  as  in  axis  cylinder,  in  a  special  development  of  the  connective  tis- 
sue sheath.  In  addition  to  these  special  nerve-endings,  nerve-fibres 
appear  to  terminate  everywhere  in  the  skin  between  the  cells  of  the 
Malpighian  stratum  of  the  epidermis  in  the  ends,  and  in  certain  animals 
some  of  them  appear  to  end  in  special  and  rather  large  cells. 

It  is  practically  impossible  to  distinguish  between  what  is  called 
mere  contact  and  touch  in  which  the  element  of  pressure  comes  in. 
The  acuteness  of  the  sense  of  touch  depends  very  largely  on  the  cutane- 
ous circulation,  which  is  of  course  largely  influenced  by  external  temper- 
ature. Hence  the  numbness,  familiar  to  every  one,  produced  by  the 
application  of  cold  to  the  skin. 

Acuteness  of  the  Se7ise. — The  perfection  of  the  sense  of  touch  on 
different  parts  of  the  surface  is  proportioned  to  the  power  which  such 
parts  possess  of  distinguishing  and  isolating  the  sensations  produced  by 
two  points  placed  close  together.  This  power  depends,  at  least  in  part, 
on  the  number  of  primitive  nerve-fibres  distributed  to  the  part;  for  the 
fewer  the  primitive  fibres  which  an  organ  receives,  the  more  likely  is  it 
that  several  impressions  on  different  contiguous  points  will  act  on  only 
one  nervous  fibre,  and  hence  be  confounded,  and  perhaps  produce  but 
one  sensation.  Experiments  have  been  made  to  determine  the  tactile 
properties  of  different  parts  of  the  skin,  as  measured  by  this  power  of 
distinguishing  distances.  These  consist  in  touching  the  skin,  while  the 
eyes  are  closed,  with  the  points  of  a  pair  of  compasses  sheathed  with 
cork,  and  in  ascertaining  how  close  the  points  of  compasses  might  be 
brought  to  each  other,  and  still  be  felt  as  two  bodies. 


THE   SENSES. 


633 


Table  of  variations  in  the  tactile  sensibility  of  the  different   parts, — The  mea- 
surement indicates  the  least  distance  at  which   the   t  ' 
2iair  of  comjxisses  could  be  separately  distinguished. 

Tip  of  tongue      ....... 

Palmar  surface  of  third  phalanx  of  forefinger 
Palmar  surface  of  second  phalanges  of  fingers 
Red  surface  of  under-lip        .... 

Tip  of  nose  ....... 

Middle  of  dorsum  of  tongue  .... 

Palm  of  hand      ....... 

Centre  of  hard  palate      ...... 

Dorsal  sui-face  of  first  phalanges  of  fingers 
Back  of  hand  ...... 

Dorsum  of  foot  near  toes    ..... 

■Gluteal  region  ...... 

Sacral  region 

Upper  and  lower  parts  of  forearm 

Back  of  neck  near  occiput  .... 

Upper  dorsal  and  mid-lumbar  regions  . 

Middle  part  of  forearm 

Middle  of  thigh 

Mid-cervical  region 

Mid-dorsal  region 


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Moreover,  in  the  case  of  the  limbs,  it  was  found  that  before  they 
were  recognized  as  two,  the  points  of  the  compasses  had  to  be  further 
separated  when  the  line  joining  them  was  in  the  long  axis  of  the  limb, 
than  when  in  the  transverse  direction. 

According  to  Weber  the  mind  estimates  the  distance  between  two 
points  by  the  number  of  unexcited  nerve-endings  which  intervene  be- 
tween the  two  points  touched.  It  would  appear  that  a  certain  number 
of  intervening  unexcited  nerve-endings  are  necessary  before  two  points 
touched  can  be  recognized  as  separate,  and  the  greater  this  number  the 
more  clearly  are  the  points  of  contact  distinguished  as  separate.  By 
practice  the  delicacy  of  a  sense  of  touch  may  be  very  much  increased. 
A  familiar  illustration  occurs  in  the  case  of  the  blind,  who,  by  constant 
practice,  can  acquire  the  power  of  reading  raised  letters  the  forms  of 
which  are  almost  if  not  quite  undistinguishable  by  the  sense  of  touch  to 
an  ordinary  person. 

Localization. — The  power  of  correctly  localizing  sensations  of  touch 
is  gradually  derived  from  experience.  Thus  infants  when  in  pain  sim- 
ply cry,  but  make  no  effort  to  remove  the  cause  of  irritation,  as  an  older 
child  or  adult  would,  doubtless  on  account  of  their  imperfect  knowledge 
of  its  exact  situation. 

Illusions. — The  different  degrees  of  sensitiveness  possessed  by  differ- 
ent parts  may  give  rise  to  errors  of  judgment  in  estimating  the  distance 
between  two  points  where  the  skin  is  touched.  Thus,  if  blunted  points 
of  a  pair  of  compasses  (maintained  at  a  constant  distance  apart)  be 
slowly  drawn  over  the  skin  of  the  cheek  toward  the  lips,  it  is  almost  im- 
possible to  resist  the  conclusion  that  the  distance  betAveen  the  j)oints  is 


634  HANDBOOK    OF    PHYSIOLOGY. 

gradually  increasing.  When  they  reach  the  lips  they  seem  to  be  consid- 
erably further  apart  than  on  the  cheek.  Thus,  too,  our  estimate  of  the 
size  of  a  cavity  in  a  tooth  is  usually  exaggerated  when  based  upon  sensa- 
tion derived  from  the  tongue  alone.  Another  curious  illusion  may  here 
be  mentioned.  If  we  close  the  eyes,  and  place  a  small  marble  or  pea 
between  the  crossed  fore  and  middle  fingers,  we  seem  to  be  touching  two 
marbles.  This  illusion  is  due  to  an  error  of  judgment.  The  marble  is 
touched  by  two  surfaces  which,  under  ordinary  circumstances,  could 
only  be  touched  by  two  separate  marbles,  hence  the  mind,  taking  no- 
cognizance  of  the  fact  that  the  fingers  are  crossed,  forms  the  conclusion 
that  two  sensations  are  due  to  two  marbles. 

Temperature. — The  whole  surface  of  the  body  is  more  or  less  sen- 
sitive to  difiPerences  of  temperature.  The  sensation  of  heat  is  distinct 
from  that  of  touch :  and  it  would  seem  reasonable  to  suppose  that  there 
are  special  nerves  and  nerve-endings  for  temperature.  At  any  rate  the 
power  of  discriminating  temperature  may  remain  unimpaired  when  the 
sense  of  touch  is  temporarily  in  abeyance.  Thus  if  the  ulnar  nerve  be 
compressed  at  the  elbow  till  the  sense  of  touch  is  very  much  dulled  in 
the  fingers  which  it  supplies,  the  sense  of  temperature  remains  quite 
unaffected. 

The  sensations  of  heat  and  cold  are  often  exceedingly  fallacious,  and 
in  many  cases  are  no  guide  at  all  to  the  absolute  temperature  as  indi- 
cated by  a  thermometer.  All  that  we  can  with  safety  infer  from  our 
sensations  of  temperature,  is  that  a  given  object  is  warmer  or  cooler 
than  the  skin.  Thus  the  temperature  of  our  skin  is  the  standard;  and 
as  this  varies  from  hour  to  hour  according  to  the  activity  of  the  cutane- 
ous circulation,  our  estimate  of  the  absolute  temperature  of  any  body 
must  necessarily  vary  too.  If  we  put  the  left  hand  into  water  at  5°  C. 
(40°  F.)  and  the  right  into  water  at  45°  C.  (110°  F.),  and  then  immerse 
both  in  water  at  27°  C.  (80°  F.),  it  will  feel  warm  to  the  left  hand  but 
cool  to  the  right.  Again,  a  piece  of  metal  which  has  really  the  same 
temperature  as  a  given  piece  of  wood  will  feel  much  colder,  since  it  con- 
ducts away  the  heat  much  more  rapidly.  For  the  same  reason  air  in 
motion  feels  very  much  cooler  than  air  of  the  same  temperature  at  rest. 

In  some  cases  we  are  able  to  form  a  fairly  accurate  estimate  of  abso- 
lute temperature.  Thus,  by  plunging  the  elbow  into  a  bath,  a  practised 
bath-attendant  can  tell  the  temperature  sometimes  within  half  a  degree 
centigrade. 

The  temperatures  which  can  be  readily  discriminated  are  between 
10°-45°  C.  (50°-115°  F. );  very  low  and  very  high  temperatures  alike 
produce  a  burning  sensation.  A  temperature  appears  higher  according 
to  the  extent  of  cutaneous  surface  exposed  to  it.  Thus,  water  of  a  tem- 
perature which  can  be  readily  borne  by  the  hand,  is  quite  intolerable  if ' 


THE    SENSES.  635 

the  whole  body  be  immersed.  So,  too,  water  appears  much  hotter  to 
the  hand  than  to  a  single  finger. 

The  delicacy  of  the  sense  of  temperature  coincides  in  the  main  with 
that  of  touch,  and  appears  to  depend  largely  on  the  thickness  of  the 
skin;  hence,  in  the  elbow,  where  the  skin  is  thin,  the  sense  of  tempera- 
ture is  delicate,  though  that  of  touch  is  not  remarkably  so.  Weber  has 
further  ascertained  the  following  facts:  two  compass  points  so  near  to- 
gether on  the  skin  that  they  produce  but  a  single  impression,  at  once 
give  rise  to  two  sensations,  when  one  is  hotter  than  the  other.  More- 
over, of  two  bodies  of  equal  weight,  that  which  is  the  colder  feels  heavier 
•than  the  other. 

As  every  sensation  is  attended  with  an  idea,  and  leaves  behind  it  an 
idea  in  the  mind  which  can  be  reproduced  at  w'ill,  we  are  enabled  to  com- 
pare the  idea  of  a  past  sensation  with  another  sensation  really  present. 
Thus  we  can  compare  the  weight  of  one  body  with  another  which  we 
had  previously  felt,  of  which  the  idea  is  retained  in  our  mind.  Weber 
was  indeed  able  to  distinguish  in  this  manner  between  temperatures, 
experienced  one  after  the  other,  better  than  between  temperatures  to 
which  the  two  hands  were  simultaneousl}^  subjected.  This  power  of 
comparing  present  with  past  sensations  diminishes,  however,  in  propor- 
tion to  the  time  which  has  elapsed  between  them.  After -sensations  left 
by  impressions  on  nerves-of  common  sensibility  or  touch  are  very  vivid 
and  durable.  As  long  as  the  condition  into  which  the  stimulus  has 
thrown  the  organ  endures,  the  sensation  also  remains,  though  the  excit- 
ing cause  should  have  long  ceased  to  act.  Both  painful  and  pleasurable 
sensations  afford  many  examples  of  this  fact. 

Subjective  sensations,  or  sensations  dependent  on  internal  causes,  are 
in  no  sense  more  frequent  than  in  the  sense  of  touch.  All  the  sensations 
of  pleasure  and  pain,  of  heat  and  cold,  of  lightness  and  weight,  of  fa- 
tigue, etc.,  may  be  produced  by  internal  causes.  Neuralgic  pains,  the 
sensation  of  rigor,  formication  or  the  creeping  of  ants,  and  the  states  of 
the  sexual  organs  occurring  during  sleep,  afford  striking  examples  of 
subjective  sensations.  The  mind  has  a  remarkable  power  of  exciting 
sensations  in  the  nerves  of  common  sensibility :  just  as  the  thought  of 
the  nauseous  excites  sometimes  the  sensation  of  nausea,  so  the  idea  of 
pain  gives  rise  to  the  actual  sensation  of  pain  in  a  part  predisi^osed  to 
it;  numerous  examples  of  this  influence  might  be  quoted. 

Pain. — xVs  regards  painful  sensations,  three  views  can  be  taken :  1, 
that  it  is  a  special  sensation  provided  with  a  special  conducting  apparatus 
in  each  part  of  the  body;  2,  that  it  is  produced  by  an  over-stimulation 
of  the  special  nerves  concerned  with  touch  or  temperature,  or  of  the 
other  nerves  of  special  sense;  or  3,  that  it  is  an  over-stimulation  of  the 
nerves  of  common  sensation,  which  tell  us  of  the  condition  of  our  own 


636  HANDBOOK    OF    PHYSIOLOGY. 

bodies,  both  of  the  surface  and  also  of  the  mternal  organs.  There 
seems  to  be  much  in  favor  of  all  of  these  views.  It  is,  however,  certain 
that  even  if  any  variety  of  pain  be  a  special  sensation,  some  kind  of 
pain  may  be  produced  by  stimulation  of  the  bare  sensory  nerves  apart 
from  any  special  form  of  nerve  termination.  It  is  said  that  the  main 
difference  between  the  common  sensation  which  tells  us  of  the  condition 
of  all  parts  of  the  body  and  of  which  thirst  and  hunger  are  but  exam- 
ples, the  one  informing  us  of  the  condition  of  the  palate  and  the  other 
of  the  state  of  our  stomach,  and  the  special  sense  of  touch  and  tempera- 
ture, is  that  the  latter  are  provided  with  special  apparatus.  By  means 
of  this  apparatus  we  are  able  to  localize  tlie  sensation  from  which  it  is 
possible  to  form  judgments.  Such  a  special  apparatus  is  evidently  not 
absolutely  essential  for  the  sensation  of  pain,  but  this  does  not  exclude 
the  idea  that  pain  may  result  from  over-stimulation  of  a  nerve  of  special 
sense  or  of  its  termination. 

The  Muscular  Sense. ^The  estimate  of  a  weight  is  usually  based 
on  two  sensations:   1,  of  pressure  on  the  skin,  and  2,  the  muscular  sense. 

The  estimate  of  weight  derived  from  a  combination  of  these  two 
sensations  (as  in  lifting  a  weight)  is  more  accurate  than  that  derived 
from  the  former  alone  (as  when  a  weight  is  laid  on  the  hand) ;  thus 
Weber  found  that  by  the  former  method  he  could  generally  distinguish 
19|  oz.  from  20  oz.,  but  not  19f  oz.  from  20,  while  by  the  latter  he  could 
at  most  only  distinguish  14-^  oz.  from  15  oz. 

It  is  not  the  absolute,  but  the  relative,  amount  of  the  difference  of 
weight  which  we  have  thus  the  faculty  of  perceiving. 

It  is  not,  however,  certain,  that  our  idea  of  the  amount  of  muscular 
force  used  is  derived  solely  from  the  muscular  sense.  We  have  the 
power  of  estimating  very  accurately  beforehand,  and  of  regulating,  the 
amount  of  nervous  influence  necessary  for  the  production  of  a  certain 
degree  of  movement.  When  we  raise  a  vessel,  with  the  contents  of 
which  we  are  not  acquainted,  the  force  we  employ  is  determined  by  the 
idea  we  have  conceived  of  its  weight.  If  it  should  happen  to  contain 
some  very  heavy  substance,  as  quicksilver,  we  shall  probably  let  it  fall; 
the  amount  of  muscular  action,  or  of  nervous  energy,  which  we  had 
exerted  being  insufficient.  The  same  thing  occurs  sometimes  to  a  person 
descending  stairs  in  the  dark;  he  makes  the  movement  for  the  descent 
of  a  step  which  does  not  exist.  It  is  possible  that  in  the  same  way  the 
idea  of  weight  and  pressure  in  raising  bodies,  or  in  resisting  forces,  may 
in  part  arise  from  a  consciousness  of  the  amount  of  nervous  energy 
transmitted  from  the  brain  rather  than  from  a  sensation  in  the  muscles 
themselves.  The  mental  conviction  of  the  inability  longer  to  support  a 
weight  must  also  be  distinguished  from  the  actual  sensation  of  fatigue 
in  the  muscles. 


THE    SEXSES.  637 

So,  with  regard  to  the  ideas  derived  from  sensations  of  touch  com- 
bined with  movements,  it  is  doubtful  how  far  the  consciousness  of  the 
extent  of  muscular  movement  is  obtained  from  sensations  in  tlie  muscles 
themselves.  The  sensation  of  movement  attending  the  motions  of  the 
hand  is  very  slight ;  and  persons  who  do  not  know  that  the  action  of 
particular  muscles  is  necessary  for  the  production  of  given  movements, 
do  not  suspect  that  the  movement  of  the  fingers,  for  example,  depends 
on  an  action  in  the  forearm.  The  mind  has,  nevertheless,  a  very  definite 
knowledge  of  the  changes  of  position  produced  by  movements;  and  it 
is  on  this  that  the  ideas  which  it  conceives  of  the  extension  and  form  of 
a  body  are  in  great  measure  founded. 

There  is  no  marked  development  of  common  sensibility  to  be  made 
oat  in  muscles:  they  may  be  cut  without  the  production  of  pain.  On  the 
other  hand,  there  is  no  doubt  that  afferent  impulses  must  pass  upward 
from  muscles  and  tendons  acquainting  the  brain  with  their  condition. 
This,  then,  must  be  a  special  sense.  It  has  been  suggested  that  the  minute 
end-bulbs  of  Golgi  found  in  tendons,  and  that  the  Pacinian  corpuscles  in 
the  neighborhood  of  joints,  are  the  terminal  organs  of  this  special  sense. 

Judgment  of  the  Form  and  Size  of  Bodies. — By  the  sense  of  touch  the 
mind  is  made  acquainted  with  the  size,  form,  and  other  external  char- 
acters of  bodies.  And  in  order  that  these  characters  may  be  easily 
ascertained,  the  sense  of  touch  is  especially  developed  in  those  parts 
which  can  be  readily  moved  over  the  surface  of  bodies.  Touch,  in  its 
more  limited  sense,  or  the  act  of  examining  a  body  by  the  touch,  consists 
merely  in  a  voluntary  employment  of  this  sense  combined  with  move- 
ment, and  stands  in  the  same  relation  to  the  sense  of  touch,  or  common 
sensibility,  generally,  as  the  act  of  seeking,  following,  or  examining 
odors,  does  to  the  sense  of  smell.  The  hand  is  the  best  adapted  for  it, 
by  reason  of  its  peculiarities  of  structure, — namely,  its  capability  of 
pronation  and  supination,  which  enables  it,  by  the  movement  of  rota- 
tion, to  examine  the  whole  circumference  of  the  body;  the  power  it 
possesses  of  opposing  the  thumb  to  the  rest  of  the  hand,  and  the  relative 
mobility  of  the  fingers;  and  lastly  from  the  abundance  of  the  sensory 
terminal  organs  which  it  possesses.  In  forming  a  conception  of  the 
figure  and  extent  of  a  surface,  the  mind  multiplies  the  size  of  the  hand 
or  fingers  used  in  the  inquiry  by  the  number  of  times  which  it  is  con- 
tained in  the  surface  traversed;  and  by  repeating  this  process  w4th 
regard  to  the  different  dimensions  of  a  solid  body,  acquires  a  notion  of 
its  cubical  extent,  but,  of  course,  only  an  imperfect  notion,  as  other 
senses,  e.g..,  the  sight,  are  required  to  make  it  complete. 

It  is  impossible  in  this  consideration  to  say  how  much  of  our  knowl- 
edge of  the  thing  touched  depends  upon  pressure  and  how  much  upon, 
the  muscular  sense. 


638  HANDBOOK    OF    PHYSIOLOGY. 


II.  Taste. 


Conditions  necessary. — The  conditions  for  the  perceptions  of  taste 
are: — 1,  the  presence  of  a  nerve  and  nerve-centre  with  special  endow- 
ments; 2,  the  excitation  of  the  nerve  by  the  sapid  matters,  which  for 
this  purpose  must  be  m  a  state  of  solution;  3,  a  temperature  of  about  37° 
to  40°  C.  (98°  to  100°  F,).  The  nerves  concerned  in  the  production  of 
the  sense  of  taste  have  been  already  considered  (p.  302  et  seq.)  The  mode 
of  action  of  the  substances  which  excite  taste  consists  in  the  production 
of  a  change  in  the  condition  of  the  gustatory  nerves,  and  the  conduction 
of  the  stimulus  thus  produced  to  the  nerve-centre;  and,  according  to 
the  difference  of  the  susbtances,  an  infinite  variety  of  changes  of  condi- 
tion of  the  nerves,  and  consequently  of  stimulations  of  the  gustatory 
centre,  may  be  induced.  The  matters  to  be  tasted  must  either  be  in 
solution  or  be  soluble  in  the  moisture  covering  the  tongue;  hence  insolu- 
ble substances  are  usually  tasteless,  and  produce  merely  sensations  of 
touch.  Moreover,  for  the  perfect  action  of  a  sapid,  as  of  an  odorous  sub- 
stance, it  is  necessary  that  the  sentient  surface  should  be  moist.  Hence, 
when  the  tongue  and  fauces  are  dry,  sapid  substances,  even  in  solution, 
are  with  difficulty  tasted. 

The  nerves  of  taste,  like  the  nerves  of  other  special  senses,  may  have  their 
peculiar  properties  excited  by  various  other  kinds  of  irritation,  such  as  elec- 
tricity and  mechanical  impressions.  Thus,  a  small  current  of  air  directed 
upon  the  tongue  gives  rise  to  a  cool  saline  taste,  like  that  of  saltpetre ;  and  a 
distinct  sensation  of  taste  similar  to  that  caused  by  electricity,  may  be  pro- 
duced by  a  smart  tap  applied  to  the  papillae  of  the  tongue.  Moreover,  the 
mechanical  irritation  of  the  fauces  and  palate  produces  the  sensation  of  nausea, 
whicli  is  probably  only  a  modification  of  taste. 

Seat. — The  principal  seat  (apparent  seat,  that  is,  to  our  senses)  of 
the  sense  of  taste  is  the  tongue.  But  the  result  of  experiments  as  well 
as  ordinary  experience  show  that  the  soft  palate  and  its  arches,  the  uvula, 
tonsils,  and  probably  the  upper  part  of  the  pharynx,  are  also  endowed 
with  taste.  These  parts,  together  with  the  base  and  posterior  parts  of 
the  tongue,  are  supplied  with  branches  of  the  glosso-pharyngeal  nerve, 
and  evidence  has  been  already  adduced  that  the  sense  of  taste  is  conferred 
upon  them  by  this  nerve.  In  most,  though  not  in  all  persons,  the  an- 
terior parts  of  the  tongue,  especially  the  edges  and  tip,  are  endowed 
with  the  sense  of  taste.  The  middle  of  the  dorsum  is  only  feebly  en- 
dowed with  this  sense,  probably  because  of  the  density  and  thickness  of 
the  epithelium  covering  the  filiform  papillae  of  this  part  of  the  tongue, 
which  will  prevent  the  sapid  substances  from  penetrating  to  their  sensi- 
tive parts. 

Other  Functions. — Beside  the  sense  of  taste,  the  tongue,  by  means 


THE    SENSES.  639 

also  of  its  papilla,  is  endued  (2)  especially  at  its  side  and  tip,  with  a  very 
delicate  and  accurate  sense  of  touch,  which  renders  it  sensible  of  the 
impressions  of  heat  and  cold,  pain  and  mechanical  pressure,  and  conse- 
quently of  the  form  of  surfaces.  The  tongue  may  lose  its  common  sen- 
sibility, and  still  retain  the  sense  of  taste,  and  vice  versa.  This  fact 
renders  it  probable  that,  although  the  senses  of  taste  and  of  touch  may 
be  exercised  by  the  same  papilla?  supplied  by  the  same  nerves,  yet  the 
nervous  conductors  for  these  two  different  sensations  are  distinct,  just 
as  the  nerves  for  smell  and  common  sensibility  in  the  nostrils  are  dis- 
tinct; and  it  is  quite  conceivable  that  the  same  nervous  trunk  may  con- 
tain fibres  differing  essentially  in  their  specific  properties.  Facts  already 
detailed  seem  to  prove  that  the  lingual  branch  of  the  fifth  nerve  is  the 
conductor  of  sensations  of  taste  in  the  anterior  part  of  the  tongue ;  and 
it  is  also  certain,  from  the  marked  manifestations  of  pain  to  which  its 
division  in  animals  gives  rise,  that  it  is  likewise  a  nerve  of  common  sen- 
sibility. The  glosso-pharyngeal  also  seems  to  contain  fibres  both  of 
common  sensation  and  of  the  special  sense  of  taste. 

The  functions  of  the  tongue  in  connection  with  (3)  speech,  (4)  mas- 
tication, (5)  deglutition,  (0)  suction,  have  been  referred  to  in  other 
chapters. 

Taste  and  Smell:  Fei'cepfiofis. — The  concurrence  of  common  and  two 
kinds  of  special  sensibility,  i.e.,  touch  and  taste  in  the  same  part,  makes 
it  sometimes  difficult  to  determine  whether  the  impression  produced  by 
a  substance  is  perceived  through  the  ordinary  sensitive  fibres,  or  through 
those  of  the  sense  of  taste.  In  many  cases,  indeed,  it  is  probable  that 
both  sets  of  nerve-fibres  are  concerned,  as  when  irritating  acrid  substances 
are  introduced  into  the  mouth. 

Much  of  the  perfection  of  the  sense  of  taste  is  often  due  to  the  sapid 
substances  being  also  odorous,  and  exciting  the  simultaneous  action  of 
the  sense  of  smell.  This  is  shown  by  the  imperfection  of  the  taste  of 
such  substances  when  their  action  on  the  olfactory  nerves  is  prevented 
by  closing  the  nostrils.  Many  fine  wines  lose  much  of  their  apparent 
excellence  if  the  nostrils  are  held  close  while  they  are  drunk. 

Varieties  of  Tastes. — Among  the  most  clearly  defined  tastes  are  the 
siveet  and  bitter  (which  are  more  or  less  opposed  to  each  other),  the  acid, 
alkaline,  salt,  and  metallic  tastes.  Acid  and  alkaline  taste  may  be  ex- 
cited by  electricity.  If  a  piece  of  zinc  be  jilaced  beneath  and  a  piece  of 
copper  above  the  tongue,  and  their  ends  brought  into  contact,  an  acid 
taste  (due  to  the  feeble  galvanic  current)  is  produced.  The  delicacy  of 
the  sense  of  taste  is  sufficient  to  discern  1  part  of  sulj)huric  acid  in  1000 
of  water;  but  it  is  far  surpassed  in  acuteness  by  the  sense  of  smell.  Ex- 
periments have  shown  that  it  is  possible  to  entirely  do  away  with  the 
power  of  tasting  bitters  and  sweets  while  the  taste  for  acids  and  salts 


640  HANDBOOK    OF    PHYSIOLOGY. 

remains.  This  is  done  by  chewing  the  leaves  of  an  Indian  plant 
(Gymnema  sylvestre).  It  has  also  been  shown  that  the  power  of  tasting 
sweet  substances  disappears  before  that  of  tasting  bitter.  Other  experi- 
ments have  shown  that  the  apparatus  for  salt  and  for  acid  tastes  are 
distinct.  It  is  also  demonstrable  that  bitters  are  most  appreciated  at  the 
back  and  sweets  at  the  tip  of  the  tongue,  that  salts  are  also  most  potent  at 
the  tip,  and  acids  at  the  sides  of  the  tongue.  All  these  tastes  then,  are 
almost  certainly  provided  with  a  distinct  apparatus.  It  is  clear  there- 
fore that  the  taste  buds  cannot  be  the  only  terminal  organs  for  the  sense 
of  taste,  if  from  no  other  reason,  at  any  rate  from  their  exceedingly 
limited  distribution  in  the  human  tongue. 

Although  the  taste  apparatus  is  bilateral  the  sensation  or  perception 
is  single,  and  in  this  resjject  taste  resembles  vision. 

After-taste. — Very  distinct  sensations  of  taste  are  frequently  left  after 
the  substances  which  excited  them  have  ceased  to  act  on  the  nerve ;  and 
such  sensations  often  endure  for  a  long  time,  and  ^modify  the  taste  of 
other  substances  ap])lied  to  the  tongue  afterward.  Thus,  the  taste  of 
sweet  substances  spoils  the  flavor  of  wine,  the  taste  of  cheese  improves  it. 
There  appears,  therefore,  to  exist  the  same  relation  between  tastes  as 
between  colors,  of  which  those  that  are  opposed  or  complementary  render 
each  other  more  vivid,  though  no  general  principles  governing  this  rela- 
tion have  been  discovered  in  the  case  of  tastes.  In  the  art  of  cooking, 
however,  attention  has  at  all  times  been  paid  to  the  consonance  or  har- 
mony of  flavors  in  their  combination  or  order  of  succession,  just  as  in 
painting  and  music  the  fundamental  jsrinciples  of  harmony  have  been 
employed  empirically  while  the  theoretical  laws  were  unknown. 

Frequent  and  continued  repetitions  of  the  same  taste  render  the  per- 
ception of  it  less  and  less  distinct,  in  the  same  way  that  a  color  becomes 
more  and  more  dull  and  indistinct  the  longer  the  eye  is  fixed  upon  it. 
Thus,  after  frequently  tasting  first  one  and  then  the  other  of  two  kinds 
of  wine,  it  becomes  impossible  to  discriminate  between  them. 

The  simple  contact  of  a  sapid  substance  with  the  surface  of  the 
gustatory  organ  seldom  gives  rise  to  a  distinct  sensation  of  taste ;  it  needs 
to  be  diffused  over  the  surface,  and  brought  into  intimate  contact  with 
the  sensitive  parts  by  compression,  friction,  and  motion  between  the 
tongue  and  palate. 

Subjective  Sensatiotis  of  Taste. — The  sense  of  taste  seems  capable  of 
being  excited  only  by  external  causes,  such  as  changes  in  the  conditions 
of  the  nerves  or  nerve-centres,  produced  by  congestion  or  other  causes, 
which  excite  subjective  sensations  in  the  other  organs  of  sense.  But 
little  is  known  of  the  subjective  sensations  of  taste;  for  it  is  difficult  to 
distinguish  the  phenomena  from  the  effects  of  external  causes,  such  as 
changes  in  the  nature  of  the  secretions  of  the  mouth. 


THE    SENSES. 


641 


III.   Smell. 

Conditio7is  necessary. — (1.)  The  first  conditions  essential  to  the  sense 
of  smell  are  a  special  nerve  and  nerve-terminations  in  the  form  of  special 
cells,  the  changes  in  whose  condition  stimulate  a  special  nerve-centre, 
and  are  perceived  in  sensations  of  odor,  for  no  other  nervous  structure 
is  capable  of  these  sensations,  even  though  acted  on  by  the  same  causes. 
The  same  substance  which  excites  the  sensation  of  smell  in  the  olfac- 
tory centre  may  cause  another  peculiar  sensation  through  the  nerves  of 
taste,  and  may  produce  an  irritating  and  burning  sensation  on  the  nerves 
of  touch ;  but  the  sensation  of  odor  is  yet  separate  and  distinct  from 
these,  though  it  maybe  simultaneously  perceived.  (2.)  The  material 
causes  of  odors  are,  usually,  in  the  case  of  animals  living  in  the  air, 


Fig.  391.— Nerves  of  the  septum  nasi,  seen  from  the  right  side.  -i.—l.  the  olfactory  bulb; 
1,  the  olfactory  nerves  passing  through  the  foramina  of  the  cribriform  plate,  and  descending  to 
be  distributed  on  the  septum ;  3,  the  internal  or  septal  twig  of  the  nasal  branch  of  the  ophthal- 
mic nerve;  3,  naso-palatine  nei-ves.     (From  Sappey,  after  Ilirschfeld  and  Leveill^.) 

either  solids  suspended  in  a  state  of  extremely  fine  division  in  the  atmos- 
phere ;  or  gaseous  exhalations  often  of  so  subtle  a  nature  that  they  can 
be  detected  by  no  other  reagent  than  the  sense  of  smell  itself.     The 
matters   of  odor  must,  in  all  cases,   be  dissolved  in  the  mucus  of  the 
mucous  membrane  before  they  can  be  immediately  applied  to,  or  affect, 
the  olfactory  nerves;  therefore   a  further   condition   necessary  for  the. 
perception  of  odors  is,  that  the  mucous  membrane  of  the  nasal  cavity: 
be  moist.     When  the   Sclmeiderian  membrane  is  dry,  the  sense  of  smell 
is  impaired  or  lost;  in  the  first  stage  of  catarrh,  when   the  secretion  of 
mucus  within  the  nostrils  is  lessened,  the  faculty  of  perceiving  odor  is 
either  lost,  or  rendered  very  imperfect.      (3.)  In  animals  living  in  the 
air,  it  is  also  requisite  that  the  odorous  matter  should  be  transmitted  in 
a  current  tlirough  the  nostrils.      This  is  effected  by  an  insjjiratory  move- 
41 


G42 


HANDBOOK    OF    PHYSIOLOGY. 


^„ 


ment,  the  mouth  being  closed;  hence  we  have  voluntary  influence  over 
the  sense  of  smell;  for  by  interrupting  respiration  we  prevent  the  per- 
ception of  odors,  and  by  repeated  quick  inspiration,  assisted,  as  in  the 
act  of  sniffing,  by  the  action  of  the  nostrils,  we  render   the   imj^ression 

more  intense.      An  odorous  substance  in  a  liquid 

form  injected  into  the  nostrils  appears  incapable 

of  giving  rise  to  the  sensation    of  smell;    thus 

Weber  could  not  smell  the  slightest  odor  when 

his   nostrils  were   completely   filled   with    water 

containing  a  large  quantity  of  eau-de-Cologne. 

jfy      -        ^.:^^  "^^^^  ^^^^  '^^  ^^^  entirely  an  organ  for  the  seat 

"  -       of  smell.      In  fact  the  nasal  cavities  are  divided 

p  ^      into  three  districts  called  respectively,  (a)  7'egio 

p-  vestibularis,  which  is  the  entrance  to  the  cavity. 

It  is  lined  with  a  mucous  membrane  very  closely 

__^^  ^      resembling  the  skin,  and  contains  hair  (vibrissce) 

Fis.393.— Section  through   witli    sabaccous   ghiuds ;    {b)   regio   respiratoria, 

the    olfactory    mucous  uiem-        t   •    t     •       i      i        n       i  i.ji  ^ 

brane  of  the  new-hora  child,    wliich  mcludes  the  lowcr  mcatus  01  the  nose,  and 

a,  non-nuclear ;  and  b,  nucle-       n,,  i      j-    l^  i  i    /   \      •  i    • 

ated  portions  of  the  epithe-   all  the  rcst  01   the  nasal  r)assages  except  (c),  it  is 

lium;   c,  nerves;  del,  glands,  i       -n  i  -,  -,         i       ,  • 

marked  out  by  Schuitze  as   covcred  With  iiiucous  membrane  covcrcd  by  strati- 

Bowman's.     (M.   Schuitze.)         r.     i        i  -i-    j.     n         -^.i     t  rr>i 

bed  columnar  ciliated  epithelium.  Ihe  mucosa  is 
thick  and  consists  of  fibrous  connective  tissue,  it  contains  a  certain  num- 
ber of  tubular  mucous  and  serous  glands;  and  (r)  regio  olfactoria,  which 
includes  the  anterior  two-thirds  of  the  superior  meatus, the  middle  meatus, 
and  the  upper  half  of  the  septum  nasi.  It  is  cf  a  yellowish  color.  It  con- 
sists of  a  thicker  mucous  membrane  than  in  (/>),  made  up  of  loose  areolar 
connective  tissue  covered  by  epithelium  of  a  special  variety,  resting  upon 
a  basement  membrane.  The  cells  of  the  epithelium  are  of  several  kinds, 
firstly,  columnar  cells  not  ciliated  (fig.  394),  consisting  of  a  granular  body 
containing  pigment,  with  the  broad  end  at  the  surface,  and  below  taper- 
ing into  an  irregular  branched  process  or  processes,  the  terminations  of 
which  are  lost  in  the  next  layer — each  cell  has  a  conspicuous  ovoid 
nucleus,  staining  well  in  ha?matoxylin — these  cells  are  the  continuations 
of  the  columnar  ciliated  epithelium  of  {b).  The  second  kind  consists  of 
a  small  cell  body  with  large  spherical  nucleus,  staining  imperfectly  in 
hfematoxylin,  situated  between  the  ends  of  the  first  kind  of  cell,  and 
sending  upward  a  process  to  the  surface  between  the  cells  of  the  first 
kind,  and  from  the  other  pole  of  the  nucleus  a  process  toward  the 
mucosa.  The  latter  process  is  very  delicate  and  may  be  varicose.  The 
upper  process  may  be  prolonged  beyond  the  surface  as  a  cilium.  These 
cells  are  numerous,  and  the  nuclei  of  the  cells  not  being  on  the  same 
level,  a  comparatively  thick  nuclear  layer  is  the  result.  Below  them  is 
a  layer  of  irregular  branched  nucleated  cells  placed  upon  the  basement 


THE    SENSES. 


643 


membrane.  It  is  doubtful  if  all  the  nuclei  of  the  nuclear  layer  send 
processes  in  both  directions  to  the  surface  and  to  the  mucosa.  In  the 
mucosa  are  peculiar  glands,  small  and  twisted,  made  up  of  large  cells 
arranged  parallel  inclosing  a  canal,  and  called  Bowman's  glands.  They 
are  probably  serous  or  mucous  secreting  glands. 

The  branches  of  the  olfactory  nerves  retain  much  of  the  same  soft  and 
grayish  texture  which  distinguishes  those  of  the  olfactory  tracts  within 
the  cranium.  Their  filaments,  also,  are  peculiar,  more  resembling  those 
of  the  sympathetic  nerve  than  the  filaments  of  the  other  cerebral  nerves 
do,  containing  no  outer  white  substance,  and  being  finely  granular  and 
nucleated.  The  fibres  are  supposed  to  terminate  in  the  processes  of  the 
second  variety  of  cell  lining  the  olfactory  mucous  membrane,  and  called 
rod  cells,  the  columnar  cells  are  looked  upon  only  as  supporting  cells. 
Some,  however,  look  upon  both  kinds  of  cells  as  olfactory  in  function. 

The  sense  of  smell  is  derived  exclusively  through  those  parts  of  the  nasal 
cavities  in  which  the  olfactory  nerves  are  distributed;  the  accessory  cavi- 
ties or  sinuses  communicating  with  the  nostrils  seem  to  have  no  relation  to 
it.  Air  impregnated  with  the  vapor  of  camphor  was  injected  into  the  front- 
al sinus  through  a  fistulous  opening  and  odorous  substances  have  been 
ii.jected  into  the  antrum  of  Ilighmore;  but  in  neither  case  was  any 


Fig:.  393. — Nerves  of  the  outer  waUs  of  the  nasal  fossa?.  3-5. — 1,  network  of  the  branches  of 
the  olfactory  nerve,  descending  upon  the  region  of  the  superior  and  middle  turbinated  bones: 
2,  external  twig  of  the  ethmoidal  branch  of  the  nasal  nerves;  3,  spheno-palatine  ganglion;  4, 
ramification  of  the  anterior  palatine  aerves;  5,  posterior,  and  6,  middle  divisions  of  the  palatine 
nerves;  7,  branch  to  the  region  of  the  inferior  turbinated  bone;  8,  branch  to  the  region  of  the 
superior  and  middle  turbinated  bones;  9,  naso-palatine  branch  to  the  septum  cut  short.  (Froo) 
Sappey,  after  Hirschfeld  and  Leveill6.) 

odor  perceived  by  the  patient.  The  purposes  of  these  sinuses  appear  to 
be,  that  the  bones,  necessarily  large  for  the  action  of  the  muscles  and 
other  parts  connected  with  them,  may  be  as  light  as  possible,  and  that 
there  may  be  more  room  for  the  resonance  of  the  air  in  vocalizing. 


644 


HANDBOOK    OF    PHYSIOLOGY. 


The  former  purpose,  which  is  in  other  bones  obtained  by  filling  their 
cavities  with  fat,  is  here  attained,  as  it  is  in  many  bones  of  birds,  by 
their  being  filled  with  air. 

Other  Functions  of  the  Nasal  Region. — All  parts  of  the  nasal  cavities, 
whether  or  not  they  can  be  the  seats  of  the  sense  of  smell,  are  endowed 
with  common  sensibility  by  the  nasal  branches  of  the  first  and  second 
divisions  of  the  fifth  nerve.  Hence  the  sensations  of  cold,  heat,  itch- 
ing, tickling,  and  pain;  and  the  sensation  of  tension  or  pressure  in  the 
nostrils.  That  these  nerves  cannot  perform  the  function  of  the  olfac- 
tory nerves  is  proved  by  cases  in  which  the  sense  of  smell  is  lost,  while  the 
mucous  membrane  of  the  nose  remains  susceptible  of  the  various  modi- 
fications of  common  sensation  and  of  touch.  But  it  is  often  difficult  to 
distinguish  the  sensation  of  smell  from  that  of  mere  feeling,  and  to 
ascertain  what  belongs  to  each  separately.     This  is  the  case  particularly 


Fig.  394. — Cells  from  the  olfactory  regions  of  the  rabbit,     st.  Supporting  cells;  ?%  ?•',  varieties  of 
rod-cells;  /,  ciliated  cell;  s,  cilia-like  process;  6,  cells  from  Bowman's  gland.     (Stohr.J) 

with  the  sensations  excited  in  the  nose  by  acrid  vapors,  as  of  ammonia, 
horse-radish,  mustard,  etc.,  which  resemble  much  the  sensations  of 
the  nerves  of  touch;  and  the  difficulty  is  the  greater,  when  it  is  remem- 
bered that  these  acrid  vapors  have  nearly  the  same  action  upon  the 
mucous  membrane  of  the  eyelids.  It  was  because  the  common  sensi- 
bility of  the  nose  to  these  irritating  substances  remained  after  the 
destruction  of  the  olfactory  nerves,  that  Magendie  was  led  to  the  erro- 
neous belief  that  the  fifth  nerve  might  exercise  this  special  sense. 

Varieties  of  Odorous  Sensations. — Animals  do  not  all  equally  perceive 
the  same  odors ;  the  odors  most  plainly  perceived  by  an  herbivorous  animal 
and  by  a  carnivorous  animal  are  different.  The  Carnivora  have  the 
power  of  detecting  most  accurately  by  the  smell  the  special  peculiarities 
of  animal  matters,  and  of  tracking  other  animals  by  the  scent;  but  have 
apparently  very  little  sensibility  to  the  odors  of  plants  and  flowers. 
Herbivorous  animals  are  peculiarly  sensitive  to  the  latter,  and  have  a 
narrower  sensibility  to  animal  odors,  especially  to  such  as  proceed  from 
other  individuals  than  their  own  species.      Man  is  far  inferior  to  many 


THE    SENSES,  645 

animals  of  both  classes  (which  appear  to  have  a  special  epithelial 
arrangement  called  Jacobson''s  orgcm,  for  the  purpose  of  ''scent"),  in 
respect  of  the  acuteness  of  smell ;  but  his  sphere  of  susceptibility  to  various 
odors  is  more  uniform  and  extended.  The  cause  of  this  diiference  lies 
probably  in  the  endowments  of  the  cerebral  parts  of  the  olfactory  appa- 
ratus. The  delicacy  of  the  sense  of  smell  is  most  remarkable;  it  can  dis- 
cern the  presence  of  bodies  in  quantities  so  minute  as  to  be  uudiscover- 
able  even  by  spectrum  analysis;  yTo.o^Tro-.-oo-g-  of  ^  grain  of  musk  can  be  dis- 
tinctly smelt  (Valentin).  Opj)osed  to  the  sensation  of  an  agreeable  odor  is 
that  of  a  disagreeable  or  disgusting  odor,  which  corresponds  to  the  sensa- 
tions of  pain,  dazzling  and  disharmony  of  colors,  and  dissonance  in  the 
other  senses.  The  cause  of  this  difference  in  the  effect  of  different  odors  is 
unknown;  but  this  much  is  certain,  that  odors  are  pleasant  or  offensive 
in  a  relative  sense  only,  for  many  animals  pass  their  existence  in  the 
midst  of  odors  which  to  us  are  highly  disagreeable.  A  great  difference 
ill  this  respect  is,  indeed,  observed  amongst  men:  many  odors,  generally 
thought  agreeable,  are  to  some  persons  intolerable;  and  different  per- 
sons describe  differently  the  sensations  that  they  severally  derive  from 
the  same  odorous  substances.  There  seems  also  to  be  in  some  persons 
an  iusensibility  to  certain  odors,  comparable  with  that  of  the  eye  to  cer- 
tain colors;  and  among -different  persons,  as  great  a  difference  in  the 
acuteness  of  the  sense  of  smell  as  among  others  in  the  acuteness  of  sight. 
"NVe  have  no  exact  jDroof  that  a  relation  of  harmony  and  disharmony  exists 
between  odors  as  between  colors  and  sounds;  though  it  is  probable  that 
such  is  the  case,  since  it  certainly  is  so  with  regard  to  the  sense  of  taste ; 
and  since  such  a  relation  would  account  in  some  measure  for  the  differ- 
ent degrees  of  perceptive  power  in  different  persons;  for  as  some  have 
no  ear  for  music  (as  it  is  said),  so  others  have  no  clear  ai^preciation  of 
the  relation  of  odors,  and  therefore  little  pleasure  in  them. 

Subjective  sensations. — Tbe  sensations  of  the  olfactory  nerves,  iude^ 
pendent  of  the  external  application  of  odorous  substances,  have  hitherto 
been  little  studied.  The  friction  of  the  electric  machine  jsroduces  a 
smell  like  that  of  phosphorus.  Ritter,  too,  has  observed,  that  when  a 
galvanic  current  is  applied  to  the  organ  of  smell,  besides  the  impulse 
to  sneeze,  and  the  tickling  sensation  excited  in  the  filaments  of  the  fifth 
nerve,  a  smell  like  that  of  ammonia  was  excited  by  the  negative  pole,  and 
an  acid  odor  by  the  positive  jjole;  whichever  of  these  sensations  were  jn'o-- 
duced,  it  remained  constant  as  long  as  the  circle  was  closed,  and  changed 
to  the  other  at  the  moment  of  the  circle  being  opened.  Subjective  sen 
sations  occur  frequently  in  connection  with  the  sense  of  smell.  Fre- 
quently a  person  smells  something  which  is  not  present,  and  which  othev 
persons  cannot  smell;  this  is  very  frequent  with  nervous  people,  but  it  oc- 
casionally happens  to  every  one.     In  a  man  who  was  constantly  conscious 


646 


HANDBOOK    OF    PHYSIOLOGY. 


of  a  bad  odor,  the  arachnoid  was  found  after  death  to  be  beset  with 
deposits  of  bone,  and  a  lesion  in  the  middle  of  the  cerebral  hemispheres 
was  also  discovered.  Dubois  was  acquainted  with  a  man  who,  ever  after 
a  fall  from  his  horse,  which  occurred  several  years  before  his  death, 
believed  that  he  smelt  a  bad  odor. 

I\'.   Hearing. 

Anatomy  of  the  Ear. — For  descriptive  purposes,  the  Ear,  or  Organ 
of  Hearing,  is  divided  into  three  parts,  (l)the  external,  (2)  the  middle, 
and  (3)  the  internal  ear.     The  two  first  are  only  accessory  to  the  third 


Fig.  395. — Diagrammatic  view  from  before  of  the  parts  composinpc  the  orpan  of  hearing  of 
tke  left  side.  The  temporal  bone  of  the  left  side,  with  the  accdiiipanying  soft  parts,  has  been 
detached  from  the  head,  and  a  section  has  been  carried  throut,'h  it  transversely,  so  as  to  remove 
the  front  of  the  meatus  externus,  half  the  tympanic  membrane,  the  upper  ami  anterior  wall  of 
the  tympanum  and  Eustachian  tube.  The  meatus  internus  has  also  been  opened,  and  the  bony 
labyrinth  exposed  Vjy  the  removal  of  tlie  surroundinf;  parts  of  the  petrous  bone.  1,  the  pinna 
and  lobe;  2.  2',  meatus  externus;  2',  membrana  tympani ;  3,  cavity  of  the  tympanum;  3',  its 
opening  backward  into  the  mastoid  cells;  between  3  and  3',  the  chain  of  small  bones;  4,  Eusta- 
chian tube;  5,  meatus  internus,  containing  the  facial  (uppermost)  and  the  auditory  nerves;  6, 
placed  on  the  vestibule  of  the  labyrinth  above  the  fenestra  ovalis;  a,  apex  of  the  petrous  bone; 
S,  internal  carotid  artery;  c,  styloid  process;  d,  facial  nerve  issuing  from  the  stylo-mastoid 
Iforamen;  e,  mastoid  process;  /,  squamous  part  of  the  bone  covered  by  integument,  etc.    C Arnold.) 

or  internal  ear,  which  contains  the  essential  parts  of  an  organ  of  hear- 
ing. The  accompanying  figure  shows  very  well  the  relation  of  these 
divisions,  one  to  the  other  (fig.  395). 

External  Ear. — The  external  ear  consists  of  the  jnnna  or  auricle 
and  the  external  auditory  canal  or  meattis. 

The  principal  parts  of  the  pin?ia  (fig.  395)  are  two  prominent  rims 
inclosed  one  within  the  other  [helix  and  antihelix),  and  inclosing  a  cen- 
tral hollow  named   the   concha;  in   front  of  the  concha,  a  prominence 


THE    SENSES. 


G47 


directed  backward,  the  tragus,  and  opposite  to  this  one  directed  for- 
Avard,  the  antitragus.  From  the  concha,  the  auditory  canal,  with  a 
slight  arch  directed  upward,  i)asses  inward  and  a  little  forward  to  the 
membrana  tympani,  to  which  it  thus  serves  to  convey  the  vibrating  air. 
Its  outer  part  consists  of  fibro-cartilage  continued  from  the  concha;  its 
iniier  part  of  bone.  Botli  are  lined  by  skin  continuous  with  that  of 
the  pinna,  and  extending  over  the  outer  part  of  the  memhrana  tympani. 

Toward  the  outer  part  of  the  canal  are  fine  hairs  and  sebaceous 
glands,  while  deeper  in  the  canal  are  small  glands,  resembling  the  sweat- 
glands  in  structure,  which  secrete  the  cerumen. 

Middle  Ear  or  Tympanum. — The  middle  ear,  or  tympanum  (3, 
fig.  395),  is  separated  by  the  meml)rana  tympani  from  the  external 
auditory  canal.  It  is  a  cavity  in  the  temporal  bone,  opening  through 
its  anterior  and  inner  w'all  into  the  Eustachian   tube,   a  cvlindriform 


Fig. 


Fig.  398. 
1,  the  head;  2,  neck;   3,  short 


Fip.  396.— The  hammer-bone  or  malleus,  seen  from  the  front, 
process;  4.  long  process.     (Schwalbe.) 

Fig.  397.— The  incus,  or  anvil-bone.  1.  body;  2,  ridged  articulation  for  the  malleus:  4,  pro- 
cessus brevis,  with  5.  rough  articular  surface  for  ligamem  of  incus;  6,  processus  magnus,  with 
articulating  surface  for  stapes ;  V,  nutrient  foramen.     (Schwalbe. ) 

Fig.  398.— The  stapes,  or  stirrup-bone.  1,  base;  2  and  3,  arch;  4,  head  of  bone,  which  articu- 
lates with  orbicular  process  of  tne  incus;  5.  constricted  part  of  neck;  6,  one  of  the  crura. 
(Schwalbe.) 

flattened  canal,  dilated  at  both  ends,  composed  partly  of  bone  and  partly 
of  elastic  cartilage,  and  lined  with  mucous  membrane,  which  forms  a 
communication  between  the  tympanum  and  the  pharynx.  It  opens  into 
the  cavity  of  the  pharynx  just  behind  the  posterior  aperture  of  the  nos- 
trils. The  cavity  of  the  tympanum  communicates  posteriorly  with  air 
cavities,  the  wrt^/otf/ ce/fe  in  the  mastoid  process  of  the  temporal  bone; 
but  its  only  opening  to  the  external  air  is  through  the  Eustachian  tube 
(4,  fig.  395).  The  walls  of  the  tympanum  are  osseous,  except  where  aper- 
tures in  them  are  closed  wdth  membrane,  as  at  the  fenestra  rotunda  and 
fenestra  ovalis,  and  at  the  outer  part  where  the  bone  is  rei^laced  by  the 
membrana  tympani.  The  cavity  of  the  tympanum  is  lined  with  mucous 
membrane,  the  epithelium  of  which  is  ciliated  and  continuous  with  that 
of  the  pharynx.  It  contains  a  chain  of  small  bones  {ossicula  auditus) 
which  extends  from  the  membrana  tympani  to  the  fenestra  ovalis. 


648  HANDBOOK    OF    PHYSIOLOGY. 

The  memhrana  tympani  is  placed  in  a  slanting  direction  at  the  bot- 
tom of  the  external  auditory  canal,  its  plane  being  at  an  angle  of  about 
45°  with  the  lower  wall  of  the  canal.  It  is  formed  chiefly  of  a  tough 
and  tense  fibrous  membrane,  the  edges  of  which  are  set  in  a  bony  groove; 


Fig.  399.— Interior  view  of  the  tympanum,  with  membrana  tympani  and  bones  in  natural 
position.  1,  Membrana  tympani ;  2,  Eustachian  tube;  3,  tensor  tympani  muscle;  4,  lig.  mallei 
super. ;  6,  corda-tympani  nerve;  a,  6,  and  c,  sinuses  about  ossicula.     (Schwaltoe.) 

its  outer  surface  is  covered  with  a  continuation  of  the  cutaneous  lining 
of  the  auditory  canal,  its  inner  surface  with  part  of  the  ciliated  mucous 
membrane  of  the  tympanum. 

The  ossicles  axe  three  in  number;  named  malleus,  incus,  and  stapes. 
The  malleus,  or  hammer-bone,  is  attached  by  a  long  slightly-curved  pro- 
cess, called  its  handle,  to  the  membrana  tympani ;  the  line  of  attachment 
being  vertical,  including  the  whole  length  of  the  handle,  and  extending 
from  the  upper  border  to  the  centre  of  the  membrane.  The  head  of  the 
malleus  is  irregularly  rounded;  its  neck,  or  the  line  of  boundary  between 
it  and  the  handle,  supports  two  processes;  a  short  conical  one,  which 
receives  the  insertion  of  the  tensor  ti/mpani,  and  a  slender  one,  2)rocessus 
gi'acilis,  which  extends  forward,  and  to  which  the  Iclt afar  tipnpnni  muscle 
is  attached.  The  incus,  or  anvil-bone,  shaped  like  a  bicuspid  molar  tooth, 
is  articulated  by  its  broader  part,  corresponding  with  the  surface  of  the 
crown  of  a  tooth,  to  the  malleus.  Of  its  two  fang-like  processes,  one, 
directed  backward,  has  a  free  end  lodged  in  a  depression  in  the  mastoid 
bone ;  the  other,  curved  downward  and  more  pointed,  articulates  by  means 
of  a  roundish  tubercle,  formerly  called  os  orbicnlare,  with  the  stapes,  a 
little  bone  shaped  exactly  like  a  stirrup,  of  which  the  base  or  bar  fits  into 
the  fenestra  ovalis.  To  the  neck  of  the  stapes,  a  short  process,  correspond- 
ing with  the  loop  of  the  stirrup,  is  attached  the  stapedius  muscle. 

The  bones  of  the  ear  are  covered  with  mucous  membrane  reflected  over 
them  from  the  wall  of  the  tympanum ;  and  are  movable  both  altogether 
and  one  upon  the  other.  The  malleus  moves  and  vibrates  with  every 
movement  and  vibration  of  the  membrana  tympani,  and  its  move- 
ments are  communicated  through  the  incus  to  the  stapes,  and  through 


THE   SEXSES. 


649 


It  to  the  membrane  closing  the  fenestra  ovalis.  The  malleus,  also, 
is  movable  in  its  articulation  with  the  incus;  and  the  membrana 
tympani  moving  with  it  is  altered  in  its  degree  of  tension  by  the  laxator 
and  tensor  tympani  muscles.  The  stapes  is  movable  on  the  process  of 
the  incus,  when  the  stapedius  muscle  acting,  draws  it  backward.  The 
axis  round  which  the  malleus  and  incus  rotate  is  the  line  joining  the  pro- 
cessus gracilis  of  the  malleus  and  the  posterior  (short)  process  of  the  incus. 

The  Internal  Ear. — The  proper  organ  of  hearing  is  formed  by  the 
distribution  of  the  auditory  nerve  within  the  internal  ear,  or  lahyrintli, 
a  set  of  cavities  within  the  petrous  portion  of  the  temporal  bone.  The 
bone  which  forms  the  w^alls  of  these  cavities  is  denser  than  that  around 
it,  and  forms  the  osseous  labyrinth;  the  membrane  within  the  cavities 
forms  the  memhranoiis  labyrinth.  The  membranous  labyrinth  contains  a 
fluid  called  endolymph;  while  outside  it,  between  it  and  the  osseous 
labyrinth,  is  a  fluid  called  perilymph.  This  fluid  is  not  pure  lymj)h ; 
as  it  contains  mucin. 

The  osseous  labyrinth  consists  of  three  principal  parts,  namely 
the  vestibtile,  the  cochlea,  and  the  semicircular  canals. 

The  vestibule  is  the  middle  cavity  of  the  labyrinth,  and  the  central 
organ  of  the  whole  auditory  apparatus.     It  presents,  in  its  inner  wall, 


Fig.  400. 


Fig.  401. 


Fig.  400. — Right  bony  labyrinth,  viewed  from  the  outer  side.  The  specimen  here  represented 
Is  prepared  by  separating  piecemeal  the  looser  substance  of  the  petrous  bone  from  the  dense 
wails  which  immediately  inclose  the  labjTinth.  1,  the  vestibule;  2,  fenestra  ovalis;  3.  superior 
semicircular  canal ;  4,  horizontal  or  external  canal ;  5,  posterior  canal ;  *.  ampullte  of  the  semi- 
circular canals;  C,  first  turn  of  the  cochlea;  7,  second  turn;  8,  apex;  9,  fenestra   rotunda.     The 

smaller  figure  in  outline  below  shows  the  natural  size.     ^p.     (Sommering.) 

Fig.  401.— Vie-\  of  the  interior  of  the  left  labjTinth.  The  bony  wall  of  the  labyrinth  is  re- 
moved siperiorly  and  externally.  1.  Fovea  hemielliptica:  2.  fovea  heniispherica :  3,  common 
opening  of  the  sunerior  and  posterior  semicircular  canals;  4,  opening  of  the  aqueduct  of  the 
vestibule;  5,  the  superior.  6,  the  posterior,  and  7,  the  external  semicircular  canals;  8.  spiral 
tube  of  the  cochlea  (scala  tj-mpani) ;  9,  opening  of  the  aqueduct  of  the  cochlea ;  10.  placed  on 

the  lamina  spiralis  in  the  scala  vestibuli.    -^     (Sommering.) 

several   openings   for   the   entrance   of  the   divisions   of  the   auditory 
nerve;    in   its    outer  wall,  the  fenestra   ovalis  (2,   fig.   400),   an   open- 


GoO  HANDBOOK    OF    PHYSIOLOGY. 

ing  filled  by  the  base  of  the  stapes;  in  its  posterior  and  superior 
walls,  five  openings  by  which  the  semicircular  canals  communicate  with 
it:  in  its  anterior  wall,  an  opening  leading  into  the  cochlea.  The  hinder 
part  of  the  inner  wall  of  the  vestibule  also  presents  an  opening,  the 
orifice  of  the  aquceductus  vestibuli^  a  canal  leading  to  the  posterior  mar- 
gin of  the  petrous  bone,  with  uncertain  contents  and  unknown  purpose. 

T\\Q  semicircular  canals  (figs.  400,  401)  are  three  arched  cylindriform 
bony  canals,  set  in  the  substance  of  the  petrous  bone.  They  all  open  at 
both  ends  into  the  vestibule  (two  of  them  first  coalescing).  The  ends  of 
each  are  dilated  just  before  opening  ifito  the  vestibule;  and  one  end 
being  more  dilated  than  the  other  is  called  an  amjmlla.  Two  of  the 
canals  form  nearly  vertical  arches ;  of  these  the  superior  is  also  anterior ; 
the  posterior  is  inferior;  the  third  canal  is  horizontal,  and  lower  and 
shorter  than  the  others. 

The  cochlea  (6,  7,  8,  figs.  400  and  401),  a  small  organ,  shaped  like  a 
common  snail-shell,  is  situated  in  front  of  the  vestibule,  its  base  resting 
on  the  bottom  of  the  internal  meatus,  where  some  apertures  transmit 
to  it  the  cochlear  filaments  of  the  auditory  nerve.  In  its  axis,  the 
cochlea  is  traversed  by  a  conical  column,  the  modiolus,  round  which  a 
spiral  canal  winds  with  about  two  turns  and  a  half  from  the  base  to  the 
apex.  At  the  apex  of  the  cochlea  the  canal  is  closed ;  at  the  base  it 
presents  three  openings,  of  which  one,  already  mentioned,  communicates 
with  the  vestibule;  another  called  fenestra  rotunda,  is  separated  by  a 
membrane  from  the  cavity  of  the  tympanum ;  the  third  is  the  orifice  of 
the  aquceductus  coclilece,  a  canal  leading  to  the  jugular  fossa  of  the 
petrous  bone,  and  corresponding,  at  least  in  obscurity  of  purpose  and 
origin,  to  the  aquseductus  vestibuli.  The  spiral  canal  is  divided  into  two 
passages,  or  scala?,  by  a  partition  of  bone  and  membrane,  the  lamina 
spiralis.  The  osseous  part  or  zone  of  this  lamina  is  connected  with  the 
modiolus. 

The  Membranous  Labyrinth. — The  membranous  labyrinth  corre- 
sponds generally  with  the  form  of  the  osseous  labyrinth,  so  far  as  regards 
the  vestibule  and  semicircular  canals,  but  is  separated  from  the  walls  of 
these  parts  by  perilymph,  except  where  the  nerves  enter  into  connection 
within  it.  The  labyrinth  is  a  closed  membrane  containing  endolymph, 
which  is  of  much  the  same  composition  as  perilymph,  but  contains  less 
solid  matter.  It  is  somewhat  viscid,  as  is  the  iierilymph,  and  it  is 
secreted  by  the  epithelium  lining  its  cavity;  all  the  sonorous  vibrations 
impressing  the  auditory  nerves  in  these  parts  of  the  internal  ear,  are 
conducted  through  fluid  to  a  membrane  suspended  in  and  containing 
fluid.  In  the  cochlea,  the  membranous  labyrinth  completes  the  septum 
between  the  two  scal.ce,  and  incloses  a  spiral  canal,  previously  mentioned, 
called  canalis  membranaceus  or  canalis  cochlem  (fig.  403).     The  fluid  in. 


THE    SEXSES.  651 

the  scalce  of  the  cochlea  is  continuous  with  the  peril3^mph  in  the  vesti- 
bule and  semicircular  canals,  and  there  is  no  fluid  extenud  to  its  lining 
membrane.  The  vestibular  2:)ortiou  of  the  membranous  labyrinth  cam- 
prises  two,  probably  communicating  cavities,  of  which  the  larger  and 
upjDcr  is  named  the  utricuJus;  the  lower,  the  sacculus.  They  are 
lodged  in  depressions  in  the  bony  labyrinth,  termed  respectively /orfYf 
hemieUiptica  and  fovea  liemispherira.  Into  the  former  open  the  orifices  of 
the  membranous  semicircular  canals;  into  the  latter  the  canalis  cocMece. 
The  membranous  labyrinth  of  all  these  parts  is  laminated,  transparent, 
very  vascular,  and  covered  on  the  inner  surface  with  nucleated  cells,  of 
which  those  that  line  the  ampullar  are  prolonged  into  stiff  hair-like  pro- 
cesses; the  same  appearance,  but  to  a  much  less  degree,  being  visible  in 
the  utricule  and  saccule.  In  the  cavities  of  the  utriculus  and  sacculus 
j-re  small  masses  of  calcareous  particles,  otoconia  or  otoliths;    and  the 


Fia:.  402.— View  of  the  osseous  cochlea  divided  through  the  middle.  1,  central  canal  of  the 
\aodiolus;  a,  lamina  spiralis  ossea;  3,  scala  tympani ;  4,  scala  vestibuli;  5,  porous  substance  of 
l;he  modiolus  near  one  of  the  sections  of  the  canalis  spiralis  modioli.     X  5.     (Arnold.^ 

same,  although  in  more  minute  quantities,  are  to  be  found  in  the  interior 
(»f  some  other  parts  of  the  membranous  labyrinth. 

Auditory  Nerve. — All  the  organs  now  described  are  provided  for  the 
appropriate  exposure  of  the  filaments  of  the  auditory  nerve  to  sonorous 
vibrations.  It  is  characterized  as  a  nerve  of  special  sense  by  its  softness 
(whence  it  derived  its  name  ot portio  mollis  of  the  seventh  pair),  and  by 
the  fineness  of  its  component  fibres.  It  enters  the  bony  canal  (the  meatus 
auditorius  interims),  with  the  facial  nerve  and  the  nervus  intermedins, 
and,  traversing  the  bone,  enters  the  labyrinth  at  the  ang]^  between  the 
base  of  the  cochlea  and  the  vestibule,  in  two  divisions;  one  for  the  ves- 
tibule and  semicircular  canals,  and  the  other  for  the  cochlea. 

There  are  two  branches  for  the  vestibule,  one,  superior,  distributed 
to  the  utricule  and  to  the  superior  and  horizontal  semicircular  canals, 
r^nd  the  other,  inferior,  ending  in  the  saccule  and  posterior  semicircular 
.'-anal.  Where  the  nerve  comes  in  connection  with  the  utricule  and 
tc-.ccule,  the  structure  of  the  membrane  is  modified  somewhat  and  the 
}»laces  are  called  maculm  acusticm.  The  epithelium  in  this  region  is,  as 
've  shall  see  directly,  considerably  specialized,  and  where  the  nerve  is  in 
connection  with  the  ampullae  of  the  semicircular  canals,  too,  the  struct- 
i^re  is  altered,  becoming  elevated  into  a  horse-shoe  ridge,  which  projects 


652  HANDBOOK    OF    PHYSIOLOGY. 

iuto  the  interior  of  the  cavity,  forming  the  crista  acustica.  Here,  too, 
the  epithelium  is  of  a  special  kind.  The  nerve  fibres  spread  out  and 
radiate  on  the  inner  surface  of  the  membranous  labyrinth:  their  exact 
termination  is  uncertain.  The  distribution  of  the  other  division  of  the 
auditory  nerve,  the  cochlear,  will  be  more  clearly  understood  after  the 
description  of  the  cochlea  itself. 

Structure. — The  structure  of  the  membranous  labyrinth  consists  of 
three  coats,  externally  a  layer  of  areolar  tissue,  next  a  hyaloid  membrane, 
elevated  into  minute  papillse,  and  internally  a  layer  of  flattened  epi- 
thelium. At  the  position  where  the  branches  of  the  vestibular  branch 
of  the  auditory  nerve  join  it,  viz.,  at  the  saccule,  utricule,  and  ampullae 
of  the  semicircular  canals,  there  is  a  marked  difference  in  the  structure, 
the  external  and  middle  layers  are  thicker  and  the  epithelium  becomes 
columnar.  The  epithelium  in  which  the  fibres  of  the  vestibular  nerve 
are  said  to  terminate  are  of  two  kinds,  called  cylinder  or  hair  cells,  and 
rod  cells.  The  hair  cells  occupy  only  one-half  of  the  thickness  of  the 
membrane;  from  their  inner  end  hair-like  processes  project  into  the 
cavity  of  the  labyrinth.  Their  outer  end  is  rounded  and  contains  n 
large  round  nucleus.  To  these  cells  the  primitive  fibrillae  of  the  axis 
cylinders  pass  up,  some  of  them  being  distinctly  varicose.  The  exact 
relation  of  the  nerve  fibrillge  to  the  hair-cells  is  unknown;  by  some  tlmy 
are  believed  actually  to  enter  the  cells,  by  others  they  are  stated  to  form 
a  kind  of  nest  of  fibrillae  into  which  the  cells  fit.  The  rod-cells  are  of 
somewhat  varying  form.  They  are  elongated  cells  extending  from  the 
surface  to  the  basement  membrane,  broad  at  the  upper  or  surface  end, 
and  containing  oval  nuclei  toward  their  attached  end,  but  not  exactly  at 
the  same  level  in  all  cases.  These  nuclei,  therefore,  form  a  distinct 
broad  nuclear  layer  on  a  vertical  section  of  the  membrane,  as  the  cellt; 
are  numerous,  much  more  so,  indeed,  than  the  other  variety  of  cell. 
The  lower  or  attached  part  of  the  cell  may  be  branched. 

The  membranous  part  of  the  cochlea,  with  a  muscular  zone,  forming 
its  outer  majjgin,  is  attached  to  the  outer  wall  of  the  canal.  Commen(i- 
ing  at  the  base  of  the  cochlea,  between  its  vestibular  and  tympanic  open- 
ings, it  forms  a  partition  between  these  apertures;  the  two  scalae  are, 
therefore,  in  correspondence  with  this  arrangement,  named  'scala  vesti- 
iuli  and  scala  tympatii  (fig.  403).  At  the  apex  of  the  cochlea,  the 
lamina  spiralis  ends  in  a  small  hamnlus,  the  inner  and  concave  part  of 
which,  being  detached  from  the  summit  of  the  modiolus,  leaves  a  small 
aperture  named  helicotrema,  by  which  the  two  scalae,  separated  in  all  the 
rest  of  their  length,  communicate. 

Besides  the  scala  vestibuli  and  scala  tympani,  there  is  a  third  space- 
between  them,  called  scala  media  or  canal  memhranaceus  (CC,  fig.  403). 
In  section  it  is  triangular,  its  external  wall  being  formed  by  the  wall  of 


THE   SENSES.  653 

the  cochlea,  its  upper  wall  (separating  it  from  the  scala  vestibuli)  by 
the  membrane  of  Reissner,  and  its  lower  wall  (separating  it  from  the 
scala  tympani)  by  the  basilar  membrane,  these  two  meeting  at  the  outer 
edge  of  the  bony  lamina  spiralis.  Following  the  turns  of  the  cochlea  to 
its  apex,  the  scala  media  there  terminates  blindly ;  while  toward  the  base 
of  the  cochlea  it  is  also  closed  with  the  exception  of  a  very  narrow  pas- 
sage (canalis  reuniens)  uniting  it  with  the  sacculus.  The  scala  media 
(like  the  rest  of  the  membranous  labyrinth)  contains  endolympli. 

Organ  of  Corti. — Upon  the  basilar  membrane  are  arranged  cells  of 
various  shapes.     About  midway  between  the  outer  edge  of  the  lamina 


Fig.  403.— Section  through  one  of  the  coils  of  the  cochlea  C<liagrammatic).  ST,  scala  tjTii- 
pani;  SV,  scala  vestibuli:  CC.  canalis  cochlear  or  canalis  membranaceus :  i?.  membrane  of 
Reissner;  Iso,  lamina  spiralis  ossea:  Us.  limbus  laminae  spiralis:  ss.  sulcus  spiralis:  nc,  cochlear 
nerve:  gs,  ganglion  spirale:  t.  membrana  tectoria  fbelow  the  membrana  tectoria  is  the  lamina 
recticularis) ;  /^  membrana  basilaris ;  Co,  rods  of  Corti;  Up,  ligamentum  spirale.     (Quain.) 

spiralis  and  the  outer  wall  of  the  cochlea  are  situated  the  rods  of  Corti. 
Viewed  sideways,  they  are  seen  to  consist  of  an  external  and  internal 
pillar,  each  rising  from  an  expanded  foot  or  base  on  the  basilar  mem- 
brane (o,  11,  fig.  -lO-i).  They  slant  inward  toward  each  other,  and  each 
ends  in  a  swelling  termed  the  head;  the  head  of  the  inner  pillar  overly- 
ing that  of  the  outer  (fig.  404).  Each  pair  of  pillars  forms,  as  it  were, 
a  pointed  roof  arching  over  a  space,  and  by  a  succession  of  them  a  little 
tunnel  is  formed. 

It  has  been  estimated  that  there  are  about  3000  of  these  jmirs  of  pil- 
lars, in  proceeding  from  the  base  of  the  cochlea  toward  its  apex.  They 
are  found  progressively  to  increase  in  length,  and  become  more  oblique; 
in  other  words  the  tunnel  becomes  wider,  but  diminishes  in  height  as  we 
approach  the  apex  of  the  cochlea.  Leaning,  as  it  were,  against  these 
external  and  internal  pillars  are  certain  other  cells,  of  which  the  external 
ones,  hair  cells,  terminate  in  small  hair-like  processes.  Most  of  the 
above  details  are  shown  in  the  accompanying  figure  (fig.  404).  This 
complicated  structure  rests,  as  we  have  seen,  upon  the  basilar  membrane; 
it  is  roofed  in  by  a  remarkable  fenestrated  membrane  or  lamina  reticu- 


G54 


HANDBOOK    OF    PHYSIOLOGY, 


laris  into  the  fenestra?  of  which  the  tops  of  the  various  rods  and  cells 
are  received.  AVhen  viewed  from  above,  the  organ  of  Corti  shows  a 
remarkable  resemblance  to  the  key-board  of  a  piano.     In  close  relation 


Fig.  404.  —Vertical  section  of  the  organ  of  Corti  from  the  dog.  1  to  2,  Homogeneous  layer 
of  the  so-called  meniltrana  basilaris;  it,  vestibular  layer;  v,  tympanal  layer,  with  nuclei  and 
protoiilasm :  n.  iirolrmgation  of  tympanal  periosteum  of  lamina  spiralis  ossea:  c,  thickened 
commencement  of  the  membrana  basilaris  near  the  point  of  perforation  of  the  nerves  h;  d, 
blood-vessel  fvas  spirale);  p,  blood-vessel;  /,  nerves;  g.  the  epithelium  of  the  sulcus  spiralis 
internus;  j,  internal  or  tufted  cell,  with  basil  process  fc,  "surrounded  with  nuclei  and  protoplasm 
(of  the  granular  layer),  into  which  the  nerve-fibres  radiate:  I.  hairs  of  the  internal  hair-cell;  «, 
base  or  foot  of  inner  jiillar  of  organ  of  Corti;  ni,  head  of  the  same  uniting  with  the  correspond- 
ing part  of  an  external  pillar,  whose  under  half  is  missing,  while  the  next  pillar  beyond,  o,  pre- 
sents both  middle  portion  and  base;  r  s  d,  three  external  hair-cells;  t,  bases  of  two  neighboring 
hair  or  tufted  cells ;  x,  so-called  supporting  cell  of  Hensen ;  iv,  nerve-fibre  terminating  in  the  firsi 
of  the  external  hair-cells;  I  I  to  I,  lamina  reticularis,     x  800.     (Waldeyer.) 

with  the  rods  of  Corti  and  the  cells  inside  and  outside  them,  and  proba 
bly  projecting  by  free  ends  into  the  little  tunnel  containing  fluid  (roofed 
in  by  them),  are  filaments  of  the  auditory  nerve.  These  are  derived 
frctai  the  cochlear  division  already  mentioned.  This  passes  up  the  axiii 
of  the  cochlea,  and  in  its  course  gives  off  fibres  to  the  lamina  spiralis. 
These  fibres  are  thick  at  their  origin,  but  thin  out  peripherally,  and 
containing  bipolar  ganglion  cells  form  the  ganglioii  spirale.  Beyond 
the  ganglion  at  the  edge  of  the  lamina  the  fibres  pass  up  and  become 
connected  with  the  orsfan  of  Corti. 


The  Physiology  of  Hearing. 

All  the  acoustic  contrivances  of  the  organ  of  hearing  are  means  for 
conducting  sound.  Since  all  matter  is  capable  of  propagating  sonorous 
vibrations,  the  simplest  conditions  must  be  sufficient  for  mere  hearing; 
for  all  substances  surrounding  the  auditory  nerve  would  stimulate  it. 
The  whole  development  of  the  organ  of  hearing,  therefore,  can  have  for  its 
object  merely  the  rendering  more  perfect  the  propagation  of  the  sono- 
rous vibrations,  and  their  multiplication  by  resonance;  and,  in  fact,  the 
whole  of  the  acoustic  apparatus  may  be  shown  to  have  reference  to  these 
principles. 

The  external  auditory  passages  influence  the  propagation  of  sound 


THE    SEJ^SES.  655 

to  the  tympanum  in  three  ways: — 1,  by  causing  the  sonorous  unduhitions, 
entering  directly  from  the  atmosphere,  to  be  transmitted  by  the  air  in 
the  passage  immediately  to  the  membrana  tympani,  and  thus  preventing 
them  from  being  dispersed ;  2,  by  the  walls  of  the  passage  conducting 
the  sonorous  undulations  imparted  to  the  external  ear  itself,  by  the 
shortest  23ath  to  the  attachment  of  the  membrana  tympani,  and  so  to  this 
membrane;  3,  by  the  resonance  of  the  column  of  air  contained  within  the 
passage;  4,  the  external  ear,  especially  Avhen  the  tragus  is  provided  with 
hairs,  is  also,  doubtless,  of  service  in  protecting  the  meatus  and  mem- 
brana tympani  against  dust,  insects,  and  the  like. 

Regarding  the  cartilage  of  the  external  ear,  therefore,  as  a  conductor 
of  sonorous  vibrations,  all  its  inequalities,  elevations,  and  depressions, 
become  of  evident  im^iortance;  for  those  elevations  and  depressions  ujion 
which  the  undulations  fall  perpendicularly,  will  be  affected  by  them  in 
the  most  intense  degree;  and,  in  consequence  of  the  various  form  and 
position  of  these  inequalities,  sonorous  undulations,  in  whatever  direc- 
tion they  may  come,  must  fall  perpendicularly  upon  the  tangent  of  some 
one  of  them.  This  affords  an  explanation  of  the  extraordinary  form 
given  to  this  part. 

In  animals  living  in  the  atmosphere,  the  sonorous  vibrations  are  con- 
veyed to  the  auditory  nerve  by  three  different  media  in  succession; 
namely,  the  air,  the  solid  parts  of  the  body  of  the  animal  and  of  the 
auditory  apparatus,  and  the  fluid  of  the  labyrinth.  Sonorous  vibrations 
are  imparted  too  imperfectly  from  air  to  solid  bodies,  for  the  propaga- 
tion of  sound  to  the  internal  ear  to  be  adequately  effected  by  that  means 
alone;  yet  already  an  instance  of  its  being  thus  propagated  has  been 
mentioned.  In  passing  from  air  directly  into  water,  sonorous  vibra- 
tions suffer  also  a  considerable  diminution  of  their  strength;  but  if  a 
tense  membrane  exists  between  the  air  and  the  water,  the  sonorous  vi- 
brations are  communicated  from  the  former  to  the  latter  medium  with 
very  great  intensity.  This  fact,  of  which  Miiller  gives  experinicntal 
proof,  furnishes  at  once  an  explanation  of  the  use  of  the  fenestra  rotunda, 
and  of  the  membrane  closing  it.  They  are  the  means  of  communicat- 
ing, in  full  intensity,  the  vibrations  of  the  air  in  the  tympanum  to 
the  fluid  of  the  labyrinth.  This  peculiar  property  of  membranes  is  the 
result,  not  of  their  tenuity  alone,  but  of  the  elasticity  and  capability  of 
displacement  of  their  particles;  and  it  is  not  impaired  when,  like  the 
membrane  of  the  fenestra  rotunda,  they  are  not  impregnated  with 
moisture. 

Sonorous  vibrations  are  also  communicated  without  any  perceptible 
loss  of  intensity  from  the  air  to  the  water,  when  to  the  membrane  form- 
ing the  medium  of  communication,  there  is  attached  a  short,  solid  body, 
which  occupies  the  greater  part  of  its  surface,  and  is  alone  in  contact 


656  HANDBOOK    OF    PHYSIOLOGY. 

with  the  water.  This  fact  elucidates  the  action  of  the  fenestra  ovalis, 
and  of  the  plate  of  the  stapes  which  occupies  it,  and,  with  the  preceding 
fact,  shows  that  both  fenestrse — that  closed  by  membrane  only,  and  that 
with  which  the  movable  stapes  is  connected — transmit  very  freely  the 
sonorous  vibrations  from  the  air  to  the  fluid  of  the  labyrinth. 

A  small,  solid  body,  fixed  in  an  opening  by  means  of  a  border  of 
membrane,  so  as  to  be  movable,  communicates  sonorous  vibrations  from 
air  on  the  one  side,  to  water,  or  the  fluid  of  the  labyrinth,  on  the  other 
side,  much  better  than  solid  media  not  so  constructed.  But  the  propa- 
gation of  sound  to  the  fluid  is  rendered  much  more  perfect  if  the  solid 
conductor  thus  occupying  the  opening,  or  fenestra  ovalis,  is  by  its  other 
end  fixed  to  the  middle  of  a  tense  membrane,  which  has  atmospheric  air 
on  both  sides.  A  tense  membrane  is  a  much  better  conductor  of  the 
vibrations  of  air  than  any  other  solid  body  bounded  by  definite  surfaces: 
and  the  vibrations  are  also  communicated  very  readily  by  tense  mem- 
branes to  solid  bodies  in  contact  with  them.  Thus,  then,  the  membrana 
tympani  serves  for  the  transmission  of  sound  from  the  air  to  the  chain 
of  ossicles.  Stretched  tightly  in  its  osseous  ring,  it  vibrates  vvith  the 
air  in  the  auditory  passage,  as  any  thin  tense  membrane  will,  when  the 
air  near  it  is  thrown  into  vibrations  by  the  sounding  of  a  tuning-fork 
or  a  musical  string.  And,  from  such  a  tense  vibrating  membrane,  the 
vibrations  are  communicated  with  great  intensity  to  solid  bodies  which 
touch  it  at  any  point.  If,  for  example,  one  end  of  a  flat  piece  of  wood 
be  applied  to  the  membrane  of  a  drum,  while  the  other  end  is  held  in 
the  hand,  vibrations  are  felt  distinctly  when  the  vibrating  tuning-fork 
is  held  over  the  membrane  without  touching  it ;  but  the  wood  alone, 
isolated  from  the  membrane,  will  only  very  feebly  propagate  the  vibra- 
tions of  the  air  to  the  hand. 

In  comparing  the  membrana  t3^mpani  to  the  membrane  of  a  drum, 
however,  it  is  necessary  to  point  out  certain  important  differences. 

When  a  drum  is  struck,  a  certain  definite  tone  is  elicited  (funda- 
mental tone);  similarly  a  drum  is  thrown  into  vibration  when  certain 
tones  are  sounded  in  its  neighborhood,  while  it  is  quite  unaffected  by 
others.  In  other  words  it  can  only  take  up  and  vibrate  in  response  to 
those  tones  whose  vibrations  nearly  correspond  in  number  with  those  of 
its  own  fundamental  tone.  The  tympanic  membrane  can  take  up  an 
immense  range  of  tones  produced  by  vibrations  ranging  from  30  to  4000 
or  5000  per  second.  This  would  be  clearly  impossible  if  it  Avere  an 
evenly  stretched  membrane. 

The  fact  is,  that  the  membrana  tympani  is  by  no  means  evenly 
stretched,  and  this  is  due  partly  to  its  slightly  funnel-like  form,  and 
partly  to  its  being  connected  with  the  chain  of  auditory  ossicles.  Fur- 
ther,  if  ihe  membrane  were  quite  free  in  its  centre,  it  would  go  on 


THE   SENSES.  657 

vibrating  as  a  drum  does  some  time  after  it  is  struck,  and  each  sound 
would  be  prolonged,  leading  to  considerable  confusion.  This  evil  is 
obviated  by  the  ear-bones,  which  check  the  continuance  of  the  vibrations 
like  the  "  dampers"  in  a  pianoforte. 

The  ossicles  of  the  ear  are  the  better  conductors  of  the  sonorous  vi- 
brations communicated  to  them,  on  account  of  being  isolated  by  an 
atmosphere  of  air,  and  not  continuous  with  the  bones  of  the  cranium; 
for  every  solid  body  thus  isolated  by  a  different  medium,  propagates 
vibrations  with  more  intensity  through  its  own  substance  than  it  com- 
municates them  to  the  surrounding  medium,  which  thus  prevents  a 
depression  of  the  sound;  just  as  the  vibrations  of  the  air  in  the  tubes 
used  for  conducting  the  voice  from  one  apartment  to  another  are  pre- 
vented from  being  disjjersed  by  the  solid  walls  of  the  tube.  The  vibra- 
tions of  the  membrana  tympani  are  transmitted,  therefore,  by  the  chain 
of  ossicula  to  the  fenestra  ovalis  and  fluid  of  the  labyrinth,  their  disper- 
sion in  the  tympanum  being  prevented  by  tlie  difficulty  of  the  transition 
of  vibrations  from  solid  to  gaseous  bodies. 

The  necessity  of  the  presence  of  air  on  the  inner  side  of  the  mem- 
brana tympani,  in  order  to  enable  it  and  the  ossicula  auditus  to  fulfil  the 
objects  just  described,  is  obvious.  AVithout  this  provision,  neither 
would  the  vibrations  of  the  membrane  be  free,  nor  the  chain  of  bones 
isolated,  so  as  to  propagate  the  sonorous  undulations  with  concentration 
of  their  intensity.  But  while  the  oscillations  of  the 
membrana  tympani  are  readily  communicated  to  the  air 
in  the  cavity  of  the  tympanum,  those  of  the  solid  ossi- 
cula will  not  be  conducted  away  by  the  air,  but  will  be 
proj^agated  to  the  labyrinth  without  being  dispersed  in 
the  tympanum. 

The  propagation  of  sound  through  the  ossicula  tym- 
pani to  the  labyrinth,  must  be  affected  either  by  oscil- 
lations of  the  bones,  or  by  a  kind  of  molecular  vibration 
of  their  particles,  or,  most  probably,  by  both  these  kinds 
of  motion. 

It  has  been  shown  that  the  existence  of  the  mem- 
brane over  the  fenestra  rotunda  will  permit  approxima-  gram  %^°fiiustrate 
tion  and  removal  of  the  stapes  to  and  from  the  laby-  sici^'^of'the  mkidie 
rinth.  When  by  the  stapes  the  membrane  of  the  tion  of  souDd°tcf the 
fenestra  ovalis  is  pressed  toward  the  labyrinth,  the  '°'^®™'^  ^^'■• 
membrane  of  the  fenestra  rotunda  may,  by  the  pressure  communicated 
through  the  fluid  of  the  labyrinth,  be  pressed  toward  the  cavity  of  the 
tympanum. 

The  long  process  of  the  malleus  receives  the  undulations  of  the  mem- 
brana tympani  (fig.  405,  a,  a)  and  of  the  air  in  a  direction  indicated  by 
42 


658  HANDBOOK    OF    PHYSIOLOGY. 

the  arrows,  nearly  perpendicular  to  itself.  From  the  long  process  of 
the  malleus  they  are  propagated  to  its  head  (b) :  thence  into  the  incus  (c), 
the  long  process  of  which  is  parallel  with  the  long  process  of  the  malleus. 
From  the  long  process  of  the  incus  the  undulations  are  communicated 
to  the  stapes  (r/),  which  is  united  to  the  incus  at  right  angles.  The 
several  changes  in  the  direction  of  the  chain  of  bones  have,  however,  no 
influence  in  changing  the  character  of  the  undulations,  which  remain  the 
same  as  in  the  meatus  externus.  From  the  long  process  of  the  malleus, 
the  undulations  are  communicated  by  the  stapes  to  the  fenestra  ovalis 
in  a  perpendicular  direction. 

Increasing  tension  of  the  membrana  tympani  diminishes  the  facility 
of  transmission  of  sonorous  undulations  from  the  air  to  it. 

The  dry  membrana  tympani,  on  the  approach  of  a  body  emits  a  loud 
sound,  rejects  particles  of  sand  strewn  upon  it  more  strongly  when  lax 
tlian  when  very  tense;  and  it  has  been  inferred,  therefore,  that  hearing 
is  rendered  less  acute  by  increasing  the  tension  of  the  membrana  tym- 
pani. 

The  pharyngeal  orifice  of  the  Eustachian  tube  is  usually  shut;  dur- 
ing swallowing,  however,  it  is  opened;  this  may  be  shown  as  follows: — 
If  the  nose  and  mouth  be  closed  and  the  cheeks  blown  out,  a  sense  of 
pressure  is  produced  in  both  ears  the  moment  we  swallow;  this  is  due, 
doubtless,  to  the  bulging  out  of  the  tympanic  membrane  by  the  com- 
pressed air,  which  at  that  moment  enters  the  Eustachian  tube. 

Similarly  the  tymjianic  membrane  may  be  pressed  in  by  rarefying 
the  air  in  the  tympanum.  This  can  be  readily  accomplished  by  closing 
the  mouth  and  nose,  and  making  an  inspiratory  effort  and  at  the  same 
time  swallowing.  In  both  cases  the  sense  of  hearing  is  temporarily 
dulled;  proving  that  equality  of  pressure  on  both  sides  of  the  tympanic 
membrane  is  necessary  for  its  full  efficiency. 

The  principal  office  of  the  Eustachian  tube  has  relation  to  the  pre- 
vention of  these  effects  of  increased  tension  of  the  membrana  tympani. 
Its  existence  and  openness  will  provide  for  the  maintenance  of  the  equi- 
librium between  the  air  within  the  tympanum  and  the  external  air,  so 
as  to  prevent  the  inordinate  tension  of  the  membrana  tympani  which 
would  be  produced  by  too  great  or  too  little  pressure  on  either  side. 
While  discharging  this  office,  however,  it  will  serve  to  render  sounds 
clearer,  as  the  apertures  in  violins  do;  to  supply  the  tympanum  with 
air;  and  to  bean  outlet  for  mucus.  If  the  tube  vikire permanentli/ open, 
the  sound  of  one's  own  voice  would  probably  be  greatly  intensified,  a 
condition  which  would  of  course  interfere  with  the  perception  of  other 
sounds.  At  any  rate,  it  is  certain  that  sonorous  vibrations  can  be  prop- 
agated up  the  tube  to  the  tympanum  by  means  of  a  catheter  insetted 
into  the  pharyngeal  orifice  of  the  Eustachian  tube. 


THE    SENSES,  659 

The  influence  of  the  tensor  tympani  muscle  in  modifying  hearing 
may  also  be  probably  explained  in  connection  with  the  regulation  of  the 
tension  of  the  membrana  tympani.  If,  through  reflex  nervous  action, 
it  can  be  excited  to  contraction  by  a  very  loud  sound,  then  it  is  mani- 
fest that  a  very  intense  sound  would,  through  the  action  of  this  muscle, 
induce  a  deafening  or  muffling  of  the  ears.  In  favor  of  this  supposition 
we  have  the  fact  that  a  loud  sound  excites,  by  reflection,  nervous  action, 
winking  of  the  eyelids,  and,  in  persons  of  irritable  nervous  system,  a 
sudden  contraction  of  many  muscles. 

The  exact  influence  of  the  stapedius  muscle  in  hearing  is  unknown. 
It  acts  upon  the  stapes  in  such  a  manner  as  to  make  it  rest  obliquely  in 
the  fenestra  ovalis,  depressing  that  side  of  it  on  which  it  acts,  and  ele- 
vating the  other  side  to  the  same  extent.  It  prevents  too  great  a  move- 
ment of  the  bone. 

The  fluid  of  the  labyrinth  is  the  most  general  and  constant  of  the 
acoustic  provisions  of  the  labyrinth.  In  all  forms  of  organs  of  hearing, 
the  sonorous  vibrations  affect  the  auditory  nerve  through  the  medium 
of  liquid — the  most  convenient  medium,  on  many  accounts,  for  such  a 
j^urpose. 

The  otoliths  in  the  labyrinth  would  reinforce  the  sonorous  vibrations 
by  their  resonance,  even  if  they  did  not  actually  touch  the  membranes 
upon  which  the  nerves  are  expanded;  but,  inasmuch  as  these  bodies  lie 
in  contact  with  the  membranous  parts  of  the  labyrinth,  and  the  vestibu- 
lar nerve-fibres  are  imbedded  in  them,  they  communicate  to  these  mem- 
branes and  the  nerves,  vibratory  impulses  of  greater  intensity  than  the 
fluid  of  the  labyrinth  can  impart.  This  appears  to  be  their  office.  So- 
norous undulations  in  water  are  not  perceived  by  the  hand  itself  immersed 
in  the  water,  but  are  felt  distinctly  through  the  medium  of  a  rod  held 
in  the  hand.  The  fine  hair-like  prolongations  from  the  epithelial  cells 
of  the  ampulla  have,  probably,  the  same  function. 

The  function  of  the  semicircular  canals  in  the  co-ordination  of 
movements  necessary  to  the  maintenance  of  the  equilibrium  of  the  body 
has  already  been  indicated. 

The  cochlea  seems  to  be  constructed  for  the  spreading  out  of  the 
nerve-fibres  over  a  wide  extent  of  surface,  upon  a  solid  lamina  which 
communicates  with  the  solid  walls  of  the  labyrinth  and  cranium,  at  the 
same  time  that  it  is  in  contact  with  the  fluid  of  the  labyrinth,  and 
which,  besides  exposing  the  nerve-fibres  to  the  influence  of  sonorous 
undulations,  by  two  media,  is  itself  insulated  by  fluid  on  either  side. 

The  connection  of  the  lamina  spiralis  with  the  solid  walls  of  the 
labyrinth,  adapts  the  cochlea  for  the  perception  of  the  sonorous  undula- 
tions propagated  by  the  solid  parts  of  the  head  and  the  walls  of  the  laby- 
rinth.    The  membranous  labyrinth  of  the  vestibule  and  semicircular 


660  HANDBOOK    OF    PHYSIOLOGY. 

cauals  is  suspended  free  in  the  perilymph,  and  is  destined  more  particu- 
larly for  the  perception  of  sounds  through  the  medium  of  that  fluid, 
whether  the  sonorous  undulations  be  imparted  to  the  fluid  through  the 
fenestras,  or  by  the  intervention  of  the  cranial  bones,  as  when  sounding 
bodies  are  brought  into  communication  with  the  head  or  teeth.  The 
spiral  lamina  on  which  the  nervous  fibres  are  expanded  in  the  cochlea, 
is,  on  the  contrary,  continuous  with  the  solid  walls  of  the  labyrinth,  and 
receives  directly  from  them  the  impulses  which  they  transmit.  This  is 
an  important  advantage;  for  the  impulses  imparted  by  solid  bodies, 
have,  coeter is  paribus,  a  greater  absolute  intensity  than  those  communi- 
cated by  water.  And,  even  Avhen  a  sound  is  excited  in  the  water,  the 
sonorous  undulations  are  more  intense  in  the  water  near  the  surface  of 
the  vessel  containing  it,  than  in  other  parts  of  the  water  equally  distant 
from  the  point  of  origin  of  the  sound;  thus  we  may  conclude  that, 
cceteris  paribus,  the  sonorous  undulations  of  solid  bodies  act  with  greater 
intensity  than  those  of  water.  Hence,  we  perceive  at  once  an  imjiortant 
use  of  the  cochlea. 

This  is  not,  however,  the  sole  office  of  the  cochlea;  the  spiral  lamina, 
as  well  as  the  membranous  labyrinth,  receives  sonorous  impulses  through 
the  medium  of  the  fluid  of  the  labyrinth  from  the  cavity  of  the  vestibule, 
and  from  the  fenestra  rotunda.  The  lamina  spiralis  is,  indeed,  much 
better  calculated  to  render  the  action  of  these  undulations  ujDon  the 
auditory  nerve  eflficient,  than  the  membranous  labyrinth  is;  for  as  a  solid 
body  insulated  by  a  different  medium,  it  is  capable  of  resonance. 

The  rods  of  Corti  are  probably  arranged  so  that  each  is  set  to  vibrate 
in  unison  with  a  particular  tone,  and  thus  strike  a  j^articular  note,  the 
sensation  of  which  is  carried  to  the  brain  by  those  filaments  of  the  audi- 
tory nerve  with  which  the  little  vibrating  rod  is  connected.  The  dis- 
tinctive function,  therefore,  of  these  minute  bodies  is,  probably,  to 
render  sensible  to  the  brain  the  various  musical  notes  and  tones,  one  of 
them  answering  to  one  tone,  and  one  to  another;  while  perhaps  the 
other  parts  of  the  organ  of  hearing  discriminate  between  the  intensities 
of  different  sounds,  rather  than  their  qualities. 

"  In  the  cochlea  we  have  to  do  with  a  series  of  apparatus  adapted  for 
performing  sympathetic  vibrations  with  wonderful  exactness.  We  have 
here  before  us  a  musical  instrument  which  is  designed,  not  to  create 
musical  sounds,  but  to  render  them  perceptible,  and  which  is  similar  in 
construction  to  artificial  musical  instruments,  but  which  far  surpasses 
them  in  the  delicacy  as  well  as  the  simplicity  of  its  execution.  For, 
while  in  a  piano  every  string  must  have  a  separate  hammer  by  means  of 
which  it  is  sounded  the  ear  possesses  a  single  hammer  of  an  ingenious 
form  in  its  ear  bones,  which  can  make  every  string  of  the  organ  of  Corti 
sound  separately."     (Bernstein.) 


THE    SENSES.  661 

Since  about  3000  rods  of  Corti  are  present  in  the  human  ear,  this 
would  give  about  400  to  each  of  the  seven  octaves  which  are  within  the 
compass  of  the  ear.  Thus  about  32  would  go  to  each  semi-tone.  "Weber 
asserts  that  accomplished  musicians  can  appreciate  differences  in  pitch 
as  small  as  grth  of  a  tone.  Thus  on  the  theory  above  advanced,  the 
delicacy  of  discrimination  would,  in  this  case,  appear  to  have  reached 
its  limits. 

Sounds. 

Any  elastic  body,  e.g.,  air,  a  membrane,  or  a  string  performing  a 
certain  number  of  regular  vibrations  in  the  second,  gives  rise  to  what 
is  termed  a  musical  sound  or  tone.  We  must,  however,  distinguish  be- 
tween a  musical  sound  and  a  mere  noise ;  the  latter  being  due  to  irregular 
vibrations. 

Musical  sounds  are  distinguished  from  each  other  by  three  qualities. 
1.  /Strength  or  intensity,  which  is  due  to  the  amplitude  or  length  of  the 
vibrations.  2.  Pitch,  which  depends  upon  the  number  of  vibrations  in 
a  second.  3.  Quality,  Color,  or  Timhre.  It  is  by  this  property  that 
we  distinguish  the  same  note  sounded  on  two  instruments,  e.g.,  a  piano 
and  a  flute.  It  has  been  proved  by  Helmholtz  to  depend  on  the  number 
of  secondary  tones,  termed  harmonics,  which  are  present  with  the  pre- 
dominating or  fundamental  tone. 

It  would  appear  that  two  impulses,  which  are  equivalent  to  four  single 
or  half  vibrations,  are  sufficient  to  produce  a  definite  note,  audible  as 
such  through  the  auditory  nerve. 

The  maximum  and  minimum  of  the  intervals  of  successive  impulses 
still  appreciable  through  the  auditory  nerve  as  determinate  sounds,  have 
been  determined  by  Savart.  If  their  intensity  is  sufficiently  great, 
sounds  are  still  audible  which  result  from  the  succession  of  48,000  half 
vibrations,  or  24,000  impulses  in  a  second;  and  this,  probably,  is  not 
the  extreme  limit  in  acuteness  of  sounds  perceptible  by  the  ear.  For 
the  opposite  extreme,  he  has  succeeded  in  rendering  sounds  audible 
which  were  produced  by  only  fourteen  or  eighteen  half  vibrations,  or 
seven  or  eight  impulses  in  a  second;  and  sounds  still  deeper  might  prob- 
ably be  heard,  if  the  individual  impulses  could  be  sufficiently  prolonged. 

Direction. — The  j^ower  of  perceiving  the  direction  of  sounds  is  not 
a  faculty  of  the  sense  of  hearing  itself,  but  is  an  act  of  the  mind  judging 
on  experience  previously  acquired.  From  the  modifications  which  the 
sensation  of  sound  undergoes  according  to  the  direction  in  which  the 
sound  reaches  us,  the  mind  infers  the  position  of  the  sounding  body. 
The  only  true  guide  for  this  inference  is  the  more  intense  action  of  the 
sound  upon  one  than  upon  the  other  ear.  But  even  here  there  is  room 
for  much  deception,  by  the  influence  of  reflexion  or  resonance,  and  by 


662  HANDBOOK    OF   PHYSIOLOGY. 

the  proimgation  of  sound  from  a  distance,  without  loss  of  intensity, 
tlirough  curved  conducting  tubes  filled  with  air.  By  means  of  such  tubes, 
or  of  solid  conductors,  which  convey  the  sonorous  vibrations  from  their 
source  to  a  distant  resonant  body,  sounds  may  be  made  to  appear  to  orig- 
inate in  a  new  situation.  The  direction  of  sound  may  also  be  judged 
of  by  means  of  one  ear  only;  the  position  of  the  ear  and  head  being 
varied,  so  that  the  sonorous  undulations  at  one  moment  fall  upon  the 
ear  in  a  perpendicular  direction,  at  another  moment  obliquely.  But 
when  neither  of  these  circumstances  can  guide  us  in  distinguishing  the 
direction  of  sound,  as  when  it  falls  equally  upon  both  ears,  its  source 
being,  for  example,  either  directly  in  front  or  behind  us,  it  becomes 
impossible  to  determine  Avhence  the  sound  comes. 

Distance. — The  distance  of  the  source  of  sounds  is  not  recognized  by 
the  sense  itself,  but  is  inferred  from  their  intensity.  The  sense  itself  is 
always  seated  but  in  one  place,  namely,  in  our  ear;  but  it  is  interpreted 
as  coming  from  an  exterior  soniferous  body.  When  the  intensity  of  the 
voice  is  modified  in  imitation  of  the  effect  of  distance,  it  excites  the 
idea  of  its  originating  at  a  distance.  Ventriloquists  take  advantage  of 
the  difficulty  with  which  the  direction  of  sound  is  recognized,  and  also 
the  influence  of  the  imagination  over  our  judgment,  when  they  direct 
their  voice  in  a  certain  direction,  and  at  the  same  time  pretend,  them- 
selves, to  hear  the  sounds  as  coming  from  thence. 

Intensity. — By  removing  one  or  several  teeth  from  the  toothed  wheel 
the  fact  has  been  demonstrated  that  in  the  case  of  the  auditory  nerve, 
as  in  that  of  the  optic  nerve,  the  sensation  continues  longer  than  the  im- 
pression which  causes  it;  for  a  removal  of  a  tooth  from  the  wheel  pro- 
duced no  interruption  of  the  sound.  The  gradual  cessation  of  the  sen- 
sation of  sound  renders  it  difficult,  however,  to  determine  its  exact 
duration  beyond  that  of  the  impression  of  the  sonorous  impulses. 

So  we  see  that  the  effect  of  the  action  of  sonorous  undulations  upon 
the  nerve  of  hearing,  endures  somewhat  longer  than  the  period  during 
which  the  undulations  are  passing  through  the  ear.  If,  however,  the 
impressions  of  the  same  sound  be  very  long  continued,  or  constantly 
repeated  for  a  long  time,  then  the  sensation  produced  may  continue  for 
a  very  long  time,  more  than  twelve  or  twenty-four  hours  even,  after  the 
original  cause  of  the  sound  has  ceased. 

Binaural  Sensations. — Corresponding  to  the  double  vision  of  the 
same  object  with  the  two  eyes,  is  the  double  hearing  with  the  two  ears; 
and  analogous  to  the  double  vision  with  one  eye,  dependent  on  unequal 
refraction,  is  the  double  hearing  of  a  single  sound  with  one  ear,  owing 
to  the  sound  coming  to  the  ear  through  media  of  unequal  conducting 
power.  The  first  kind  of  double  hearing  is  very  rare;  instances  of  it, 
however,  have  been  recorded.     The  second  kind  which  depends  on  the 


THE    SENSES,  6G3 

unequal  cunducting  power  of  two  media  through  which  the  same  sound 
is  transmitted  to  the  ear,  may  easily  be  experienced.  If  a  small  bell  be 
sounded  in  water,  while  the  ears  are  closed  by  plugs,  and  a  solid  con- 
ductor be  interposed  between  the  water  and  the  ear,  two  sounds  will  be 
heard  differing  in  intensity  and  tone;  one  being  conveyed  to  the  ear 
through  the  medium  of  the  atmosphere,  the  other  through  the  conduct- 
ing-rod. 

Subjective  Sensafio)is. — Subjective  sounds  are  the  result  of  a  state  of 
irritation  or  excitement  of  the  auditory  nerve  produced  by  other  causes 
than  sonorous  impulses.  A  state  of  excitement  of  this  nerve,  however 
induced,  gives  rise  to  the  sensation  of  sound.  Hence  the  ringing  and 
buzzing  in  the  ears  heard  by  jDersons  of  irritable  and  exhausted  nervous 
system,  and  by  j^atients  with  cerebral  disease,  or  disease  of  the  auditory 
nerve  itself;  hence  also  the  noise  in  the  ears  heard  for  some  time  after  a 
long  journey  in  a  rattling,  noisy  vehicle.  Eitter  found  that  electric 
currents  also  excite  sounds  in  the  ears.  From  the  above  truly  subjective 
sound  we  must  distinguish  those  dependent,  not  on  a  state  of  the  audi- 
tory nerve  itself  merely,  but  on  sonorous  vibrations  excited  in  the  audi- 
tory apparatus.  Such  are  the  buzzing  sounds  attendant  on  vascular 
congestion  of  the  head  and  ear,  or  on  aueurismal  dilatation  of  the  ves- 
sels. Frequently  even  the  simple  pulsatory  circulation  of  the  blood  in 
the  ear  is  heard.  To  the  sounds  of  this  class  belong  also  the  buzz  or 
hum,  heard  during  the  contraction  of  the  palatine  muscles  in  the  act  of 
yawning,  .during  the  forcing  of  air  into  the  tymjaanum  so  as  to  make 
tense  the  membrana  tympani,  and  in  the  act  of  blowing  the  nose,  as  well 
as  during  the  forcible  depression  of  the  lower  jaw. 

Irritation  or  excitement  of  the  auditory  nerve  is  capable  of  giving 
rise  to  movements  in  the  body,  and  to  sensations  in  other  organs  of 
sense.  In  both  cases  it  is  probable  that  the  laws  of  reflex  action,  through 
the  medium  of  the  brain,  come  into  play.  An  intense  and  sudden  noise 
excites,  in  every  person,  closure  of  the  eyelids,  and,  in  nervous  indi- 
viduals, a  start  of  the  whole  body  or  an  unpleasant  sensation,  like  that 
produced  by  an  electric  shock,  throughout  the  body,  and  sometimes  a 
particular  feeling  in  the  external  ear.  Various  sounds  cause  in  many 
people  a  disagreeable  feeling  in  the  teeth,  or  a  sensation  of  cold  tickling 
through  the  body,  and,  in  some  people,  intense  sounds  are  said  to  make 
the  saliva  collect. 

V.  Sight. 

Anatomy  of  the  Optical  Ajjparatus. — The  ei/elids  consist  of  two  mov- 
able folds  of  skin,  each  of  which  is  kept  in  shape  by  a  thin  plate  of 
yellow  elastic  tissue.  Along  their  free  edges  are  inserted  a  number  of 
curved  hairs   (ei/elashes),   which,   when  the  lids  are  half  closed,   serve 


664  HANDBOOK    OF    PHYSIOLOGY. 

to  protect  the  eye  from  dust  and  other  foreign  bodies:  their  tactile  sen- 
sibility is  also  very  delicate. 

On  the  inner  surface  of  the  elastic  tissue  are  disposed  a  number  of 
small  racemose  glands  (Meibomian),  whose  ducts  open  near  the  free  edge 
of  the  lid. 

The  orbital  surface  of  each  lid  is  lined  by  a  delicate,  highly  sensitive 
mucous  membrane  [conjunctiva),  which  is  continuous  with  the  skin  at 
the  free  edge  of  each  lid,  and  after  lining  the  inner  surface  of  the  eyelid 
is  reflected  on  to  the  eyeball,  being  somewhat  loosely  adherent  to  the 
sclerotic  coat.  The  epithelial  layer  is  continued  over  the  cornea  at  its 
anterior  epithelium.  At  the  inner  edge  of  the  eye  the  conjunctiva 
becomes  continuous  with  the  mucous  lining  of  the  lachrymal  sac  and 
duct,  which  again  is  continuous  with  the  mucous  membrane  of  the 
inferior  meatus  of  the  nose. 

The  lachrymal  gland,  composed  of  several  lobules  made  up  of  acini 
resembling  the  serous  salivary  glands,  is  lodged  in  the  upper  and  outer 
angle  of  the  orbit.  Its  secretion,  which  issues  from  several  ducts  on 
the  inner  surface  of  the  upper  lid,  under  ordinary  circumstances  just 
suffices  to  keep  the  conjunctiva  moist.  It  passes  out  through  two  small 
openings  (puncta  lachrymalia)  near  the  inner  angle  of  the  eye,  one  in 
each  lid,  into  the  lachrymal  sac,  and  thence  along  the  nasal  duct  into 
the  inferior  meatus  of  the  nose.  The  excessive  secretions  poured  out 
under  the  influence  of  any  irritating  vapor  or  painful  emotion  overflows 
the  lower  lid  in  the  form  of  tears. 

The  eyelids  are  closed  by  the  contraction  of  a  sphincter  muscle 
{orbicularis),  supplied  by  the  facial  nerve;  the  upper  lid  is  raised  by  the 
levator  ])al])ebr(B  superioris,  which  is  supplied  by  the  third  nerve. 

The  Eyeball. 

The  eyeball  or  the  organ  of  vision  (fig.  406)  consists  of  a  variety  of 
structures  which  may  be  thus  enumerated : — 

The  sclerotic,  or  outermost  coat,  envelops  about  five-sixths  of  the 
eyeball:  continuous  with  it,  in  front,  and  occupying  the  remaining 
sixth,  is  the  cornea.  Immediately  within  the  sclerotic  is  the  choroid 
coat,  and  within  the  choroid  is  the  retina.  The  interior  of  the  eyeball 
is  well-nigh  filled  by  the  aqueous  and  vitreous  humors  and  the  crystalline 
lens;  but,  also,  there  is  suspended  in  the  interior  a  contractile  and  per- 
forated curtain, — the  iris,  for  regulating  the  admission  of  light,  and 
behind  at  the  junction  of  the  sclerotic  and  cornea  is  the  ciliary  muscle, 
the  function  of  which  is  to  adapt  the  eye  for  seeing  objects  at  various 
distances. 

Structure  of  the  Sclerotic  Coat. — The  sclerotic  coat  is  composed  of 


THE    SENSES. 


665 


white  fibrous  tissue,  with  some  elastic  fibres  near  the  inner  surface, 
arranged  iu  variously  disposed  and  interlacing  layers.  Many  of  the 
bundles  of  fibres  cross  the  others  almost  at  right  angles.     It  is  strong, 


Ciliary  muscle 

Ciliarj  process 

Canal  of  Petit 

Cornea 

Anterior  cheunber 

JLens 
Iris 

Ciliary  process 
Ciliary  muscle 


Fig.  406.— Seciton  of  the  anterior  four-fifths  of  the  eyeball. 

tough,  and  opaque,  and  not  very  elastic.  It  is  separated  from  the 
choroid  by  a  considerable  lymphatic  space  (pej^ichoroidal),  and  this  is  iu 
connection  with  smaller  spaces  lined  with  endothelium  in  the  sclerotic 
«oat  itself.  There  is  a  lymphatic  space  also  outside  the  sclerotic  sepa- 
rating it  from  a  loose  investment  of  connective  tissue  called  the  capsule 
of  Tenon.  The  innermost  layer  is  made  up  of  loose  connective  tissue 
and  pigment-cells,  and  is  called  the  lamina  fusca. 

Structure  of  the   Cornea. — The  cornea  is  a  transparent  membrane 
which  forms  a  segment  of  a  smaller  sphere  than  the  rest  of  the  eyeball. 


Fig.  407.— Vertical  section  of  rabbit's  cornea,  a,  Anterior  epithelium,  showing  the  different 
shapes  of  the  cells  at  various  depths  from  the  free  surface ;  6,  portion  of  the  substance  or 
cornea.     (Klein.) 

and  is  let  in,  as  it  were,  into  the  sclerotic  with  which  it  is  continuous 
all  round.     It  is  covered  by  laminated  epithelium  («,  fig.  407),  consist- 


66G 


HANDBOOK    OF    PHYSIOLOGY. 


iug  of  seven  or  eight  layers  of  cells,  of  which  the  superficial  ones  are 
flattened  and  scaly,  and  the  deeper  ones  more  or  less  columnar.  Imme- 
diately beneath  this  is  the  anterior  elastic  lamina  of  Bowman,  which 


\\     /'    (' 


■^ig. 


—Horizontal  preparation  of  cornea  of  frog;  showing  the  network  of  branched  cornea- 
corpuscles.     The  ground  substance  is  completely  colorless.     X  400.  (Klein.) 


differs,  only  in  being  more  condensed  tissue,  from  the  general  structure 
of  the  cornea  or  cornea  proper. 

This  latter  tissue,  as  well  as  its  epithelium  is,  in  the  adult,  com- 
pletely destitute  of  blood-vessels;  it  consists  of  an  intercellular  ground- 
substance  of  rather  obscurely  fibrillated  flattened  bundles  of  connective 
tissue,  arranged  parallel  to  the  free  surface,  and  forming  the  boundaries 
of  branched  anastomosing  spaces  in  which  the  cornea-corpuscles  lie, 
l^hese  branched  cornea-corpuscles  have  been  seen  to  creep  by  amoeboid 


Fig,  409.— Surface  view  of  part  of  lamella  of  kitten's  cornea,  prepared  first  with  caustic 
potash  and  then  with  nitrate  of  silver.  fBy  this  method  the  branched  cornea-corpuscles  with 
their  granular  protoplasm  and  large  oval  nuclei  are  brought  out.)  x  450.  (Klein  and  Noble 
Smith.) 

movement  from  one  branched  space  into  another.  At  its  posterior  sur- 
face the  cornea  is  limited  by  the  ^05/^mor  elastic  lamina^  or  mernbrane 
of  Descemet,  similar  in  structure  to  the  anterior  elastic  lamina,  the  inner 
layer  of  which  consists  of  a  single  stratum  of  epithelial  cells  (fig.  410,  d). 
JVerves. — The  nerves  of  the  cornea  are  both  large  and  numerous:  they 


THE    SENSES. 


667 


are  derived  from  the  ciliary  nerves.  They  traverse  the  substance  of  the 
cornea,  in  which  some  of  them  near  the  anterior  surface  break  up  into  axis 
cylinders,  and  their  primitive  fibrillte.  The  latter  form  a  plexus  imme- 
diately beneath  the  epithelium,  from  which  delicate  fibrils  pass  up 
between  the  cells  anastomosing  with  horizontal  branches,  and  forming  a 
deep  intra-epithelial  plexus,  from  which  still  finer  fibres  ascend,  till  near 
the  surface  they  form  a  superficial  intra-epithelial  net-work.  Most  of 
the  primitive  fibrillae  have  a  beaded  or  varicose  appearance.     The  cornea 


Fig.  410. 


Fig.  411. 


Fig.  410.  — Vertical  section  of  ralibit's  cornea,  stained  with  gold  chloride,  e.  Laminated 
anterior  epithelium.  Immediatelv  beneath  tliis  is  the  anterior  elastic  huuina  of  Bowman,  n, 
Nerves  forming  a  delicate  sub-e])ithe!iul  iilexus,  and  sending  iij)  fine  twigs  lictwcen  tlie  ei)ithelial 
cells  to  end  in  a  second  plexus  mi  t lie  five  surface:  (7,  Descemefs  membrane,  c<,)nsisting  of  a 
fine  elastic  layer,  and  a  single  layer  of  epithelial  cells;  the  substance  of  the  cornea,  /,  is  seeu 
to  hf  tibrillated,  and  contains  many  layers  of  Ijranched  corpuscles,  arranged  parallel  to  the  free- 
surface,  and  here  seen  edgewise.     (Schofield.) 

Fig.  411. — Section  tlirough  the  choroid  coat  of  the  human  eye.  1,  elastic  membrane,  struc- 
tiu'eless  or  finely  tibrillated;  3.  choriu-caiiillaris  or  tunica  Ruyschiana;  3,  Propt'r  snlistance  of 
the  choroid  with  large  vessels  cut  through;  4,  suprachoroidea ;  5,  sclerotic.       (Schwalbe.  j 


has  no  blood-vessels  penetrating  its  structure,  nor  yet  lymphatic  vessels 
proper.  It  is  nourished  by  the  circulation  of  lymph  in  the  spaces  in 
which  the  cornea  corpuscles  lie.  These  communicate  freely  and  form  a 
lymph-canalicular  system. 

Strvdure  of  the  Choroid  Coat  {tunica  vasculosa). — This  coat  is 
attached  to  the  inner  layer  of  the  sclerotic  in  front  at  the  corneo-scleral 
junction  and  behind  at  the  entrance  of  the  optic  nerve,  elsewhere  it  is, 


668  HANDBOOK    OF    PHYSIOLOGY, 

connected  to  it  only  by  loose  connective  tissue.  Its  external  coat  is 
formed  chiefly  of  elastic  fibres  and  large  jDigment  corpuscles  loosely 
arranged  and  containing  lymphatic  spaces  lined  with  endothelium.  This 
is  the  sniwaclioroidea.  More  internally  is  a  layer  of  arteries  and  veins 
arranged  in  a  system  of  venous  whorls,  together  with  elastic  fibres  and 


Fig.  412.— Section  through  the  eye  carried  through  the  ciliary  processes.  1,  Cornea;  2,  mem- 
"brane  of  Descemet ;  3,  sclerotic;  3',  corneo-scleral  junction;  4,  canal  of  Schlemm;  5,  vein;  6, 
nucleated  network  on  inner  wall  of  canal  of  Schlemm;  7,  lig.  pectinatum  iridis,  ahc;  8,  iris 
stroma;  9,  pigment  of  iris;  TO,  ciliary  processes;  11,  ciliary  muscle;  12,  choroid  tissue;  13, 
meridional  and  14,  radiating  fibres  of  ciliary  muscle;  15,  ring  muscle  of  Miiller;  16,  circular  or 
angular  bundles  of  ciliary  muscle.     (Schwalbe.) 

pigment  cells.  The  lymphatics,  too,  are  w^ell  developed  around  the 
blood-vessels,  and  there  are  besides  distinct  lymph  spaces  lined  with  en- 
dothelium. Internally  to  this  is  a  layer  of  fine  capillaries,  very  dense  and 
derived  from  the  arteries  of  the  outer  coat  and  ending  in  veins  in  that 
coat.  It  contains  corpuscles  without  j^igment,  and  lymph  spaces  which 
.surround  the  blood-vessels  {meiyibrana  chorio-capillaris) .  It  is  separated 
from  the  retina  by  a  fine  elastic  membrane  {memhrane  of  Bruch),  which 
is  either  structureless  or  finely  fibrillated. 

The  choroid  coat  ends  in  front  in  what  are  called  {,[\e  ciliary  processes 
(fig.  413).  These  consist  of  from  70  to  80  meridionally  arranged 
radiating  plaits,  which  consist  of  blood-vessels,  fibrous  connective  tissue, 
and  pigment  corpuscles.  They  are  lined  by  a  continuation  of  the  mem- 
brane of  Bruch.  The  ciliary  processes  terminate  abruptly  at  the  margin 
of  the  lens.  The  ciliary  muscle  (13,  14  and  15,  fig.  412),  which  may  be 
considered  to  form  part  of  the  processes,  is  situated  between  the 
sclerotic  (at  the  corneo-scleral  junction)  and  the  folds  of  the  ciliary 
processes.  It  is  a  ring  of  muscle,  3  mm.  broad  and  8  mm.  thick,  made 
up  of  fibres  running  in  two  or  three  directions,  {a)  Meridional  fibres 
near  the  sclerotic  and  passing  to  the  choroid ;  {b)  radial  fibres,  passing 
toward  the  centre ;  and  (c)  circular  fibres,  more  internal,  and  constitut- 
ing the  so-called  ciliary  sphincter. 

The  Iris. — The  iris  is  a  continuation  of  the  choroid  inward  beyond 


THE   SEXSES. 


669 


the  ciliary  processes.  It  is  a  fibro-muscular  membrane  perforated  by  a 
central  aperture,  the  pupil.  It  is  made  up  chiefly  of  blood-vessels  and 
connective  tissue  with  pigment  and  unstriated  muscle. 

Posteriorly  are  two  layers  of  pigment  cells  {uvea),  in  which  are  repre- 
sented the  two  layers  of  cells  of  which  the  optic  vesicle  is  originally 
formed,  and  behind  which  are  the  retina  proper  and  its  pigment  layer. 
In  the  iris  representatives  of  both  layers  are  deeply  pigmented.  The 
structure  of  the  iris  proper  is  made  of  connective  tissue  in  front  with 
corpuscles  which  may  or  may  not  be  pigmented,  and  behind  of  similar 
tissue  supporting  blood-vessels  inclosed  in  connective  tissue.  The  pig- 
ment cells  are  usually  well  developed  here,  as  are  also  many  nerve-fibres 
radiating  toward  the  pupil.  Surrounding  the  pupil  is  a  layer  of  circu- 
lar unstriped  muscle,  the  sphincter  pupillm.  In  some  animals  there  are 
also  muscle-fibres  which  radiate  from  the  sphincter  in  the  substance  of 
the  iris  forming  the  dilator  pxpillce.  The  iris  is  covered  anteriorly  b}' 
a  layer  of  endothelium  continued  upon  it  from  the  posterior  surface  of 
the  cornea;  posteriorly  there  is  a  very  fine  layer  which  is  a  continuation 
of  the  membrana  limitans  interna  of  the  retina. 

The  Lens. — The  lens  is  situated  behind  the  iris,  being  inclosed  in  a 
distinct  capsule,  the  posterior  surface  of  which  is  less  thick  than  the 
anterior.  It  is  supported  in  place  by  the  suspensory  ligament,  fused 
to  the  anterior  surface  of  the  capsule.  The  suspensory  ligament  is 
derived  from  the  hyaloid  membrane,  which  incloses  the  vitreous  humor. 

Structure. — The  lens  is  made  up  of  a  series  of  concentric  laminae 
(fig.  414),  which  when  it  has  been  hardened,  can  be  peeled  off  like  the 


Fit;.  413.  Fig.  414. 

Fig  413  —Ciliary  processes,  as  seen  from  behind.  1,  posterior  surface  of  the  iris,  with  the 
sphincter  muscle  of  the  pupil ;  2.  anterior  part  of  the  choroid  coat ;  3,  one  of  the  ciliary  processes, 
of  which  about  seventy  are  represented,     i^.  ,.  r^      v,     ^ 

Fig  414.— Laminated  structure  of  the  crystalline  lens.  The  laminre  are  split  up  after  hara- 
ening  in  alcohol.  1,  the  denser  central  part  or  nucleus;  2,  the  successive  external  layers.  X  4. 
(Arnold.) 

leaves  of  an  onion.     The  laminae  consist  of  long  ribbon-shaped  fibres, 
which  in  the  course  of  development  have  originated  from  cells. 


670 


HANDBOOK    OF    PHYSIOLOGY. 


The  lens  itself  is  made  up  of  transparent  longitudinal  fibres,  hexag- 
onal and  prismatic,  thickened  posteriorly.  Those  fibres  at  the  cortex 
have  nuclei  and  are  smooth,  those  near  the  centre  are  without  nuclei 
and  have  serrated  edges.  The  fibres  are  united  together  by  a  scanty 
amount  of  cement  substance. 

The  arrangement  is  such  that  no  fibres  run  the  whole  half  of  the 
lens,  from  front  to  back,  since,  if  a  fibre  starts  near  the  anterior  pole, 
its  other  end  is  far  from  the  posterior  pole  (fig.  415.) 

The  epithelium  of  the  lens  consists  of  a  layer  of  cubical  cells  anteriorly, 
which  merges  at  the  equator  into  the  lens  fibres.  The  development  of 
the  lens  explains  this  transition.  The  lens  at  first  consists  of  a  closed 
sac  composed  of  a  single  layer  of  epithelium.  The  cells  of  the  posterior 
part  soon  elongate  forward  and  obliterate  the  cavity,  the  anterior  cells  do 


rig.  415.— Meridional  section  through  the  lens  of  a  rabbit.     1,  Lens  capsule;  2,  epithelium  of 
lens;  3,  transition  of  the  epithelium  into  the  fibres;  4,  lens  fibres.     (Bubuchin.) 


not  grow,  but  at  the  edge  they  become  continuous  with  the  posterior 
cells,  which  are  gradually  developed  into  fibres.  The  lens  contains 
globulin  or  crystullin,  but  no  native-albumin;  it  also  contains  choles- 
terin.  The  capsule  is  a  homogeneous  transparent  elastic  membrane. 
The  hardest  portion  of  the  lens  is  that  which  is  most  internal.  It  forms 
the  so-called  nucleus  of  the  lens  (fig.  414,  1). 

Corneoscleral  junction. — At  this  junction  the  relation  of  parts  (fig. 
412)  is  so  important  as  to  need  a  short  description.  In  the  neighbor- 
hood, the  iris  and  ciliary  processes  join  with  the  cornea.  The  proper 
substance  of  the  cornea  and  tlie  posterior  elastic  lamina  become  continuous 
with  the  iris,  at  the  angle  of  the  iris,  and  the  iris  sends  forward  processes 
toward  the  posterior  elastic  lamina,  forming  the  ligfonentum  pectinafu7n 
iridis,  and  these  join  with  fibres  of  the  elastic  lamina.  The  endothelial 
covering  of  the  posterior  surface  of  the  cornea  is,  as  we  have  seen,  con- 
tinuous over  the  front  of  the  iris.  At  the  iridic  angle,  the  compact 
inner  substance  of  the  cornea  is  looser,  and  between  the  bundles  are 
lymph  spaces  filled  with  fluid,  called  the  spaces  of  Fontana.  They  are 
little  developed  in  the  human  cornea.  Where  the  cornea  and  sclerotic 
join,  there  is  an  intermediate  part  which  resembles  both,  but  which  is 
still  not  transparent,  as  the  internal  part  remains  scleral  in  structure. 

The  spaces  which  are  present  in  the  broken  up  bundle.s  of  corneal 
tissue  at  the  angle  of  the  iris,  are  continuous  with  the  larger  lymphatic 


THE    SEXSES.  671 

space  of  the  anterior  chamber.  Above  the  angle  at  the  corneo-scleral 
junction  is  a  canal,  which  is  called  the  ca7ial  of  Schlemm.  It  is  a  lym- 
phatic channel,  but  appears  to  be  in  communication  with  blood-vessels, 
as  it  may  be  under  certain  circumstances  filled  with  blood. 

Structure  of  the  Retina. — The  retina  (fig,  416)  is  a  delicate  membrane, 
concave  with  the  concavity  directed  forward  and  apparently  ending  in 
front,  near  the  outer  part  of  the  ciliary  jjrocesses,  in  a  finely  notched 
edge, — the  or  a  serrata,  but  really  represented  to  the  very  margin  of  the 
pupil.  Semitransparent  when  fresh,  it  soon  becomes  clouded  and  opaque, 
with  a  pinkish  tint  from  the  blood  in  its  minute  vessels.  It  results  from 
the  sudden  spreading  out  or  expansion  of  the  optic  nerve,  of  whose  ter- 


Fig.  416.— A  section  of  the  retina,  choroid,  and  part  of  the  sclerotic,  moderately  magnified : 
a,  membrana  limitans  interna:  b.  nerve-fibre  layer  tra%-ersed  by  Miiller"s  siistentacular  fibres  (of 
the  connective  tissue  system) ;  c,  ganglion-cell  layer;  d,  molecular  layer;  e,  internal  nuclear  layer; 
/,  internuclear  layer ;'(/,  external  nuclear  layerV /i,  membrana  limitans  externa,  nmniug  along 
the  lower  part  of  i,  the  layer  of  rods  and  cones;  A-,  pigment  cell  layer;  Im,  internal  and  external 
vascular  portions  of  the  choroid,  the  tu-st  containing  capillaries,  the  second  larger  blood-vessels, 
cut  in  transverse  section;  n,  sclerotic.     (W.  Pye.) 

minal  fibres,  apparently  deprived  of  their  external  white  substance,  to- 
gether with  nerve  cells,  it  is  essentially  composed. 

Exactly  in  the  centre  of  the  retina  is  a  round  yellowish  elevated  spot, 
abput  2T-  of  an  inch  (1  mm.)  in  diameter,  having  a  minute  depression  in 
the  centre,  called  after  its  discoverer  the  macula  lutea,  or  yellow  sjjot  of 
Scemmering.  The  minute  depression  in  its  centre  is  called  the  fovea 
centralis.     About  ^  of  an  inch  (2.5  mm.)  to  the  inner  side  of  the  yel- 


G72  IIANDHOOK    OF    PHYSIOLOGY. 

low  spot,  is  the  point  at  which  the  optic  uerve  enters  the  eyeball,  and 
begins  to  spread  out  its  fibres  into  the  retina. 

The  optic  nerve  passes  forward  from  the  ventral  surface  of  the  cere- 
brum toward  the  orbit  inclosed  in  prolongations  of  the  membranes,  the 
dura  mater,  arachnoid  and  pia  mater,  which  cover  the  brain.  The 
external  sheath  at  the  entrance  of  the  nerve  into  the  eyeball  becomes 
continuous  with  the  sclerotic,  which  at  this  part  is  perforated  by  holes 
to  allow  of  passage  of  the  optic  nerve  fibres  and  the  pia  mater  with 
the  choroid,  the  perforated  part  being  the  lamina  ci'ibrosa.  The 
pia  mater  here  becomes  incomplete,  and  the  subarachnoid  and  the 
superarachnoid  spaces  become  continuous.  The  pia  mater  sends  in  pro- 
cesses into  the  nerve  to  support  the  fibres.  The  fibres  of  the  nerve- 
themselves  are  exceedingly  fine,  and  are  surrounded  by  the  myelin  sheath, 
but  do  not  possess  the  ordinary  external  nerve  sheath.  As  they  pass  into 
the  retina  they  lose  their  myelin  sheaths  and  jDroceed  as  axis  cylinders. 
Neuroglia  supports  the  nerve  fibres  in  the  optic  nerve  trunk.  In  the 
centre  of  the  nerve  is  a  small  artery,  the  arteria  centralis  retinm.  The 
number  of  fibres  in  the  optic  nerve  is  said  to  be  upward  of  500,000, 
The  axis  cylinders  pass  on  to  the  retina,  turning  over  the  edges  of 
the  porus  opticus^  to  be  distributed  on  the  inner  surface  of  the  retina, 
as  far  as  the  ora  serrata,  as  a  layer  of  optic  nerve-fibres,  and  separated 
from  the  hyaloid  membrane  which  contains  the  vitreous  humor  to  be 
presently  described,  by  a  very  thin  layer,  the  membrana  limitans  interna. 

The  retina  consists  of  certain  nervous  elements  arranged  in  several 
layers,  and  supported  by  a  very  delicate  connective  tissue. 

The  following  ten  layers,  from  within  outward,  are  usually  to  be 
distinguished  in  a  vertical  section  (figs.  416,  417,  417  a). 

1.  Membrana  limitans  interna:  a  delicate  membrane  in  contact  with 
the  vitreous  humor.  This  is  formed  by  the  junction  laterally  of  the 
base  of  the  sustentacular  or  supporting  fihres  of  3Iilllcr,  which  ajipear  to- 
bear  the  same  relation  to  the  retina  as  the  neuroglia  does  to  the  brain. 
The  supporting  character  of  these  fibres  may  be  seen  in  fig.  417. 

2.  Optic  nerve  fibres. — This  layer  is  of  very  varying  thickness  in' 
different  parts  of  the  retina :  it  consists  of  non-medullated  fibres  which 
interlace,  and  some  of  which  are  continuous  with  processes  of  the  large- 
nerve-cells  forming  the  next  layer.  The  fibres  are  supjjorted  by  the 
sustentacular  fibres.  They  become  less  and  less  numerous  anteriorly  and 
end  at  the  ora  serrata. 

3.  Layer   of  ganglionic   corpuscles,   consisting  of    large    multipolar- 
nerve-cells  with  large  and  round  nuclei,  sometimes  forming  a  single- 
layer.      In  some  parts  of  the  retina,  especially  near  the  macula  lutea^ 
this  layer  is  very  thick,  consisting  of  several  distinct  strata  of  nerve-cells. 
These  cells  lie  in  the  spaces  of  a  connective-tissue  framework.     They 


THE    SENSES. 


673 


are  arranged  with  their  single  axis  cylinder-processes  inward.  These 
pass  into  and  are  continuous  with  the  layer  of  optic  nerve-fibres.  Ex- 
ternally the  cells  send  oif  several  branched  processes  which  pass  into  the 
next  layer  and  are  lost  to  view,  these  having  become  by  a  further 
branching,  exceedingly  fine. 

4.   Inner  molecular  layer. — This  presents  a  finely  granulated  appear- 
ance.    It  consists  of  a  punctiform  connective  tissue  traversed  by  number- 


inner  limb  ■ — -/ 
of  rod. 


Rod  fibre. 


Inner  molec- 
ular layer. 


Fig.  417. 


Fig.  417  a. 


Fig.  417.— Diagram  showing  the  sustentaciilar  fibres  of  the  retina  fibre-basket  above  the  ex- 
ternal lumlmr  membrane,  m,  nucleus  of  the  fibre;  i\  base  of  the  fibre.  (From  MacKendrick 
after  Stcihr.) 

Fig.  417  A.— Diagram  showing  the  nervous  elements  of  retina.  1,  nerve  fibre  to  ganglion 
cell ;  2,  pi-ocesses  of  ganglion  cell  going  outward ;  3,  nerve  fibre  passing  direct  to  granule  in  inner 
nuclear  layer ;  4,  process  of  ganglion  cell  to  granule;  5,  fibre  from  cone-granule  breaking  up 
into  fibrils  which  are  connected  with  rod  and  cone  fibrils.     (From  MacKendrick,  after  Stohr.) 

less  very  fine  fibrillar  processes  of  the  nerve-cells  and  the  minute  branch- 
ings of  the  processes  of  the  nuclear  cells  of  the  next  layer. 

5.  Inner  nuclear  layer. — This  consists  chiefly  of  numerous  small 
round  cells,  with  a  very  small  quantity  of  protoplasm  surrounding  a 
large  ovoid  nucleus;  they  are  generally  bipolar,  giving  oif  one  process 
outward  and  another  inward.  They  greatly  resemble  the  ganglion  cor- 
puscles of  the  cerebellum,  and  are  of  three  kinds  at  least:  the  most 
internal,  is  small  and  round,  sending  in  several  processes  into  the  inner 
molecular,  but  none  in  the  other  direction ;  the  central,  sends  a  long  and 
varicose  filament  to  break  up  into  minute  branchings  in  the  inner 
43 


674  HANDBOOK    OF    PHYSIOLOGY. 

molecular  layer  and  two  in  the  other  direction,  and  produce  in  the  in- 
ternuclear  layer  a  very  fine  plexus  of  fibrils,  while  the  external,  a  rather 
larger  cell  which  is  placed  with  its  long  axis  transverse,  sends  downward 
a  long  and  oblique  process  which  terminates  in  minute  branchings  at  the 
internal  part  of  the  inner  molecular  layer,  and  two  thick  processes  which 
end  in  a  similar  arborescence  in  the  internuclear  layer.  Besides  these 
there  are  large  oval  nuclei  (fig.  417)  belonging  to  the  sustentacular 
connective  tissue  fil^res. 

6.  Intergranular,  internuclear,  or  outer  molecular  layer. — This  layer 
closely  resembles  the  inner  molecular  layer,  but  is  much  thinner.  It 
consists  of  finely  dotted  connective  tissue  with  nerve  fibrils,  and  consists 
of  the  branchings  of  the  rod  and  cone  fibres  on  the  one  hand  and  of  the 
inner  nuclear  cells  on  the  other. 

7.  External  nuclear  layer. — This  layer  consists  of  small  cells  resem- 
bling those  of  the  internal  granular  layer;  they  have  been  classed  as  rod 
and  cone  fibres,  according  as  they  are  connected  with  the  rods  and 
cones  respectively,  and  will  be  described  with  them.  They  are  lodged 
in  the  meshes  of  a  connective  tissue  framework.  Both  the  internal  and 
external  granular  layer  stain  very  rapidly  and  deeply  with  hasmatoxylin, 
while  the  rod  and  cone  layer  remains  quite  unstained. 

8.  Memhrana  limitans  externa. — A  delicate,  well-defined  membrane, 
clearly  marking  the  internal  limit  of  the  rod  and  cone  layer,  and  made 
up  by  the  junction  of  the  base  of  the  sustentacular  fibres  externally. 
Small  hair-like  processes  project  outward  between  the  rods  and  cones  to 
support  them. 

9.  Layer  of  rods  and  cones. — This  layer  is  considered  to  be  the  most 
important  of  all  those  of  which  the  retina  consists.  It  is  believed  to  be 
continuous  directly  or  indirectly  with  the  nervous  layers  proper.  It 
consists  of  bodies  more  or  less  alike,  but  differing  in  details  somewhat, 
arranged  at  right  angles  to  the  external  limitans  membrane,  and  sup- 
ported by  hair-like  j)rocess  {basket)  proceeding  from  the  latter  for  a 
short  distance. 

The  rods. — Each  rod  (fig.  417  a)  is  made  up  of  two  parts,  very  differ- 
ent in  structure,  called  the  outer  and  inner  limbs.  The  outer  limb  of  the 
rods  is  about  30//  long  and  2,a  broad,  is  transparent,  and  doubly  refrac- 
tive. It  is  said  to  be  made  up  of  fine  superimposed  discs.  It  stains 
with  osmic  acid  but  not  with  hcematoxylin,  and  resembles  in  some  ways 
the  myelin  sheath  of  a  medullated  nerve.  It  swells  up  on  exposure  to 
light,  and  is  part  of  the  layer  in  which  the  pigment  called  visual  piirple 
is  found.  The  inner  limb  is  about  as  long  but  slightly  broader  than  the 
outer,  is  longitudinally  striated  at  its  outer  and  granular  at  its  inner 
part.  It  stains  with  hasmatoxylin  but  not  with  osmic  acid.  Each  rod 
so  constructed  is  connected  internally  with  a  rod  fibre,  very  fine,  but 


THE   SENSES.  675 

perhaps  here  and  there  varicose;  in  the  middle  of  the  fibre  is  a  nuclear 
body,  or  rod  granule,  striped  broadly  transversely,  and  situated  about 
the  middle  of  the  external  nuclear  layer;  the  internal  end  of  the  rod 
fibre  terminates  in  minute  branchings  in  the  internuclear  layer. 

The  cones. — Each  cone  (tig.  417  a),  like  the  rods,  is  made  up  of  two 
limbs,  outer  and  inner.  The  outer  limb  is  tapering  and  not  cylindrical 
like  the  corresponding  jDart  of  the  rod,  and  about  one-third  only  of  its 
length,  but  it  resembles  this  in  structure.  There  is,  however,  no  visual 
purple  found  in  the  cone.  The  inner  limb  of  the  cone  is  broader  in  the 
centre,  each  cone  is  in  connection  bv  its  internal  end  with  a  cone  fibre, 
which  has  much  the  same  structure  as  the  rod  fibre,  but  is  much  stouter 
and  has  its  nucleus  nearer  the  external  limitans  membrane.  Its  inner 
end  terminates  in  much  the  same  way. 

In  the  rod  and  cone  layer  of  birds,  the  cones  usually  predominate 
largely  in  number,  whereas  in  man  the  rods  are  by  far  the  more  numer- 
ous, except  in  the  fovea  centralis,  where  cones  only  are  present,  as  is 
the  case  at  the  anterior  ]iart  of  the  retina  near  the  ora  serrata.  The 
number  of  cones  has  been  estimated  at  3,000,000.  In  nocturnal  birds, 
however,  such  as  the  owl,  only  rods  are  present,  and  the  same  appears 


Fig.  418.— The  posterior  half  of  the  retina  of  the  left  eye,  viewed  from  before;  s,  the  cut 
edge  of  the  sclerotic  coat :  c/i,  the  choroid;  r,  the  retina;  in  the  interior  at  the  middle  the 
macula  lutea  with  the  depression  of  the  fovea  centralis  is  represented  by  a  slight  oval  shade; 
toward  the  left  side  the  light  spot  indicates  the  coUiculus  or  eminence  at  the  entrance  of  the 
optic  nerve,  from  the  centre  of  which  the  arteria  centralis  is  seen  spreading  its  branches  into 
the  retina,  leaving  the  part  occupied  by  the  macula  comparatively  free.     (After  Henle. ) 

to  be  the  case  in  many  nocturnal  and  burrowing  mammalia,  e.g.,  bat, 
hedge-hog,  mouse,  and  mole. 

10.  Pigment-cell  lager,  which  was  formerly  considered  part  of  the 
choroid.  It  consists  of  cells  Avhicli  cover  and  entirely  surround  the 
outer  limbs  of  the  rods  and  cones. 

Differences  in  Structure  of  different  j^arts. — Toward  the  centre  of  the 
macula  lutea  all  the  layers  of  the  retina  become  greatly  thinned  out  and 


G76  HANDBOOK    OF    PHYSIOLOGY. 

almost  disappear,  except  the  rod  and  cone  layer,  which  considerably  in- 
creases in  thickness  but  at  the  fovea  centralis  comes  to  consist  almost 
entirely  of  long  slender  cones  and  cone-fibres,  which  curve  toward  the 
periphery.  They  are  supported  by  neuroglia,  which  is  also  found  inter- 
nally as  a  thin  layer,  the  rods  being  absent.  There  are  capillaries  here, 
but  none  of  the  larger  branches  of  the  retinal  arteries. 

Toward  the  edge  of  the  macula  lutea,  not  only  are  all  the  layers 
present,  but  the  ganglionic  layer  consists  of  many  strata  of  cells  (7  or  8), 
and  with  this  increase  there  is  also  an  increase  in  the  thickness  of  the 
inner  nuclear  layer.  The  cells  are  generally  bipolar.  Toward  the  centre 
the  layers  diminish  in  this  order:  optic  nerve-fibres,  ganglionic  layer, 
inner  molecular  layer,  and  inner  nuclear  layer.  The  rods  grow  scanty 
and  then  are  absent. 

At  the  ora  serrata  the  layers  are  not  perfect  and  disappear  in  this 
order:  nerve-fibres  and  ganglion  cells,  then  the  rods,  leaving  only  the 
inner  limbs  of  the  cones,  these  cease,  then  the  outer  molecular  layer, 
the  inner  and  outer  nuclear  layers  coalesce,  and  then  the  inner  molecular 
layer.     The  Miillerian  fibres  persist. 

At  the  pars-ciliaris  retinre,  the  retina  is  represented  by  a  layer  of 
columnar  cells,  derived  from  the  fusion  of  the  nuclear  layers.  The  cells 
are  covered  by  the  membrana  limitans  interna,  and  externally  are  in 
contact  with  the  pigment  layers  of  the  retina,  which  is  continued  over 
the  ciliary  processes. 

The  cliamiers  of  the  eye. — The  r/w/e/'ior  chamber  is  the  space  behind 
the  cornea  and  in  front  of  the  lens.  It  is  filled  with  aqueous  humor, 
which  is  essentially  a  diluted  lymph  with  a  small  amount  of  proteid  in 
it,  viz. ,  of  fibrinogen,  serum-globulin,  and  septum-albumin.  It  is  seldom 
spontaneously  coagulable.  It  contains  salts,  chiefly  sodium  chloride, 
sometimes  a  substance  which  reduces  copper  suljohate,  but  is  not  sugar, 
and  a  trace  of  urea  and  sarcolactic  acid.  There  are  no  formed  elements 
in  the  fluid.  It  is  stated  that  the  aqueous  humor  is  secreted  by  glands 
in  the  ciliary  region,  but  the  cavity  is  itself  obviously  a  lymph  sac. 

The  posterior  chamber,  or  that  behind  the  lens,  contains  the  vitreous 
humor,  which  is  a  semifluid  substance  contained  in  the  meshes  of  an 
indistinct  connective  tissue.  It  is  inclosed  in  a  distinct  membrane 
called  memhrana  hyaloidea,  from  the  anterior  surface  of  this  membrane 
at  the  ora  serrata  fibres  pass  off  to  the  back  of  the  lens  capsule,  forming 
an  incomplete  canal,  called  the  Canal  of  Petit,  the  membrane  itself  being 
the  Zonule  of  Zinn.  The  hyaloid  membrane  separates  the  vitreous  from 
the  retina. 

Blood-vessels  of  the  Eyeball. — The  eye  is  very  richly  supplied 
with  blood-vessels.  In  addition  to  the  conjunctival  vessels  which  are 
derived  from  the  palpebral  and  lachrymal  arteries,  there  are  at  least  two 


THE   SENSES.  677 

other  distinct  sets  of  vessels  supplying  the  tunics  of  the  eyeball.  (1)  The 
vessels  of  the  sclerotic,  choroid,  and  iris,  and  (2)  the  vessels  of  the  retina. 
(1. )  These  are  the  short  and  long  2Josterior  ciliary  arteries  which  pierce 
the  sclerotic  in  the  posterior  half  of  the  eyeball,  and  the  anterior  ciliary 
which  enter  near  the  insertions  of  the  recti.  These  vessels  anastomose 
and  form  a  very  rich  choroidal  plexus;  they  also  supply  the  iris  and 


Fig.  419. — Section  through  the  macula  hitea  and  fovea  centralis  of  human  retina,     a,  fovea;    6, 
descent  of  the  macula  toward  fovea.     The  numbers  indicate  the  layers  of  the  retina.     (Kuhnt.) 

ciliary  processes,  forming  a  very  highly  vascular  circle  round  the  outer 
margin  of  the  iris  and  adjoining  portion  of  the  sclerotic. 

The  distinctness  of  these  vessels  from  those  of  the  conjunctiva  is 
well  seen  in  the  difference  between  the  bright  red  of  blood-shot  eyes 
(conjunctival  congestion),  and  the  pink  zone  surrounding  the  cornea 
which  indicates  deep  seated  ciliary  congestion. 

(2.)  The  retinal  ve.'^sels  (fig.  418)  are  derived  from  the  arteria  cen- 
tralis retinee,  which  enters  the  eyeball  along  the  centre  of  the  optic 
nerve.  They  ramify  all  over  the  retina,  chiefly  in  its  inner  layers. 
They  can  be  seen  by  direct  ophthalmoscopic  examination. 

The  Optical  Apparatus. 

The  optical  apparatus  may  be  supposed,  for  the  sake  of  description, 
to  consist  of  several  parts.  Firstly^  of  a  system  of  transparent  refract- 
ing surfaces  and  media  by  means  of  which  images  of  external  objects  are 
brought  to  a  focus  upon  the  back  of  the  eye;  and  secondly^  of  a  sensitive 
screen,  the  retina,  which  is  a  specialized  termination  of  tlie  optic  nerve, 
capable  of  being  stimulated  by  luminous  objects,  and  of  sending  through 
the  optic  nerve,  such  an  impression  as  to  produce  in  the  brain  visual 
sensations.  To  these  main  parts  may  be  added,  tMrdly,  an  apparatus 
for  focussing  objects  at-different  distances  from  the  eye,  called  accommo- 
dation. Even  this  does  not  complete  the  description  of  the  whole  organ 
of  vision,  since  both  eyes  are  usually  employed  in  vision,  and  fourthly, 
an  arrangement  exists  by  means  of  which  the  eyes  may  be  turned  in 
the  same  direction  by  a  system  of  muscles,  so  that  binocular  vision  is 
possible. 


678  HANDBOOK    OF    PHYSIOLOGY. 

The  arrangement  of  the  optic  nerve-fibres,  and  of  the  continuation 
of  these  backward  in  the  optic  chiasma,  and  thence  to  special  districts  of 
the  brain,  have  already  been  discussed. 

The  eye  may  be  compared  to  a  photographic  camera.,  and  the  trans- 
parent media  corresponds  to  the  photographic  lens.  In  such  a  camera 
images  of  external  objects  are  thrown  upon  a  ground-glass  screen  at  the 
back  of  a  box,  the  interior  of  which  is  jjainted  black.  In  the  eye,  the 
camera  proper  is  represented  by  the  eyeball  with  its  choroidal  pigment, 
the  screen  by  the  retina,  and  the  lens  by  the  refracting  media.  In  the 
case  of  the  camera,  the  screen  is  enabled  to  receive  clear  images  of  objects 
at  different  distances,  by  an  apparatus  for  focussing.  The  corresponding 
contrivance  in  the  eye  is  the  accommodation. 

The  iris,  which  is  capable  of  allowing  more  or  less  light  to  pass  into 
the  eye,  corresponds  with  the  different  sized  diaphragms  used  in  the 
protographic  apparatus. 

Refractive  media  and  surfaces. — At  first  sight  it  would  seem  as  if  the 
refracting  apparatus  of  the  eye  were  very  complicated,  seeing  that  it 
consists  of  so  many  parts.  These  parts  are :  the  anterior  surface  of  the 
cornea  itself,  the  posterior  surface  •  of  the  cornea,  the  aqueous  humor, 
the  anterior  surface  of  the  lens,  the  substance  of  the  lens  itself  (which  is 
also  unequally  refractive),  the  posterior  surface  of  the  lens,  and  the  vit- 
reous humor.  Thus  there  are  four  surfaces,  and  at  least  including  the 
air,  five  media.  For  all  practical  purposes,  however,  these  may  be  re- 
solved into  a  somewhat  simpler  form,  and  the  cornea  may  be  considered 
as  one  surface,  the  anterior,  and  one  medium ;  the  aqueous  and  vitreous 
humors  as  one  medium ;  the  lens,  as  two  surfaces  and  one  medium.  It 
will  be  as  well  to  consider  the  laws  which  govern  the  refraction  of  light 
under  such  circumstances. 

In  its  simplest  form,  we  may  consider  the  refraction  through  a  simple 
transparent  spherical  surface,  separating  two  media  of  different  density. 

The  rays  of  light  which  fall  upon  the  surface  exactly  perpendicularly 
do  not  suffer  refraction,  but  pass  through,  cutting  the  optic  axis  (0  A, 
fig.  420),  a  line  which  passes  exactly  through  the  centre  of  the  surface, 
at  a  certain  point,  the  nodal  point  (fig.  420,  N),  or  centre  of  curvature. 
Any  rays  which  do  not  so  strike  the  curved  surface  are  refracted  toward 
the  optical  axis.  Eays  which  impinge  upon  the  sj)herical  surface  paral- 
lel to  the  optical  axis,  will  meet  at  a  point  behind,  upon  the  said  axis 
which  is  called  the  chief  posterior  focus  (fig.  420,  FJ ;  and  again  there 
is  a  point  in  the  optical  axis  in  front  of  the  surface,  rays  of  light  from 
which  so  strike  the  surface  that  they  are  refracted  in  a  line  parallel  with 
the  axis  df";  such  a  point  (fig.  420,  FJ  is  called  the  chief  anterior 
focus.  The  optic  axis  cuts  the  surface  at  what  is  called  the  j^rincipal 
point. 


THE    SENSES.  679 

It  is  quite  obvious  that  the  eye,  even  in  the  simplified  form  above 
indicated,  is  a  much  more  complicated  optical  apparatus  than  the  one 
described  in  the  figure.     It  is,  however,  possible  to  reduce  the  refractive 


Fig.  420.— Diagram  of  a  simple  optical  system  (after  M.  Foster).  The  curved  surface,  6,  d, 
is  supposed  to  separate  a  less  refractive  medium  toward  the  left  from  a  more  refractive  mediimi 
toward  the  right. 

surfaces  and  media  to  a  simpler  form  vehen  the  refractive  indices  of  the 
different  media  and  the  curvature  of  each  surface  are  known.  All  of 
these  data  have  been  very  carefully  collected.     They  are  as  follows: — 

Index  of  refraction  of  aqueous  and   vitreous  =  1.3365 

lens        .         .         .         .  =  1.4371 

Radius  of  curvature  of  cornea  .         .         .  =  7. 829  mm. 

"  "  anterior  surface  of  lens  =  10  " 

posterior  "  =  6  " 

Distance  from  anterior  surface  of  cornea  and 

anterior  surface  of  lens        .         .         .         .  =  3.6        " 
Distance  from  posterior  surface  of  cornea  and 

posterior  surface  of  lens        .         .         .         .  =  7. 3        " 

With  these  data,  it  has  been  found  comparatively  easy  to  reduce  by 
calculation  the  different  surfaces  of  different  curvatures,  into  one  mean 
curved  surface  of  known  curvature,  and  the  differently  refracting  media 
into  one  mean  medium  the  refractive  power  of  which  is  known. 

The  simplest  so-called  schematic  eye  formed  upon  this  principle, 
suggested  by  Listing  as  the  reduced  eye,  lias  the  following  dimensions : — 

From  anterior  surface  of  cornea  to  the  princi- 
pal point =  2.3448  mm. 

From  the  nodal  point  to  the  posterior  surface 

of  lens =  .4764  " 

Posterior  chief  focus  lies  behind  cornea  .         .  =  22.8237  " 

Anterior  chief  focus  in  front  of  cornea    .         .  =  12.8326  " 

Radius  of  curvature  of  ideal  surface         .         .  =  5. 1248  " 

In  this  reduced  or  simplified  eye  the  principal  posterior  focus,  about 
23  mm.  behind  the  spherical  surface,  would  correspond  to  the  position 
of  the  retina  behind  anterior  surface  of  cornea.  The  refracting  surface 
would  be  situated  about  midway  between  the  posterior  surface  of  the 
cornea  and  the  anterior  surface  of  the  lens. 

The  optical  axis  of  the  eye  is  a  line  drawn  through  the  centres  of 


680 


HANDBOOK    OF    PHYSIOLOGY. 


curvature  of  the  cornea  and  lens,  prolonged  backward  to  touch  the  retina 
between  the  porus  opticus  and  fovea  centralis,  and  this  differs  from  the 
visual  axis  which  passes  through  the  nodal  point  of  the  reduced  eye  to 


Fig.  421.  —Diagram  of  tlie  optical  angle. 

the  fovea  centralis;  this  forms  an  angle  of  5°  with  the  optical  axis. 
By  some  the  oj^tical  axis  and  the  visual  axis  are  considered  to  be  iden- 
tical. The  visual  or  optical  angle  is  included  between  the  lines  drawn 
from  the  borders  of  any  object  to  the  nodal  point;  if  the  lines  be  pro- 


Fig.  421  A. 


-Diagram  of  the  method  of  the  formation  of  an  inverted  image  exactly  focussed 
upon  the  retina.     The  dotted  line  is  the  ideal  surface  of  curvature. 


longed  backward  they  include  an  equal  angle.  It  has  been  shown  by 
Helmholtz  that  the  smallest  angular  distance  between  two  points  which 
can  be  appreciated  =  50  seconds,  the  size  of  the  retinal  image  being 
3.65//;  this  practically  corresponds  to  the  diameter  of  the  cones  at  the 


Fig.  422.— Diagram  of  the  course  of  a  ray  of  light,  to  show  how  a  blurred  or  indistinct  image 
is  formed  if  the  object  be  not  exactly  focussed  upon  retina.  The  surface  C  C  should  be  sup- 
posed to  represent  the  ideal  curvature.  The  nodal  point  should  be  nearer  the  posterior  surface 
of  lens  as  in  fig.  421  a. 

fovea  centralis  which  =  3,a,  the  distance  between  the  centres  of   two  ad- 
jacent cones  being  =  4//. 

The  image  of  an  object,  then,  is  thus  formed  upon  the  retina.     An 


THE    SENSES,  681 

object  may  be  considered  as  a  series  of  jDoints,  from  each  of  which  a 
pencil  of  light  diverges  to  the  eye,  and  this  pencil  has  for  its  centre  or 
axis,  a  ray  which  impinging  upon  the  refractive  surface  j)erj)endicularly 
to  the  surface  is  not  refracted,  but  passes  through  the  nodal  point,  and 
is  prolonged  backward  to  the  retina,  whereas  the  diverging  rays  are  also 
made  to  converge  to  a  principal  posterior  focus  behind  the  lens,  or  the 
chief  axis  of  the  pencil  of  light  proceeding  from  the  point  in  question, 
and  this  focus,  if  the  image  is  to  be  clear,  should  fall  on  the  retina. 

Thus  from  each  point  of  an  object  a  corresponding  image  is  formed 
on  the  retina,  so  that  an  image  of  the  distal  object  is  produced.  It  is 
an  inverted  image.  Whether  the  image  is  blurred  or  not  depends  upon 
the  refractive  power  of  the  media,  and  upon  the  distance  of  the  anterior 
surface  of  the  cornea  from  the  retina.  If  the  refractive  media  are  too 
powerful,  or  the  eye  too  long,  the  image  is  formed  in  front  of  the  retina 
(fig.  422) ;  if  the  reverse,  the  image  is  formed  behind  the  retina,  and  in 
both  cases  an  indistinct  and  blurred  image  is  the  result. 

Accommodation. 

The  distinctness  of  the  image  formed  upon  the  retina,  is  mainly  de- 
pendent on  the  rays  emitted  by  each  luminous  point  of  the  object  being 
brought  to  a  perfect  focus  upon  the  retina.  If  this  focus  occur  at  a 
point  either  in  front  of,  or  behind  the  retina,  indistinctness  of  vision 
ensues,  in  the  way  we  have  already  described,  with  the  production  of  a 
halo.  The  focal  distance,  i.e.,  the  distance  from  a  lens  of  the  point  at 
which  the  luminous  rays  are  collected,  besides  being  regulated  by  the 
degree  of  convexity  and  density  of  the  lens,  varies  with  the  distance  of 
the  object  from  the  lens,  being  greater  as  this  is  shorter,  and  vice  versd. 
Hence,  since  objects  placed  at  various  distances  from  the  eye  can  within 
a  certain  range,  different  in  different  persons,  be  seen  with  almost  equal 
distinctness,  there  must  be  some  provision  by  which  the  eye  is  enabled  to 
adapt  itself,  so  that  whatever  length  the  focal  distance  may  be,  the  focal 
point  may  always  fall  exactly  upon  the  retina. 

This  power  of  accommodation,  or  the  adaptation  of  the  eye  to  vision 
at  different  distances,  has  received  the  most  varied  explanations.  It  is 
obvious  that  the  effect  might  be  produced  in  either  of  two  ways,  viz.,  {a) 
by  altering  the  convexity,  and  thus  the  refracting  power,  either  of  the 
cornea  or  of  the  lens;  or  (Z>)  by  changing  the  position  either  of  the 
retina  or  of  the  lens,  so  that  whether  the  object  be  near  or  distant,  the 
focal  points  to  which  the  rays  are  converged  by  the  lens  may  always  fall 
exactly  on  the  retina.  The  amount  of  either  of  these  changes,  which 
would  be  required  in  even  the  widest  range  of  vision,  would  be  extremely 
small.     For,  from  the  refractive  powers  of  the  media  of  the  eye,  the  dif- 


682  HANDBOOK    OF    PHYSIOLOGY. 

f erence  between  the  focal  distances  of  the  images  of  an  object  at  a  distance, 
and  of  one  at  the  distance  of  four  inches,  is  only  about  0,143  of  an  inch 
(3.5  mm.).  On  this  calculation  the  change  in  the  distance  of  the  retina 
from  the  lens  required  for  vision  at  all  distances,  supposing  the  cornea 
and  lens  to  remain  the  same,  Avould  not  be  more  than  about  one  line. 

The  adaptation  of  the  eye  for  objects  at  different  distances  is  pri- 
marily due  to  a  varying  shape  of  the  lens,  its  front  surface  becoming 
more  or  less  convex,  according  as  the  distance  of  the  object  looked  at  is 
near  or  far.  The  nearer  the  object,  the  more  convex,  up  to  a  certain 
limit,  the  front  surface  of  the  lens,  and  vice  versa;  the  back  surface  tak- 
ing little  or  no  share  in  the  production  of  the  effect  required.  And  this 
surface,  which  during  rest  is  more  convex  than  the  anterior,  becomes 
the  less  convex  of  the  two  during  accommodation.  The  following  simple 
experiment  illustrates  this  point:  If  a  lighted  candle  be  held  a  little  to 
one  side  of  a  person's  eye,  an  observer  looking  at  the  eye  from  the  other 
side  sees  three  distinct  images  of  the  flame  (fig.  423).  The  first  and 
brightest  is  (1)  a  small  erect  image  formed  by  the  anterior  convex  surface 
of  the  cornea ;  the  second  (2)  is  also  erect,  but  larger  and  less  distinct  than 
the  preceding,  and  is  formed  at  the  anterior  convex  surface  of  the  lens; 
the  third  (3)  is  smaller,  inverted,  and  indistinct;  it  is  formed  at  the 
posterior  surface  of  the  lens,  which  is  concave  forward,  and  therefore, 
like  all  concave  mirrors,  gives  an  inverted  image.  If  now  the  eye  under 
observation  be  made  to  look  at  a  near  object,  the  second  image  becomes 
smaller,  clearer,  and  approaches  the  first.  If  the  eye  be  now  adjusted 
for  a  far  point,  the  second  image  enlarges  again,  becomes  less  distinct, 
and  recedes  from  the  first.     In  both  cases  alike  the  first  and  third  images 


Fig.  423. — Diagram  showing  three  reflections  of  a  candle.  1,  From  the  anterior  surface  of 
cornea ;  2,  from  the  anterior  surface  of  lens ;  3,  from  the  posterior  surface  of  lens.  For  further 
explanation,  see  text.  The  experiment  is  best  performed  by  employing  an  instrument  invented 
by  Helmholtz,  termed  a  Phakoscope. 

remain  unaltered  in  size,  distinctness,  and  relative  position.  This 
proves  that  during  accommodation  for  near  objects  the  curvature  of  the 
cornea,  and  of  the  ^josterior  of  the  lens,  remains  unaltered,  while  the 
anterior  surface  of  the  lens  becomes  more  convex  and  approaches  the 
cornea. 


THE   SEXSES. 


683 


The  experiment  (fig.  423  a)  is  more  striking  when  two  candles  are 
used,  and  the  images  of  the  two  candles  from  the  front  surface  of  the 
lens  during  accommodation  not  only  approach  those  from  the  cornea, 


B 

Fig.  423  A.  Fig.  4-,'4. 

Fig.  433  A.— Diagram  of  Sanson's  images.  A,  when  the  eyes  are  not,  and  B,  when  they  are 
focussed  for  near  objects.  The  fig.  to  the  right  in  A  and  B  is  the  inverted  image  from  the  pos- 
terior surface  of  the  lens. 

Fig.  424,— Phakoscope  of  Helmlioltz.  At  B  B'  are  two  prisms,  by  which  the  light  of  a  candle 
is  concentrated  on  the  eye  of  the  person  experimented  with  at  C.  A  is  the  aperture  for  the 
eye  of  the  observer.  The  observer  notices  three  double  images,  as  in  fig.  423,  reflected  from  the 
eye  under  examination  when  the  eye  is  fixed  upon  a  distant  object:  the  position  of  the  images 
having  been  noticed,  the  eye  is  then  made  to  focus  a  near  object,  such  as  a  reed  pushed  up  by 
C;  the  images  from  the  anterior  surface  of  the  lens  will  be  observed  to  move  toward  each  other, 
in  consequence  of  the  lens  becoming  more  convex. 

but  also  apjiroach  one  another,  and  become  somewhat  smaller.      [San- 
son''s  images.) 

Mechanism  of  accommodation. — The  lens  having  no  inlierent  power 
of  contraction,  its  changes  of  outlines  must  be  jiroduced  by  some  power 
from  without;  this  j)ower  is  supplied  by  the  ciliary  muscle.  It  is  some- 
times termed  the  tejisor  clioroidece.  Its  action  is  to  draw  forward  the 
choroid,  and  by  so  doing  to  slacken  the  tension  of  the  suspensory  liga- 
ment of  the  lens  which  ari.ses  from  it.  The  anterior  surface  of  the  lens 
is  kept  flattened  by  the  action  of  this  ligament.  The  ciliary  muscle 
during  accommodation  by  diminishing  its  tension,  diminishes  to  a  pro- 
portional degree  the  flattening  of  which  it  is  the  cause.  On  diminution 
or  cessation  of  the  action  of  the  ciliary  muscle,  the  lens  returns  to  its 
former  shape,  by  virtue  of  the  elasticity  of  the  suspensory  ligament 
(fig.  425).  From  this  it  will  appear  that  the  eye  is  usually  focussed 
for  distant  objects.  In  viewing  near  objects  the  pupil  contracts,  the 
opposite  effect  taking  place  on  withdrawal  of  the  attention  from  near 
objects,  and  fixing  it  on  those  distant. 


684  HANDBOOK    OF    PHYSIOLOGY. 

Range  of  Distinct  Vision.  JVear-point. — In  every  eye  there  is  a  limit 
to  the  power  of  accommodation.  If  a  book  be  brought  nearer  and 
nearer  to  the  eye,  the  tyjie  at  last  becomes  indistinct,  and  cannot  be 
brought  into  focus  by  any  effort  of  accommodation,  however  strong. 
This,  which  is  termed  the  near-jwint,  can  be  determined  by  the  foUow- 


Fig.  425. — Diagram  representing  by  dotted  lines  the  alteration  in  the  shape  of  the  lens  on  ac- 
commodation for  near  objects.     (E.  Landolt.) 

ing  experiment  {Sclieiner).  Two  small  holes  are  pricked  in  a  card  with 
a  pin  not  more  than  a  twelfth  of  an  inch  (2  mm.)  apart,  at  any  rate 
their  distance  from  each  other  must  not  exceed  the  diameter  of  the  pu- 
pil. The  card  is  held  close  in  front  of  the  eye,  and  a  small  needle 
viewed  through  the  pin-holes.  At  a  moderate  distance  it  can  be  clearly 
focussed,  but  when  brought  nearer,  beyond  a  certain  point,  the  image 
appears  double  or  at  any  rate  blurred.  This  point  where  the  needle 
ceases  to  ajipear  single  is  the  near-point.  Its  distance  from  the  eye  can 
of  course  be  readily  measured.  It  is  usually  about  5  or  G  inches  (13 
cm.).     In  the  accompanying  figure   (fig.  426)  the  lens  J  represents  the 


Fig.  426. — Diagram  of  experiment  to  ascertain  the  minimmn  distance  of  distinct  vision. 

eye;  e/"the  two  pin-holes  in  the  card,  nn  the  retina;  a  represents  the  po- 
sition of  the  needle.  When  the  needle  is  at  a  moderate  distance,  the 
two  pencils  of  light  coming  from  e  and/,  are  focussed  at  a  single  point  on 
the  retina  7i7i.  If  the  needle  be  brought  nearer  than  the  near-point,  the 
strongest  effort  of  accommodation  is  not  sufficient  to  focus  the  two  pen- 


THE    SENSES.  685 

cils,  they  meet  at  a  point  beliiud  the  retina.  The  effect  is  the  same 
as  if  the  retina  were  shifted  forward  to  mm.  Two  images  h.g.  are 
formed,  one  from  each  hole.  It  is  interesting  to  note  that  when  two 
images  are  produced,  the  lower  one  g  really  appears  in  the  position  q, 
while  the  upper  one  appears  in  the  position  p.  This  may  be  readily 
verified  by  covering  the  holes  in  succession. 

During  accommodation  two  other  changes  take  place  in  the  eyes, 
(1)  The  eyes  converge  by  the  action  of  the  extra-ocular  muscles  chiefly 
by  the  internal  and  inferior  recti,  or  internal  and  superior  recti.  The 
superior  oblique  and  the  inferior  oblique  may  also  be  used  to  turn  the 
eye  upward  or  downward. 

Movements  of  the  Eye. — The  eyeball  possesses  movement  around  three  axes 
indicated  in  fig.  427,  viz.,  an  antero-posterior,  a  vertical,  and  a  transverse, 
passing  through  a  centre  of  rotation  a  little  behind  the  centre  of  the  optic  axis. 
The  movements  are  accomplished  by  pairs  of  muscles. 

Direction  of  Movement.  By  what  muscles  accomplished. 

Inward  .....  .         Internal  rectus. 

Outward External  rectus. 

yy  T  \  Superior  rectus. 

'-'P^'^''^ ]  Inferior  oblique. 

T~,  1  i  Inferior  rectus. 

Downward ]  Superior  oblique. 

T  ,        5  1  (  Internal  and  superior  rectus. 

Inward  and  upward    .         ._        •  •  -j  inferior  oblique. 

._  ,        ,    ,  ,  (  Internal  and  inferior  rectus. 

Inward  and  downward   .         .         .     .      -^  Superior  oblique. 

^    .         .        ,  ,  \  External  and  superior  rectus. 

Outward  and  upward  .         .  .      ",  inferior  oblique 

^   ,         ,        T   ,  1  S  External  and  inferior  rectus. 

Outward  and  downward  .         .     .      j  Superior  oblique. 

(2)  The  second  change  which  takes  place  in  the  eyes  is,  that  the 
piqnls  contract.  The  contraction  of  all  of  the  muscles  which  have  to  do 
with  accommodation,  viz. ,  of  the  ciliary  muscle,  of  the  recti  muscles, 
and  of  the  sphincter  pupilla3  is  under  the  control  of  the  third  nerve. 
But  the  superior  oblique  may  also  be  employed,  in  which  case  the  fourth 
nerve  is  also  concerned. 

Contraction  of  the  pupil  may  also  occur  under  the  following  circum- 
stances: (1)  On  exposure  of  the  eye  to  a  bright  light;  (2)  on  the  local 
application  of  eserine  (active  principle  of  Calabar  bean) ;  (3)  on  the 
administration  internally  of  opium,  aconite,  and  in  the  early  stages  of 
chloroform  and  alcohol  poisoning;  (4)  on  division  of  the  cervical 
sympathetic  or  stimulation  of  the  third  nerve,  and  dilatation  of  the  pupil 
occurs  (1)  in  a  dim  light;  (2)  when  the  eye  is  focussed  for  distant  ob- 
jects; (3)  on  the  local  application  of  atropine  and  its  allied  alkaloids; 
(4)  on  the  internal  administration  of  atropine  and  its  allies;  (5)  in 
the  later  stages  of  poisoning  by  chloroform,  opium,  and  other  drugs; 
(6)  on  paralysis  of  the  third  nerve ;  (7)  on  stimulation  of  the  cervical 


686  HANDBOOK    OF    PHYSIOLOGY. 

sympathetic,  or  of  its  centre  in  the  floor  of  the  front  of  the  aqueduct  of 
Sylvius.  The  contraction  of  the  pupil  appears  to  be  under  the  control 
of  a  centre  in  the  bull)  or  in  the  corpora  quadrigemina,  and  this  is 
reflexly  stimulated  by  a  bright  light,  and  the  dilatation  when  the  reflex 
centre  is  not  in  action  is  due  to  the  more  powerful  sympathetic  action; 
but  in  addition,  it  appears  that  both  contraction  and  dilatation  may  be 


Fig.  427.  —Diagram  of  the  axes  of  rotation  to  the  eye.     The  thin  lines  indicate  axes  of  rotation, 
the  thick  the  position  of  muscular  attachment. 

produced  by  a  local  mechanism,  u23on  which  certain  drugs  can  act,  which 
is  independent  of  and  probably  often  antagonistic  to  the  action  of  the 
central  apparatus  of  the  third  and  sympathetic  nerve.  The  action  of  the 
fifth  nerve  upon  the  jsupil  is  not  well  understood,  but  its  apparent  effect 
in  producing  dilatation  is  due  to  the  mixture  of  sympathetic  fibres 
with  its  nasal  branch.  The  sympathetic  influence  upon  the  radiating 
fibres  is  believed  to  be  conveyed  not  by  the  long  ciliary  branches  of  that 
nerve,  but  by  the  short  ciliary  branches  from  the  ophthalmic  ganglion. 
The  close  sympathy  subsisting  between  the  two  eyes  is  nowhere  better 
shown  than  by  the  condition  of  the  pupil.  If  one  eye  be  shaded  by  the 
hand  its  pupil  will  of  course  dilate;  but  the  pupil  of  the  other  eye  will 
also  dilate,  though  it  is  unshaded. 

Defects  in"  the  Optical  Apparatus. 

Defects  in  the  Refracting  Media. — Under  this  head  we  may  con- 
sider the  defects  known  as  (1)  Myopia,  (2)  Hypermetropia,  (3)  Astig- 
matism, (4)  Spherical  Aberration,  (5)  Chromatic  Aberration. 


THE    SENSES. 


G87 


The  normal  (emmetropic)  eye  is  so  adjusted  that  parallel  raj-s  are 
brought  exactly  to  a  focus  on  the  retina  without  any  effort  of  accommo- 
dation (1,  fig.  428).  Hence  all  objects  except  near  ones  (practically  all 
objects  more  than  twenty  feet  off)  are  seen  without  any  effort  of  accom- 
modation; in  other  words,  the  far-point  of  the  normal  eye  is  at  an  infinite 
distance.  In  viewing  near  objects  we  are  conscious  of  the  effort  (the  con- 
traction of  the  ciliary  muscle)  by  which  the  anterior  surface  of  the  lens  is 
rendered  more  convex,  and  rays  which  would  otherwise  be  focussed  heliind 
the  retina  are  converged  upon  the  retina  (see  dotted  lines  2,  fig.  428). 


Fig.  428. —Diagram  showing— 1,  normal  Ct^mmetropic^)  eye  briiitrinK  paraUel  rays  exactly  to 
a  focus  on  the  retina:  2,  normal  eye  adaiHed  to  a  near  point:  without  accommodation  the  rays 
would  be  focussed  behind  the  retina,  but  by  increasing  the  curvature  of  the  anterior  surface  of 
the  lens  (shown  by  a  dotted  line)  the  rays  "are  focussed  on  the  retina  (as  indicated  by  the  meet- 
ing of  the  two  do'tted  lines);  i.  hypermetropic  eye.  in  this  case  the  axis  of  the  eye  is  shorter, 
and  the  lens  flatter,  than  normal;  parallel  rays  are  focussed  behind  the  retina;  4,  myopic  eye; 
in  this  case  the  axis  of  the  eye  is  abnormally'  long,  and  the  lens  too  convex;  parallel  rays  are 
focussed  in  front  of  the  retina. 

1.  Myopia  (short-sight)  (4,  fig.  428).— This  defect  is  due  to  an  abnor- 
mal elongation  of  the  eyeball.  The  eye  is  usually  larger  than  normal 
and  is  always^ longer  than  normal;  the  lens  is  also  probably  too  convex. 
The  retina  is  too  far  from  the  lens  and  consequently  parallel  rays  are 


G88  HANDBOOK    OF    PHYSIOLOGY, 

focussed  in  front  of  the  retina,  and,  crossing,  form  little  circles  on  the 
retina;  thus  the  images  of  distant  objects  are  blurred  and  indistinct. 
The  eye  is,  as  it  were,  permaiiently  adjusted  for  a  near-point.  Rays 
from  a  point  near  the  eye  are  exactly  focussed  in  the  retina.  But  those 
which  issue  from  any  object  beyond  a  certain  distance  {far-point)  cannot 
be  distinctly  focussed.  This  defect  is  corrected  hy  concave  glasses  which 
cause  the  rays  entering  the  eye  to  diverge;  hence  they  do  not  come  to  a 
focus  so  soon.  Such  glasses  of  course  are  only  needed  to  give  a  clear 
vision  of  distant  objects.  For  near  objects,  except  in  extreme  cases,  they 
are  not  required. 

Hy2)ernietro2na  (long-sight)  (3,  fig.  428). — This  is  the  reverse  defect. 
The  eye  is  too  short  and  the  lens  too  flat.  Parallel  rays  are  focussed 
leliind  the  retina:  an  effort  of  accommodation  is  required  to  focus  even 
parallel  rays  on  the  retina;  and  when  they  are  divergent,  as  in  viewing 
a  near  object,  the  accommodation  is  insufficient  to  focus  them.  Thus 
in  well-marked  cases  distant  objects  require  an  effort  of  accommodation 
and  near  ones  a  very  powerful  effort.  Thus  the  ciliary  muscle  is  con- 
stantly acting.  This  defect  is  obviated  by  the  use  of  convex  glasses, 
which  renders  the  pencils  of  light  more  convergent.  Such  glasses  are  of 
course  especially  needed  for  near  objects,  as  in  reading,  etc.  They  rest 
the  eye  by  relieving  the  ciliary  muscle  from  excessive  work. 

3.  Astigmatism. — This  defect,  which  was  first  discovered  by  Airy,  is 
due  to  a  greater  curvature  of  the  eye  in  one  meridian  than  in  others. 
The  eye  may  be  even  myopic  in  one  plane  and  hypermetropic  in  others. 
Thus  vertical  and  horizontal  lines  crossing  each  other  cannot  both  be 
focussed  at  once;  one  set  stands  out  clearly  and  the  others  are  blurred 
and  indistinct.  This  defect,  which  is  present  in  a  slight  degree  in  all 
eyes,  is  generally  seated  in  the  cornea,  but  occasionally  in  the  lens  as 
well;  it  may  be  corrected  by  the  use  of  cylindrical  glasses  (i.e.,  curved 
only  in  one  direction). 

4.  Sjjherical  Aberration. — The  rays  of  a  cone  of  light  from  an  object 
situated  at  the  side  of  the  field  of  vision  do  not  meet  all  in  the  same 
point,  owing  to  their  unequal  refraction ;  for  the  refraction  of  the  rays 
which  pass  through  the  circumference  of  a  lens  is  greater  than  that  of 
those  traversing  its  central  portion.  This  defect  is  known  as  spherical 
aberration,  and  in  the  camera,  telescope,  microscope,  and  other  optical 
instruments,  it  is  remedied  by  the  interposition  of  a  screen  with  a  circu- 
lar aperture  in  the  path  of  the  rays  of  light,  cutting  off  all  the  marginal 
rays  and  only  allowing  the  passage  of  those  near  the  centre.  Such  cor- 
rection is  effected  in  the  eye  by  the  iris,  which  forms  an  annular 
diaphragm  to  cover  the  circumference  of  the  lens,  and  to  prevent  the 
rays  from  passing  through  any  part  of  the  lens  but  its  centre  which  cor- 
responds to  the  pupil.     The  posterior  surface  of  the  iris  is  coated  with 


THE    SENSES.  689 

pigment,  to  prevent  the  passage  of  rays  of  light  through  its  substance. 
The  image  of  an  object  will  be  most  defined  and  distinct  when  the 
pupil  is  narrow,  the  object  at  the  proper  distance  for  vision,  and  the 
light  abundant ;  so  that,  while  a  sufficient  number  of  rays  are  admitted, 
the  narrowness  of  the  pupil  may  prevent  the  production  of  indistinctness 
of  the  image  by  aplierical  aberration.  But  even  the  image  formed  by 
the  rays  passing  through  the  circumference  of  the  lens,  when  the  pupil 
is  much  dilated,  as  in  the  dark,  or  in  a  feeble  light,  may,  under  certain 
circumstances,  be  well  defined. 

Distinctness  of  vision  is  further  secured  by  the  pigment  of  the  outer 
surface  of  the  retina,  the  posterior  surface  of  the  iris  and  the  ciliary 
processes,  which  absorbs  any  rays  of  light  that  may  be  reflected  within 
the  eye,  and  prevents  their  being  thrown  again  upon  the  retina  so  as  to 
interfere  with  the  images  there  formed.  The  pigment  of  the  retina  is 
especially  important  in  this  respect;  for  with  the  exception  of  its  outer 
layer  the  retina  is  very  transparent,  and  if  the  surface  behind  it  were  not 
of  a  dark  color,  but  capable  of  reflecting  the  light,  the  luminous  rays 
which  had  already  acted  on  the  retina  would  be  reflected  again  through 
it,  and  would  fall  upon  other  parts  of  the  same  membrane,  producing 
both  dazzling  from  excessive  light,  and  indistinctness  of  the  images. 

5.  Chromatic  Aberration. — In  the  passage  of  light  through  an  ordi- 
nary convex  lens,  decomposition  of  each  ray  into  its  elementary  colored 
part,  commonly  ensues,  and  a  colored  margin  appears  around  the  image, 
owing  to  the  unequal  refraction  which  the  elementary  colors  undergo. 
In  optical  instruments  this,  which  is  termed  chromatic  aherration.,  is  con- 
nected by  the  use  of  two  or  more  lenses,  difiiering  in  shape  and  density, 
the  second  of  v/hich  continues  or  increases  the  refraction  of  the  rays 
produced  by  the  first,  but  by  recombining  the  individual  parts  of  each 
ray  into  its  original  white  light,  corrects  any  chromatic  aberration  which 
may  have  resulted  from  the  first.  It  is  probable  that  the  unequal  refrac- 
tive power  of  the  transparent  media  in  front  of  the  retina  may  be  the 
means  by  which  the  eye  is  enabled  to  guard  against  the  effect  of  chromatic 
aberration.  The  human  eye  is  achromatic,  however,  only  so  long  as 
the  image  is  received  at  its  focal  distance  upon  the  retina,  or  so  long  as 
the  eye  adapts  itself  to  the  different  distances  of  sight.  If  either  of 
these  conditions  be  interfered  with,  a  more  or  less  distinct  appearance 
of  colors  is  produced. 

An  ordinary  ray  of  white  light  in  passing  through  a  prism,  is  refract- 
ed, i.e..,  bent  out  of  its  course,  but  the  different  colored  rays  which  go 
to  make  up  white  light  are  refracted  in  different  degrees,  and  therefore 
appear  as  colored  bands  fadic/g  off  into  each  other:  thus  a  colored  band 
known  as  the  "  spectrum"  is  produced,  the  colors  of  which  are  arranged 
as  follows — red,  orange,  yellow,  green,  blue,  indigo,  violet;  of  these 
44 


690  HANDBOOK    OF    PHYSIOLOGY. 

tlie  red  ray  is  the  least,  and  the  violet  the  most  refracted.  Henee,  as 
Ilelmholtz  has  shown,  a  small  white  object  cannot  be  accurately  focussed 
on  the  retina,  for  if  we  focus  for  the  red  rays,  the  violet  are  out  of  focus, 
and  vice  versa :  such  objects,  if  not  exactly  focussed,  are  often  seen  sur- 
rounded by  a  pale  yellowish  or  bluish  fringe. 

For  similar  reasons  a  red  surface  looks  nearer  than  a  blue  one  at  an 
equal  distance,  because,  the  red  rays  being  less  refrangible,  a  stronger 
effort  of  accommodation  is  necessary  to  focus  them,  and  the  eye  is  adjusted 
as  if  for  a  nearer  object,  and  therefore  the  red  surface  apj^ears  nearer. 

From  the  insufficient  adjustment  of  the  image  of  a  small  white  ob- 
ject, it  appears  surrounded  by  a  sort  of  halo  or  fringe.  This  phenom- 
enon is  termed  Irradiation.  It  is  from  this  reason  that  a  white  square 
on  a  black  ground  appears  larger  than  a  black  square  of  the  same  size  on 
a  white  ground. 

As  an  02:)tical  instrument,  the  eye  is  stqjerior  to  the  camera  in  the 
following,  among  many  other  particulars,  which  may  be  enumerated  in 
detail.  1.  The  correctness  of  images  even  in  a  large  field  of  view.  2. 
The  simplicity  and  efficiency  of  the  means  by  which  chromatic  aberra- 
tion is  avoided.  3.  The  perfect  efficiency  of  its  adaptation  to  different 
distances.  In  the  photographic  camera,  it  is  well  known  that  only  a  com- 
paratively small  object  can  be  accurately  focussed.  In  the  photograph 
of  a  large  object  near  at  hand,  the  upper  and  lower  limits  are  always 
inore  or  less  hazy,  and  vertical  lines  appear  curved.  This  is  due  to  the 
fact  that  the  image  produced  by  a  convex  lens  is  really  slightly  curved  and 
can  only  be  received  without  distortion  on  a  slightly  curved  concave 
screen,  hence  the  distortion  on  a  flat  surface  of  ground  glass.  It  is 
different  with  the  eye,  since  it  jiossesses  a  concave  background,  upon 
which  the  field  of  vision  is  depicted,  and  Avitli  which  the  curved  form  of 
the  image  coincides  exactly.  Thus,  the  defect  of  the  camera  obscura 
is  entirely  avoided ;  for  the  eye  is  able  to  embrace  a  large  field  of  vision, 
the  margins  of  which  are  depicted  distinctly  and  without  distortion.  If 
the  retina  had  a  plane  surface  like  the  ground  glass  plate  in  a  camera, 
it  must  necessarily  be  much  larger  than  is  really  the  case  if  we  were  to 
see  as  much;  moreover,  the  central  portion  of  the  field  of  vision  alone 
would  give  a  good  clear  picture  (Bernstein). 

Defective  Accoinmodation — Preshijojna. — This  condition  is  due  to  the 
gradual  loss  of  the  power  of  accommodation  which  is  part  of  the  general 
decay  of  old  age.  In  consequence  the  patient  would  be  obliged  in  read- 
ing to  hold  his  book  further  and  further  away  in  order  to  focus  the 
letters,  till  at  last  the  letters  are  held  too  far  for  distinct  vision.  The 
defect  is  remedied  by  weak  convex  glasses,  which  are  very  commonly 
worn  by  old  people.  It  is  due  chiefly  to  the  gradual  increase  in  density 
of  the  lens,  which  is  unable  to  swell  out  and  become  convex  when  near 


THE    SENSES.  G91 

objects  are  looked  at,  and  also  to  a  weakening  of  the  ciliary  muscle,  and 
a  general  loss  of  elasticity  in  the  parts  concerned  in  the  mechanism. 

Visual  Sexsatioxs. 

Excitation  of  the  Retina. — Light  is  the  normal  agent  in  the  ex- 
citation of  the  retina.  The  only  layer  of  the  retina  capable  of  reacting 
to  the  stimulus  is  the  rods  and  cones.  The  proofs  of  this  statement 
may  be  summed  up  thus: — 

(1.)  The  point  of  entrance  of  the  optic  nerve  into  the  retina,  where 
the  rods  and  cones  are  absent,  is  insensitive  to  light  and  is  called  the 
hlind  spot.  The  phenomenon  itself  is  very  readily  demonstrated.  If 
we  direct  one  eye,  the  other  being  closed,  ujion  a  jjoint  at  such  a  dis- 
tance to  the  side  of  any  object,  that  the  image  of  the  latter  must  fall 
upon  the  retina  at  the  point  of  entrance  of  tlie  optic  nerve,  this  image 
is  lost  either  instantaneously,  or  very  soon.  If,  for  example,  we  close  the 
left  eye,  and  direct  the  axis  of  the  right  eye  steadily  toward  the  circular 


spot  here  represented,  vrhile  the  page  is  held  at  a  distance  of  about  six 
inches  from  the  eye,  both  dot  and  cross  are  visible.  On  gradually  in- 
creasing the  distance  between  the  eye  and  the  object,  by  removing  the 
book  farther  and  farther  from  the  face,  and  still  keeping  the  right  eye 
steadily  on  the  dot,  it  will  be  found  that  suddenly  the  cross  disajipears 
from  view,  while  on  removing  the  book  still  farther,  it  suddenly  comes 
in  sight  again.  The  cause  of  this  phenomenon  is  simply  that  the  por- 
tion of  retina  which  is  occupied  by  the  entrance  of  the  optic  nerve,  is 
quite  blind;  and  therefore  that  when  it  alone  occupies  the  field  of  vision, 
objects  cease  to  be  visible.  (2.)  In  the  fovea  centralis  and  macula 
lutea  which  contain  rods  and  cones  but  no  oi3tic  nerve-fibres,  light  pro- 
duces the  greatest  effect.  In  the  latter,  cones  occur  in  large  numbers, 
and  in  the  former  cones  without  rods  are  found,  whereas  in  the  rest  of  the 
retina  which  is  not  so  sensitive  to  light,  there  are  fewer  cones  than  rods. 
We  may  conclude,  therefore,  that  cones  are  even  more  im.jDortant  to 
vision  than  rods.  (3.)  If  a  small  lighted  candle  be  moved  to  and  fro 
at  the  side  of  and  close  to  one  eye  in  a  dark  room  while  the  eyes 
look  steadily  forward  into  the  darkness,  a  remarkable  branching 
figure  {Purlcinje's  figures)  is  seen  floating  before  the  eye,  consisting  of 
dark  lines  on  a  reddish  ground.  As  the  candle  moves,  the  figure  moves 
in  the  opposite  direction,  and  from  its  whole  appearance  there  can  be  no 
doubt  that  it  is  a  reversed  picture  of  the  retinal  vessels  projected  before 
the  eye.  The  two  large  branching  arteries  passing  up  and  down  from 
the  optic  disc  are  clearly  visible  together  with  their  minutest  branches. 


692  HANDBOOK    OF    PHYSIOLOGY. 

A  little  to  one  side  of  the  disc,  in  a  part  free  from  vessels,  is  seen  the 
yellow  spot  in  the  form  of  a  slight  depression.  This  remarkable  apjiear- 
ance  is  due  to  shadows  of  the  retinal  vessels  cast  by  the  candle.  The 
branches  of  these  vessels  are  chiefly  distributed  in  the  nerve-fibre  and 
ganglionic  layers;  and  since  the  light  of  the  candle  falls  on  the  retinal 
vessels  from  in  front,  the  shadow  is  cast  behind  them,  and  hence  those 
elements  of  the  retina  which  perceive  the  shadows  must  also  lie  behind 
the  vessels.  Here,  then,  we  have  a  clear  proof  that  the  light-perceiving 
elements  of  the  retina  are  not  the  fibres  of  the  optic  nerve  forming  the 
innermost  layer  of  the  retina,  but  the  external  layers  of  the  retina,  rods 
and  cones,  which  indeed  appear  to  be  the  special  terminations  of  the 
optic  nerve-fibres. 

Duration  of  Visual  Sensations. — The  duration  of  the  sensation  pro- 
duced by  a  luminous  impression  on  the  retina  is  always  greater  than  that 
of  the  impression  which  produces  it.  However  brief  the  luminous  impres- 
sion, the  effect  on  the  retina  always  lasts  for  about  one-eighth  of  a  second. 
Thus,  supposing  an  object  in  motion,  say  a  horse,  to  be  revealed  on  a 
dark  night  by  a  flash  of  lightning.  The  object  would  be  seen  apparently 
for  an  eighth  of  a  second,  but  it  would  not  appear  in  motion;  because, 
although  the  image  remained  on  the  retina  for  this  time,  it  was  really 
revealed  for  such  an  extremely  short  period  (a  flash  of  lightning  being 
almost  instantaneous)  that  no  appreciable  movement  on  the  part  of 
the  object  could  have  taken  place  in  the  period  during  which  it  was 
revealed  to  the  retina  of  the  observer.  And  the  same  fact  is  proved  in  a 
reverse  way.  The  spokes  of  a  rapidly  revolving  wheel  are  not  seen  as 
distinct  objects,  because  at  every  point  of  the  field  of  vision  over  which 
the  revolving  spokes  pass,  a  given  impression  has  not  faded  before  another 
comes  to  replace  it.  Thus  every  part  of  the  interior  of  the  wheel 
appears  occupied. 

The  duration  of  the  after -sensation,  produced  by  an  object,  is  greater 
in  a  direct  ratio  with  the  duration  of  the  impression  which  caused  it. 
Hence  the  image  of  a  bright  object,  as  of  the  panes  of  a  window  through 
which  the  light  is  shining,  may  be  perceived  in  the  retina  for  a  con- 
siderable period,  if  we  have  previously  kept  our  eyes  fixed  for  some  time 
on  it.  But  the  image  in  this  case  is  negative.  H,  however,  after 
shutting  the  eyes  for  some  time,  we  open  them  and  look  at  an  object  for 
an  instant,  and  again  close  them,  the  after-image  \&  positive. 

Intensity  of  Visual  Sensations. — It  is  quite  evident  that  the  more 
luminous  a  body  the  more  intense  is  the  sensation  it  produces.  But  the 
intensity  of  the  sensation  is  not  directly  proportional  to  the  intensity 
of  the  luminosity  of  the  object.  It  is  necessary  for  light  to  have  a  cer- 
tain intensity  before  it  can  excite  the  retina,  but  it  is  impossible  to  fix  an 
arbitrary  limit  to  the  power  of  excitability.     As  in  other  sensations,  so 


THE    SENSES.  693 

also  in  visual  sensations,  a  stimulus  may  be  too  feeble  to  produce  a  sen- 
sation. If  it  be  increased  in  amount  sufficiently  it  begins  to  produce  an 
elfect  which  is  increased  on  the  increase  of  the  stimulation ;  this  in- 
crease in  the  effect  is  not  di7'ecily  proportional  to  the  increase  in  the 
excitation,  but,  according  to  Fechner''s  Imv,  "  as  the  logarithm  of  the 
stimulus,"  i.e.,  in  each  sensation,  there  is  a  constant  ratio  between  the 
increase  in  the  stimulus  and  the  increase  in  the  sensation,  this  constant 
ratio  for  each  sensation  expresses  the  least  perceptible  increase  in  the 
sensation  or  minimal  increment  of  excitation. 

This  law,  which  is  true  only  within  certain  limits,  may  be  best 
understood  by  an  example.  When  the  retina  has  been  stimulated  by  the 
light  of  one  candle,  the  light  of  two  candles  will  produce  a  difference  in 
sensation  which  can  be  distinctly  felt.  If,  however,  the  first  stimulus 
had  been  that  of  an  electric  light,  the  addition  of  the  light  of  a  candle 
would  make  no  difference  in  the  sensation.  So,  generally,  for  an  addi- 
tional stimulus  to  be  felt,  it  may  be  proportionately  small  if  the  original 
stimulus  have  been  small,  and  must  be  greater  if  the  original  stimulus 
have  been  great.  The  stimulus  increases  as  the  ordinary  numbers,  while 
the  sensation  increases  as  the  logarithm. 

Part  of  the  light  which  enters  the  eye  is  absorbed  and  produces  some 
change  in  the  retina,  of  which  we  shall  treat  further  on;  the  rest  is 
reflected. 

Every  one  is  perfectly  familiar  with  the  fact,  that  it  is  quite  impos- 
sible to  see  the  fundus  or  back  of  another  person's  eye  by  simply  looking 
into  it.  The  interior  of  the  eye  forms  a  perfectly  black  background  to 
the  pupil.  The  same  remark  applies  to  an  ordinary  photographic 
camera,  and  may  be  illustrated  by  the  difficulty  we  experience  in  seeing 
into  a  room  from  the  street  through  the  window,  unless  the  room  be 
lighted  within.  In  the  case  of  the  eye  this  fact  is  partly  due  to  the 
feebleness  of  the  light  reflected  from  the  retina,  most  of  it  being  absorbed 
by  the  retinal  pigment,  as  mentioned  above;  but  far  more  to  the  fact  that 
every  such  ray  is  reflected  straight  to  the  source  of  light  (e.g.,  candle),  and 
cannot,  therefore,  be  seen  by  the  unaided  eye  without  intercepting  the 
incident  light  from  the  candle,  as  well  as  the  reflected  rays  from  the 
retina.     This  difficulty  is  surmounted  by  the  use  of  the  ophthalmoscope. 

The  ophthalmoscope,  brought  into  use  by  Helmholtz,  consists  in  its  simplest 
form  of  o,  a  sliglitly  concave  mirror  of  metal  or  silvered  glass  perforated  in 
the  centre,  and  fixed  into  a  handle ;  and  b,  a  biconvex  lens  of  about  2^— S  inches 
focal  length.  Two  methods  of  examining  the  eye  with  this  instrument  are  in 
common  use — the  direct  and  the  indirect:  both  metliods  of  investigation  should 
be  employed.  A  normal  eye  should  be  examined ;  a  drop  of  a  solution  of  atro- 
pia  (two  grains  to  the  ounce)  or  of  homatropia  hydrobromate,  should  be  in- 
stilled about  twenty  minutes  before  the  examination  is  commenced  ;  the  ciliary 
muscle  is  thereby  paralyzed,  the  power  of  accommodation  is  abolished,  and  the 


694 


HANDBOOK    OF    PHYSIOLOGY. 


pupil  is  dilated.  This  will  materially  facilitate  the  examination ;  but  i-t  is 
quite  possible  to  observe  all  the  details  to  be  presently  described  without  the  use 
of  this  drug.  The  room  being  now  darkened,  the  observer  seats  liimself  in  front 
of  the  pei'son  whose  eye  he  is  about  to  examine,  placing  himself  upon  a  some- 
what higlier  level.  A  brilliant  and  steady  liglit  is  placed  close  to  the  left  ear 
of  the  patient.  The  atropia  having  been  put  into  the  right  eye  only  of  the  pa- 
tient, this  eye  is  examined.  Taking  the  mirror  in  his  right  hand,, and  looking 
through  the  central  hole,  the  operator  directs  a  beam  of  light  into  the  eye  of 


Fig'.  429. — Diagram  to  illustrate  the  action  of  the  Ophthalmoscope,  when  a  plane  concave 
glass  is  used.  c.  observer's  eye.  The  light  reflected  from  any  point,  d,  on  retina  of  a,  would 
naturally  be  fooussed  at  e ;  if  the  lens  6  is  used  it  would  be  focussed  at  r,  in  other  words,  at 
back  of  c.  The  image  would  be  enlarged,  as  though  of  </,  and  would  be  inverted.  (After  Mc- 
Gregor Robertson.) 

the  patient.  A  red  glare,  known  as  the  reflex,  is  seen  ;  it  is  due  to  the  illumi- 
nation of  the  retina.  The  patient  is  then  told  to  look  at  the  little  finger  of  the 
observer's  right  hand  as  he  holds  the  mirror ;  to  effect  this  the  eye  is  rotated 
somewhat  inward,  and  at  the  same  time  the  reflex  changes  from  red  to  a 
lighter  color,  owing  to  the  reflection  from  the  optic  disc.  The  observer  now 
approximates  the  mirror,  and  with  it  his  eye  to  the  eye  of  the  patient,  taking 
care  to  keep  the  light  fixed  upon  the  pupil,  so  as  not  to  lose  the  reflex.  At  a 
certain  point,  which  varies  with  different  eyes,  but  is  usually  when  there  is  an 
interval  (5f  about  two  or  three  inches  between  the  observed  and  the  observing 
eye,  the  vessels  of  the  retina  Avill  become  visible  as  lines  running  in  different 
directions.  Distinguish  the  smaller  and  brighter  red  arteries  from  the  larger 
and  darker  colored  veins.  Examine  carefully  the  fundus  of  the  eye,  i.e.,  the 
red  surface — until  the  optic  disc  is  seen ;  trace  its  circular  outline,  and  observe 


Fig.  430. — Diagram  to  illustrate  action  of  ophthalmoscope  when  a  bi-convex  glass  is  used. 
The  fig.  d  on  retina  of  a  is  under  ordinary  conditions  focussed  at  /  and  inverted.  If  the  lens  b 
be  placed  between  eyes,  the  image /i  is  seen  by  the  eye  c  as  an  enlarged  image.  (After  McGregor 
Robertson.) 


the  small  central  white  spot,  the  porus  opticus,  physiological  p)it :  near  the 
centre  is  the  central  artery  of  the  retina  breaking  up  upon  the  disc  into  brandies  ; 
veins  also  are  present,  and  correspond  roughly  to  the  course  of  the  arteries. 
Trace  the  vessels  over  the  disc  on  to  the  retina.  The  optic  disc  is  bounded  by 
two  delicate  rings,  the  more  external  being  the  choroidal,  while  the  moi'e  in- 
ternal is   the  sclerotic   opening.     Somewhat  to  the  outer  side,  and  only  visible 


THE   SENSES. 


695 


after  some  practice,  is  the  yelloio  spot,  with  the  smaller  lighter- colored  fovea 
centralis  in  its  centre.     Tliis  constitutes  the  direct  method  of  examination  (fig. 
429)  ;  by  it  the  various  details  of  the  fundus  are  seen 
as  they  really  exist,  and   it  is  this  method  which 
should  be  adopted  for  ordinary  use. 

If  the  observer  is  ametropic,  i.e.,  is  myopic  or 
hypermetropic,  he  will  be  unable  to  employ  the 
direct  method  of  examination  until  he  has  remedied 
his  defective  vision  by  the  use  of  proper  glasses. 

In  the  indirect  method  (fig.  430)  the  patient  is 
placed  as  before,  and  the  operator  holds  the  mirror 
in  his  right  hand  at  a  distance  of  twelve  to  eighteen 
inches  from  the  patient's  right  eye.  At  the  same 
time  he  rests  his  left  little  finger  lightly  upon  the 
right  temple,  and  holding  the  lens  between  his 
thumb  and  forefinger,  two  or  three  inches  in  front 
of  the  patient's  eye,  directs  the  light  through  the 
lens  into  the  eye.  The  red  reflex,  and  subsequently 
the  white  one,  having  been  gained,  the  operator 
slowly  moves  his  mirror,  and  with  it  his  eye,  toward 
or  away  from  the  face  of  the  patient,  until  the  out- 
line of  one  of  the  retinal  vessels  becomes  visible, 
when  very  slight  movements  on  the  part  of  tlie 
operator  will  suffice  to  bring  into  view  the  details 
of  the  fundus  above  described,  but  the  image  will 
be  much  smaller  and  inverted.  The  lens  should  be 
kept  fixed  at  a  distance  of  two  or  three  inches,  the 
mirror  being  alone  moved  until  the  disc  becomes 
visible  :  should  the  image  of  the  mirror,  however, 
obscure  the  disc,  the  lens  may  be  slightly  tilted. 


Fig.  431.— The  ophthalmo- 
scope. The  small  upper  mir- 
ror is  for  direct,  the  larger 
for  indirect  illumination. 


Visual  Purple. — The  method  by  Avhich  a  ray  of  light  is  able  to 
stimulate  the  endings  of  the  optic  nerve  in  the  retina  in  such  a  manner 
that  a  visual  sensation  is  perceived  by  the  cerebrum  is  not  yet  under- 
stood. It  is  supposed  that  the  change  effected  by  the  agency  of  the 
light  which  falls  upon  the  retina  is  in  fact  a  chemical  alteration  in  the 
protoplasm,  and  that  this  change  stimulates  the  optic  nerve-endings. 
The  discovery  of  a  certain  temporary  reddish-purple  pigmentation  of  the 
outer  limbs  of  the  retinal  rods  in  certain  animals  {e.g.,  frogs)  which  had 
been  killed  in  the  dark,  forming  the  so-called  rhodo]]si/i  or  visual pviyle, 
appeared  likely  to  offer  some  explanation  of  the  matter,  especially  as  it 
was  also  found  that  the  pigmentation  disappeared  when  the  retina  was 
exposed  to  light,  and  reappeared  when  the  light  was  removed,  and  also 
that  it  underwent  distinct  changes  of  color  when  other  than  white 
light  was  used.  It  was  also  found  that  if  the  operation  were  performed 
quickly  enough,  the  image  of  an  object  {optogram)  might  be  fixed  in  the 
pigment  on  the  retina  by  soaking  the  retina  of  an  animal,  which  has 
been  killed  in  the  dark,  in  alum  solution. 


696  HANDBOOK   OF   PHYSIOLOGY. 

The  visual  purple  canuot  however  be  absolutely  essential  to  the  due 
production  of  visual  sensations,  as  it  is  absent  from  the  retinal  cones, 
and  from  the  macula  lutea  and  fovea  centralis  of  the  human  retina,  and 
does  not  appear  to  exist  at  all  in  the  retinae  of  some  animals,  e.^.,  bat, 
dove,  and  hen,  which  are,  nevertheless,  possessed  of  good  vision. 

However  the  fact  remains  that  liglit  falling  upon  the  retina  {a) 
hleaches  the  visual  purple^  and  this  must  be  considered  as  one  of  its  effects. 
It  has  been  found  that  certain  pigments,  also  sensitive  to  light,  are  con- 
tained in  the  inner  segments  of  the  cones.  Tljese  colored  bodies  are  said 
to  be  oil  globules  of  various  colors,  red,  green,  and  yellow,  called  cliromo- 
2)lianes,  and  are  found  only  in  the  retinas  of  animals  not  mammals.  The 
rhodopsin  at  any  rate  appears  to  be  derived  in  some  way  from  the  retinal 
pigment,  since  the  color  is  not  renewed  after  bleaching  if  the  retina  be 
detached  from  its  pigment  layer,  {h)  The  second  change  produced  by 
the  action  of  the  light  upon  the  retina  is  the  movement  of  the  j^igment 
cells.  On  the  stimulation  of  light  the  granules  of  pigment  in  the  cells 
which  overlie  the  outer  part  of  the  rod  and  cone  layer  of  the  retina 
become  diffused  in  the  parts  of  the  cells  between  the  rods  and  cones,  the 
melanin  or /msc?';^  granules,  as  they  are  called,  passing  down  into  the  pro- 
cesses of  the  cells,  (c)  A  movement  of  the  cones  and  possibly  of  the  rods 
is  also  said  to  occur,  as  has  been  already  incidentally  mentioned;  on  the 
stimulus  of  light  the  outer  parts  of  the  cones,  which  in  an  eye  protected 
from  light  extend  to  the  pigment  layer,  are  retracted.  It  is  even 
thought  that  the  contraction  is  under  the  control  of  the  nervous  system ; 
and  finally,  according  to  the  careful  researches  of  Dewar  and  McKen- 
drick,  and  of  Holmgren,  it  appears  that  the  stimulus  of  light  is  able  to 
produce  {d)  a  variation  of  the  natural  electrical  currents  of  the  retina. 
The  current  is  at  first  increased  and  then  diminished.  McKendrick 
believes  that  this  is  the  electrical  expression  of  those  chemical  changes 
in  the  retina  of  which  we  have  already  spoken. 

Visual  Perceptions  and   Judgments. 

Reversion  of  the  Image. — It  will  be  as  well  to  repeat  here  that 
the  direction  given  to  the  rays  by  their  refraction  is  regulated  by  that 
of  the  central  ray,  or  axis  of  the  cone,  toward  which  the  rays  are  bent. 
The  image  of  any  point  of  an  object  is,  therefore,  as  a  rule  (the  exceptions 
to  which  need  not  here  be  stated),  always  formed  in  a  line  identical  with 
the  axis  of  the  cone  of  light,  as  in  the  line  of  B  (5),  or  a  a  (fig.  432),  so  that 
the  spot  where  the  image  of  any  point  will  be  formed  upon  the  retina 
may  be  determined  by  prolonging  the  central  ray  of  the  cone  of  light, 
or  that  ray  which  traverses  the  centre  of  the  pupil.  Thus  a  «  is  the 
axis  or  central  ray  of  the  cone  of  light  issuing  from  a  ;  b  J  the  central 


THE    SEXSES.  697 

ray  of  the  cone  of  light  issuing  from  B;  the  image  of  A  is  formed  at  «, 
the  image  of  b  at  h,  in  the  inverted  position :  therefore  what  in  the  ob- 
ject was  above  is  in  the  image  below,  and  vice  versa, — the  right-hand 
part  of  the  object  is  in  the  image  to  the  left,  the  left-hand  to  the  right. 
If  an  opening  be  made  in  an  eye  at  its  superior  surface,  so  that  the 
retina  can  be  seen  through  the  vitreous  humor,  this  image  of  any  bright 
object,  such  as  the  windows  of  the  room,  maybe  jjerceived  inverted  upon 
the  retina.  Or  still  better,  if  the  eye  of  any  albino  animal,  such  as  a 
white  rabbit,  in  which  the  coats,  from  the  absence  of  pigment,  are  trans- 
parent, is  dissected  clean,  and  held  with  the  cornea  toward  the  window, 
a  very  distinct  image  of  the  window  completely  inverted  is  seen  depicted 
on  the  liosterior  translucent  wall  of  the  eye.     \'o1kmann  has  also  shown 


Fig    432. — Diagram  of  the  formation  of  the  image  on  the  retina. 

that  a  similar  experiment  may  be  successfully  j)erformed  in  a  living  per- 
son possessed  of  large  prominent  eyes,  and  an  unusually  transparent 
sclerotic. 

An  image  formed  at  any  point  on  the  retina  is  referred  to  a  point 
outside  the  eye,  lying  on  a  straight  line  drawn  from  the  point  on  the 
retina  outward  through  the  centre  of  the  pupil.  Thus  an  image  on  the 
left  side  of  the  retina  is  referred  by  the  mind  to  an  object  on  the  right 
side  of  the  eye,  and  rice  rersd.  Thus  all  images  on  the  retina  are  men- 
tally, as  it  were,  jirojected  in  front  of  the  eye,  and  the  objects  are  seen 
erect  though  the  image  on  the  retina  is  inverted.  Much  needless  con- 
fusion and  difficulty  have  been  raised  on  this  subject  for  want  of  re- 
membering that  when  we  are  said  to  5^e  an  object,  the  mini  is  merely 
conscious  of  the  picture  on  the  retina,  and  when  it  refers  it  to  the  ex- 
ternal object,  or  "  projects"  it  outside  the  eye,  it  necessarUy  reverses  it 
and  sees  the  object  as  erect,  though  the  retinal  image  is  inverted. 
This  is  further  corroborated  by  the  sense  of  touch.  Thus  an  object 
whose  picture  falls  on  the  left  half  of  the  retina  is  reached  by  the  riglit 
hand,  and  hence  is  said  to  lie  to  the  riglit.  Or,  again,  an  object  whose 
image  is  formed  on  the  upper  part  of  the  retina  is  readily  touched  by 
the  feet,  and  is  therefore  said  to  be  in  the  hirer  part  of  the  field,  and 
so  on. 

Hence  it  is  also,  that  no  discordance  arises  between  the  sensations  of 
inverted  vision  and  those  of  touch,  which  perceives  everything  in  its 


G98  HAXDBOOK    OP    PHYSIOLOGY. 

erect  position;  for  the  images  of  all  objects,  even  of  our  own  limbs,  on 
the  retina,  are  equally  inverted,  and  therefore  maintain  the  same  rela- 
tive position. 

Even  the  image  of  our  hand,  while  used  in  touch,  is  seen  inverted. 
The  position  in  which  we  see  objects,  we  call,  therefore,  the  erect  posi- 
tion. A  mere  lateral  inversion  of  our  body  in  a  mirror,  where  the  right 
hand  occupies  the  left  of  the  image,  is  indeed  scarcely  remarked :  and 
there  is  but  little  discordance  between  the  sensations  acquired  by  touch 
in  regulating  our  movements  by  the  image  in  the  mirror,  and  those  of 
sight,  as,  for  example,  in  tying  a  knot  in  the  cravat.  There  is  some 
want  of  harmony  here,  on  account  of  the  inversion  being  only  lateral, 
and  not  complete  in  all  directions. 

The  perception  of  the  erect  position  of  objects  appears,  therefore,  to 
be  the  result  of  an  act  of  the  mind.  And  this  leads  us  to  a  consideration 
of  the  several  other  properties  of  the  retina,  and  of  the  co-operation  of 
the  mind  in  the  several  other  j)arts  of  the  act  of  vision.  To  these  belong 
not  merely  the  act  of  sensation  itself  and  the  perception  of  the  changes 
produced  in  the  retina,  as  light  and  colors,  but  also  the  conversion  of  the 
mere  images  depicted  in  the  retina  into  ideas  of  an  extended  field  of 
vision,  of  proximity  and  distance,  of  the  form  and  size  of  objects,  of  the 
reciprocal  influence  of  different  parts  of  the  retina  upon  each  other,  the 
simultaneous  action  of  the  two  eyes,  and  some  other  phenomena. 

Field  of  Vision. — The  actual  size  of  the  field  of  vision  depends  on 
the  extent  of  the  retina,  for  only  so  many  images  can  be  seen  at  any  one 
time  as  can  occupy  the  retina  to  the  same  time;  and  thus  considered, 
the  retina,  the  conditions  of  which  are  perceived  by  the  brain,  is  itself 
the  field  of  vision.  But  to  the  mind  of  the  individual  the  size  of  the 
field  of  vision  has  no  determinate  limits;  sometimes  it  appears  very 
small,  at  another  time  very  large;  for  the  mind  has  the  power  of  pro- 
jecting images  on  the  retina  toward  the  exterior.  Hence  the  mental 
field  of  vision  is  very  small  when  the  sphere  of  the  action  of  the  mind  is 
limited  to  impediments  near  the  eye:  on  the  contrary,  it  is  very  exten- 
sive when  the  projection  of  the  images  on  the  retina  toward  the  exterior, 
by  the  influence  of  the  mind,  is  not  impeded.  It  is  very  small  when 
we  look  into  a  hollow  body  of  small  capacity  held  before  the  eyes;  large 
when  we  look  out  upon  the  landscape  through  a  small  opening;  more  ex- 
tensive when  we  look  at  the  landscape  through  a  window ;  and  most  so 
when  our  view  is  not  confined  by  any  near  object.  In  all  these  cases  the 
idea  which  we  receive  of  the  size  of  the  field  of  vision  is  very  different, 
although  its  absolute  size  is  in  all  the  same,  being  dependent  on  the  ex- 
tent of  the  retina.  Hence  it  follows,  that  the  mind  is  constantly  co- 
operating in  the  acts  of  vision,  so  that  at  last  it  becomes  difficult  to  say 
what  belongs  to  mere  sensation,  and  what  to  the  influence  of  the  mind. 


THE    SEXSES.  699 

By  a  mental  operation  of  this  kind,  we  obtain  a  correct  idea  of  the  size 
of  individual  objects,  as  well  as  of  the  extent  of  the  field  of  vision. 
To  illustrate  this,  it  will  he  well  to  refer  to  fig.  433. 

The  angle  x,  included  between  the  decussating  central  rays  of  two 
cones  of  light  issuing  from  different  points  of  an  object,  is  called  the 


Fig.  433. 

optical  angle — angulus  optictis  sen  visorius.  This  angle  becomes  larger, 
the  greater  the  distance  between  the  points  A  and  b  ;  and  since  the  angles 
X  and  1/  are  equal,  the  distance  between  the  points  a  and  b  in  the  image 
on  the  retina  increases  as  the  angle  becomes  larger.  Objects  at  different 
distances  from  the  eye,  but  having  the  same  optical  angle  x — for  exam- 
ple, the  objects,  c,  d,  and  e, — must  also  throw  images  of  equal  size  upon 
the  retina;  and,  if  they  occupy  the  same  angle  of  the  field  of  vision, 
their  image  must  occupy  the  same  spot  in  the  retina. 

Nevertheless,  these  images  appear  to  the  mind  to  be  of  very  unequal 
size  when  the  ideas  of  distance  and  proximity  come  into  play;  for,  from 
the  image  a  li,  the  mind  forms  the  conception  of  a  visual  space  extend- 
ing to  e,  d,  or  c,  and  of  an  object  of  the  size  which  that  represented  by 
the  image  on  the  retina  appears  to  have  when  viewed  close  to  the  eye,  or 
under  the  most  usual  circumstances. 

Estimation  of  Size. — Our  estimate  of  the  size  of  various  objects  is 
based  partly  on  the  visual  angle  under  which  they  are  seen,  but  much 
more  on  the  estimate  we  form  of  their  distance.  Thus  a  lofty  mountain 
many  miles  off  may  be  seen  under  the  same  visual  angle  as  a  small  hill 
near  at  hand,  but  we  infer  that  the  former  is  much  the  larger  object 
because  we  know  it  is  much  further  ofl:  than  the  hill.  Our  estimate  of 
distance  is  often  erroneous,  and  consequently  the  estimate  of  size  also. 
Thus  persons  seen  vralking  on  the  top  of  a  small  hill  againts  a  clear 
twilight  sky  apjDcar  unusually  large,  because  we  over-estimate  their  dis- 
tance, and  for  similar  reasons  most  objects  in  a  fog  appear  immensely 
magnified.  The  same  mental  process  gives  rise  to  the  idea  of  depth  in 
the  field  of  vision;  this  idea  being  fixed  in  our  mind  principally  by  the 
circumstance  that,  as  we  ourselves  move  forward,  different  images  in 
succession  become  depicted  on  our  retina,  so  that  we  seem  to  pass 
between  these  images,  which  to  the  mind  is  the  same  thing  as  passing 
between  the  objects  themselves. 


700  HANDBOOK    OF    PHYSIOLOGY. 

The  action  of  tlie  sense  of  vision  in  relation  to  external  objects  is, 
therefore,  quite  different  from  that  of  the  sense  of  touch.  The  objects 
of  the  latter  sense  are  immediately  present  to  it;  and  our  own  body,  with 
which  they  come  in  contact,  is  the  measure  of  their  size.  The  part  of 
a  table  touched  by  the  hand  appears  as  large  as  the  part  of  the  hand 
receiving  an  imjoression  from  it,  for  a  part  of  our  body  in  which  a  sensa- 
tion is  excited,  is  here  the  measure  by  which  we  judge  of  the  magnitude 
of  the  object.  In  the  sense  of  vision,  on  the  contrary,  the  images  of  ob- 
jects are  mere  fractions  of  the  objects  themselves  realized  upon  the 
retina, the  extent  of  which  remains  constantly  the  same.  But  the  imagina- 
tion, which  analyzes  the  sensations  of  vision,  invests  the  images  of  ob- 
jects, together  with  the  whole  field  of  vision  in  the  retina,  with  very 
varying  dimensions;  the  relative  size  of  the  image  in  proportion  to  the 
whole  field  of  vision,  or  of  the  affected  parts  of  the  retina  to  the  whole 
retina,  alone  remaining  unaltered. 

Estimation  of  Direction. — The  direction  in  which  an  object  is 
seen,  depends  on  the  part  of  the  retina  which  receives  the  image,  and  on 
the  distance  of  this  part  from,  and  its  relation  to,  the  central  point  of 
the  retina.  Thus,  objects  of  which  the  images  fall  upon  the  same  parts 
of  the  retina  lie  in  the  same  visual  direction;  and  when,  by  the  action 
of  the  mind,  the  images  or  affections  of  the  retina  are  projected  into  the 
exterior  world,  the  relation  of  the  images  to  each  other  remains  the 
same. 

Estimation  of  Form. — The  estimation  of  the  form  of  bodies  by 
sight  is  the  result  partly  of  the  mere  sensation,  and  partly  of  the  associ- 
ation of  ideas.  Since  the  form  of  the  images  perceived  by  the  retina 
depends  wholly  on  the  outline  of  the  part  of  the  retina  affected,  the  sen- 
sation alone  is  adequate  to  the  distinction  of  only  superficial  forms  of 
each  other,  as  of  a  square  from  a  circle.  But  the  idea  of  a  solid 
body  as  a  sphere,  or  a  body  of  three  or  more  dimensions,  e.g.,  a  cube, 
can  only  be  attained  by  the  action  of  the  mind  constructing  it  from  the 
different  superficial  images  seen  in  different  positions  of  the  eye  with 
regard  to  the  object,  and,  as  shown  by  AVheatstone  and  illustrated  in  the 
stereoscope,  from  two  different  perspective  projections  of  the  body  being 
present  simultaneously  to  the  mind  by  the  two  eyes.  Hence,  when,  in 
adult  age,  sight  is  suddenly  restored  to  persons  blind  from  infancy,  all 
objects  in  the  field  of  vision  appear  at  first  as  if  painted  flat  on  one 
surface;  and  no  idea  of  solidity  is  formed  until  after  long  exercise  of 
the  sense  of  vision  combined  with  that  of  touch. 

The  clearness  with  which  an  object  is  perceived  irrespective  of  accom- 
modation, would  apj)ear  to  depend  largely  on  the  number  of  rods  and 
cones  which  its  retinal  image  covers.  Hence  the  nearer  an  object  is  to 
the  eye    (within  moderate  limits)   the  more  clearly  are  all   its  details 


THE    SEIfSES.  701 

seen.  Moreover,  if  we  want  carefully  to  examine  any  object,  we  always 
direct  the  eyes  straight  to  it,  so  that  its  image  shall  fall  on  the  yellow 
spot  where  an  image  of  a  given  area  will  cover  a  larger  number  of  cones 
than  anywhere  else  in  the  retina.  It  has  been  found  that  the  images  of 
two  points  must  be  at  least  3/i  apart  on  the  yellow  spot  in  order  to  be 
distinguished  separately;  if  the  images  are  nearer  together,  the  points 
appear  as  one.  The  diameter  of  each  cone  in  this  part  of  the  retina  is 
about  3/i. 

Estimation  of  Movement. — We  judge  of  the  motion  of  an  object, 
partly  from  the  motion  of  its  image  ov^r  the  surface  of  the  retina,  and 
partly  from  the  motion  of  our  eyes  following  it.  If  the  image  upon  the 
retina  moves  while  our  eyes  and  our  body  are  at  rest,  we  conclude  that 
the  object  is  changing  its  relative  position  witli  regard  to  ourselves.  In 
such  a  case  the  movement  of  the  object  may  be  apparent  only,  as  when 
we  are  standing  upon  a  body  which  is  in  motion,  such  as  a  ship.  If,  on 
the  other  hand,  the  image  does  not  move  with  regard  to  the  retina,  but 
remains  fixed  upon  the  same  spot  of  that  membrane,  while  our  eyes  fol- 
low the  moving  body,  we  judge  of  the  motion  of  the  object  by  the  sensa- 
tion of  the  muscles  in  action  to  move  the  eye.  If  the  image  moves  over 
the  surface  of  the  retina  while  the  muscles  of  the  eye  are  acting  at  the 
same  time  in  a  manner  corresponding  to  this  motion,  as  in  reading,  we 
infer  that  the  object  is  stationary,  and  we  know  that  we  are  merely 
altering  the  relations  of  our  eyes  to  the  object.  Sometimes  the  object 
appears  to  move  when  both  object  and  eye  are  fixed,  as  in  vertigo. 

The  mind  can,  by  the  faculty  of  attention,  concentrate  its  activity 
more  or  less  exclusively  upon  the  sense  of  sight,  hearing,  and  touch  alter- 
nately. When  exclusively  oc(?upied  with  the  action  of  one  sense,  it  is 
scarcely  conscious  of  the  sensations  of  the  others.  The  mind,  when  deeply 
immersed  in  contemplations  of  another  nature,  is  indifferent  to  the  ac- 
tions of  the  sense  of  sight,  as  of  every  other  sense.  We  often,  when 
deep  in  thought,  have  our  eyes  open  and  fixed,  but  see  nothing,  because 
of  the  stimulus  of  ordinary  light  being  unable  to  excite  the  brain  to 
perception,  when  otherwise  engaged.  The  attention  Avhich  is  thus 
necessary  for  vision,  is  necessary  also  to  analyze  what  the  field  of  vision 
presents.  The  mind  does  not  perceive  all  the  objects  presented  by  the 
field  of  vision  at  the  same  time  with  equal  acuteness,  but  directs  itself 
first  to  one  and  then  to  another.  The  sensation  becomes  more  intense, 
according  as  the  particular  object  is  at  the  time  the  principal  object  of 
mental  contemplation.  Any  compound  mathematical  figure  produces  a 
different  impression  according  as  the  attention  is  directed  exclusively  to 
one  or  the  other  part  of  it.  Thus  in  fig.  433  a,  we  may  in  succession 
have  a  vivid  perception  of  the  whole,  or  of  distinct  parts  only ;  of  the 
six  triangles  near  the  outer  circle,  of  the  hexagon  in  the  middle,  of  the 


702  HANDBOOK    OF    PHYSIOLOGY, 

three  large  triangles.  The  more  uumerous  and  varied  the  parts  of  which 
a  figure  is  composed  the  more  scope  does  it  afford  for  the  play  of  the 
attention.     Hence  it  is  that  architectural  ornaments  have  an  enlivening 


Fig.  433  A. 

effect  on  the  sense  of  vision,  since  they  afford   constantly  fresh  subject 
for  the  action  of  tlie  mind. 

Color  Sensations, — If  a  ray  of  sunlight  be  allowed  to  pass  through 
a  prism,  it  is  decomposed  by  its  passage  into  rays  of  different  colors, 
which  are  called  the  colors  of  the  spectrum ;  they  are  red,  orange,  yellow, 
green,  blue,  indigo,  and  violet.  The  red  rays  are  the  least  turned  out  of 
their  course  by  the  prism,  and  the  violet  the  most,  while  the  other  colors 
occupy  in  order  places  between  these  two  extremes.  The  differences  in 
the  color  of  the  rays  depend  upon  the  number  of  vibrations  producing 
each,  the  red  rays  being  the  least  rapid  and  the  violet  the  most.  In 
addition  to  the  colored  rays  of  the  spectrum,  there  are  others  which  are 
invisible,  but  which  have  definite  properties,  those  to  the  left  of  the  red, 
and  less  refrangible,  being  the  calorific  rays  which  act  upon  the  ther- 
mometer, and  those  to  the  right  of  the  violet,  which  are  called  the  actinic 
or  chemical  rays,  which  have  a  powerful  chemical  action.  The  rays 
which  can  be  perceived  by  the  brain,  i.e.,  the  colored  rays,  must  stimu- 
late the  retina  in  some  special  manner  in  order  that  colored  vision  may 
result,  and  two  chief  explanations  of  the  method  of  stimulation  have 
been  suggested. 

(1.)  The  one,  originated  by  Young  and  elaborated  by  Helmholtz,  holds 
that  there  are  three  primary  colors,  viz.,  red,  green,  and  violet,  and  that 
in  the  retina  are  contained  rods  or  cones  which  answer  to  each  of  these 
primary  colors,  whereas  the  innumerable  intermediate  shades  of  color  are 
produced  by  stimulation  of  the  three  primary  color  terminals  in  different 
degrees,  the  sensation  of  white  being  produced  at  the  same  time  when 
the  three  elements  are  equally  excited.  Thus  if  the  retina  be  stimulated 
by  rays  of  certain  wave  length,  at  the  red  end  of  the  spectrum,  the 
terminals  of  the  other  colors,  green  and  violet,  are  hardly  stimulated  at 
all,  but  the  red  terminals  are  strongly  stimulated,  the  resulting  sensation 
being  red.  The  orange  rays  excite  the  red  terminals  considerably,  the 
green  rather  more,  and  the  violet  slightly,  the  resulting  sensation  being 
that  of  orange,  and  so  on  (fig.  434). 

(2.)  The  second  theory  of  color  (Hering's)  supposes  that  there  are  six 


THE   SEXSES. 


703 


primary  color  sensations,  of  three  pair  of  antagonistic  or  complemental 
colors,  black  and  white,  red  and  green,  and  yellow  and  blue,  and  that 
these  are  jiroduced  by  the  changes  either  of  disintegration  or  of  assimu- 
lation  taking  j^lace  in  certain  substances,  somewhat  it  may  be  supposed  of 
the  nature  of  the  visual  purple,  which  (the  theory  suj^poses  to)  exist  in 
the  retina.  Each  of  the  substances  corresponding  to  a  pair  of  colors, 
being  capable  of  undergoing  two  changes,  one  of  construction  and  the 
other  of  disintegration,  with  the  result  of  producing  one  or  other  color. 
For  instance,  in  the  white-black  substance,  when  disintegration  is  in 
excess  of  construction  or  assimilation,  the  sensation  is  white,  and  when 
assimilation  is  in  excess  of  disintegration  the  reverse  is  the  case;  and 
similarly  with  the  red-green  substance,  and  with  the  yellow-blue  sub- 
stance.    When  the  repair  aud  disintegration  are  equal  with  the  first 


vcd 


jB         t>      Y         Gv-. 


Fig.  434. 


^iolei 


Ihlue 


(^reeji 


Fiff.  434. — Diagram  of  the  three  primary  color  sensations.  (Young-Helmholtz  theorj'  )  1,  is 
the  red;  2,  green,  and  3,  violet,  primary  color  sensations.  The  lettering  indicates  the  colors  of 
the  spectrum.  The  diagram  indicates  by  the  height  of  the  curve  to  what  extent  the  several 
primary  sensations  of  cmor  are  excited  by  vibrations  of  different  wave  lengths. 

Fig.  435. — Diagram  of  the  various  simple  and  compound  colors  of  light,  and  those  which  are 
complemental  of  each  other,  i.e..  which,  when  mixed,  produce  a  neutral  gray  tint.  The  three 
simple  colors,  I'ed.  yellow,  and  blue,  are  placed  at  the  angles  of  an  equilateral  triangle,  which 
are  connected  together  by  means  of  a  circle;  the  mixed  colors,  green,  orange,  and  violet,  are 
placed  intermediate  Vietween  the  corresponding  simple  or  homogeneous  colors;  and  the  com- 
plemental colors,  of  which  the  pigments,  when  mixed,  would  constitute  a  gray,  and  of  which  the 
prismatic  spectra  would  together  p)oduce  a  white  light,  will  be  found  to  be  placed  in  each  case 
opposite  to  each  other,  but  connected  by  a  line  passing  through  the  centre  of  tlie  circle.  The  fig- 
ure is  also  useful  in  showing  the  further  shades  of  color  which  are  complementary  of  each 
other.  If  the  circle  be  supposed  to  contain  every  transition  of  color  between  the  six  marked 
down,  those  which,  when  united,  yield  a  white  or  gray  color,  will  always  be  found  directly  op- 
posite to  each  other ;  thus,  for  example,  the  intermediate  tint  between  "orange  and  red  is  com- 
plemental of  the  middle  tint  between  green  and  blue. 

substance,  the  visual  sensation  is  gray;  but  in  the  other  pairs  when  this 
is  the  case,  no  sensation  occurs.  The  rays  of  the  spectrum  to  the  left 
produce  changes  in  the  red-green  substance  only,  with  a  resulting  sensa- 
tion of  red,  while  the  (orange)  rays  further  to  the  right  affect  both  the 
red-green  and  the  yellow-blue  substauces;  blue  rays  cause  constructive 
changes  in  the  yellow-Viue  substances  but  none  in  the  red-green  and  so 
on.  These  changes  produced  in  the  visual  substances  in  the  retina  are 
perceived  by  the  brain  as  sensations  of  color. 

The  spectra  left  by  the  images  of  Avhite  or  luminous  objects  are 
ordinarily  white  or  luminous;  those  left  by  dark  objects  are  dark.  Some- 
times, however,  the  relation  of   the  light  aud  dark  parts  in   the  image 


704  HANDBOOK    OF    PHYSIOLOGY. 

may,  under  certain  circumstances,  be  reversed  in  the  spectrum;  what 
was  bright  may  be  dark,  and  wliat  was  dark  may  appear  light.  This 
occurs  whenever  the  eye,  which  is  the  seat  of  the  spectrum  of  a  luminous 
object,  is  not  closed,  but  fixed  upon  another  bright  or  white  surface,  as 
a  white  wall,  or  a  sheet  of  white  paper.  Hence  the  spectrum  of  the  sun, 
which,  while  light  is  excluded  from  the  eye,  is  luminous,  appears  black 
or  gray  when  the  eye  is  directed  upon  a  white  surface.  The  explanation 
of  this  is,  that  the  part  of  the  retina  which  has  received  the  luminous 
image  remains  for  a  certain  period  afterward  in  an  exhausted  or  less 
sensitive  state,  while  that  which  has  received  a  dark  image  is  in  an 
unexhausted,  and  therefore  much  more  excitable  condition. 

The  ocular  spectra  which  remain  after  the  impression  of  colored  ob- 
jects upon  the  retina  are  always  colored;  and  their  color  is  not  that  of 
the  object,  or  of  the  image  produced  directly  by  the  object,  but  the  oppo- 
site, or  complemental  color.  The  spectrum  of  a  red  object  is,  therefore, 
green;  that  of  a  green  object,  red;  that  of  violet,  yellow;  that  of  yellow, 
violet,  and  so  on.  The  reason  of  this  is  obvious.  The  part  of  the 
retina  which  receives,  say,  a  red  image,  is  wearied  by  that  particular 
color,  but  remains  sensitive  to  the  other  rays  which  with  red  make  up 
white  light ;  and,  therefore,  these  by  themselves  reflected  from  a  white 
object  produce  a  green  hue.  If,  on  the  other  hand,  the  first  object 
looked  at  be  green,  the  retina  being  tired  of  green  rays,  receives  a  red 
image  when  the  eye  is  turned  to  a  white  object.  And  so  with  the  other 
colors;  the  retina  while  fatigued  by  yellow  rays  will  suppose  an  object  to 
be  violet,  and  vice  versa;  the  size  and  shape  of  the  spectrum  correspond- 
ing with  the  size  and  shape  of  the  original  object  looked  at.  The  colors 
which  thus  reciprocally  excite  each  other  in  the  retina  are  those  placed 
at  opposite  points  of  the  circle  in  fig.  435.  The  peripheral  jjarts  of  the 
retina  do  not  react  to  rays  of  red.  The  area  of  the  retina  which  is 
capable  of  receiving  impressions  of  color,  and  therefore  the  field  of 
vision,  is  slightly  different  for  each  color. 

Color  Blindness  or  Daltonisin. — Daltonism  or  color-blindness  is  a  by 
no  means  uncommon  visual  defect.  One  of  the  commonest  forms  is  the 
inability  to  distinguish  between  red  and  green.  The  simplest  explana- 
tion of  such  a  condition  is,  that  the  elements  of  the  retina  which  receive 
the  impression  of  red,  etc.,  are  absent,  or  very  imperfectly  developed,  or, 
according  to  the  other  theory,  that  the  red-green  substance  is  absent 
from  the  retina.  Other  varieties  of  color  blindness  in  which  the  other 
color-perceiving  elements  are  absent  have  been  shown  to  exist  occasionally. 

The  Eeciprocal  Action  of  Different  Parts   of  the   Retina. 

Although  each  elementary  part  of  the  retina  represents  a  distinct 
portion  of  the  field  of  vision,  yet  the  different  elementary  parts,  or  sensi- 


THE    SENSES.  705 

tive  points  of  that  membrane,  have  a  certain  influence  on  each  other ; 
the  particular  condition  of  one  influencing  the  other,  so  that  the  image 
perceived  by  one  part  is  modified  by  the  image  depicted  in  the  other. 
The  phenomena  which  result  from  this  relation  between  the  different 
parts  of  the  retina,  ma}^  be  arranged  in  two  classes:  the  one  including 
those  where  the  condition  existing  in  the  greater  extent  of  the  retina  is 
imjjarted  to  the  remainder  of  that  membrane;  the  other,  consisting  of 
those  in  which  the  condition  of  the  larger  portion  of  the  retina  excites, 
in  the  less  extensive  portion,  the  opposite  condition. 

1.  When  two  opposite  impressions  occur  in  contiguous  parts  of  an 
image  on  the  retina,  the  one  impression  is,  under  certain  circumstances, 
modified  by  the  other.  If  the  impressions  occupy  each  one-half  of  the 
image,  this  does  not  take  place ;  for  in  that  case,  their  actions  are  equally 
balanced.  But  if  one  of  the  impressions  occupies  only  a  small  part  of 
the  retina,  and  the  other  the  greater  part  of  its  surface,  the  latter  may, 
if  long  continued,  extend  its  influence  over  the  whole  retina,  so  that 
the  opposite  less  extensive  impression  is  no  longer  perceived,  and  its 
place  becomes  occupied  by  the  same  sensation  as  the  rest  of  the  field  of 
vision.  Thus,  if  we  fix  the  eye  for  some  time  upon  a  strip  of  colored 
paper  lying  upon  a  white  surface,  the  image  of  the  colored  object,  espe- 
cially when  it  falls  on  the  lateral  parts  of  the  retina  will  gradually  dis- 
appear, and  the  white  surface  be  seen  in  its  place. 

2.  In  the  second  class  of  phenomena,  the  affection  of  one  part  of  the 
retina  influences  that  of  another  part,  not  in  such  a  manner  as  to  ob- 
literate it,  but  so  as  to  cause  it  to  become  the  contrast  or  oj^posite  of 
itself.  Thus  a  gray  spot  upon  a  white  ground  appears  darker  than  the 
same  tint  of  gray  would  do  if  it  alone  occupied  the  whole  field  of  vision, 
and  a  shadow  is  always  rendered  deeper  when  the  light  which  gives  rise  to 
it  becomes  more  intense,  owing  to  the  greater  contrast. 

The  former  phenomena  ensue  gradually,  and  only  after  the  images 
have  been  long  fixed  on  the  retina ;  the  latter  are  instantaneous  in  their 
production,  and  are  permanent. 

In  the  same  way,  also,  colors  may  be  produced  by  contrast.  Thus,  a 
very  small  dull  gray  strip  of  paper,  lying  upon  an  extensive  surface  of 
any  bright  color,  does  not  appear  gray,  but  has  a  faint  tint  of  the  color 
which  is  the  complement  of  that  of  the  surrounding  surface.  A  strip 
of  gray  paper  upon  a  green  field,  for  example,  often  appears  to  have 
a  tint  of  red,  and  when  lying  upon  a  red  surface,  a  greenish  tint;  it  has 
an  orange-colored  tint  upon  a  bright  blue  surface,  and  a  bluish  tint 
upon  an  orange-colored  surface;  a  yellowish  color  upon  a  bright  violet, 
and  a  violet  tint  upon  a  bright  yellow  surface.  The  color  excited  thus,  as 
a  contrast  to  the  exciting  color,  being  wholly  independent  of  any  rays  of 
the  corresponding  color  acting  from  without  upon  the  retina,  must  arise  as 
45 


7ud  HANDBOOK    OF    PHYSIOLOGY. 

an  oppos.ce  or  antagonistic  condition  of  tliat  membrane;  and  the  opposite 
conditions  of  wliicli  the  retina  thns  becomes  the  subject  would  seem  to 
balance  each  other  by  their  reciprocal  reaction.  A  necessary  condition 
for  the  production  of  the  contrasted  colors  is,  that  the  part  of  the  retina 
in  which  the  new  color  is  to  be  excited,  shall  be  in  a  state  of  comparative 
repose;  hence  the  small  object  itself  must  be  gray.  A  second  condition 
is,  that  the  color  of  the  surrounding  surface  shall  be  very  bright,  that  is, 
shall  contain  much  white  light. 

Binocular  Vision. 

Although  the  sense  of  sight  is  exercised  by  the  two  eyes,  yet  the  im- 
pression of  an  object  conveyed  to  the  mind  is  single.  V^arious  theories 
have  been  advanced  to  account  for  this  phenomenon. 

By  Gall  it  was  supposed  that  we  do  not  really  employ  both  eyes  si- 
multaneously in  vision,  but  always  see  with  only  one  at  a  time.  This 
especial  employment  of  one  eye  in  vision  certainly  occurs  in  persons 
whose  eyes  are  of  very  unequal  focal  distance,  but  in  the  majority  of 
individuals  both  eyes  are  simultaneously  in  action,  in  the  perception  of 
the  same  object;  this  is  shown  by  the  double  images  seen  under  certain 
conditions.  If  two  fingers  be  held  up  before  the  eyes,  one  in  front  of 
the  other,  and  vision  be  directed  to  the  more  distant,  so  that  it  is  seen 
singly,  the  nearer  will  appear  double;  while,  if  the  nearer  one  be 
regarded,  the  most  distant  will  be  seen  double;  and  one  of  the  double 
images  in  each  case  will  be  found  to  belong  to  one  eye,  the  other  to  the 
other  eye. 

Diplopia. — Single  vision  results  only  when  certain  parts  of  the  two 
retinas  are  affected  simultaneously;  if  different  parts  of  the  retina  re- 
ceive the  image  of  the  object,  it  is  seen  double.  This  may  be  readily 
illustrated  as  follows: — the  eyes  are  fixed  upon  some  near  object,  and  one 
of  them  is  pressed  by  the  thumb  so  as  to  be  turned  slightly  in  or  out;  two 
images  of  the  object  (Diplopia)  are  at  once  perceived,  just  as  is  frequently 
the  case  in  persons  who  squint.  This  diplopia  is  due  to  the  fact  that  the 
images  of  the  object  do  not  fall  on  corresponding  points  in  the  two 
retinse. 

The  parts  of  the  retinas  in  the  two  eyes  which  thus  correspond  to 
each  other  in  the  property  of  referring  the  images  which  affect  them 
simultaneously  to  the  same  spoi  in  the  field  of  vision,  are,  in  man,  just 
those  parts  which  would  correspond  to  each  other,  if  one  retina  were 
placed  exactly  in  front  of,  and  over  the  other  (as  in  fig.  436).  Thus, 
as  we  have  noticed  in  speaking  of  the  distribution  of  the  optic  nerve- 
fibres,  the  temporal  portion  of  one  eye  corresponds  to,  or,  to  use  a  better 
term,  is  identical  Avith  the  nasal  portion  of  the  other  eye;  or  a  of  the 


THE   SENSES.  707 

eye  a  (fig.  43G),  with  a  of  the  eye  b.  The  upper  part  of  one  retina  is 
also  identical  with  the  upper  part  of  the  other;  and  the  lower  parts  of 
the  two  eyes  are  identical  with  each  other.  The  distribution  of  the  optic 
nerve-fibres  correspond  with  their  distribution.  The  identical  points  on 
the  upper  and  lower  parts  of  the  retinse  may  also  be  shown  by  the  fol- 
lowing simple  experiment. 

Pressure  upon  any  part  of  the  ball  of  the  eye,  so  as  to  affect  the  retina, 
produces  a  luminous  circle,  seen  at  the  opposite  side  of  the  field  of  vision 
to  that  on  which  the  pressure  is  made.  If,  now,  in  a  dark  room,  we 
press  with  the  finger  at  the  uj)per  part  of  one  eye,  and  at  the  lower  part 
of  the  other,  two 'luminous  circles  are  seen,  one  above  the  other;  so, 
also,  two  figures  are  seen  when  pressure  is  made  simultaneously  on  the 
two  outer  or  the  two  inner  sides  of  both  eyes.  It  is  certain,  therefore, 
that  neither  the  upper  part  of  one  retina  and  the  lower  part  of  the  other 
are  identical,  nor  the  outer  lateral  parts  of  the  two  retina?,  nor  their 
inner  lateral  portions.      But  if  pressure  be  made  with  the  fingers    upon 


Fig.  4.36. — Diagram  to  show  the  corresponding  parts  of  both  retina. 

both  eyes  simultaneously  at  their  lower  part,  one  luminous  ring  is  seen 
at  the  middle  of  the  upper  part  of  the  field  of  vision;  if  the  pressure  be 
applied  to  the  upper  part  (3f  both  eyes  a  single  luminous  circle  is  seen  in 
the  middle  of  the  field  of  \dsion  below.  So,  also,  if  we  press  upon  the 
outer  side  a  of  the  eye  a,  and  upon  the  inner  side  «'  of  the  eye  b,  a 
single  spectrum  is  produced,  and  is  apparent  at  the  extreme  right  of  the 
field  of  vision ;  if  upon  the  point  h  of  one  eye,  and  the  point  V  of  the 
other,  a  single  spectrum  is  seen  to  the  extreme  left. 

The  spheres  of  the  two  retinge  may,  therefore,  be  regarded  as  lying 
one  over  the  other,  as  in  c,  fig.  436 ;  so  that  the  left  portion  of  one  eye  lies 
over  the  identical  left  portion  of  the  other  eye,  the  right  portion  of  one 
eye  over  the  identical  right  portion  of  the  other  eye ;  and  with  the 
upper  and  lower  portions  of  the  two  eyes,  a  lies  over  a',  h  over  h ,  and  c 
over  c' .  The  points  of  the  one  retina  intermediate  between  a  and  c  are 
again  identical  with  the  corresponding  points  of  the  other  retina  between 
a'  and  c' ;  those  between  h  and  c  of  the  one  retina,  with  those  between  V 
and  c  of  the  other.  If  the  axes  of  the  eyes,  A  and  b-  (fig.  437),  be  so 
directed  that  they  meet  at  a,  an  object  at  a  will  be  seen  singly,  for  the 


708 


HANDBOOK    OF    PHYSIOLOGY. 


point  a  of  the  one  retina,  and  a  of  the  other  are  identical.  So,  also,  if 
the  object  /5  be  so  situated  that  its  image  falls  in  both  eyes  at  the  same 
distance  from  the  central  point  of  the  retina, — namely,  at  l  in  the  one 
eye,  and  at  V  in  the  other, — [i  will  be  seen  single,  for  it  affects  identical 
parts  of  the  two  retinae.     The  same  will  apply  to  the  object  y. 

In  quadrupeds,  the  relation  between  the  identical  and  non-identical 
parts  of  the  retina  cannot  be  the  same  as  in  man;  for  the  axes  of  their 
eyes  generally  diverge,  and  can  never  be  made  to  meet  in  one  point  of 
an  object.  When  such  an  animal  regards  an  object  situated  directly  in 
front  of  it,  the  image  of  the  object  must  fall,  in  both  eyes,  on  the  outer 
portion  of  the  retinae.  Thus  the  image  of  the  object  a  (fig.  438)  will  fall 
at  a'  in  one,  and  at  a!'  in  the  other:  and  these  points  a'  and  a"  must  be 
identical.     So,  also,  for  distinct  and  single  vision  of  objects,  h  or   c,  the 


Fig.  437. 


Fig.  438. 


Fig.  437.— Diagram  to  show  the  simultaneous  action  of  the  eyes   in  viewing  objects  in  dif- 
ferent directions. 

Fig.  438.  —Diagram  to  show  the  corresponding  parts  of  the  retina  in  the  horse. 

points  V  and  V  or  c'  c\  in  the  two  retinae,  on  which  the  images  of  these 
objects  fall,  must  be  identical.  All  points  of  the  retina  in  each  eye 
which  receive  rays  of  light  from  lateral  objects  only,  can  have  no  corre- 
sponding identical  points  in  the  retina  of  the  other  eye;  for  otherwise 
two  objects,  one  situated  to  the  right  and  the  other  to  the  left,  would 
appear  to  lie  in  the  same  spot  of  the  field  of  vision.  It  is  probable, 
therefore,  that  there  are  in  the  eyes  of  animals,  parts  of  the  retinae 
which  are  identical,  and  parts  which  are  not  identical,  i.e.^  parts  in  one 
which  have  no  corresponding  parts  in  the  other  eye.  And  the  relation 
of  the  two  retinae  to  each  other  in  the  field  of  vision  may  be  represented 
as  in  fig.  439. 

The  cause  of  the  impressions  on  the  identical  points  of  the  two  retinae 
giving  rise  to  but  one  sensation,  and  the  perception  of  a  single  image, 


THE    SEXSES, 


709 


must  either  lie  in  the  structural  organization  of  the  deeper  or  cere- 
bral portion  of  the  visual  apparatus,  or  be  the  result  of  a  mental  opera- 
tion; for  in  no  other  case  is  it  the  property  of  the  corresponding  nerves 
of  the  two  sides  of  the  body  to  refer  their  sensations  as  one  to  one  spot. 


Many  attempts  have  been  made  to  explain  this  remarkable  relation 
between  the  eyes,  by  referring  it  to  anatomical  relation  between  the 
optic  nerves.  The  circumstance  of  the  inner  j^ortion  of  the  fibres  of  the 
two  optic  nerves  decussating  at  the  commissure,  and  passing  to  the  eye 
of  the  opposite  side,  while  the  outer  portion  of  the  fibres  continue  their 
course  to  the  eye  of  the  same  side,  so  that  the  left  side  of  both  retinae  is 
formed  from  one  root  of  the  nerves,  and  the  right  side  of  both  retinae 
from  the  outer  root,  naturally  led  to  an  attempt  to  explain  the  phenomenon 
by  this  distribution  of  the  fibres  of  the  nerves  And  this  explanation  is 
favored  by  cases  in  which  the  entire  of  one  side  of  the  retina,  as  far  as 
the  central  jDoint  in  both  eyes,  sometimes  becomes  insensible.  But 
Midler  has  endeavored  to  show  the  inadequateness  of  this  theory  to  ex- 
plain the  phenomenon,  unless  it  be  supposed  that  each  fibre  in  each  cere- 
bral portion  of  the  optic  nerves  divides  in  the  optic  commissure  into  two 


Fig.  440.— Diagrams  to  iUustrate  tliree  theories  to  explain  the  action  of  symmetrical  parts  of 

the  retina. 

branches  for  the  identical  points  of  the  two  retinae,  as  is  shown  in  a, 
fig.  440.     But  there  is  no  foundation  for  such  supjDOsition. 

By  another  theory  it  is  assumed  that  each  optic  nerve  contains  exactly 
the  same  number  of  fibres  as  the  other,  and  that  the  corresponding  fibres 
of  the  two  nerves  are  united  in  the  sensorium  (as  in  fig.  440,  b).  But 
in  this  theory  no  account  is  taken  of  the  partial  decussation  of  the  fibres 
of  the  nerves  in  the  optic  commissure. 


710 


HANDBOOK    OF    PHYSIOLOGY. 


According  to  a  third  theory,  the  fibres  a  and  «',  fig,  440,  c,  coming 
from  identical  points  of  the  two  retinae,  are  in  tlie  optic  commissure 
brought  into  one  optic  nerve,  and  in  the  brain  either  are  united  by  a 
loop,  or  spring  from  the  same  point.  The  same  disposition  prevails  in 
the  case  of  the  identical  fibres  I  and  V .  According  to  this  theory,  the 
left  half  of  each  retina  would  be  represented  in  the  left  hemisphere  of 
the  brain,  and  the  right  half  of  each  retina  in  the  right  hemisphere. 

Another  explanation  is  founded  on  the  fact,  that  at  the  anterior  part 
of  the  commissure  of  the  optic  nerve,  certain  fibres  pass  across  from  the 
distal  portion  of  one  nerve  to  the  corresponding  portion  of  the  other 
nerves,  as  if  they  were  commissural  fibres  forming  a  connection  between 
the  retinae  of  the  two  eyes.  It  is  supposed,  indeed,  that  these  fibres  may 
connect  the  corresponding  parts  of  the  two  retinas,  and  may  thus  explain 
their  unity  of  action ;  in  the  same  way  that  corresponding  parts  of  the 
cerebral  hemispheres  are  believed  to  be  connected  together  by  the  com- 
missural fibres  of  the  corpus  callosum,  and  so  enabled  to  exercise  unity  of 
function. 

Judgment  of  Solidity. — On  the  whole,  it  is  probable,  that  the  power 
of  forming  a  single  idea  of  an  object  from  a  double  impression  conveyed 


F      1 


Fig.  441.— Diagrams  to  iUustrate  how  a  judgment  of  a  figure  of  three  dimensions  is  obtained. 

by  it  to  the  eyes  is  the  result  of  a  mental  act.  This  view  is  supported 
by  the  same  facts  as  those  employed  by  Wheatstone  to  show  that  this 
power  is  subservient  to  the  purpose  of  obtaining  a  right  perception  of 
bodies  raised  in  relief.  When  an  object  is  placed  so  near  the  eyes  that 
to  view  it  the  optic  axes  must  converge,  a  different  perspective  projec- 
tion of  it  is  seen  by  each  eye,  these  perspectives  being  more  dissimilar  as 
the  convergence  of  the  optic  axes  becomes  greater.  Thus,  if  any  figure 
of  three  dimensions,  an  outline  cube,  for  example,  be  held  at  a  moderate 
distance  before  the  eyes,  and  viewed  with  each  eye  successively  while  the 
head  is  kept  perfectly  steady,  a  (fig.  441)  will  be  the  picture  presented 
to  the  right  eye,  and  b  that  seen  by  the  left  eye.  Wheatstone  has  shown 
that  on  this  circumstance  depends  in  a  great  measure  our  conviction 
of  the  solidity  of  an  object,  or  of  its  projection  in  relief.  If  different 
perspective  drawings  of  a  solid  body,  one  representing  the  image  seen  by 
the  right  eye,  the  other  that  seen  by  the  left  (for  example,  the  drawing 


THE    SENSES.  711 

of  a  cube,  a,  b,  fig.  441)  be  presented  to  corresponding  parts  of  the  two 
retina?,  as  may  be  readily  done  by  means  of  the  stereoscope,  the  mind 
will  perceive  not  merely  a  single  representation  of  the  object,  but  a  body 
projecting  in  relief,  the  exact  counterpart  of  that  from  which  the  draw- 
ings were  made. 

By  transposing  tAvo  stereoscopic  pictures  a  reverse  effect  is  produced ; 
the  elevated  parts  appear  to  be  depressed,  and  rice  versa.  An  instru- 
ment contrived  with  this  purpose  is  termed  apsei(dosc02)e.  Viewed  with 
this  instrument  a  bust  appears  as  a  liollow  mask,  and  as  may  readily  be 
imagined  the  effect  is  most  bewildering. 

There  can  be  no  doubt  in  order  that  the  image  of  an  object  should  fall 
upon  corresponding  points  in  the  two  retinae,  it  is  essential  that  the  move- 
ments of  the  eyes  should  be  accurately  co-ordinated,  and  the  method  of 
this  co-ordination  is  not  so  easily  understood  when  examined  carefully. 
Thus,  suppose  the  eyes  be  directed  downward  and  to  the  left.  On  the  left 
side,  the  inferior  rectus,  the  external  rectus,  and  the  superior  oblique 
would  contract,  and,  on  the  right  side  the  inferior  rectus,  internal  rectus, 
and  superior  oblique.  In  other  words,  a  different  set  of  muscles  on 
either  side,  and  suj^plied  to  a  certain  extent  by  different  nerves.  There 
must  be  some  co-ordinating  centre  for  these  binocular  movements.  It  is 
thought  that  this  centre  is  localized  in  the  anterior  corpus  quadrigemi- 
num,  since  stimulation  of  it  causes  conjugal  lateral  movement  of  the  visual 
axes  to  the  opposite  side,  and  stimulation  at  another  spot  produces  move- 
ments downward  and  inward.  The  posterior  longitudinal  bundle  of  fibres 
described  as  found  in  the  pons  and  crus,  appears  to  be  concerned  in  some 
way  with  the  simultaneous  movement  of  the  eyes;  it  appears  to  unite  the 
nuclei  of  the  three  nerves  to  the  ocular  muscles,  the  sixth,  fourth,  and 
third.  In  it  are  said  to  be  contained  fibres  from  the  sixth  nerve  of  the 
opposite  side  which  go  to  the  nucleus  of  the  third  nerve  of  the  same  side; 
and  this  would  serve  to  connect  the  nerve  supply  of  the  internal  rectus 
of  one  side,  and  the  external  rectus  of  the  other  side.  It  appears,  how- 
ever, that  there  is  no  evidence  to  assume  that  the  fibres  of  the  sixth 
nerve  decussate,  but  thpse  of  the  fourth  nerve  do  entirely,  and  those  of 
the  third,  partially. 


CHAPTER  XVIII. 

THE    REPRODUCTIVE    ORGANS. 

Before  describing  the  method  of  Keproduction,  or  the  way  which  the 
species  is  propagated,  it  will  be  advisable  to  describe 

The  Genital  Orgaxs  of  the  Female. 

The  female  organs  of  generation  (fig.  442)  consist  of  two  ovaries,  the 
function  of  which  is  the  formation  of  ova;  of  a  Fallopian  tube,  or 
oviduct,  connected  with  each  ovary,  for  the  purpose  of  conducting  the 
ovum  from  the  ovary  to  the  uterus  in  the  cavity  of  which,   if  impreg- 


Fig.  442.  —Diagrammatic  view  of  the  uterus  and  its  appendages,  as  seen  from  behind.  The 
uterus  and  upper  part  of  the  vagina  have  been  laid  open  by  removing  the  posterior  wall ;  the 
Fallopian  tube,  round  ligament,  and  ovarian  ligament  have  been  cut  short,  and  the  broad  liga- 
ment removed  on  the  left  side;  it,  the  upper  part  of  the  uterus;  c,  the  cervix  opposite  the  os  in- 
ternum; tlie  triangular  shape  of  the  uterine  cavity  is  shown,  and  the  dilatation  of  the  cervical 
cavity  with  the  rugae  termed  arbor  vitae;  v,  upper  part  of  the  vagina ;  od.  Fallopian  tube  or 
oviduct;  the  narrow  communication  of  its  cavity  with  that  of  the  cornu  of  the  uterus  on  each 
side  is  .seen;  ?,  round  ligament;  /o,  ligament  of  the  ovary;  o,  ovary;  (,  wide  outer  part  of  the 
right  Fallopian  tube;  fi,  its  fimbriated  extremity;  po,  parovarium;  h,  one  of  the  hydatids  fre- 
quently found  connected  with  the  broad  ligament.     }^.     (Allen  Thomson.) 

nated,  it  is  retained  until  the  embryo  is  fully  developed,  and  fitted  to 
maintain  its  existence  independently  of  internal  connection  with  the 
parent;  and,  lastly,  of  a  canal,  or  vagina,  with  its  appendages,  for  the 
reception  of  a  male  organ  in  the  act  of  copulation,  and  for  the  subsequent 
discharge  of  the  foetus. 

The  Ovaries. — The  ovaries  are  two  oval  compressed  bodies,  situated 
in  the  cavity  of  the  pelvis,  one  on  each  side,  and  are  adherent  to  the 
posterior  surface  of  the  broad  ligament  by  their  anterior  border.      This 


THE    REPRODUCTIVE    ORGANS,  713 

"border  of  the  ovary  is  called  the  hilum,  and  it  is  at  this  point  that  the 
blood-vessels  and  nerves  enter  it.  Each  ovary  measures  about  an  inch 
and  a  half  in  length  (3.75  cm.),  three  quarters  of  an  inch  in  width 
(1.86  cm.),  and  nearly  half  an  inch  (1.25  cm.)  in  thickness,  and  is 
attached  to  the  uterus  by  a  narrow  fibrous  cord  (the  ligament  of  the 
ovary),  and,  more  slightly,  to  the  Fallopian  tubes,  by  one  of  the  fimbriae 
into  which  the  walls  of  the  extremity  of  the  tube  expand. 

Structure. — A  layer  of  condensed  connective  tissue,  called  the  tunica 
albnginea,  surrounds  the  ovary,  and  this  is  covered  on  the  outside  by  epi- 
thelium (germ-epithelium),  the  cells  of  which  although  continuous  with, 


FiR.  443. — View  of  a  section  of  the  ovary  of  the  cat.  1,  outer  covering  and  free  border  of 
the  ovary;  1',  attached  border;  2,  the  ovarian  stroma,  presenting  a  fibrous  and  vascular  struct- 
ure; 3,  granular  substance  lying  external. to  the  fibrous  stroma;  4,  blood-vessels;  5,  ovigerms  in 
their  earliest  stages  occupying  a  part  of  the  granular  layer  near  the  surface;  6,  ovigerms  which 
have  begun  to  enlarge  and  to  pass  more  deeply  into  the  ovary;  7,  ovigerms  round  which  the 
Graafian  follicle  and  tunica  granulosa  are  now  formed,  and  which  have  passed  somewhat  deeper 
into  the  ovary  and  are  surrounded  by  the  fibrous  stroma;  8,  more  advanced  Graafian  follicle 
with  the  ovum  imbedded  in  the  layer  of  cells  constituting  the  proligerous  disc;  9,  the  most  ad- 
vanced follicle  containing  the  ovum,  etc.  ;  9',  a  follicle  from  which  the  ovimi  lias  accidentally 
escaped;  10,  corjjus  luteum.     x  6.     (Schron.) 

and  originally  derived  from,  the  squamous  epithelium  of  the  peritoneum, 
are  short  columnar  (A,  fig,  444). 

The  internal  structure  of  the  organ  consists  of  a  peculiar  soft  fibrous 
tissue — a  kind  of  undeveloped  connective  tissue,  with  long  nuclei 
closely  resembling  unstriped  muscle  (C,  fig. 444) — or  stroma,  abundantly 
supplied  with  blood-vessels,  and  having  embedded  in  it,  in  various  stages 
of  development,  numerous  minute  follicles  or  vesicles,  the  Graafian 
follicles,  or  sacculi,  containing  the  ova  (fig.  444). 

If  the  ovary  be  examined  at  any  period  between  early  infancy  and 
advanced  age,  but  especially  during  that  period  of  life  in  which  the 
power  of  conception  exists,  it  wnll  be  found  to  contain  a  number  of 
these  vesicles.  Immediately  after  the  tunica  albuginea  (fig.  444)  they 
are  small  and  numerous,  either  arranged  as  a  continuous  layer,  as  in  the 
•cat  or  rabbit,  or  in  groups,  as  in  the  human  ovary.     These  small  follicles 


714  HANDBOOK    OF    PHYSIOLOGY. 

embedded  in  the  soft  stroma  of  fine  connective  tissue  and  unstriped 
muscle  form  here  the  cortical  layer;  they  are  sometimes  called  ovisacs. 

Each  of  the  small  follicles  of  this  layer  has  an  external  membranous 
envelope,  or  membrana  propria.     This  envelope  or  tunic  is  lined  with  a 


Fig.  444. — Section  of  the  ovary  of  a  cat.  A,  germinal  epithelium;  B,  immature  Graafian 
follicle;  C,  stroma  of  ovary;  D,  vitelline  membrane  containing  the  ovum;  E,  Graafian  follicle 
showing  lining  cells;  F,  follicle  from  which  the  ovum  has  fallen  out.     (V.  D.  Harris.) 

layer  of  nucleated  cells,  forming  a  kind  of  epithelium  or  internal  tunic, 
and  named  the  ynemhrana  granulosa.  The  cavity  of  the  follicle  is  filled 
up  by  a  nucleated  mass  of  protoplasm  inclosed  in  a  very  delicate  mem- 
brane, which  is  the  Ovum.  The  large  spherical  nucleus  contains  one 
or  more  nucleoli.  The  nucleus  is  known  as  the  germinal  vesicle,  and 
the  nucleolus  as  the  germinal  spot. 

The  central  portion  of  the  stroma  of  the  ovary  extends  from  the  cor- 
tical layer  to  the  hilum  of  the  organ,  at  which  enter  the  numerous 
arteries,  fibrous  tissue,  and  unstriped  muscle,  forming  a  highly  vascular 
zona  vasculosa.  Within  this  central  zone  are  contained  the  fully-devel- 
oped Graafian  follicles,  varying  in  size  however,  but  considerably  larger 
than  those  of  the  cortical  layer.  In  these  follicles  the  cavity  is  not 
nearly  filled  by  the  ovum,  which  is  attached  at  one  side  to  the  zona 
granulosa  by  a  collection  of  small  cells,  the  discus  proligerus,  the 
remainder  of  the  cavity  being  filled  with  fluid,  the  liquor  folliculi.  The 
envelope  of  the  ovum,  or  zona  pellucida,  is  much  thicker.  The  zona 
granulosa  is  formed  of  several  layers  of  cells,  instead  of  one  only.  Its 
membrana  propria  is  much  thicker,  so  as  to  form  a  distinct  fibrous  in- 
vestment; the  membrana  fibrosa  and  the  blood-vessels  surrounding  it  are 
numerous,  and  may  be  said  to  form  a  membrana  vasculosa  about  it. 

Tjie  human  ovum  measures  about  y^  of  an  inch  (about  .2  mm.)  in 
diameter.     Its  external  investment,  or  the  zona  pellucida,  or  vitelline 


THE    REPRODUCTIVE    ORGANS. 


715 


membrane^  is  a  transparent  membrane,  about  arW  ^f  an  inch  (10m)  in 
thickness,  which  under  the  microscopic  appears  as  a  bright  ring  (fig. 
445),  bounded  externally  and  internally  by  a  dark  outline.  Within  this 
transparent  investment  or  zona  pellucida,  and  usually  in  close  contact 
with  it,  lies  the  yolk  or  viteUus,  which  is  composed  of  granules  and  glob* 
nles  of  various  sizes,  imbedded  in  a  more  or  less  fluid  substance.  The 
smaller  granules,  which  are  tbe  more  numerous,  resemble  in  their  appear- 
ance, as  well  as  their  constant  motion,  pigment-granules.  The  larger 
granules  or  globules,  which  have  the  aspect  of  fat-globules,  are  in 
greatest  number  at  the  periphery  of  the  yolk.  The  number  of  the  gran- 
ules is  greatest  in  the  ova  of  carnivorous  animals.  In  the  human  ovum 
their  quantity  is  comparatively  small. 

In  the  substance  of  the  yolk  is  imbedded  the  germinal  vesicle,  or  ves- 
icula  germinativa,  5-^  of  an  inch  (.05  mm.)  (fig.  445).  The  vesicle  is  of 
greatest  relative  size  in  the  smallest  ova,  and  is  in  them  surrounded 
closely  by  the  yolk,  nearly  in  the  centre  of  which  it  lies.  During  the 
development  of  the  ovum,  the  germinal  vesicle  increases  in  size  much  less 
rapidly  than  the  yolk,  and  comes  to  be  placed  near  to  its  surface.  It 
consists  of  a  fine,  transparent,  structureless  membrane,  containing  a  clear, 
watery  fluid,  in  which  are  sometimes  a  few  granules;  and  at  that  part  of 
the  periphery  of  the  germinal  vesicle  which  is  nearest  to  the  periphery  of 
the  yolk  is  situated  the  germinal  spot,  or  macula  germinativa,  of  a  finely 


Nucleus  or  germinal  vesicle. 
Nucleolus  or  germinal  spot. 

Space  left  by  retraction  of 
yolk. 

Yolk  or  vitellus. 


Vitelline  membrane. 


Fig.  445.  — Semidiagrammatie  represention  of  a  himsan  ovxmi,  showing  the  parts  of  an  animal 

cell.    (Cadiat.) 

granulated  appearance  and  of  a  yellowish  color,  strongly  refracting  the 
rays  of  light. 

Such  are  the  parts  of  which  the  Graafian  follicle  and  its  contents, 
including  the  ovum,  are  composed.  With  regard  to  the  mode  and  order 
of  development  of  these  parts  there  is  considerable  uncertainty. 

The  Graafian  follicles  are  formed  in  the  following  manner : — The  em- 
bryonic ovary  is  covered  with  short  columnar  cells,  or  the  so-called  germ- 
inal epithelium.  The  cells  of  this  layer  undergo  proliferation,  so  as  to 
form  several  strata,  and  grow  into  tlie  ovarian  stroma  as  longer  or  shorter 


710 


HANDBOOK    OF    PHYSIOLOGY, 


columns  or  tubes.  By  degrees  these  tubes  become  cut  off  from  the  surface 
epithelium,  and  form  cell  nests,  small,  if  near  the  surface,  larger  if  in 
the  depth  of  the  stroma.  The  nests  increase  in  size  from  multiplication 
of  their  cells,  and  may  even  give  off  new  nests  laterally  by  constriction  of 
them  in  various  directions.  Certain  of  the  cells  of  the  germinal 
epithelium  enlarge,  and  form  ova ;  and  the  formation  of  ova  also  takes 
place  in  the  nests  Avithin  the  stroma.  The  ova  of  a  nest  may  multiply 
by  division.  The  small  cells  of  a  nest  surround  the  ova,  and  form  their 
membrana  granulosa,  and  the  stroma  growing  up  separates  the  surrounded 
ova  into  so  many  Graafian  follicles.  The  other  layers,  namely,  the  mem- 
brana fibrosa  and  the  membrana  vasculosa,  are  derived  from  the  stroma. 

The  smallest  follicles  are  formed  at  the  surface,  and  make  up  the  cor- 
tical layer.  It  is  said  by  some  that  the  superficial  follicles  as  they  ripen 
become  more  deeply  placed  in  the  ovarian  stroma;  and,  again,  that  as 
they  increase  in  size,  they  make  their  way  toward  the  surface  (fig,  443). 

When  mature,  they  form  little  prominences  on  the  exterior  of  the 
ovary,  covered  only  by  a  thin  layer  of  condensed  fibrous  tissue  and  epithe- 
lium.    Only  a  few  follicles  ever  reach  maturity. 

From  the  earliest  infancy,  and  through  the  whole  fruitful  period  of 
life,  there  appears  to  be  a  constant  formation,  development,  and  matura- 


Fig.  446.- 


-Germinal  epithelium  of  the  ssrface  of  the  ovary  of  five  days'  chick, 
blasts;  6,  larger  ovoblasts.     (Cadiat.) 


a,  small  ovo- 


tion  of  Graafian  vesicles,  with  their  contained  ova.  Until  the  period  of 
puberty,  however,  the  process  is  comparatively  inactive;  for,  previous  to 
this  period,  the  ovaries  are  small  and  pale,  the  Graafian  vesicles  in  them 
are  very  minute,  and  probably  never  attain  full  development,  but  soon 
shrivel  and  disappear,  instead  of  bursting,  as  matured  follicles  do; 
the  contained  ova  are  also  incapable  of  being  impregnated.  But,  coin- 
cident with  the  other  changes  which  occur  in  the  body  at  the  time  of 
puberty,  the  ovaries  enlarge,  and  become  very  vascular,  the  formation 
of  Graafian  vesicles  is  more  abundant,  the  size  and  degree  of  development 
attained  by  them  are  greater,  and  the  ova  are  capable  of  being  fecun- 
dated. 

The  Fallopian  Tubes  (Oviducts). — The  Fallopian  tubes  are  about 
four  inches  in  length  (10  cm.),  and  extend  between  the  ovaries  and  the 


THE    REPRODUCTIVE    ORGANS.  717 

upper  angles  of  the  uterus.  At  the  point  of  attachment  to  the  uterus, 
each  tube  is  very  narrow ;  but  iu  its  course  to  the  ovary  it  increases  to 
about  an  eighth  of  an  inch  (3  mm.)  in  thickness;  at  its  distal  extremity, 
which  is  free  and  floating,  it  bears  a  number  of  fimbrim,  one  of  which, 
longer  than  the  rest,  is  attached  to  the  ovary.  The  canal  by  which  each 
tube  is  traversed  is  narrow,  especially  at  its  point  of  entrance  into  the 
uterus,  at  which  it  will  scarcely  admit  a  bristle;  its  other  extremity  is 
wider,  and  opens  into  the  cavity  of  the  abdomen,  surrounded  by  the  zone 
of  fimbriis.  Externally,  the  Fallopian  tube  is  invested  with  peritoneum; 
internally,  its  canal  is  lined  with  mucous  membrane,  which  is  apt  to  be 
thrown  into  numerous  longitudinal  folds,  covered  with  ciliated  epithe- 
lium: between  the  peritoneal  and  mucous  coats  the  walls  are  comjiosed, 
like  those  of  the  ut'erus,  of  fibrous  tissue  and  unstriped  muscular  fibres, 
chiefly  circular  in  arrangement. 

The  Uterus. — The  uterus  {u.  c,  fig.  442)  is  a  somewhat  pyriform 
shaped  organ,  and  in  the  unimpregnated  state  is  about  three  inches  (7.5 
cm.)  in  length,  two  (5  cm.)  in  breadth  at  its  upper  part  ov  fundus,  but  at 
its  lower  jiointed  part,  neck  or  cervix,  only  about  half  an  inch  (1.25  cm.). 
The  part  between  the  fundus  and  neck  is  termed  the  hody  of  the 
uterus:  it  is  about  an  inch  (2.5  cm.)  in  thickness. 

Structure. — The  uterus  is  constructed  of  three  principal  layers,  or 
coats — serous,  fibrous  and  muscular,  and  mucous,  {a)  The  serous  coat, 
which  has  the  same  general  structure  as  the  peritoneum,  covers  the 
organ  before  and  behind,  but  is  absent  from  the  front  surface  of  the 
neck.  (J))  The  middle  coat  is  composed  of  unstriped  muscle,  arranged 
in  the  human  uterus  in  three  layers  from  without  inward,  longitudinal, 
circular,  oblique  and  circular.  They  become  enormously  developed  dur- 
ing pregnancy.  The  arteries  and  veins  are  found  in  large  numbers  in 
the  outer  part  of  their  coat,  so  as  to  form  almost  a  special  vascular  coat. 
(t)  The  mucous  membrane  of  the  uterus  is  lined  by  columnar  ciliated 
epithelium,  which  extends  also  to  the  interior  of  the  tubular  glands,  of 
which  the  mucous  membrane  is  largely  made  up. 

In  the  cervix  uteri  the  mucous  membrane  is  arranged  in  jiermanent 
longitudinal  folds,  2)ahncB  2)licut(B.  The  glands  of  this  part  are  of  the 
tubulo-racemose  type,  branching  repeatedly  and  extending  deeply  into 
the  substance  of  the  cervix.  They  are  lined  by  columnar  epithelium, 
and  open  on  the  ridges  and  furrows  of  the  mucous  membrane.  They 
secrete  a  thick  glairy  mucus,  resembling  unboiled  white  of  egg. 

The  mucous  membrane  of  the  cavity  of  the  body  of  the  uterus 
forms  a  thin  membrane  about  -^  inch  (1  mm.)  thick,  and  is  covered  on  its 
surface  by  columnar  ciliated  epithelium.  Imbedded  in  its  substance  are 
numerous  simple  tubular  glands  set  somewhat  obliquely  and  lined  with 
columnar  ciliated  epithelium.       These  glands  often  bifurcate  at  their 


718  HANDBOOK    OF    PHYSIOLOGY. 

lower  ends.  The  glands  are  imbedded  in  a  delicate  connective  tissue, 
consisting  of  round  and  spindle-shaped  cells. 

The  cavity  of  the  uterus  corresponds  in  form  to  tliat  of  the  organ 
itself:  it  is  very  small  in  the  uuimpregnated  state,  the  sides  of  its  mucous 
surface  being  almost  in  contact.  Into  its  upper  part,  at  each  side,  opens 
the  canal  of  the  corresponding  Fallopian  tube:  below,  it  communicates 
with  the  vagina  by  a  fissure-like  opening  in  its  neck,  the  as  uteris  the 
margins  of  which  are  distinguished  into  two  lips,  an  anterior  and  pos- 
terior. 

The  Vagina  is  a  membranous  canal,  five  or  six  inches  (12.5  to  15 
cm.)  long,  extending  obliquely  downward  and  forward  from  the  neck 
of  the  uterus,  which  it  emt/races,  to  the  external  organs  of  generation. 
It  is  lined  with  mucous  membrane,  covered  with  stratified  squamous 
epithelium,  which  in  the  ordinary  contracted  state  of  the  canal  is  thrown 
into  transverse  folds.  External  to  the  mucous  membrane  the  walls  of 
the  vagina  are  constructed  of  unstriped  muscle  and  fibrous  tissue, 
within  which  in  the  submucosa,  esj)ecially  around  the  lower  part  of  the 
tube,  is  a  layer  of  erectile  tissue.  This  exists  also  in  the  mucosa.  The 
lower  extremity  of  the  vagina  is  embraced  by  an  orbicular  muscle,  the 
spliinder  vagince;  its  external  orifice,  in  the  virgin,  is  partially  closed  by 
a  fold  or  ring  of  mucous  membrane,  termed  the  hymen.  The  external 
organs  of  generation  consist  of  the  clitoris,  a  small  elongated  body, 
situated  above  and  in  the  middle  line,  and  constructed  of  two  erectile 
masses  or  corpora  cavernosa.  They  are  not  perforated  by  the  urethra; 
of  two  folds  of  mucous  membrane,  termed  laMa  interna,  or  nymphce;  and, 
in  front  of  these,of  two  other  folds,  the  labia  externa,  ov  pudenda,  formed 
of  the  external  integument,  and  lined  internally  by  mucous  membrane. 
Between  the  nymphse  and  beneath  the  clitoris  is  an  angula  space,  termed 
the  vestibule,  at  the  centre  of  whose  base  is  the  orifice  of  the  meatus 
urinarius.  Numerous  mucous  follicles  are  scattered  beneath  the  mucous 
membrane  composing  these  parts  of  the  external  organs  of  generation; 
and  at  the  side  of  the  lower  part  of  the  vagina  are  two  larger  lobulated 
glands,  vulvo-vaginal  or  Duverney's  glands,  which  are  analogous  to  Cow- 
per's  glands  in  the  male.  The  ducts  of  these  glands  are  about  ^  inch 
(12.5  mm.)  long  and  open  immediately  external  to  the  hymen  at  the 
mid-point  of  the  lateral  wall  of  the  vaginal  orifice.  The  vulvo-vaginal 
glands  secrete  a  thick  brownish  mucus. 

The  Genital  Organs  of  the   Male. 

The  male  organs  of  generation  comprise  the  two  Testes,  in  which 
the  semen  is  formed ;  each  with  a  duct,  the  Vas  Deferens,  and  accessory 
Vesicula  Semmalis;  the  Penis,  an  erectile  organ,   through  which  the 


THE    REPRODUCTIVE    ORGANS. 


719 


semen  as  well  as  the  urine  is  discharged.  The  Prostate  gland^  the 
exact  function  of  which  is  not  understood,  is  generally  included  in  the 
same  class. 

The  Testes. — The  secreting  structure  of  the  testicle  and  its  duct 
are  disposed  of  in  two  contiguous,  parts  (1)  the  body  of  the  testicle  proper, 
inclosed  within  a  thick  and  tough  white  fibrous  membrane,  the  tunica 
albuginea,  on  the  outer  surface  of  which  is  the  serous  covering  formed  by 
the  tunica  vaginalis,  and  (2)   the  epididymis  and  vas  deferens. 

The  Vas  deferens,  or  duct  of  the  testicle,  which  is  about  two  feet 
(60  cm.)  in  length,  is  constructed  externally  of  connective  tissue,  and 
internally  is  lined  by  a  mucous  membrane,  covered  with  columnar  epithe- 
lium ;  while  between  these  two  coats  is  a  middle  coat,  very  firm  and  tough, 
made  up  of  unstriped  muscle,  chiefly  arranged  longitudinally,  but  also 
containing  some  circular  fibres.  When  followed  back  to  its  origin,  the 
vas  deferens  is  found  to  pass  to  the  lower  part  of  the  epididymis,  with 


Fig.  447. 


Fig.  448. 


Fig.  447.— Plan  of  a  vertical  section  of  fie  testicle,  showing  the  arrangement  of  the  ducts. 
The  true  length  and  diameter  of  the  ducts  have  been  disregarded,  a  a,  tubuli  seminiferi  coiled 
up  in  the  separate  lobes;  6,  tubuli  recti  or  vasa  recta;  c,  rete  testis;  d,  vasa  efEerentia  ending 
in  the  coni  vasculosi ;  I,  e,  g,  convoluted  canal  of  the  epididymis ;  h,  vas  deferens ;  /,  section  of 
the  back  part  of  the  tunica  albuginea;  i,  ?,  fibrous  processes  running  between  the  lobes;  s,  me- 
diastinum. 

Fig,  448. — Section  of  the  epididymis  of  a  dog.— The  tube  is  cut  in  several  places,  both  trans- 
versely and  obliquely;  it  is  seen  to  be  lined  by  a  ciliated  epithelium,  the  nuclei  of  which  are 
well  shown,     c,  connective  tissue.     (Schofleld.) 


which  it  is  directly  continuous  (fig. 447) ,  and  assumes  there  a  much  smaller 
diameter  with  an  exceedingly  tortuous  course. 

The  Epididymis,  which  is  lined,  except  at  its  lowest  part,  by  co- 


720  HANDBOOK    OF    PHYSIOLOGY. 

luinnar  ciliated  epithelium  (fig.  447),  is  commonly  described  as  con- 
sisting (fig.  447)  of  a, globus  minor  {g),  the  body  (e),  and  the  globus  7naj or 
{I.)  When  unravelled  it  is  found  to  be  constructed  of  a  single  tube,  meas- 
uring about  twenty  feet  in  length. 

At  the  globus  major  this  duct  divides  into  ten  or  twelve  small 
branches,  the  convolutions  of  which  form  coniform  masses,  named  Coni 
vasculosi;  and  the  ducts  continued  from  these,  the  Vasa  efferetitia,  after 
anastomosing,  one  with  another  in  what  is  called  the  Rete  testis,  lead 
finally  as  the  Tubuli  recti  ov  Vasa  recta  to  the  seminal  tubules  (tubuli 
seminiferi),  which  form  the  proper  substauce  of  the  testicle.  The 
epithelium  lining  the  coni  vasculosi  and  vasa  etferentia  is  columnar  and 
ciliated ;  that  of  the  rete  testis  is  squamous. 

The  seminal  tubules  are  arranged  in  lobules,  separated  from  one 
another  by  incomplete  fibrous  septa  or  cords,  which  pass  from  the  front 
of  the  tunica  albuginea  internally  to  a  firm  incomplete  vertical  septum 
of  thick  extending  fibrous  tissue  at  the  posterior  border,  from  the  upper 
to  near  the  lower  part,  called  the  corjms  Highmori,  or  tnediastiniim 
testis.  Through  this  very  firm  fibrous  tissue  pass  the  seminal  tubes  from 
the  vasa  recta.  The  tunica  albuginea  is  covered  by  a  very  fine  plexus  of 
blood-vessels  internally,  derived  from  the  spermatic  vessels.  The  fibrous 
cords  which  may  contain  unstriped  muscle  are  also  covered  with  a  similar 
capillary  plexus. 

Tubuli  Semhiiferi. — The  seminal  tubes,  which  compose  the  paren- 
chyma of  the  testicle,  are  loosely  arranged  in  lobules  between  the  connec- 
tive tissue  septa. 

They  are  relatively  large,  very  wavy,  and  much  convoluted;  and 
they  possess  a  few  lateral  branches,  by  which  they  become  connected 


Fig.  449.— From  a  section  of  the  testis  of  dog,  showing  portions  of  seminal  tubes.  A,  semi- 
nal epithelial  cells,  and  numerous  small  cells  loosely  arranged ;  B,  the  small  cells  or  sperm- 
atoblasts converted  into  spermatozoa;  groups  of  these  in  a  further  stage  of  development. 
(Klein.) 

into  a  network.  They  form  terminal  loops,  and  in  the  peripheral  por- 
tion of  the  testis  the  tubules  are  possessed  of  minute  lateral  caecal 
branchlets. 

Each  seminal  tubule  in  the  adult  testis  is  limited  by  a  membrana 


THE    REPRODUCTIVE    ORGANS. 


721 


propria,  which  appears  as  a  hyaline  elastic  membrane,  but  which  is 
really  made  up  of  several  incomplete  layers  of  flattened  cells,  contain- 
ing oval  flattened  nuclei  at  regular  intervals.  Inside  this  membrana 
propria  are  several  layers  of  epithelial  cells,  the  seminal  cells  (fig.  449). 
These  consist  of  two  or  more  layers,  the  outermost  being  situated  next 
the  membrana  propria.     These  cells  are  of  two  kinds,  those  that  are  in 


Fig  450.— Section  of  a  tubule  of  the  testicle  of  a  rat,  to  show  the  formation  of  the  sperm- 
atozoa;  a  spermatozoa;  6,  seminal  cells;  c.  spermatoblasts,  to  which  the  spermatozoa  are  still 
adherent ;  d,  membrana  propria ;  e,  flhro-plastic  elements  of  the  connective  tissue.     (Cadiat. ) 


a  resting  state,  which  generally  form  a  complete  layer,  and  those  that 
are  in  a  state  of  division,  of  which  there  may  be  two  layers.  The  latter 
are  called  mother  cells,  and  the  smaller  cells  resulting  from  their  division 
are  called  daughter  cells  or  spermatoblasts.  From  these  the  sperma- 
tozoa are  formed,  their  head  corresponding  with  the  nuclei  of  the 
daughter  cells;  and  during  their  development  they  lie  in  groups  (figs. 
449,450),  and  are  supported  by  irregular  masses  of  so-called  nutritive 
cells;  but  when  fully  formed,  they  become  detached,  and  fill  the  lumen 
of  the  seminiferous  tubule  (fig.  450).  This  detachment  is  effected  by 
the  liquefaction  of  the  nutritive  cells  in  which  the  groups  of  spermatozoa 
are  imbedded. 

In  the  fine  connective  tissue  which  supports  the  tubules  of  the  testis, 
are  to  be  found  flattened  and  nucleated  epithelial  cells,  probably  the 
remains  of  the  Wolffian  body.  The  lymphatics  of  the  testes  are  numer- 
ous, and  may  be  injected  by  inserting  the  needle  of  an  injecting  syringe 
into  the  tunica  albuginea,  and  pressing  in  the  injection  with  slight 
effort. 

The  Vesiculae  Seminales. — The  vesiculae  seminales  have  the  appear- 
ance of  outgrowths  from  the  vasa  deferentia.  Each  vas  deferens,  just 
46 


722  HANDBOOK    OF    PHYSIOLOGY. 

before  it  enters  the  prostate  gland,  through  part  of  which  it  passes  to 
terminate  in  tlie  urethra,  gives  oft  a  side  branch,  which  bends  back 
from  it  at  an  acute  angle:  and  this  branch  dilating,  variously  branching, 
and  pursuing  in  both  itself  and  its  branches  a  tortuous  course,  forms 
the  vesicula  seminalis. 

Structure. — Each  vesicula  may  be  unravelled  into  a  single  branching 
tube  sacculated,  convoluted,  and  folded  up. 

The  structure  resembles  closely  that  of  the  vasa  deferentia.  The 
mucous  membrane,  like  that  of  the  gall-bladder,  is  minutely  wrinkled 
and  set  with  folds  and  ridges  arranged  so  as  to  give  it  a  finely  reticu- 
lated appearance. 

The  Penis. — The  penis  is  composed  of  three  long  more  or  less 
cylindrical   masses,    inclosed     in    remarkably  firm   fibrous    sheaths,   of 


Fig.  451.— Dissection  of  the  base  of  the  bladder  and  prostate  gland,  showing  the  vesiculae 
seminales  and  vasa  deferentia.  a,  lower  surface  of  the  bladder  at  the  place  of  reflection  of  the 
peritoneum ;  6,  tlie  part  above  covered  hy  the  peritoneum ;  ?',  left  vas  deferens,  ending  in  e,  the 
ejaculatory  duct;  the  vas  deferens  has  been  divided  near  »,  and  all  except  the  vesical  por- 
tion has  been  taken  away;  s,  left  vesicuhv  setniiialis  joining  the  same  duct;  s,  s,  the  right  vas 
deferens  and  right  vesicula  seminalis,  which  has  been  unravelled;  »,  under  side  of  the  prostate 
gland;  m,  part  of  the  urethra;  w,  u.  the  xu-eters  (cut  short),  the  right  one  turned  aside. 
(Haller.) 

which  two,  the  corpora  cavernosa^  are  alike,  and  are  firmly  joined 
together,  and  receive  below  and  between  them  the  third  part,  or  corpus 
spongiosum.  The  urethra  j^asses  through  the  corpus  spongiosum.  The 
penis  is  attached  to  the  S3'mphysis  pubis  by  its  root.  The  enlarged  ex- 
tremity or  glans  penis  is  continuous  with  the  corpus  spongiosum.  The 
integument  covering  the  penis  forms  a  loose  fold  from  the  junction  of 
the  glans  with  the  body,  called  the  prepuce  or  foreskin. 


THE    KEPRODUCTIVE    ORGANS. 


723 


Structure.  —  [a.)  The  urethra  is  lined  by  stratified  pavement  epithe- 
lium in  the  prostatic  portion;  in  front  of  the  bulb  the  eijithelium 
becomes  columnar,  while  at  the  fossa  navicularis  it  is  again  lined 
with  stratified  j)avement  epithelium.  The  mucous  membrane  consists 
chiefly  of  fibrous  connective-tissue,  intermixed  with  which  are  many  elastic 
fibres.     It  is  surrounded  by  unstriped  muscular  tissue.     In  the  inter- 


Fig.  452.— Erectile  tissue  of  the  human  penis,    a,  fibrous    trabeculae  with  their  ordinary 
capiUaries;  6,  section  of  the  venous  sinuses;  c,  muscular  tissue.     (Cadiat.) 


mediate  portion  many  large  veins  run  amongst  the  bundles  of  muscular 
tissue.     Many  mucous  glands,  glands  of  Littre^  are  present. 

{p.)  The  coriwra  cavernosa,  a  true  erectile  structure,  are  surrounded 
by  a  dense  fibrous  and  elastic  sheath,  and  from  the  inner  surface  of  this, 
and  from  the  septum  which  sejaarates  the  two  corpora  cavernosa,  pass 
numerous  bundles  of  fibrous,  elastic,  and  plain  muscular  fibres,  called 
trabecnlce,  and  these  by  their  anastomosis  form  a  series  of  irregular 
spaces.  These  spaces  are  lined  with  endothelium,  and  are  filled  with 
venous  blood.  The  inter-trabecular  sjaaces  or  sinuses  of  one  corpus 
cavernosum  anastomose  with  those  of  the  other,  especially  in  front  where 
the  dividing  septum  is  incomplete, 

(c. )  The  corpus  spongiosum  urethra  consists  of  an  inner  portion  or 
plexus  of  longitudinal  veins,  and  of  an  outer  or  really  cavernous  portion 
identical  in  structure  with  that  which  has  just  been  described.  The 
lymphatics  of  the  penis  are  very  numerous,  both  superficially  and  also 
around  the  urethra.     They  join  the  inguinal  glands. 

The  nerves,  derived  from  the  pudic  nerves  and  hypogastric  plexus, 
are  distributed  to  the  skin  and  mucous  membrane  and  to  the  corpora 
cavernosa  and  spongiosum  respectively.  The  nerves  are  provided  with 
end  bulbs  and  Pacinian  corpuscles  in  the  glans  penis,  and  form  also  a 
dense  subepithelial  plexus. 

Gowpefs  glands,  are  two  small  glands,  the  ducts  of  which  open  into 


724 


HANDBOOK    OF    PHYSIOLOGY. 


the  second  part  of  the  urethra.  They  are  small  round  bodies,  of  the 
size  of  a  pea,  yellow  in  color,  resembling  the  sublingual  gland;  in 
structure  they  are  compound  tubular  mucous  glands. 

The  Prostate  Gland. — The  prostate  is  situated  (fig.  451)  at  the 
neck  of  the  urinary  bladder,  and  incloses  the  commencement  of  the 
urethra.  It  is  somewhat  chestnut-shaped.  It  measures  an  inch  and  a 
half  in  breadth,  and  an  inch  and  a  quarter  long,  and  half  an  inch  in 
thickness. 

Structure. — The  prostate  is  made  up  of  small  compound  tubular 
glands  imbedded  in  an  abundance  of  muscular  fibres  and  connective  tissue. 

The  glandular  substance,  which  is  nearly  absent  from  the  front  part 
of  the  organ,  consists  of  numerous  small  saccules,  opening  into  elongated 
ducts,  which  unite  into  a  smaller  number  of  excretory  ducts.      The  acini 


Big.  453.— Section  of  a  smaU  portion  of  the  prostate,     o,  gland  duct  cut  across  obliquely ;  6, 
gland  structm-e;  c,  prostatic  calculus.     (Cadiat.) 


of  the  upper  part  of  the  prostate  are  small  and  hemispherical ;  while 
in  the  middle  and  lower  parts  the  tubes  are  longer  and  more  convoluted. 
The  acini  are  of  two  kinds,  namely,  those  («)  lined  with  a  single  layer  of 
thin  and  long  columnar  cells,  each  with  an  oval  nucleus  in  outer  part  of 
wall;  and  those  {h)  acini  resembling  the  foregoing,  but  with  a  second 
layer  of  small  cortical,  polyhedral,  or  fusiform  cells  between  the  mem- 
brana  propria  and  the  columnar  cells.  The  ducts,  twelve  to  twenty  in 
number,  open  into  the  urethra.  They  are  lined  by  a  layer  of  columnar 
cells,  beneath  which  is  a  layer  of  small  polyhedral  cells. 

The  tunica  adventitia  consists  of  dense  fibrous  tissue  of  two  layers, 
between  which  is  situated  a  plexus  of  veins.  Large  vessels  pass  into  the 
interior  of  the  organ,  to  form  a  broad,  meshed,  capillary  system.  Nerves 
with  numerous  large  ganglion-cells  surround  the  cortex.  Pacinian 
bodies  are  sometimes  found  in  the  substance  of  the  organ. 


THE    EEPEODUCTIVE    ORGANS,  725 

The  muscular  tissue  of  the  prostate  not  only  forms  the  chief  part  of 
the  stroma  of  the  gland,  but  also  forms  a  continuous  layer  inside  the 
fibrous  sheath,  as  well  as  a  layer  surrounding  the  urethra,  which  is  con- 
tinous  with  the  sphincter  vesicae. 

Physiology  of  the  Sexual  Organs. 

Of  the  Female. — In  the  process  of  development  in  the  ovary  of 
individual  Graafian  vesicles,  it  has  been  already  observed,  that  as  each 
increases  in  size,  it  gradually  approaches  the  surface  of  the  ovary,  and 
when  fully  ripe  or  mature,  forms  a  little  projection  on  the  exterior. 
Coincident  with  the  increase  in  size,  caused  by  the  augmentation  of  its 
liquid  contents,  the  external  envelope  of  the  distended  vesicle  becomes 
very  thin  and  eventually  bursts.  By  these  means,  the  ovum  and  fluid 
contents  of  the  vesicle  are  liberated,  and  escape  on  the  exterior  of  the 
ovary,  whence  they  pass  into  the  Fallopian  tube  or  oviduct,  the  fimbri- 
ated processes  of  the  extremity  of  which  are  supposed  coincidentally  to 
grasp  the  ovary,  while  the  aperture  of  the  tube  is  applied  to  the  part 
corresponding  to  the  matured  and  bursting  vesicle. 

In  animals  whose  special  capability  of  being  impregnated  occurs  at 
regular  periods,  as  in  the  human  subject,  and  most  mammalia,  the 
Graafian  vesicles  and  their  contained  ova  appear  to  arrive  at  maturity, 
and  the  latter  to  be  discharged  at  such  jDcriods  only.  But  in  other 
animals,  e.g.,  the  common  fowl,  the  formation,  maturation,  and  dis- 
charge of  ova  appear  to  take  place  almost  constantly. 

It  has  long  been  known,  that  in  the  so-called  ovijjarous  animals,  the 
separation  of  ova  from  the  ovary  may  take  place  indei)endently  of  im- 
pregnation by  the  male,  or  even  of  sexual  union.  And  it  is  now 
established  that  a  like  maturation  and  discharge  of  ova,  independently 
of  coition,  occurs  in  mammalia,  the  periods  at  which  the  matured  ova 
are  separated  from  the  ovaries  and  received  into  the  Fallopian  tubes 
being  indicated  in  the  lower  mammalia  by  the  phenomena  of  heat  or 
rut:  in  the  human  female,  altliough  not  always  with  exact  coincidence, 
by  the  phenomena  of  menstruation.  If  the  union  of  the  sexes  take 
place,  the  ovum  may  be  fecundated,  and  if  no  union  occur  it  perishes. 

That  this  maturation  and  discharge  occur  periodically,  and  only 
during  the  phenomena  of  heat  in  the  lower  mammalia,  is  made  jsrobable 
by  the  facts  that,  in  all  instances  in  which  Graafian  vesicles  have  been 
found  presenting  the  appearance  of  recent  rupture,  the  animals  were  at 
the  time,  or  had  recently  been,  in  heat ;  that  on  the  other  hand,  there  is  no 
authentic  and  detailed  account  of  Graafian  vesicles  being  found  ruptured 
in  the  intervals  of  the  period  of  heat;  and  that  female  animals  do  not 
admit  the  males,  and  never  become  impregnated,  except  at  those  periods. 


726  •  HANDBOOK    OF   PHYSIOLOGY. 

Belation  of  Menstruation  to  the  Discharge  of  Ova. — The  human  female 
is  subject  to  the  same  law  as  the  females  of  other  mammiferous  animals; 
her  ova  are  matured  and  discharged  from  the  ovary  independent  of  sexual 
union.  This  maturation  and  discharge  occur,  moreover,  periodically  at 
or  about  the  epochs  of  menstruation. 

The  evidence  of  the  j)eriodical  discharge  of  ova  at  the  menstrual 
periods  is  that  in  most  cases  in  which  signs  of  menstruation  have  been 
found  in  the  uterus,  follicles  in  a  state  of  maturity  or  of  rupture  have 
been  seen  in  the  ovary ;  and  although  conception  is  not  confined  to  the 
periods  of  menstruation,  yet  it  is  more  likely  to  occur  about  a  menstrual 
epoch  than  at  other  times. 

The  exact  relation  between  the  discharge  of  ova  and  menstruation  is 
not  very  clear.  It  was  formerly  believed  that  the  monthly  flux  was  the 
result  of  a  congestion  of  the  uterus  arising  from  the  enlargement  and 
rupture  of  a  Graafian  follicle;  but  though  a  Graafian  follicle  is,  as  a 
rule,  ruptured  at  each  menstrual  epoch,  yet  several  instances  are  recorded 
in  which  menstruation  has  occurred  where  no  Graafian  follicle  can  have 
been  ruptured,  and  on  the  other  hand  cases  are  known  where  ova  have 
been  discharged  in  araenorrhaeic  women.  It  must  therefore  be  admitted 
that  menstruation  is  not  dependent  on  the  maturation  and  discharge  of 
ova. 

It  was,  moreover,  formerly  understood  that  ova  were  discharged 
toward  the  close  or  soon  after  the  cessation  of  a  menstrual  flow.  Obser- 
vations made  after  death,  and  facts  obtained  by  clinical  investigation, 
however,  do  not  support  this  view.  Eupture  of  a  Graafian  follicle  does 
not  happen  on  the  same  day  of  the  monthly  period  in  all  women.  It 
may  occur  toward  the  close  or  soon  after  the  cessation  of  a  flow;  but  only 
in  a  small  minority  of  the  subjects  examined  after  death  was  this  the 
case.  On  the  other  hand,  in  almost  all  such  subjects  of  which  there  is 
record,  rupture  of  the  follicle  appears  to  have  taken  place  before  the 
commencement  of  the  catamejiial  flow.  Moreover,  the  custom  of  the 
Jews — a  prolific  race,  to  whom  by  the  Levitical  law  sexual  intercourse 
during  the  week  following  menstruation  was  forbidden — militates 
strongly  in  favor  of  the  view  that  concej)tion  usually  occurs  before  and 
not  soon  after  a  menstrual  epoch,  and  necessarily,  therefore,  for  the  view 
that  ova  are  usually  discharged  before  the  catamenial  flow.  This,  to- 
gether with  the'  anatomical  condition  of  the  uterus  just  before  the 
catamenia,  seems  to  indicate  that  the  ovum  fertilized  is  that  which  is 
discharged  in  connection  with  the  first  absent,  and  not  that  with  the 
last  present  menstruation. 

Though  menstruation  does  not  appear  to  depend  upon  the  discharge 
of  ova,  yet  the  presence  of  the  ovaries  seems  necessary  for  the  perform- 
ance of  the  function;  for  women  do  not  menstruate  when  both  ovaries 


THE    REPRODUCTIVE    ORGANS. 


727 


have  been  removed  by  operation.  Some  instances  have  been  recently 
recorded,  indeed,  of  a  sanguineous  discharge  occurring  periodically  from 
the  vagina  after  both  ovaries  have  been  previously  removed  for  disease ; 
and  it  has  been  inferred  from  this  that  menstruation  is  a  function  inde- 
pendent of  the  ovary :  but  this  evidence  is  not  conclusive,  inasmuch  as 
it  is  possible  that  portions  of  ovarian  tissue  were  left  after  the  operation. 
Source  and  Characters  of  Menstrual  Discharge. — The  menstrual  dis- 
charge is  a  thin  sanguineous  fluid,  having  a  peculiar  odor.  It  is  of  a 
dark  color,  and   consists  of   blood,  epithelium,  and   mucus  from   the 


Fig.  454. 


Fig.  455. 


Fig.  456. 


Fig.  454.— Diagram  of  uterus  just  before  menstruation;  the  sliaded  portion  represents  the 
thiclcened  mucous  membrane. 

Fig.  45.5.— Diagram  of  utei-us  when  menstruation  has  just  ceased,  showing  the  cavity  of  the 
ut«rus  deprived  of  mucous  membrane. 

Fig.  456.— Diagram  of  uterus  a  week  after  the  menstrual  flux  has  ceased:  the  shaded  portion 
represents  renewed  mucous  membrane.     (J.  Williams.) 

uterus  and  vagina.  The  mensirual  flow  is  preceded  by  a  general  engorg- 
ment  of  all  the  pelvic  organs  with  blood.  The  cervix  and  vagina  become 
darker  in  color  and  softer  in  texture,  and  the  quantity  of  mucus  secreted 
by  the  glands  of  the  cervix  and  body  is  increased.  The  uterine  mucous 
membrane  is  swollen  and  the  glands  are  elongated  and  tortuous.  The 
discharge  of  blood,  the  source  of  which  is  the  mucous  membrane  of  the 
body  of  the  uterus,  is  probably  associated  with  uterine  contractions. 
There  is  great  difference  of  opinion  as  to  whether  or  not  any  of  the 
uterine  mucous  membrane  is  normally  shed  during  the  process  of  men- 
struation. John  Williams  believes  that  the  whole  of  the  mucous  mem- 
brane of  the  body  of  the  uterus  is  thrown  off  at  each  monthly  period, 


728  HANDBOOK    OF    PHYSIOLOGY. 

forming  a  true  decidua  mensfruaUs  (fig.  454),  while  Moricke  and  others 
believe  that  the  mucous  membrane  remains  intact.  Leopold  believes 
that  red  blood  corpuscles  escajae  from  the  congested  capillaries  and  un- 
dermine the  superficial  epithelium,  and  that  in  this  way  the  superficial 
layer  of  the  mucous  membrane  is  eroded  and  subsequently  regenerated. 
It  is  probable  that  menstruation  is  not  a  sign  of  the  capability  of  being 
impregnated,  as  much  as  of  disajipointed  impregnation, 

Me7isirual  Life. — The  occurrence  of  a  menstrual  discharge  is  one  of 
the  most  prominent  indications  of  the  commencement  of  puberty  in  the 
female  sex;  though  its  absence  even  for  several  years  is  not  necessarily 
attended  with  arrest  of  the  other  characters  of  this  period  of  life,  or 
with  inaptness  for  sexual  union,  or  incapability  of  impregnation.  The 
average  time  of  its  first  appearance  in  females  of  this  country  and  others 
of  about  the  same  latitude,  is  from  fourteen  to  fifteen ;  but  it  is  much 
influenced  by  the  kind  of  life  to  which  girls  are  subjected,  being  accel- 
erated by  habits  of  luxury  and  indolence,  and  retarded  by  contrary 
conditions.  Its  appearance  may  be  slightly  earlier  in  persons  dwelling 
in  warm  climes  than  in  those  inhabiting  colder  latitudes.  Much  of  the 
influence  attributed  to  climate  appears  due  to  the  custom  prevalent  in 
many  hot  countries,  as  in  Hindostan,  of  giving  girls  in  marriage  at  a 
very  early  age,  and  inducing  sexual  excitement  previous  to  the  proper 
menstrual  time.  The  menstrual  functions  continue  through  the  whole 
fruitful  period  of  a  woman's  life  and  usually  cease  between  the  forty- 
fifth  and  fiftieth  years. 

The  several  menstrual  periods  usually  occur  at  intervals  of  a  lunar 
month,  the  duration  of  each  being  from  three  to  six  days.  In  some 
women  the  intervals  are  so  short  as  three  weeks  or  even  less;  while  in 
others  they  are  longer  than  a  month.  The  periodical  return  is  usually 
attended  by  pain  in  the  loins,  a  sense  of  fatigue  in  the  lower  limbs,  and 
other  symptoms,  which  are  different  in  different  individuals.  Menstru- 
ation does  not  usually  occur  in  pregnant  women,  or  in  those  who  are 
suckling;  but  instances  of  its  occurrence  in  both  these  conditions  are  by 
no  means  rare. 

Corjnis  Luteuin. — Immediately  before,  as  well  as  subsequent  to,  the 
rupture  of  a  Graafian  follicle,  and  the  escape  of  its  ovum,  certain  changes 
ensue  in  the  interior  of  the  vesicle,  which  result  in  the  production  of  a 
yellowish  mass,  termed  a  Corpus  luteum. 

When  fully  formed  the  corpus  luteum  of  mammiferous  animals  is  a 
roundish  solid  body,  of  a  yellowish  or  orange  color,  and  composed  of  a 
number  of  lobules,  which  surround,  sometimes  a  small  ca\dty,  but  more 
frequently  a  small  stelliform  mass  of  white  substance,  from  which  deli- 
cate processes  pass  as  septa  between  the  several  lobules.  Very  often,  in 
the  cow  and  sheep,  there  is  no  white  substance  in  the  centre ;  and  the 


THE    REPRODUCTIVE    ORGANS. 


729 


lobules  projecting  from  the  opposite  walls  of  the  Graafian  follicle  appear 
in  a  section  to  be  separated  by  the  thinnest  j^ossible  lamina  of  semi- 
transparent  tissue. 

When  a  follicle  is  about  to  burst  and  expel  the  ovum,  it  becomes 
highh'  vascular  and  ojiaque;  and,  immediately  before  the  rupture  takes 
place,  its  walls  appear  thickened  on  the  interior  by  a  reddish  glutinous 
or  fleshy-looking  substance.  Immediately  after  the  rupture,  the  inner 
layer  of  the  wall  of  the  vesicle  appears  pulpy  and  llocculent.  It  is 
thrown  into  wrinkles  by  the  contraction  of  the  outer  layer,  and,  soon, 
red  fleshy  mammillary  processes  grow  from  it,  and  gradually  enlarge  till 
they  nearly  fill  the  vesicle,  and  even  protrude  from  the  orifice  in  the 
external  covering  of  the  ovary.  Subsequently  this  orifice  closes,  but  the 
fleshy  growth  within  still  increases  during  the  earlier  period  of  preg- 
nancy, the  color  of  the  substance  gradually  changing  from  red  to  yellow, 
and  its  consistence  becoming  firmer. 

The  human  corpus  luteum  (fig.  45?)  differs  from  that  of  the  domestic 
quadruped  in  being  of  a  firmer  texture,  and  having  more  frequently  a 


Fig.  45".— Corpora  lutea  of  different  periods.  B,  corpus  luteum  of  about  the  sixth  week 
after  impregnation,  showing  its  plicated  form  at  that  period.  1,  substance  of  the  ovary;  2,  sub- 
stance of  the  corpus  luteum :  3,  a  grayish  coagulum  in  its  cavity.  (Paterson. )  A,  corpus  lu- 
teum two  days  after  delivery;  D,  in  the  twelfth  week  after  delivery.     (Montgomery.) 

persistent  cavity  at  its  centre,  and  in  the  stelliform  cicatrix,  which  re- 
mains in  the  cases  where  the  cavity  is  obliterated,  being  proportionately 
of  much  larger  bulk.  The  quantity  of  yellow  substance  formed  is  also 
much  less:  and  although  the  deposit  increases  after  the  vesicle  has 
burst,  yet  it  does  not  usually  form  mammillary  growths  projecting  into 
the  cavity  of  the  vesicle,  and  never  protrudes  from  the  orifice,  as  is  the 
case  in  other  Mammalia.  It  maintains  the  character  of  a  uniform,  or 
nearly  uniform,  layer,  which  is  thrown  into  wrinkles,  in  consequence  of 
the  contraction  of  the  external  tunic  of  the  vesicle.  After  the  orifice  of 
the  vesicle  has  closed,  the  growth  of  the  yellow  substance  continues  dur- 
ing the  first  half  of  pregnancy,  till  the  cavity  is  reduced  to  a  compara- 
tively small  size,  or  is  obliterated ;  in  the  latter  case,  merely  a  white 
stelliform  cicatrix  remains  in  the  centre  of  the  corpus  luteum. 

An  effusion  of  blood  generally  takes  place  into  the  cavity  of  the  fol- 


730 


HANDBOOK    OF    PHYSIOLOGY. 


licle  at  the  time  of  its  rupture,  esjDecially  in  the  human  subject,  hni  it 
has  no  share  in  forming  the  yellow  body;  it  gradually  loses  its  coloring 
matter.  The  serum  of  the  blood  sometimes  remains  included  within  a 
cavity  in  the  centre  of  the  coagulum,  and  then  the  decolorized  fibrin 
forms  a  membraniform  sac,  lining  the  corpus  luteum.  At  other  times 
the  serum  is  removed,  and  the  fibrin  constitutes  a  solid  stelliform  mass. 

The  yellow  substance  of  which  the  corpus  luteum  consists,  both  in 
the  human  subject  and  in  the  domestic  animals,  is  a  growth  from  the 
inner  surface  of  the  ruptured  follicle,  the  result  of  an  increased  devel- 
oj)ment  of  the  membrana  granulosa. 

The  first  changes  of  the  internal  coat  of  the  Graafian  vesicle  in  the 
process  of  formation  of  a  corpus  luteum  seem  to  occur  in  every  case  in 
which  an  ovum  escapes;  as  well  in  the  human  subject  as  in  the  domestic 
quadrupeds.  If  the  ovum  is  impregnated,  the  growth  of  the  yellow  sub- 
stance continues  during  nearly  the  whole  period  of  gestation  and  forms 
the  large  corpus  luteum  commonly  described  as  a  characteristic  mark  of 
impregnation.  If  the  ovum  is  not  impregnated,  the  growth  of  yellow 
substance  on  the  internal  surface  of  the  vesicle  proceeds,  in  the  human 
ovary,  no  further  than  the  formation  of  a  thin  layer,  which  shortly  dis- 
appears; but  in  the  domestic  animals  it  continues  for  some  time  after 
the  ovum  has  perished,  and  forms  a  corpus  luteum  of  considerable  size. 
The  fact  that  a  structure,  in  its  essential  characters  similar  to,  though 
smaller  than,  a  corpus  luteum  observed  during  pregnancy,  is  formed  in 
the  human  subject,  independent  of  impregnation  or  of  sexual  union, 
coupled  with  the  varieties  in  size  of  corpora  lutea  formed  during  preg- 
nancy, necessarily  renders  unsafe  all  evidence  of  previous  impregnation 
founded  on  the  existence  of  a  corpus  luteum  in  the  ovary. 

The  folllowing  table  by  Dalton,  expresses  well  the  differences  between  the 
corpus  luteum  of  the  pregnant  and  unimpregnated  condition  respectively  : — 

Corpus  Luteum  of  Menstru-        Corpus  Luteum  of  Pregnancy, 

ation. 
Three-quarters  of  an  inch  in  diameter  ;  central  clot  reddish  ;  con- 
voluted wall  pale. 

Larger;  convoluted  wall  bright    yel- 
low ;  clot  still  reddish. 


At  the  end  of 

three  weeks 

One  month  . 


Two  months 


Six  months 


Nine  months 


Smaller ;  convoluted  wall 
bright  yellow ;  clot  still 
reddish. 

Reduced  to  the  condition 
of  an  insignificant  cica- 
trix. 

Absent. 


Absent. 


Seven-eighths  of  an  inch  in  dia- 
meter ;  convoluted  wall  bright 
yellow ;  clot  jDerfectly  decolor- 
ized. 

Still  as  large  as  at  end  of  second 
month  ;  clot  fibrinous  ;  convoluted 
wall  paler. 

One-half  an  inch  in  diameter;  cen- 
tral clot  converted  into  a  radi- 
ating cicatrix  ;  the  external  wall 
tolerably  thick  and  convoluted, 
but  without  any  bright  yellow 
color. 


THE    KEPEODUCTIYE    ORGAXS. 


731 


Of  the  Male. — In  order  that  the  ovum  should  be  fecundated,  it  is 
necessary  that  it  should  meet  with  the  seminal  fluid  of  the  male.  This 
is  accomplished  by  the  junction  of  the  sexes  in  the  act  of  coition, 
whereby  the  seminal  fluid  is  discharged  into  the  neighborhood  of,  if  not 
within,  the  cervix  uteri.  Before  considering  the  changes  which  are 
produced  in  the  ovum  by  impregnation,  it  will  be  as  well  to  describe  the 
nature  of  the  seminal  fluid.  This  consists  essentially  of  the  semen  se- 
creted by  the  testes,  and  to  this  are  added  a  material  secreted  by  the 
vesiculse  seminales,  as  well  as  the  secretion  of  the  prostate  gland,  and  of 
Cowper's  glands.  Portions  of  these  several  fluids  are  discharged,  to- 
gether with  the  proper  secretion  of  the  testicles. 

The  semen  is  a  viscid,  whitish,  albuminous  fluid  of  a  peculiar  odor. 
It  contains  epithelium,  granules  or  colorless  particles,  and  large  num- 
bers of  sijermatozoa,  which  are  the  characteristic  and  essential  elements. 


Fig.  458. 


Fig.  459. 


Fig.  458.— Spermatic  filaments  from  the  human  vas  deferens.     1,  magnified  300  diameters;  2, 
magnified  800  diameters;  a,  from  the  side;  6,  from  above.     (From  KoUiker.) 
Fig.  459. — Spermatozoa.     1,  Of  salamander;  2,  hmnan.     (H.  Gibbes. ) 


The  spermatozoa  are  minute  bodies  each  consisting  of  a  flattened  oval 
head  and  attached  to  it  a  long  slender  tapering  mobile  flagellum  or  tail. 
In  some  forms  of  spermatozoa  there  is  a  small  middle  piece  interposed 
between  the  head  and  the  tail.  The  head  is  about  -g-oVotli  i^^ch  (about 
4/x)  long  and  y-g-J-j^th  inch  (about  2. 5/x)  broad.  The  tail  is  about -j-^^jj-oth 
to  ^Q^Qgth  inch  (5/^-6,a)  long.  The  spermatozoa  possess  the  power  of 
active  movement,  and  it  is  by  this  sinuous,  cilia-like  movement  that 
they  are  propelled  in  the  female  and  so  helped  in  their  progress  to  meet 
the  ovum.     The  lashing  cilium-like  movement  of  a  spermatozoon  may 


732  HANDBOOK    OF    PHYSIOLOGY. 

go  on  for  hoars  or  days  in  the  alkaline  fluids  of  the  body.  It  is  stopped 
by  any  of  the  agencies  which  stop  ciliary  movement,  e.g,^  acids,  or 
strong  alkalies,  alcohol,  chloroform,  cold  to  0°  C,  and  heat  above  50°  0. 

On  examining  the  spermatozoon  of  Triton  cristatus,  one  of  the  am- 
phibia which  possess  the  largest  spermatozoa  of  all  vertebrate  animals, 
H.  Gibbes  found  that  the  organism  consisted  of  {a)  a  long  pointed  head, 
at  the  base  of  which  is  (J),  an  elliptical  structure  joining  the  head  to 
{a),  a  long  filiform  body;  [d),  a  fine  filament,  much  longer  than  the 
body,  is  connected  with  this  latter  by  (e),  a  homogeneous  membrane. 

The  head,  as  it  appears  in  the  fresh  specimen,  has  a  different  refrac- 
tive power  from  that  of  the  rest  of  the  organism,  and  with  a  high  power 
appears  to  be  a  light  green  color;  there  is  also  a  central  line  running  up 
it,  from  which  it  appears  to  be  hollow. 

The  elliptical  structure  at  the  base  of  the  head  connects  it  with  the 
long  threadlike  body,  and  the  filament  springs  from  it. 

While  the  spermatozoon  is  living,  this  filament  is  in  constant  mo- 
tion; at  first  this  is  so  quick  that  it  is  difficult  to  see  it,  but  as  its  vital- 
ity becomes  impaired  the  motion  gets  slower,  and  it  is  then  easily  per- 
ceived to  be  a  continuous  waving  from  side  to  side. 

The  spermatozoa  of  all  mammalia  examined,  consisting  of  man,  bull, 
dog,  liorse,  cat,  ing,  mouse,  rat,  guinea-pig,  had  instead  of  the  long-pointed 
head  of  the  amphibian,  a  blunt  thick  process  of  different  shapes  in  the 
different  animals;  and  from  the  root  or  neck  of  this  proceeded  the  long 
filament  just  as  in  the  amphibia,  only  so  delicate  as  to  be  invisible  except 
with  very  high  powers. 

In  man  the  head  (fig.  459)  is  club-shaped,  and  from  its  base  springs 
the  very  delicate  filament,  which  is  three  or  four  times  as  long  as  the 
body;  and  the  membrane  which  attaches  it  to  the  body  is  much  broader, 
and  allows  it  to  lie  at  a  greater  distance  from  the  body  than  in  the  sper- 
matozoa of  any  other  Mammal  examined. 

From  his  investigation,  Gibbes  concluded: — 1st,  that  the  head  of  the 
spermatozoon  is  inclosed  in  a  sheath,  which  is  a  continuation  of  the 
membrane  which  surrounds  the  filament,  and  connects  it  to  the  body, 
acting  in  fact  the  part  of  a  mesentery.  2ndly.  That  the  substance  of  the 
head  is  quite  distinct  in  its  composition  from  the  elliptical  structure, 
the  filament  and  the  long  body,  and  that  it  is  readily  acted  on  by  alkalies; 
these  reagents  have  no  effect,  however,  on  the  other  part,  exempting 
the  membraneous  sheath.  3rdly.  That  this  elliptical  structure  has  its 
analogue  in  the  mammalian  spermatozoon;  in  the  one  case  the  head  is 
drawn  out  as  a  long  pointed  process,  in  the  other  it  is  of  a  globular 
form,  and  surrounds  the  elliptical  structure.  4tlily.  That  the  motive 
power  lies,  in  a  great  measure,  in  the  filament  and  the  membrane  at- 
taching it  to  the  body. 


THE    REPEODrCTIYE    ORGAXS.  733 

The  spermatozoa  are  derived  from  the  breaking  up  of  the  seminal 
cells  or  daughter  cells.     They  must  be  looked  upon  as  modified  cells. 

The  occurrence  of  spermatozoa  in  the  impregnating  fluid  of  nearly 
all  classes  of  animals,  proves  that  they  are  essential  to  the  process  of 
impregnation,  and  their  actual  contact  with  the  ovum  is  necessary  for 
its  development. 

The  seminal  fluid  is,  probably,  after  the  period  of  puberty  secreted 
constantly,  though,  except  under  excitement,  very  slowly,  in  the  tubules 
of  the  testicles.  From  these  it  passes  along  the  vasa  deferentia  into  the 
vesiculee  seminales,  whence,  if  not  expelled  in  emission,  it  may  be  dis- 
charged, as  slowly  as  it  enters  them,  either  with  the  urine,  which  may 
remove  minute  quantities,  mingled  with  the  mucus  of  the  bladder  and 
the  secretion  of  the  prostate,  or  from  the  urethra  in  the  act  of  defalca- 
tion. 

To  the  vesiculiB  seminales  a  double  function  maybe  assigned;  for 
they  both  secrete  some  fluid  to  be  added  to  that  of  the  testicles,  and 
serve  as  reservoirs  for  the  seminal  fluid.  The  former  is  their  most  con- 
stant and  probably  most  important  office;  for  in  the  horse,  bear,  guinea- 
pig,  and  several  other  animals,  in  whom  the  vesiculae  seminales  are  large 
and  of  apparently  active  functions,  they  do  not  communicate  with  the 
vasa  deferentia,  but  pour  their  secretions,  separately,  though  it  may  be 
simultaneously,  into  the  urethra. 

There  is  a  complete  want  of  information  respecting  the  nature  and 
purposes  of  the  secretions  of  the  prostate  and  Cowper's  glands.  That 
they  contribute  to  the  right  composition  of  the  impregnating  fluid,  is 
shown  both  by  the  position  of  the  glands  and  by  their  enlarging  with 
the  testicles  at  the  approach  of  an  animal's  breeding  time.  But  that 
they  contribute  only  a  subordinate  part  is  shown  by  the  fact,  that,  when 
the  testicles  are  lost,  though  these  other  organs  be  perfect,  all  procrea- 
tive  power  ceases. 

The  fluid  part  of  the  semen  or  liquor  seminis  has  not  been  satisfac- 
torily analyzed :  but  Henle  says  it  contains  fibrin,  because  shortly  after 
being  discharged,  flocculi  form  in  it  by  spontaneous  coagulation,  and 
leave  the  rest  of  it  thinner  and  more  liquid,  so  that  the  filaments  move 
in  it  more  actively.  The  chief  constituents  of  the  semen  are  said  to  be  a 
variety  of  nnclein,  which  does  not  contain  sulphur;  cevtain p7'oteids,  one 
of  which  contains  four  per  cent,  of  sulphur;  lecithin;  cholesterin;  fat, 
and  extractives. 


CHAPTER  XIX. 

DEVELOPMENT. 

Changes  which  occur  in  the  Ovum. 

Of  the  changes  which  take  place  in  the  ovum,  some  occur  before 
and  are  as  it  were  preparatory  to  impregnation,  and  others  ensue  after 
impregnation.  It  will  be  as  well  to  consider  the  respective  changes 
separately. 

Changes  inior  to  Imijr  eg  nation. — These  changes  especially  concern 
the  germinal  vesicle,  and  have  been  observed  chiefly  in  the  ova  of  low 
types.  The  ovum  when  ripe  and  detached  from  the  ovary  consists,  it 
will  be  remembered,  of  a  granular  yolk  inclosed  within  the  protoplasmic 
zona  pellucida,  and  containing  the  germinal  vesicle  and  germinal  spot  situ- 
ated eccentrically.  The  yolk  granules  are  of  different  sizes,  from  the 
minutest  molecules  uj)  to  a  diameter  of  tthto^^^  ^o  y-^o^th  of  an  inch 
(about  25,^.).  The  germinal  vesicle  consists  of  reticulated  protoplasm 
inclosed  in  a  distinct  membrane,  and  containing  one  or  more  nucleoli 
or  germinal  spots.  The  primary  change  observed  in  the  ovum  consists 
in  alterations  in  the  shape  of  the  vesicle,  the  disaj^pearance  of  its  pro- 
toplasmic reticulum,  and  of  its  inclosing  membrane,  with  a  consequent 
indentation  and  indistinctness  of  its  outline.  Its  protoplasm  becomes 
to  a  considerable  extent  confounded  with  the  yolk  substance,  and  its 
germinal  spot  disappears.  The  next  step  in  the  process  is  the  appear- 
ance in  the  yolk  of  two  stars  in  a  clear  space  near  the  j)oles  of  the  vesi- 
cle elongated  to  a  certain  extent,  and  from  this  results  a  nuclear  sinndle, 
corresponding  to  a  nucleus  in  the  process  of  division,  with  the  stars  at 
either  end  lying  near  the  surface  of  the  yolk.  This  spindle  next  becomes 
vertical,  and  the  star  nearer  the  surface  protrudes  from  the  ovum  envel- 
oped in  a  protoplasmic  mass,  which  by  constriction  forms  the  first  jt)o/ar 
cell.  A  second  polar  cell  arises  in  the  same  way.  From  the  remainder 
of  the  spindle  within  the  yolk  two  or  three  vesicles  arise,  and  by  the 
junction  of  these  a  single  nucleus  is  formed,  which  is  called  i\ie  female 
pro-nucleus.  This  is  clearly  derived  from  the  original  germinal  vesicle. 
It  must  be  remembered  that  these  changes  have  been  so  far  observed  only 
in  a  certain  number  of  instances.  It  is  very  possible,  not  to  say  probable, 
that  such  changes  are  universal  in  the  animal  kingdom  (Balfour). 

Balfour's  view  as  to  the  formation  of  the  polar  bodies  may  be  given 


DEVELOPMENT.  735 

in  his  own  words: — ''  My  view  amounts  to  the  following,  viz.,  that  after 
the  formation  of  the  j^olar-cells,  the  remainder  of  the  germinal  vesicle 
within  the  ovum  (the  female  pro-nucleus)  is  incapable  of  further  devel- 
opment without  the  addition  of  the  nuclear  part  of  the  male  element 
(spermatozoon),  and  that  if  polar-cells  were  not  formed,  partheftogenesis 
might  normally  occur." 

Changes  following  Impregnation. — The  process  of  impregnation 
of  the  ovum  has  been  observed  most  accurately  in  the  low'er  types.  In 
mammalia,  although  spermatozoa  pass  in  numbers  through  the  volk 
envelope,  yet  their  further  progress  is  only  inferred  from  observations  on 
the  lower  animals.  The  process  in  asterias  glacialis,  according  to  Bal- 
four, is  as  follows: — The  head  of  a  single  spermatozoon  joins  with  an 
elevation  of  the  yolk  substance,  the  tail  remaining  motionless,  and  then 
disappearing.  The  head  enveloped  in  the  protoplasm  then  sinks  into  the 
yolk  and  becomes  a  nucleus,  from  which  the  yolk  substance  is  arranged 
in  radiating  lines.  This  is  the  male  pro-nucleus.  At  first,  at  some  dis- 
tance from  the  female  pro-nucleus,  it  after  a  wdiile  approaches  nearer, 
and  the  female  pro-nucleus,  which  was  before  inactive,  becomes  active. 
The  nuclei  at  last  meet  and  unite.  The  result  of  their  union  is  the/rs^ 
segmentation  sphere,  or  blasto-spJiere.  It  is  a  nucleated  protoplasmic  cell. 
The  changes  which  have  resulted  in  the  formation  of  the  blasto-sphere 
or  primitive  segmentation,  germ  are  followed  by  the  process  known  as 
segmentation  of  the  yolk. 

This  process  and  the  earlier  stages  in  development  are  so  fundamen- 
tally similar  in  all  vertebrate  animals,  from  fishes  up  to  man,  that  the 
gaps  existing  in  our  knowledge  of  the  process  in  the  higher  mammalia, 
such  as  man,  may  be,  in  part,  at  any  rate,  filled  up  by  the  more  accu- 
rate knowledge  which  we  possess  of  the  development  of  the  ovum  in 
such  animals  as  the  trout,  frog,  and  fowl. 

One  important  distinction  between  the  ova  of  various  vertebrata  should  be 
remembered.  In  the  iien's  egg,  besides  the  shell  and  the  white  or  albumen,  two 
other  structures  are  to  be  distinguished — the  ge7-7n,  often  called  the  cicatricula 
or  "tread,"  and  the  yolk,  inclosed  in  its  vitelline  membrane. 

The  gei'm  is  (as  was  mentioned  in  the  description  already  given)  essentially 
a  cell,  consisting  of  protoplasm  inclosing  a  nucleus  and  nucleolus.  It  alone 
participates  in  the  process  of  segmentation,  the  great  mass  of  the  yolk  (food- 
yolk)  remaining  quite  unaffected  by  it.  Since  only  the  germ,  which  forms  but 
a  small  portion  of  the  yolk,  undergoes  segmentation,  the  ovum  is  called  mero- 
blastic. 

In  the  mammalia,  on  the  other  hand,  there  is  no  large  unsegmented  mass 
corresponding  to  the  food-yolk  of  birds  ;  the  entire  ovum  undergoes  segmenta- 
tion, and  is  hence  termed  holoblastic. 

The  eggs  of  fishes,  reptiles,  and  birds,  are  meroblastic,  while  those  of  am- 
phibia and  mammalia  are  holoblastic. 

Of  the  changes  which  the  mammalian  ovum  undergoes  previous  to 


73G 


HANDBOOK    OF    PHYSIOLOGY. 


the  formation  of  the  embryo,  those  which  occur  while  it  is  still  in  the 
ovary  are  independent  of  impregnation :  others  take  place  after  it  has 
reached  the  Fallopian  tube.     The  knowledge  we  possess  of  these  changes 

is  derived  almost  exclusively  from  obser- 
vations on  the  ova  of  the  bitch  and  rabbit : 
but  it  may  be  inferred  that  analogous 
changes  ensue  in  the  human  ovum. 

As  the  ovum  approaches  the  middle  of 
the  Fallopian  tube,  it  begins  to  receive  a 
new  investment,  consisting  of  a  layer  of 
transparent  albuminous  or  glutinous  sub- 
stance, which  forms  upon  the  exterior  of 
the  zona  pellucida.  It  is  at  first  exceed- 
ingly fine,  and  owing  to  this,  and  to  its 
transparency,  is  not  easily  recognized, 
but  at  the  lower  part  of  the  Fallopian 
tube  it  acquires  considerable  thickness. 

Secjmentation. — The  first  visible  result 
of  fertilization  is  a  slight  amoeboid  move- 
ment in  the  protoplasm  of  the  ovum: 
this  has  been  observed  in  some  fish,'  in  the 
frog,  and  in  some  mammals.  Immediately 
succeeding  to  this  the  process  of  segmen- 
tation commences,  and  is  completed  dur- 
ing the  passage  of  the  ovum  through  the 
Fallopian  tube.  In  mammals,  in  which 
the  process  is  an  example  of  complete  seg- 
mentation, the  yolk  becomes  constricted 
in  the  middle,  and  is  surrounded  by  a 
furrow  which,  gradually  deepening,  at 
length  cuts  it  in  half,  while  the  same  pro- 
cess begins  almost  immediately  in  each 
half  of  the  yolk,  and  cuts  it  also  in  two. 
The  same  process  is  repeated  in  each  of 
the  quarters,  and  so  on,  until  at  last  by 
continual  cleavings,  the  whole  yolk  is 
changed  into  a  mulberry-like  mass  of 
small  and  more  or  less  rounded  bodies, 
sometimes  called  vitelline  spheres,  the 
whole  still  inclosed  by  the  zona  pellucida  (fig.  460).  Each  of  these  lit- 
tle spherules  contains  a  transparent  vesicle,  like  an  oil-globule,  which  is 
seen  with  difficulty,  on  account  of  its  being  enveloped  by  the  yolk-gran- 
ules which  adhere  closely  to  its  surface. 


Fig.  460. — Diagrams  of  the  vari- 
ous stages  of  cleavage  of  the  yolk. 
(Dalton.) 


DEVELOPMENT.  737 

The  cause  of  this  singuhir  siibdivisiou  of  the  yolk  is  quite  obscure : 
though  the  immediate  agent  in  its  production  seems  to  be  the  central 
vesicle  contained  in  each  division  of  the  yolk.  Originally  there  was  prob- 
ably but  one  vesicle,  situated  in  the  centre  of  the  entire  granular  mass 
of  the  yolk,  and  probably  derived  in  the  manner  already  described  from 
the  germinal  vesicle.  This  divides  and  subdivides:  each  successive  divi- 
sion and  subdivision  of  the  vesicle  being  accompanied  by  a  corresponding 
division  of  the  yolk. 

About  the  time  at  which  the  mammalian  ovum  reaches  the  uterus, 
the  process  of  division  and  subdivision  of  the  yolk  appears  to  have 
ceased,  its  substance  having  been  resolved  into  its  ultimate  and  smallest 
divisions,  while  its  surface  presents  a  uniform  finely-granular  aspect, 
instead  of  its  late  mulberry-like  appearance.  The  ovum,  indeed,  ap- 
pears at  first  sight  to  have  lost  all  trace  of  the  cleavage  process,  and, 
with  the  exception  of  being  j^aler  and  more  translucent,  almost  exactly 
resembles  the  ovarian  ovum,  its  yolk  consisting  apparently  of  a  confused 
mass  of  finely  granular  substance.  But  on  a  more  careful  examination, 
it  is  found  that  these  granules  are  aggregated  into  numerous  minute 
spheroidal  masses,  each  of  which  contains  a  clear  vesicle  or  nucleus  in 
its  centre,  and  is,  in  fact,  an  emhryonal  cell.  The  zona  pellucida,  and 
the  layers  of  albuminious  matter  surrounding  it,  have  at  this  time  the 
same  character  as  when  at  the  lower  part  of  the  Fanoj)ian  tube. 

The  passage  of  the  ovum,  from  the  ovary  to  the  uterus,  occupies 
probably  eight  or  ten  days  in  the  human  female. 

When  the  peripheral  cells,  which  are  formed  first,  are  fully  devel- 
oped, they  arrange  themselves  at  the  surface  of  the  yolk  into  a  kind  of 
membrane,  and  at  the  same  time  assume  a  polyhedral  shape  from  mutual 
pressure,  so  as  to  resemble  pavement  epithelium.  The  deeper  cells  of  the 
interior  pass  gradually  to  the  surface  and  accumulate  there,  thus  in- 
creasing the  thickness  of  the  membrane  already  formed  by  the  more 
superficial  layer  of  cells,  while  the  central  part  of  the  yolk  remains  filled 
only  with  a  clear  fluid.  By  this  means  the  yolk  is  shortly  converted 
into  a  kind  of  secondary  vesicle,  the  walls  of  which  are  composed  exter- 
nally of  the  original  vitelline  membrane,  and  within  by  the  newly  formed 
cellular  layer,  the  blastoderm  or  germinal  membrane,  as  it  is  called. 

Segmentation  in  the  Chick. — The  embryo  chick  affords  an  illustra- 
tion of  what  is  known  as  incomplete  or  partial  segmentation,  or  mero- 
blastic  segmentation.  In  the  youngest  ova  the  germinal  vesicle  is  situ- 
ated subcentrally,  but  as  development  jiroceeds  it  passes  to  the  periphery, 
and  the  protoplasm  surrounding  it  remaining  free  from  yolk  granules, 
the  germinal  disc  is  formed.  This  germinal  disc  is  not  marked  out  by 
any  sharp  line  from  the  remaining  protoplasm,  but  passes  insensibly 
into  it.  The  first  change  consists  in  the  appearance  of  a  f  urroAV  run- 
47 


738  HANDBOOK    OF    PHYSIOLOGY. 

ning  across  the  disc  dividing  it  into  two;  it  does  not  extend  across 
the  whole  breadth.  A  second  furrow,  at  right  angles,  cutting  the  first 
a  little  eccentrically,  next  apj^iears,  and  the  disc  is  thus  cut  into  four 
quadrants.  The  furrows  do  not  extend  through  the  whole  thickness  of 
the  disc,  and  the  segments  are  not  separated  out  on  the  lower  aspect. 
The  quadrants  are  next  bisected  by  radiating  furrows,  and  the  disc  is 
thus  divided  into  eight  parts.  The  central  portion  of  each  segment  is 
now  cut  off  from  the  peripheral  furrow,  so  that  a  number  of  smaller 
central  and  larger  peripheral  portions  result.  As  the  primary  division 
was  eccentric  and  the  succeeding  followed  the  same  plan,  there  results 
a  bilateral  symmetry;  but  the  relation  of  the  axis  of  symmetry  and  the 
long  axis  of  the  embryo  is  not  known.  Eapid  division  of  the  segments 
by  furrows  in  various  directions  now  ensues,  and  the  small  central  por- 
tions are  more  rapidly  broken  np  than  the  larger,  and  therefore  become 
more  numerous.  During  this  superficial  segmentation  a  similar  process 
goes  on  throughout  the  whole  mass,  and  division  goes  on  not  only  by 
vertical  but  also  by  horizontal  furrows.  The  result  of  this  process  of 
segmentation  is  that  the  original  germinal  disc  is  cut  into  a  large  num- 
ber of  small  rounded  protoplasmic  cells,  small  in  the  centre,  larger  to 
the  periphery,  and  that  the  superficial  cells  are  smaller  than  those  be- 
low: the  two  original  layers  of  the  blastoderm  are  thus  early  rei^resented. 
The  process  of  segmentation  proceeds  at  the  jjeriphery  of  the  ger- 
minal disc,  and  at  the  same  time  further  division  of  the  cells  at  the 


Fig.  461.— Vertical  section  of  area  peHucida  and  area  opaca  (left  extremity  of  figure)  of 
blastoderm  of  a  fresh-laid  egg  funincubated).  S,  superflcial  layer  corresponding  to  epiblast; 
i),  deeper  layer,  corresponding  to  hypoblast,  and  probably  in  part  to  mesoblast;  M,  large 
"formative  cells,"  filled  with  yolk  granules,  and  lying  on  the  floor  of  the  segmentation  cavity; 
A,  the  white  yolk  immediately  underlying  the  segmentation  cavity.     (Strieker.) 

centre  proceeds.  The  nucleus  of  the  original  cell  divides  coincidently 
with  the  protoplasm,  and  so  it  comes  that  the  protoplasmic  masses  are 
nucleated;  and  besides  this,  nuclei  derived  from  the  original  nucleus 
are  found  in  the  ovum  below  the  area  of  segmentation,  and  from  these 
by  the  protoplasm  which  surrounds  them  being  constricted  off  with 
them,  supplementary  segmentation  masses  come  to  be  formed.  The 
blastoderm  is  thus  formed  as  the  result  of  segmentation,  and  between  it 
and  the  subjacent  white  yolk  is  a  cavity  containing  fluid.  The  segmen- 
tation having  been  completed  toward  the  centre,  although  it  still  pro- 
ceeds at  the  periphery,  the  superficial  layer  of  the  blastoderm  becomes 


DEVELOPMENT.  739 

a  layer  of  columnar  nucleated  cells,  and  the  lower  layer  consists  of  larger 
masses  indistinctly  nucleated,  still  granular  and  rounded,  irregularly 
disposed.  In  the  segmentation  cavity  are  the  supplementary  segmenta- 
tion masses  or  formative  cells. 

When  the  egg  is  incubated,  raj^id  changes  take  j)lace  in  the  blasto- 
derm, resulting  in  the  formation  first  of  all  of  two,  then  of  the  three 
layers,  which  have  been  already  mentioned  in  the  first  chapter.  The 
superficial,  or  epiblast,  does  not  at  first  enter  into  these  changes,  but 


Fig.  462. — Impregnated  egg,  with  oommeuceuieut  of  formation  of  embryo;  showing  the  area 
germinativa  oV  embryonic  spot,  the  area  pellucida,  and  the  primitive  groove  or  trace. 
(Dalton.) 

continues  to  be  a  layer  of  nucleated  columnar  cells.  But  in  the  lower 
layer  of  larger  rounded  cells  certain  of  the  cells  become  flattened  hori- 
zontally, their  granules  disappear,  and  the  nuclei  become  distinct.  A 
membrane  of  flattened  nucleated  cells  is  then  formed,  first  of  all  toward 
the  centre  of  the  area,  afterward  peripherally  also :  this  is  the  hypoblast. 
Between  the  two  layers  some  cells,  not  belonging  to  either  layer,  remain. 
These  cells  are  almost  entirely  at  the  back  part  of  the  area.  The  for- 
mation of  the  intermediate  layer  of  mesoblast  is  more  complicated, 
and  will  now  be  described. 

At  this  period  it  is  necessary  to  return  to  the  surface  view  of  the 
blastoderm.  Before  incubation  it  is  seen  to  consist  of  a  more  or  less 
circular  transparent  area,  the  area  pellucida,  surrounded  by  an  opaque 
rim,  which  is  called  the  area  opaca.  The  area  opaca  rests  upon  the 
white  yolk:  beneath  the  area  i)ellucida  is  a  cavity  containing  fiu id.  In 
the  centre  of  the  area  pellucida  is  a  white  shining  spot,  or  nucleus  of 
Pander,  shining  through.  This  is  the  upper  dilated  extremity  of  the 
flask-shaped  accumulation  of  white  yolk  upon  whicli  the  blastoderm 
rests. 

The  yellow  yolk  consists  of  spheres  25/-t  to  IOO/ji  in  diameter,  filled  with 
highly  refractive  granules  of  an  albuminous  nature,  and  the  white  yelk 
being  distinguished  from  the  yellow  not  only  by  its  lighter  color,  but 
also  because  its  vesicles  are  smaller  than  those  of  the  yellow.     Each  con- 


740  HANDBOOK    OF    PHYSIOLOGY. 

tains  u  highly  refractive  body.  Some  large  spheres  contain  a  number  of 
spherules.  Some  of  these  are  vacuolated.  The  white  yolk  not  only  en- 
velopes the  yellow  yolk  in  a  thin  layer,  and  merges  with  the  central 
flask-shaped  mass,  already  mentioned,  but  also  is  found  in  the  yellow 
yolk,  forming  with  it  alternate  layers. 

Except  that  the  central  shining  opacity  of  the  pellucid  area  has  dis- 
appeared, that  the  size  of  the  area  has  increased,  and  that  the  opaque 


Fig.  46.3, — Transverse  section  through  embryo  chick  (26  hours).  «,  epiblast;  b,  mesoblast; 
c,  hypoblast;  rf,  central  portion  of  mesoblast,  which  is  here  fused  with  epiblast;  e,  primitive 
groove;  /,  dorsal  ridge.     (Klein.) 

area  has  also  increased,  no  other  change  can  be  remarked  up  to  the  for- 
mation of  the  two  complete  layers.  There  is,  however,  a  slight  ill- 
defined  opacity  at  the  posterior  part  of  the  area  pellucida,  known  as  the 
embryonic  shield.  This  opacity  is  probably  due  to  the  intermediate  cells 
already  mentioned  as  existing  between  the  epiblast  and  hypoblast. 

In  the  posterior  j)art  of  the  area  pellucida  now  appears  an  opaque 
streak  which  extends  about  a  third  of  the  diameter  of  the  area  toward 
the  middle  line.  This  is  the  Primitive  streak.  It  is  found  on  trans- 
verse section  of  the  blastoderm  in  this  neighborhood  to  be  due  to  a  pro- 
liferation downward  of  cells  two  or  more  deep  from  the  epiblast.  The 
area  pellucida  now  becomes  oval.     As  the  primitive  streak  becomes  more 


C7^     " 

Fig,  464.— Diagram  of  transverse  section  through  an  embryo  before  the  closing-in  of  the 
medullary  groove,  ni,  cells  of  epiblast  lining  the  medullary  groove  which  will  form  the  spinal 
cord;  h,  epiblast;  d,  hypoblast;  ch,  notochord;  tt,  proto vertebra;  sp,  mesoblast;  w,  edge  of 
lamina  dorsalis,  folding  over  medullary  groove.     (Kolliker.) 

defined  the  area  pellucida  changes  its  oval  for  a  pear  shape,  but  the 
streak  increases  in  size  faster  than  the  area,  and  so  after  a  time  is  about 
two-thirds  of  its  length.  In  the  primitive  streak  a  groove,  the  primi- 
tive groove,  runs  along  its  axis.  From  the  primitive  streak  the  cells 
from  the  under  surface  of  the  epiblast  now  extend  as  lateral  wings  to  the 
edge  of  the  pellucid  area;  they  are  not  joined  with  the  hypoblast.     The 


DEVELOPMENT. 


741 


intermediate  layer  of  cells  in  this  position  producing  the  primitive 
streak  is  a  portion  of  the  intermediate  layer  or  mesoblast.  It  is 
formed  chiefly  from  the  epiblast,  but  laterally,  especially  in  the  front 
part  of  the  primitive  streak,  it  appears  to  be  derived  at  any  rate  in  part 
from  the  cells  of  the  primitive  lower  layer.  At  the  most  anterior  part 
of  the  i)rimitive  streak,  at  the  point  which  corresponds  to  the  future 
posterior  end  of  the  embryo,  the  three  layers  are  all  joined  together. 
The  next  important  change  which  occurs  is  found  in  the  hypoblast  in 
front  of  the  primitive  streak.  The  irregular  layer  of  primitive  cells  of 
which  it  is  composed,  split  into  two  layers,  the  lower  consisting  of  flat- 


rig.  465.— Portion  of  the  germinal  membrane,  with  rudiments  of  the  embryo;  from  the  ovxim 
of  a  bitch.  The  primitive  groove,  a,  is  not  yet  closed,  and  at  its  upper  or  cephalic  end  presents 
three  dilatations,  b,  which  correspond  to  the  three  divisions  or  vesicles  of  the  brain.  At  its 
lower  extremity  the  groove  pre.sents  a  lancet-shaped  dilatation  (sinus  rhomboidalis)  c.  The 
margins  of  the  groove  consist  of  clear  pellucid  nerve-substance.  Along  the  bottom  of  the  gi-oove 
is  observed  a  faint  streak,  which  is  probably  the  chorda  dorsalis.  d.  Vertebral  plates. 
(Bischofif.) 

tened  cells  which  forms  the  hypoblast  proper  and  an  upper  consisting  of 
several  layers  of  stellate  cells,  the  mesoblast. 

In  the  preceding  account  of  the  formation  of  the  blastodermic  layers,  Bal- 
four's description  has  been  chiefly  followed.  It  differs  somewhat  from  that 
which  was  formerly  given.  The  mesoblast  was  described  as  arising  from  the 
hypoblast,  together  with  some  of  the  large  formative  cells,  which  migrate  by 
amceboid  movement  round  the  edge  of  the  hypoblast  (fig.  466,  M),  and  no  differ- 
•ence  was  made  in  the  formation  of  the  mesoblast  in  the  primitive  streak  and 
elsewhere. 

There  now  appears  in  the  middle  line  extending  forward  from  the 
primitive  streak  an  opaque  line,  which  proceeds  almost  to  the  anterior 


742  HANDBOOK    OF    PHYSIOLOGY. 

edge  of  the  area  pellucida,  stopping  short  at  a  transverse  crescent-shaped 
line,  the  future  headfokl.  I'his  line  is  the  commencing  notochord. 
It  is  a  collection  of  niesoblastic  cells  from  the  hypoblast  in  the  middle 
line,  and  remains  connected  with  the  latter  after  the  lateral  portions  of 
the  mesoblast  have  become  quite  detached  from  it.  The  notochord  and 
the  hypoblast  from  which  it  arises  are  continued  posteriorly  into  the 
primitive  streak.  Thus  the  mesoblast  of  the  area  on  either  side  of  the 
middle  line  in  which  the  embryo  is  formed  arises  from  the  hypoblast,  as 
does  also  the  notochord.  In  the  formation  of  the  medullary  plate 
which  now  appears,  the  epiblast  is  concerned.  In  the  middle  line  above 
the  collection  of  cells  that  will  become  the  notochord  that  layer  becomes 
thickened.  The  sides  of  the  central  thickened  portion  are  elevated 
somewhat  to  form  the  medullary  folds  inclosing  between  them  the 
medullary  groove.  From  this  medullary  plate  is  formed  the  central 
nervous  system.  Although  behind  the  groove  is  a  shallow  one,  if  it 
be  traced  forward  it  becomes  deeper  and  narrower,  and  at  the  headfold 
the  folds  curve  round  and  meet  in  the  middle  line.  Anterior  to  the 
headfold  is  a  second  fold  parallel  to  it,  which  is  the  commencing  amnion. 


'^ 


itf 


'  COO  „„»  j-"  ,SCi 

A 

Fig.  466. —Vertical  section  of  blastoderm  of  chick  (1st  day  of  incubation).  S,  epiblast  con- 
sisting of  short  columnar  cells;  D,  hypoblast,  consisting  of  a  single  layer  of  flattened  cells;  M, 
"formative  cells."  They  are  seen  on  the  right  of  the  figure,  passing  in  between  the  epiblast  and 
hypoblast  to  form  the  mesoblast;  A,  white  yolk  granules.  Many  of  the  large  "formative  cells" 
are  seen  containing  these  granules.     (Strieker. ) 

The  medullary  canal  is  bounded  by  its  two  folds  or  longitudinal  ele- 
vations, laminae  dorsales,  which  are  folds  consisting  entirely  of  cells  of 
the  epiblast:  these  grow  up  and  arch  over  the  medullary  groove  (fig. 
464)  till  after  some  time  they  coalesce  in  the  middle  line,  converting  it 
from  an  open  furrow  into  a  closed  tube — the  neural  canal  or  the  prim- 
itive cerebro-spinal  axis.  Over  this  closed  tube,  the  walls  of  which  con- 
sist of  more  or  less  cylindrical  cells,  the  superficial  layer  of  the  epiblast 
is  now  continued  as  a  distinct  membrane. 

The  union  of  the  medullary  folds  or  laminae  dorsalis  takes  place  first 
about  the  neck  of  the  future  embryo;  they  soon  after  unite  over  the 
region  of  the  head,  while  the  closing  in  of  the  groove  progresses  much 
more  slowly  toward  the  hinder  extremity  of  the  embryo.  The  medullary 
groove  is-  by  no  means  of  uniform  diameter  throughout,  but  even  before 
the  dorsal  laminae  have  united  over  it,  is  seen  to  be  dilated  at  the  ante- 


DEVELOPMEXT. 


743 


rior  extremity  and  obscurely  divided  by  constrictions  into  the  three 
primary  cerebral  vesicles. 

The  part  from  which  the  sjDinal  cord  is  formed  is  of  nearly  uniform 
calibre,  while  toward  the  posterior  extremity 
is  a  lozenge-shaped  dilatation,  sinus  rhom- 
boidalis,  which  is  the  last  ly^vt  to  close  in 
(fig.  465). 

While  the  changes  which  have  been  de- 
scribed are  taking  place  in  the  area  pellu- 
cida,  which  has  enlarged  to  a  certain  extent, 
the  area  opaca  has  also  considerably  extended. 
The  hypoblast  and  mesoblast  have  also  been 
prolonged  laterally,  not  by  mere  extension, 
but  also  from  the  germinal  wall,  which  is 
made  up  of  the  thickened  edge  of  the  blasto- 
derm, together  with  formative  cells  of  the 
yolk;  on  each  side  of  the  notochord  and 
medullary  canal,  the  mesoblast  remains  as  a 
longitudinal  thickening. 

It  now  however  splits  horizontally  into 
two  layers  or  laminae  {parietal  and  visceral) : 
of  these  the  former,  when  traced  out  from 
the  central  axis,  is  seen  to  be  in  close  appo- 
sition with  the  epiblast,  and  gives  origin  to 
the  parietes  of  the  trunk,  while  the  latter 
adheres  more  or  less  closely  to  the  hypoblast, 
and  gives  rise  to  the  serous  and  muscular 
walls  of  the  alimentary  canal  and  several 
other  parts. 

The  xinited  parietal  layer  of  the  mesoblast 
with  the  epiblast  is  termed  somatopleure, 
the  united  visceral  layer  and  hypoblast, 
splanchnopleure.  The  space  between  them 
is  the  pleuro-peritoneal  cavity,  which 
becomes  subdivided  by  subsequent  partitions 
into  pericardium,  pleura,  and  peritoneum. 

The  splitting  of  the  mesoblast  extends 
almost  to  the  medullary  canal,  but  a  portion 
on  either  side  (  P.  r*.  fig.  468)  remains  undi- 
vided, the  vertebral  plate.  The  divided  portion  is  known  as  the  late- 
ral plate.  The  longitudinal  thickening  of  the  vertebral  plate  is  seen 
after  a  while  to  be  divided  at  right  angles  to  the  medullary  canal  by 
bright  transverse  lines  into  a  number  of  square  segments.     These  seg- 


Fig.  46r.— Embryo  chick  (36 
hours),  viewed  from  beneatli  as  a 
transparent  object  (magnified). 
pi,  outline  of  peUucid  area,  FB, 
fore-brain,  or  first  cerebral  vesi- 
cle: from  its  sides  i)roject  op,  the 
optic  vesicle;  SO,  backward  limit 
of  somatopleure  fold,  "tucked  in" 
under  head;  o,  head-fold  of  true 
amnion;  a',  reflected  layer  of  am- 
nion, sometimes  termed  "false 
amnion;"  sp,  backward  limit  of 
splanchnopleure  folds,  along 
which  run  the  omphalomesaraic 
veins  uniting  to  form  /(,the  heart, 
which  is  continued  forward  into 
6a,  the  bulbus  arteriosus;  d,  the 
fore-gut,  lying  behind  the  heart, 
and   having   a    wide 


crescentic 


opening  between  the  splanchno- 
pleure folds;  HB,  hind-brain; 
MB,  mid-brain;  pv,  jirotoverte- 
br£e  Ij'iug  behind  the  fore-gut; 
mc,  line  of  junction  of  medullary 
folds  and  of  notochord ;  vpl,  ver- 
tebral plates;  pr,  the  primitive 
groove  at  its  caudal  end.  (Foster 
and  Balfour.) 


744 


HANDBOOK    OF    PHYSIOLOGY. 


ments,  which  are  the  surface  appearance  of  cubes  of  mesoblast,  are  the 
mesoblastic  somites  or  protovertebrae.  The  iirst  three  or  four  of 
the  protovertebraj  make  their  appearance  in  the  cervical  region,  while 
one  or  two  more  are  formed  in  front  of  this  point:  and  the  series  is 
continued  backward  till  the  whole  medullary  canal  is  flanked  by  them 


>sy 


TT 


r 


A 


Fig.  468. —Transverse  section  through  dorsal  region  of  embryo  chick  C4.5  hrs.).  One  half  of  the 
section  is  represented;  if  completed  it  would  extend  as  far  to  the  left  as  to  the  right  of  the  line 
of  the  medullary  canal  (Mc).  A,  epiblast;  C,  hypoblast,  consisting  of  a  single  layer  of  flattened 
cells;  J/c,  medullary  canal ;  Pi\  protovertebra ;  Wd,  Wolffian  duct;  So\  somatopleure ;  .S/), 
splanchnopleure;  ;?p,  pleuro-peritoneal  cavity;  ch,  notochord;  ao,  dorsal  aorta,  containing 
mood  cells ;  v,  blood-vessels  of  the  yolk-sac.     (Foster  and  Balfour. ) 

(fig.  467).  That  which  is  first  formed  corresponds  to  the  second  cervi- 
cal vertebra.  From  these  somites  the  vertebra?  and  the  trunk  muscles 
are  derived. 

Head  and  Tail  Folds.  Body  Cavity. — Every  vertebrate  animal  con- 
sists essentially  of  a  longitudinal  axis  (vertebral  column)  with  a  neural 
canal  above  it,  and  a  body-cavity  (containing  the  alimentary  canal) 
beneath. 

We  have  seen  how  the  earliest  rudiments  of  the  central  axis  and  the 
neural  canal  are  formed ;  we  must  now  consider  how  the  general  body- 


Fig.  469. —Diagrammatic  longitudinal  section  through  the  axis  of  an  embrj-o.  The  head-fold 
has  commenced,  but  the  tail-fold  has  not  yet  appeared.  FSo,  fold  of  the  somatopleure;  Fsp, 
fold  of  the  splanchnopleure;  the  line  of  reference,  Fso.  lies  outside  the  embryo  in  the  "moat," 
which  marks  off  the  overhanging  head  from  the  amnion ;  D,  inside  the  embryo,  is  that  part 
which  is  to  become  the  fore-gut;  Fso  and  Fsp,  are  both  parts  of  the  head-fold,  and  travel  to  the 
left  of  the  figure  as  development  proceeds ;  pjy,  space  between  somatopleure  and  splanchnopleure, 
pleuro-peritoneal  cavity;  Am,  commencing  head-fold  of  amnion;  NC.  neural  canal;  Ch,  noto- 
chord; Ht,  heart;  A,  B,  C,  epiblast,  mesoblast,  hypoblast.      (Foster  and  Balfour.) 

cavity  is  developed.  In  the  earliest  stages  the  embryo  lies  flat  on  the 
surface  of  the  yolk,  and  is  not  clearly  marked  off  from  the  rest  of  the 
blastoderm:  but  gradually  the  head-fold  or  crescentic  depression  (with 


DEVELOPMENT. 


745 


its  concavity  backward)  is  formed  in  the  blastoderm,  limiting  the  head 
of  the  embryo;  the  blastoderm  is,  as  it  were,  tucked  in  under  the  head, 
which  thus  comes  to  project  above  the  general  surface  of  the  membrane : 
a  similar  tucking  in  of  blastoderm  takes  place  at  the  caudal  extremity, 
and  thus  the  head  and  tail  folds  are  formed. 

Similar  depressions  mark  off  the  embryo  laterally,  until  it  is  com- 
pletely surrounded  by  a  sort  of  moat  which  it  overhangs  on  all  sides,  and 
which  clearly  defines  it  from  the  yolk. 

This  moat  runs  in  further  and  further  all  round  beneath  the  over- 
hanging embryo,  till  the  latter  comes  to  resemble  a  canoe  turned  upside- 


Fig.  470.— Diagrammatic  section  showing  the  relation  in  a  mammal  between  the  primitive 
alimentary  canal  and  the  membranes  of  ihe  ovum.  The  stage  represented  in  this  diagram  cor- 
responds to  that  of  the  fifteenth  or  seventeenth  day  in  the  human  embryo,  previous  to  the  ex- 
pansion of  the  allantois;  c.  tlie  villous  chorion;  a.  the  amnion;  a',  the  place  of  convergence  of 
the  amnion  and  reflection  of  the  false  amnion  a"  a",  or  outer  or  corneous  layer;  e,  the  head  and 
trunk  of  the  embryo,  comprising  the  primative  vertebrte  and  cerebro-spinal  axis;  i,  i,  the  simple 
alimentary  canal  in  its  upper  and  lower  portions.  Immediately  beneath  the  right  hand  i  is 
seen  the  fcetal  heart,  lying  in  the  anterior  part  of  the  pleuro-peritoneal  cavity;  v,  the  yolk-sac 
or  umbilical  vesicle;  r  i\  the  vitello-intestinal  opening;  i<,  the  allantois  connected  by  a  pedicle 
with  the  anal  portion  of  the  alimentary  canal.     (Quain.) 


down,  the  ends  and  middle  being,  as  it  were,  decked  in  by  the  folding 
or  tucking  in  of  the  blastoderm,  while  on  the  ventral  surface  there  is 
still  a  large  communication  with  the  yolk,  corresponding  to  the  well  or 
undecked  portion  of  the  canoe. 

This  communication  between  the  embryo  and  the  yolk  is  gradually 
contracted  by  the  further  tucking  in  of  the  blastoderm  from  all  sides, 
till  it  becomes  narrowed  down,  as  by  an  invisible  constricting  band,  to 


74G 


HA 


nOOK    OP    PHYSIOLOGY. 


a  mere  pedicle  which  pusses  out  of  the  body  of  the  embryo  at  the  point 
of  the  future  umbilicus. 

The  downwardly  folded  portions  of  blastoderm  are  termed  the  vis- 
ceral plates. 

Thus  we  see  that  the  body-cavity  is  formed  by  the  downward  folding 
of  the  visceral  plates,  just  as  the  neural  cavity  is  produced  by  the  up- 
ward growth  of  the  dorsal  lamini^",  the  difference  being  that,  in  the  vis- 
ceral or  ventral  lamina?,  all  three  layers  of  the  blastoderm  are  concerned. 

The  folding  in  of  the  splanchnopleure,  lined  by  hypoblast,  pinches 
off,  as  it  were,  a  portion  of  the  yelk-sac,  inclosing  it  in  the  body-cavity. 
This  forms  the  rudiment  of  the  alimentary  canal,  which  at  this  period 
ends  blindly  toward  the  head  and  tail,  while  in  the  centre  it  communi- 
cates freely  with  the  cavity  of  the  yolk-sac  through  the  canal  termed 
vitelline  or  omphalo-mesenteric  duct. 

The  yolk-sac  thus  becomes  divided  into  two  portions  which  communi- 
cate through  the  vitelline  duct,  that  portion  within  the  body  giving 


Fig.  471. 


Fis.  472. 


Figs.  471,  472  and  473. — Diagrams  showing  three  successive  stages  of  development.  Trans- 
verse vertical  sections.  The  yolk-sac,  ?/.«,  is  seen  progressively  diminishing  in  size.  In  the 
embryo  itself  the  medullary  canal  and  notochord  are  seen  in  section,  rf',  in  middle  figure,  the 
alimentary  canal,  becoming  pinched  off,  as  it  were,  from  the  yolk-sac;  a'  in  right-hand  fig>n-e, 
alimentary  canal  completely  closed;  o,  in  last  two  figures,  amnion;  etc.  cavity  of  amnion  filled 
with  amniotic  fluid ;  pp,  space  between  amnion  and  chorion  continuous  with  the  pleuro-perito- 
neal  cavity  inside  the  body;  vt.  vitelline  membrane;  ys,  yolk-sac,  or  umbilical  vesicle.  (Foster 
and  Balfour.) 

rise,  as  above  stated,  to  the  digestive  canal,  and  that  outside  the  body 
remaining  for  some  time  as  the  umhUiccd  vesicle  (fig.  473,  ys.).  The 
hypoblast  forming  the  epithelium  of  the  intestine  is  of  course  continuous 
with  the  lining  membrane  of  the  umbilical  vesicle,  while  the  visceral 
plate  of  the  mesoblast  is  continuous  with  the  outer  layer  of  the  umbilical 
vesicle. 

All  the  above  details  will  be  clear  on  reference  to  the  accompanying 
diagrams. 

At  the  posterior  end  of  the  embryo  chick,  when  the  amniotic  fold  is 
commencing  to  be  formed,  and  the  hind  fold  of  the  splanchnopleure  has 
commenced,  there  remains  for  a  time  a  communication  between  the 
neural  canal  and  the  hind  gut,  which  is  called  the  neurenteric  canal. 


DEVELOPMENT.  747 

It  passes  in  at  the  point  where  the  notochord  falls  into  the  primitive 
streak.  The  anterior  part  of  the  primitive  streak  becomes  the  tail 
swelling,  the  posterior  part  atrophies,  and  the  corresponding  lateral 
part  of  the  hlastoderm  forms  part  of  the  body-wall  of  the  embryo. 

The  anterior  part  of  the  medullary  canal  having  been  completely 
roofed  in,  the  foremost  portion  undergoes  dilatation,  and  a  bulb,  the 
first  or  anterior  cerebral  vesicle,  results.  From  either  side  of  this 
dilatation  a  process,  the  cavity  of  which  is  in  communication  with  it, 
is  separated  olf,  which  is  called  the  optic  vesicle. 

Behind  the  tirst  cerebral  vesicle  two  other  vesicles  now  arise,  the 
second  or  middle,  and  the  third  or  posterior  cerebral  vesicle,  and 
at  the  posterior  part  of  the  head  two  small  pits,  the  auditory  vesicles 
or  pits,  are  to  be  seen.  The  folding  of  the  head,  it  should  be  recol- 
lected, is  the  cause  of  the  iuclosure  below  the  neural  canal  (fig.  -IGO)  of 
a  canal  ending  blindly,  which  has  in  front  the  splanchnopleure,  and 
which  is  just  as  long  as  the  involution  of  that  membrane.  This  canal 
is  the  fore-gut.  In  the  interior  of  the  splanchnopleure  fold  below  it 
(as  seen  in  fig.  -109)  in  the  pleuro-peritoneal  cavity  the  heart  is  formed, 
\t  the  point  where  the  splanchnopleure  makes  its  turn  forward.  It 
irises  as  a  thickening  of  the  mesoblast  on  either  side  as  the  two  splanchno- 
pleure folds  diverge,  and  of  a  thickening  of  the  mesoblast  at  the  point 
of  divergence.  So  that  at  first  the  rudiment  of  the  heart  is  like  an 
inverted  V,  which  by  the  gradual  coming  together  of  the  diverging 
cords  is  converted  into  an  inverted  Y. 

The  cylinders  become  hollowed  out,  and  are  thus  converted  inta 
tubes,  which  then  coalesce.  Layers  are  separated  off  toward  the  interior, 
which  become  the  epithelial  lining,  and  the  mass  of  the  mesoblast  sur- 
rounding this,  afterward  form  the  muscle  and  serous  covering,  while  at 
first  the  rudimentary  organ  is  attached  to  the  gut  by  a  mesoblastic  mes- 
entery, the  mesocardimn. 

FcETAL  Membranes. 

Umbilical  Vesicle  {Yolk-sac). — The  splanchnopleure,  lined  by  hy- 
po])last,  forms  the  yolk-sac  in  reptiles,  birds,  and  mammals;  but  in 
amphibia  and  fishes,  since  there  is  neither  amnion  nor  allanfois,  the  wall 
of  the  yolk-sac  consists  of  all  three  layers  of  the  blastoderm,  inclosed,  of 
course,  by  the  original  vitelline  membrane. 

The  body  of  the  embryo  becomes  in  great  measure  detached  from 
the  yolk-sac  or  umbilical  vesicle,  which  contains,  however,  the  greater 
part  of  the  substance  of  the  yolk,  and  furnishes  a  source  whence  nutri- 
ment is  derived  for  the  embryo.  This  nutriment  is  absorbed  by  the 
numerous  vessels  (omphalo-mesenteric)  which  ramify  in  the  walls  of  the 
yolk-sac,  forming  what  in  birds  is  termed  the  area  vasculosa.     In 


748 


HANDBOOK    OF    PHYSIOLOGY. 


birds,  the  contents  of  the  yolk-sac  afford  nourishment  nntil  the  end  of 
incubation,  and  the  omphalo-meseuteric  vessels  are  developed  to  a  corre- 
sponding degree;  but  in  mammalia  the  office  of  the  umbilical  vesicle 
ceases  at  a  very  early  period,  as  the  quantity  of  the  yolk  is  small,  and 
the  embryo  soon  becomes  independent  of  it  by  the  connections  it  forms 
with  the  parent.  Moreover,  in  birds  as  the  sac  is  emptied,  it  is  gradu- 
.ally  drawn  into  the  abdomen  through  the  umbilical  opening,  which  then 


Fig.  475. 

Fig,  474. — Diagram  sliowiug  vascular  area  in  the  chick,  a,  area  pellucida;  6,  area  vasculosa; 
'C,  area  vitellina. 

Fig.  475.— Human  embryo  of  flf  til  week  with  umbilical  vesicle;  about  natural  size.  CDalton.) 
The  human  umbilical  vesicle  never  exceeds  the  size  of  a  small  pea. 

closes  over  it:  but  in  mammalia  it  always  remains  on  the  outside;  and 
as  it  is  emptied  it  contracts  (fig.  473),  shrivels  up,  and  together  with 
the  part  of  its  duct  external  to  the  abdomen,  is  detached  and  disapj)ears, 
either  before  or  at  the  termination  of  intra-uterine  life,  the  period  of 
its  disappearance  varying  in  different  orders  of  mammalia. 

When  blood-vessels  begin  to  be  developed,  they  ramify  largely  over 
the  walls  of  the  umbilical  vesicle,  and  are  actively  concerned  in  absorb- 
ing its  contents  and  conveying  them  away  for  the  nutrition  of  the 
•embryo. 

At  an  early  stage  of  development  of  the  foetus,  and  some  time  before 
the  completion  of  the  changes  which  have  been  just  described,  two  im- 
portant structures,  called  respectively  the  amnion  and  the  allantois,  begin 
to  be  formed. 

Amnion. — The  amnion  is  produced  as  follows: — Beyond  the  head- 
and  tail-folds  before  described  (p.  744),  the  somatopleure  coated  by  epi- 
blast,  is  raised  into  folds,  which  grow  up,  arching  over  the  embryo,  not 
only  anteriorly  and  posteriorly  but  also  laterally,  and  all  converging 
toward  one  point  over  its  dorsal  surface  (fig.  476).  The  growing  up  of 
these  folds  from  all  sides  and  their  convergence  toward  one  point  very 
closely  resembles  the  folding  inward  of  the  visceral  plates  already  de- 
scribed, and  hence,  by  some,  the  point  at  which  the  amniotic  folds 
meet  over  the  back  has  been  termed  the  amniotic  vmhilicus. 

The  folds  not  only  come  into  contact  but  coalesce.     The  inner  of 


DEVELOPMEXT.  ^  749* 

the  two  layers  forms  the  true  amnion,  while  the  outer  or  retiected  layer, 
sometimes  termed  the  false  amnion,  coalesces  with  the  inner  surface  of 
the  original  vitelline  membrane  to  form  the  subzonal  membrane  or 
false  chorion.  This  growth  of  the  amniotic  folds  must  of  course  be 
clearly  distinguished  from  the  very  similar  process,  already  described,  by 
which  at  a  much  earlier  stage  the  walls  of  the  neural  canal  are  formed. 

The  cavity  between  the  true  amnion  and  the  external  surface  of  the 
embryo  becomes  a  closed  space,  termed  the  amniotic  cavity  {ac,  fig.  -473). 

At  first,  the  amnion  closely  invests  the  embryo,  but  it  becomes  grad- 
ually distended  with  fluid  {liquor  amnii),  which,  as  pregnancy  advances, 
reaches  a  considerable  quantity. 

This  fluid  consists  of  water  containing  small  quantities  of  albumen 
and  urea.  Its  chief  function  during  gestation  appears  to  be  the  me- 
chariical  one  of  affording  equal  support  to  the  embryo  on  all  sides,  and 
of  protecting  it  as  far  as  possible  from  the  effects  of  blows  and  other 
injuries  to  the  abdomen  of  the  mother. 

The  embryo  up  to  the  end  of  pregnancy  is  thus  immersed  in  fluid, 
which  during  parturition  serves  the  important  purpose  of  gradually  and 
evenly  dilating  the  neck  of  the  uterus  to  allow  of  the  passage  of  the  fcetus: 
when  this  is  accomplished  the  amniotic  sac  bursts,  and  the  icaters  escape. 

On  referring  to  figs.  471,  472  and  473,  it  will  be  obvious  that  the 
cavity  outside  the  amnion^,  between  it  and  the  false  amnion,  is  continu- 
ous with  the  pleuro-peritoneal  cavity  at  the  umbilicus.  This  cavity  is 
not  entirely  obliterated  even  at  birth,  and  contains  a  small  quantity  ©f 
fluid,  which  is  discharged  during  parturition  either  before,  or  ab  the 
same  time  as  the  amniotic  fluid. 

AUantois. — Into  the  pleuro-peritoneal  space  the  allantois  sprouts 
out,  its  formation  commencing  during  the  development  of  the  amnion. 

Growing  out  from  or  near  the  hinder  j)ortion  of  the  intestinal  canal 
{c,  fig.  47G),  with  which  it  communicates,  the  allantois  is  at  first  a  solid 
pear-shaped  mass  of  splanchnopleiire ;  but  becoming  vesicular  by  the 
projection  into  it  of  a  hollow  outgrowth  of  hypoblast,  and  very  soon 
simply  membraneous  and  vascular,  it  insinuates  itself  between  the  amni- 
otic folds,  just  described,  and  comes  into  close  contact  and  union  with 
the  outer  of  the  two  folds,  which  has  itself,  as  before  said,  become  one 
with  the  external  investing  membrane  of  the  egg.  As  it  grows,  the 
allantois  develops  muscular  tissue  in  its  external  wall  and  becomes  ex- 
ceedingly vascular;  in  birds  (fig.  477)  it  envelops  the  whole  embryo — 
taking  up  vessels,  so  to  speak,  to  the  outer  investing  membrane  of  the 
egg,  and  lining  the  inner  surface  of  the  shell  Avith  a  vascular  membrane, 
by  these  means  affording  an  extensive  surface  in  which  the  blood  may 
be  aerated.  In  the  human  subject  and  in  other  mammalia,  the  vessels 
carried  out  by  the  allantois  are  distributed  only  to  a  special  part  of  the^ 


750 


HANDBOOK    OF    PHYSIOLOGY. 


outer  niembrano  or  false  chorion,  where,  by  interlacement  with  the  vas- 
cular system  of  the  mother,  a  structure  called  the  placenta  is  developed. 
In  mammalia,  as  the  viscei'al  lamina?  close  in  the  abdominal  cavity, 
the  allantois  is  thereby  divided  at  the  umbilicus  into  two  portions;  the 
rnter  part,  extending  from  the  umbilicus  to  the  cJiorion,  soon  shrivelling; 
while  the  inner  part  remaining  in  the  abdomen,  is  in  part  converted  into 
the  urinary  bladder;  the  portion  of  the  inner  part  not  so  converted, 
extending  from  the  bladder  to  the  umbilicus,  under  the  name  of  the 
iirachns.  After  birth  the  umbilical  cord,  and  with  it  the  external  and 
shrivelled  portion  of  the  allantois,  are  cast  ofE  at  the  umbilicus,  while 
the  urachus  remains  as  an  impervious  cord  stretched  from  the  top  of 
the  urinary  bladder  to  tlie  umbilicus,  in  the  middle  line  of  the  body, 


Fig.  470. 


Fig.  477. 


Fig.  476. — Diagram  of  fecundated  egg.  a,  umbilical  vesicle;  6,  amniotic  cavity;  c,  allantois. 
(Dalton.) 

Fig.  477. — Fecundated  egg  with  allantois  nearly  complete,  n,  inner  layer  of  amniotic  fold; 
fc,  outer  layer  of  ditto;  c,  point  where  the  amniotic  folds  come  in  contact.  The  allantois  is 
seen  penetrating  between  the  outer  and  inner  layers  of  the  amniotic  folds.  This  figure,  which 
represents  only  the  amniotic  folds  and  the  parts  within  them,  should  be  compared  with  figs. 
478,  479,  in  which  will  be  found  the  structures  external  to  these  folds.     CDalton.j 

immediately  beneath  the  joarietal  layer  of  the  peritoneum.  It  is  some- 
times enumerated  among  the  ligaments  of  the  bladder. 

It  must  not  be  supposed  that  the  phenomena  which  have  been  suc- 
cessively described,  occur  in  any  regular  order  one  after  another.  On 
the  contrary,  the  development  of  one  part  is  going  on  side  by  side  with 
that  of  another. 

The  Chorion. — It  has  been  already  remarked  that  the  allantois  is 
a  structure  which  extends  from  the  body  of  the  foetus  to  the  outer  in- 
vesting membrane  of  the  ovum,  that  it  insinuates  itself  between  tlie  two 
layers  of  the  amniotic  fold,  and  becomes  fused  with  the  outer  layer, 
which  has  itself  become  previously  joined  with  the  vitelline  membrane. 
By  these  means  the  external  investing  membrane  of  the  ovum,  or  the 
true  chorion,  as  it  is  now  called,  represents  three  layers,  namely,  the 
original  vitelline  membrane,  the  outer  layer  of  the  amniotic  fold,  and 
the  allantois. 

Very  soon  after  the  entrance  of  the  ovum  into  the  uterus,  in  the 
human  subject,  the  outer  surface  of  the  chorion  is  found  beset  with  fine 


DEVELOPMENT. 


751 


processes,  the  so-called  chorion  villi  {a,  figs.  478,  470),  Avhich  give  it 
a  rough  and  shaggy  appearance.  At  first  only  cellular  in  structure,  these 
little  outgrowths  subsequently  become  vascular  by  the  development  in 


Fig.  478.  Fis.479. 

Figs.  478  and  479. — a.  chorion  with  villi.  The  villi  are  shown  to  be  best  developed  in  the 
part  of  the  chorion  to  which  the  allantois  is  extending:  this  portion  ultimately  becomes  the 
placenta;  h,  space  between  the  two  layers  of  the  amnion;  c,  amniotic  cavity :  d.  situation  of  the 
intestine,  showing  its  connection  with'the  umbilical  vesicle;  e,  umbilical  vesicle;/,  situation  of 
heart  and  vessels ;  3,  allantois. 

them  of  loops  of  capillaries  (fig.  480) ;  and  the  latter  at  lengtli  form  the 
minute  extremities  of  the  blood-vessels  which  are,  so  to  speak,  conducted 
from  the  fa?tus  to  the  chorion  by  the  allantois.  The  function  of  the 
villi  of  the  chorion  is  evidently  the  absorption  of  nutrient  matter  for 
the  foetus;  and  this  is  probably  supplied  to  them  at  first  from  the  fluid 
matter,  secreted  by  the  follicular  glands  of  the  uterus,  in  which  they 
are  soaked.  Soon,  however,  the  foetal  vessels  of  the  villi  come  into 
more  intimate  relation  with  the  vessels  of  the 
uterus.  The  part  iit  which  this  relation  between 
the  vessels  of  the  foetus  and  those  of  the  parent 
ensues,  is  not,  however,  over  the  whole  surface  of 
the  chorion;  for,  although  all  the  villi  become 
vascular,  yet  they  become  indistinct  or  disappear 
except  at  one  part  where  they  are  greatly  devel- 
oped, and  by  their  branching  give  rise,  with  the 
vessels  of  tlie  uterus,  to  the  formation  of  the 
placenta. 

To  understand  the  manner  in  which  the  foetal 
and  maternal  blood-vessels  come  into  relation 
with  each  other  in  the  placenta,  it  is  necessary 

briefly  to  notice  the  changes  which  the  uterus  undergoes  after  impreg- 
nation. These  changes  consist  especially  of  alterations  in  structure  of 
the  superficial  part  of  the  mucous  membrane  which  lines  the  interior  of 
the  uterus,  and  which  forms,  after  a  kind  of  development  to  be  imme- 


Fig.  480. 


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HANDBOOK    OF    PHYSIOLOGY. 


diately  described,  the  memhrana  decklua,  so  called  on  account  of  its 
being  discharged  from  the  uterus  at  birth. 

Formation  of  the  Placenta. 

The  mucous  membrane  of  the  human  uterus,  which  consists  of  a 
matrix  of  connective  tissue  containing  numerous  corpuscles,  and  is  lined 
internally  by  columnar  ciliated  epithelium,  is  abundantly  beset  with 
tubular  glands,  arranged  perpendicularly  to  the  surface  (fig.  481).    These 


Fig.  481. — Section  of  the  lining  membrane  of  a  human  utenis  at  the  period  of  commencing 
pregnancy  showing  the  arrangement  and  other  peculiarities  of  the  glands,  d,  d,  d,  with  their 
orifices,  a,  a,  a,  on  the  internal  surface  of  the  organ.     Twice  the  natural  size. 

follicles  are  very  small  in  the  unimpregnated  uterus;  but  when  examined 
shortly  after  impregnation,  they  are  found  elongated,  enlarged,  and 
much  waved  and  contorted  toward  their  deep  and  closed  extremity, 
which  is  planted  at  some  depth  in  the  tissue  of  the  uterus,  and  may 
dilate  into  two  or  three  closed  sacculi. 

The  glands  are  lined  by  columnar  (  (?)  ciliated)  epithelium  and  they 
open  on  the  inner  surface  of  the  mucous  membrane  by  small  round  ori- 
fices set  closely  together  (a,  a,  fig.  481). 

On  the  internal  surface  of  the  mucous  membrane  may  be  seen  the 
circular  orifices  of  the  glands,  many  of  which  are,  in  the  early  period  of 
pregnancy,  surrounded  by  a  whitish  ring,  formed  of  the  epithelium 
which  lines  the  follicles. 

Coincidently  with  the  occurrence  of  pregnancy,  important  changes 
occur  in  the  structure  of  the  mucous  membrane  of  the  uterus.  The 
epithelium  and  sub-epithelial  connective  tissue,  together  with  the  tubu- 
lar glands,  increase  rapidly,  and  there  is  a  greatly  increased  vascularity 
of  the  whole  mucous  membrane,  the  vessels  of  the  mucous  membrane 
becoming  larger  and  more  numerous;  while  a  substance  composed  chiefly 
of  nucleated  cells  fills  up  the  interfollicular  spaces  in  which  the  blood- 
vessels are  contained.  The  effect  of  these  changes  is  an  increased  thick- 
nes,  softness,  and  vascularity  of  the  mucous  membrane,  the  superficial 
part  of  which  itself  forms  the  membrana  decidua. 

The  object  of  this  increased  development  seems  to  be  the  production. 


DEVELOPMENT. 


?03 


of  nutritive  materials  for  the  ovum ;  for  the  cavity  of  the  uterus  shortly 
becomes  filled  with  secreted  fluid,  consisting  almost  entirely  of  nucleated 
cells  in  which  the  chorion  villi  are  imbedded. 

When  the  ovum  first  enters  the  uterus  it  becomes  imbedded  in  the 
structure  of  the  decidua,  which  is  yet  quite  soft,  and  in  which  soon 
afterward  three  portions  are  distinguishable.  These  have  been  named 
the  decidua  vera,  the  decidua  rejlexa,  and  the  decidua  serotina. 

The  first  of  these,  the  decidua  vera,  lines  the  cavity  of  the  uterus; 
the  second,  or  decidua  reflexa,  is  a  part  of  the  decidua  vera  which  grows 
up  around  the  ovum,  and  wrapping  it  closely,  forms  its  immediate 
investment. 

The  third,  or  decidua  serotina,  is  the  part  of  the  decidua  vera  which 
becomes  especially  developed  in  connection  with  those  villi  of  the  cho- 
rion, which,  instead  of  disappearing,  remain  to  form  the  foetal  part  of 
the  ijlacenta. 

In  connection  with  these  villous  processes  of  the  chorion,  there  are 
developed  degressions  or  crypts  in  the  decidual  mucous  membrane,  which 
correspond  in  shape  with  the  villi  they  are  to  lodge;  and  thus  the  chori- 
onic villi  become  more  or  less  imbedded  in  the  maternal  structures. 


Fig.  482.— Diagram  of  an  early  stage  of  the  fonnation  of  the  human  placenta,  a,  embryo; 
6,  amnion ;  c,  placental  vessels ;  d,  decidua  reflexa ;  e,  allantois ;  /,  placental  villi ;  o,  mucous 
membrane.     (,Cadiat.) 

These  uterine  crypts,  it  is  important  to  note,  are  not,  as  was  once  sup- 
posed, merely  the  open  mouths  of  the  uterine  follicles. 

As  the  ovum  increases  in  size,  the  decidua  vera  and  the  decidua 
reflexa  gradually  come  into  contact,  and  in  the  third  month  of  preg- 
nancy the  cavity  between  them  has  almost  disappeared.  Though  the 
two  layers  come  into  contact  at  the  third  month,  they  are  not  closely 
amalgamated  until  the  end  of  the  sixth  month. 

The  Placenta. — During  these  changes  the  deeper  part  of  the  mu- 
48 


754 


HANDBOOK    OF    PHYSIOLOGY. 


cous  membrane  of  the  uterus,  at  and  near  the  region  where  the  placenta 
is  placed,  becomes  hollowed  out  by  sinuses,  or  cavernous  spaces,  which 
communicate  on  the  one  hand  with  arteries  and  on  the  other  with  veins 
of  the  uterus.  Into  these  sinuses  the  villi  of  the  chorion  protrude, 
pushing  the  thin  wall  of  the  sinus  before  them,  and  so  come  into  inti- 
mate relation  with  the  blood  contained  in  them.  There  is  no  direct 
comniunication  between  the  blood-vessels  of  the  mother  and  those  of  the 
foetus;  but  the  layer  or  layers  of  membrane  intervening  between  the 


Fig.  483. — Diagrammatic  view  of  a  vertical  transverse  section  of  the  uterus  at  the  seventh 
or  eighth  week  of  pregnancy,  c,  c,  c',  cavity  of  uterus,  which  becomes  the  cavity  of  the  decidua, 
opening  at  c,  c,  the  cornua,  into  the  FaUopian  tubes,  and  at  c'  into  the  cavitj'  of  the  cervix, 
which  is  closed  by  a  plug  of  mucus;  d  \\_  decidua  vera;  d  ?-,  decidua  reflexa,  with  the  sparser 
villi  imbedded  in  its  substance ;  d  s,  decidua  serotina,  involving  the  more  developed  chorionic 
viili  of  the  commencing  placenta.  The  foetus  is  seen  lying  in  the  amniotic  sac;  passing  up  from 
the  umbilicus  is  seen  the  umbilical  cord  and  its  vessels,  passing  to  their  distribution  in  the  villi 
of  the  chorion ;  also  the  pedicle  of  the  yolk-sac,  which  lies  in  the  cavity  between  the  amnion 
and  chorion.     (Allen  Thomson.) 


blood  of  the  one  and  of  the  other  offer  no  obstacle  to  a  free  interchange 
of  matters  between  them  by  diffusion  and  osmosis.  Thus  the  villi  of  the 
chorion  containing  foetal  blood,  are  bathed  or  soaked  in  maternal  blood 
contained  in  the  uterine  sinuses.  The  arrangement  may  be  roughly 
compared  to  filling  a  glove  with  foetal  blood,  and  dipping  its  fingers 
into  a  vessel  containing  maternal  blood.  But  in  the  fcetal  villi  there  is  a 
constant  stream  of  blood  into  and  out  of  the  loop  of  capillary  blood-vessels 
contained  in  it,  as  there  is  also  into  and  out  of  the  maternal  sinuses. 


DEVELOPMENT.  755 

It  would  seem  that,  at  the  villi  of  the  placental  tufts,  where  the 
foetal  and  maternal  portions  of  the  placenta  are  bi'ought  into  close  rela- 
tion with  each  other,  the  blood  in  the  vessels  of  the  mother  is 
separated  from  that  in  the  vessels  of  the  foetus  by  the  intervention  of 
two  distinct  sets  of  nucleated  cells  (fig.  484).  One  of  these  [b)  belongs 
to  the  maternal  portion  of  the  placenta,  is  placed  between  the  membrane 
of  the  villus  and  that  of  the  vascular  system  of  the  mother,  and  is  prob- 
ably designed  to  separate  from  the  blood  of  the  parent  the  materials 
destined  for  the  blood  of  the  foetus;  the  other  (/)  belongs  to  the  foetal 
portion  of  the  placenta,  is  situated  between  the  membrane  of  the  villus 
and  the  loop  of  vessels  contained  within,  and  probably  serves  for  the 
absorption  of  the  material  secreted  by  the  other  sets  of  cells,  and  for  its 
conveyance  into  the  blood-vessels  of  the  foetus.  Between  the  two  sets  of 
cells  with  their  investing  membrane  there  exists  a  space  (d),  into  which 
it  is  possible  that  the  materials  secreted  by  the  one  set  of  cells  of  the 
villus  are  j^oured  in  order  that  they  may  be  absorbed  by  the  other  set, 
and  thus  conveyed  into  a  foetal  vessel. 

Not  only,  however,  is  there  a  passage  of  materials  from  the  blood  of 
the  mother  into  that  of  the  foetus,  but  there  is  a  mutual  interchange  of 


Fig.  484. — Extremity  of  a  placental  villus,  a,  lining  membrane  of  the  vascular  system  of 
the  mother;  b.  cells  immediately  lining  a;  cl,  space  between  the  maternal  and  fcEtal  portions  of 
the  villus;  e,  internal  membrane  of  the  villus,  or  external  membrane  of  the  chorion;  /,  internal 
cells  of  the  villus,  or  cells  of  the  chorion;  g,  loop  of  umbilical  vessels.     (Goodsir. ) 

materials  between  the  blood  both  of  foetus  and  of  parent ;  the  latter  sup- 
plying the  former  with  nutriment,  and  in  turn  abstracting  from  it 
materials  which  require  to  be  removed. 

The  placenta,  therefore,  of  the  human  subject  is  composed  of  a 
foetal  part  and  a  maternal  part, — the  termi  placenta  properly  including 
all  that  entanglement  of  foetal  villi  and  maternal  sinuses,  by  means  of 
whicli  the  blood  of  the  foetus  is  enriched  and  jjurified  after  the  fashion 
necessary  for  the  proper  growth  and  development  of  those  parts  which 
it  is  designed  to  nourish. 

The  whole  of  this  structure  is  not,  as  might  be  imagined,  thrown 
off  immediately  after  birth.  The  greater  part,  indeed,  comes  away  at 
that  time,  as  the  ufter-hirtli;  and  the  separation  of  this  portion  takes 
place  by  a  rending  or  crushing  through  of  that  part  at  which  its  cohe- 
sion is  least  strong,  namely,  where  it  is  most  burrowed  and  undermined 


756  HANDBOOK    OF    PHYSIOLOGY, 

by  the  cavernous  spaces  before  referred  to.  In  this  way  it  is  cast  off 
with  the  fcetal  membrane  and  the  decidua  vera  and  reflexa,  together 
with  a  part  of  the  decidua  serotina.  The  remaining  portion  withers, 
and  disappears  by  being  gradually  either  absorbed,  or  thrown  off  in  the 
uterine  discharges  or  the  lochia,  which  occur  at  this  period. 

A  new  mucous  membrane  is  of  course  gradually  developed,  as  the 
old  one,  by  its  transformation  into  the  decidua,  ceases  to  perform  its 
original  functions. 

The  umbilical  cord,  which  in  the  latter  part  of  fcetal  life  is  almost 
solely  composed  of  the  two  arteries  and  the  single  vein  which  respectively 
convey  fatal  blood  to  and  from  the  placenta,  contains  the  remnants  of 
other  structures  which  in  the  early  stages  of  the  development  of  the 
embryo  were,  as  already  related,  of  great  comparative  importance.  Thus, 
in  early  foetal  life,  it  is  composed  of  the  following  parts : — (1. )  Externally, 
a  layer  of  the  amnion,  reflected  over  it  from  the  umbilicus.  (2)  The  um- 
bilical vesicle  with  its  duct  and  appertaining  omphalo-mesenteric  blood 
vessels.  (3.)  The  remains  of  the  allantois,  and  continuous  with  it  the 
urachus.  (4.)  The  umbilical  vessels,  which,  as  just  remarked,  ultimately 
form  the  greater  part  of  the  cord. 

The  Development  of  the  Okgans. 

Before  considering  very  briefly*  the  main  points  in  the  development 
of  the  chief  organs  and  tissues  of  the  body,  it  will  be  useful  to  have 
before  us  the  following  table,  compiled  by  Schiifer,  f  showing  the  differ- 
ent parts  derived  from  the  three  blastodermic  layers: — 

From  the  Upiblasf. — The  whole  of  the  nervous  system,  including 
not  only  the  central  organs  (brain  and  spinal  cord),  but  also  the  peri- 
pheral nerves  and  sympathetic. 

The  epithelial  structures  of  the  organs  of  special  sense. 

The  epidermis  and  its  appendages,  including  the  hair  and  nails. 

The  epithelium  of  all  the  glands  ojoening  upon  the  surface  of  the 
skin,  including  the  mammary  glands,  the  sweat  glands  and  the  sebaceous 
glands.     The  muscular  fibres  of  the  sweat  glands. 

The  epithelium  of  the  mouth  (except  that  covering  the  tongue,  and 
the  adjacent  posterior  part  of  the  floor  of  the  mouth,  which  is  derived 
from  the  hypoblast),  and  that  of  the  glands  opening  into  it. 

The  enamel  of  the  teeth. 

The  epithelium  of  the  nasal  passages,  of  the  adjacent  upper  part  of  the 
pharynx  and  of  all  the  cavities  and  glands  opening  into  the  nasal  pas- 
sages. 

*  For  a  more  detailed  account  the  reader  is  referred  to  special  text-books  of 
embrj^ology. 

f  Quain's  Anatomy,  Xth  Ed.,  Vol.  I.,  Part  I.,  p.  25. 


DEVELOPMEXT. 


r57 


From  the  Mesohlast. — The  urinary  and  generative  organs  (except  the 
epithelium  of  the  urinary  bhidder  and  urethra). 

All  the  voluntary  and  involuntary  muscles  of  the  body  (except  the 
muscular  fibres  of  the  sweat  glands). 

The  whole  of  the  vascular  and  lymphatic  system,  including  the 
:5orous  membranes  and  spleen. 

The  skeleton  and  all  the  connective  tissues  and  structures  of  the  body. 

From  the  Ili/pohlasf. — The  epithelium  of  the  alimentary  canal  from 
the  back  of  the  mouth  to  the  anus,  and  that  of  all  the  glands  which 
open  into  this  part  of  the  alimentary  tube. 

The  epithelium  of  the  Eustachian  tube  and  tympanum. 

The  epithelium  of  the  bronchial  tubes  and  air  sacs  of  the  lungs. 

The  epithelium  lining  the  vesicles  of  the  thyroid  body. 

The  epithelial  nests  of  the  thymus. 

The  epithelium  of  the  urinary  bladder  and  urethra. 

It  remains  now  to  consider  in  succession  the  development  of  the 
several  organs  and  systems  of  organs  in  the  further  progress  of  the 


,'  /  r 

/ 


-^^—Al 


Fig.  485.— Embryo  chick  f4th  day"),  viewed  as  a  transparent  object,  lying  on  its  left  side 
(magnified).  C  H,  cerebral  hemispheres:  F  B.  fore-brain  or  vesicle  of  third  ventricle,  with  P»i, 
pineal  gland  projecting  from  its  summit;  MB,  mid-brain;  C6,  cerebellum;  IV.  r,  fourth  ven- 
tricle; I/,  lens;  c  h  .s,  choroidal  slit;  Cen  F,  auditory  vesicle;  s  m,  superior  maxillary  process; 
\F,  2F,  etc.,  first,  second,  third,  and  fourth  visceral  folds;  V.  fifth  nerve,  sending  one  branch 
(ophthalmic)  to  the  eye,  and  another  to  the  first  visceral  arch;  VII,  seventh  nerve,  passing  to  the 
second  visceral  arch ;  G  Ph,  glosso-pharyngeal  nerve,  passing  to  the  third  visceral  arch ;  P  g, 
pneumogastric  nerve,  passing  toward  the  foiirtli  vi.sceral  arch;  i  v,  investing  mass;  ch,  noto- 
chord ;  its  front  end  cannot  be  seen  in  the  living  embryo,  and  it  does  not  end  as  shown  in  the  fig- 
ure, but  takes  a  sudden  bend  downward,  and  then  terminates  in  a  point;  Hf.  heart  seen  through 
the  walls  of  the  chest:  MP,  inuscle  plates;  W.  wing,  showing  commencing  differentiation  of 
segments,  corresponding  to  arm.  forearm,  and  hand;  H  L.  hind-limb,  as  yet  a  shapeless  bud, 
showing  no  differentiation.     Beneath  it  is  seen  the  curved  tail.     (Foster  and  Balfour.) 

embryo.     The  accompanying  figure  (fig.  485)  shows  the  chief  organs  of 
the  body  in  a  moderately  early  stage  of  development. 

The  Vertebral  Column  and  Cranium. — The  primitive  part  of 
the  vertebral  column  in  all  the  vertebrata  is  the  chorda  dorsalis  or  note- 


758  HANDBOOK    OF    PHYSIOLOGY. 

chord,  whicli  consists  entirely  of  soft  cellular  cartilage.  This  cord 
tapers  to  a  point  at  the  cranial  and  caudal  extremities  of  the  animal. 
In  the  progress  of  its  development,  it  is  found  to  become  inclosed  in  a 
membranous  sheath,  which  at  length  acquires  a  librous  structure,  com- 
posed of  transverse  annular  fibres.  The  chorda  dorsalis  is  to  be  regarded 
as  the  azygos  axis  of  the  spinal  column,  and,  in  particular,  of  the  future 
bodies  of  the  vertebrae,  although  it  never  itself  passes  into  the  state  of 
hyaline  cartilage  or  bone,  but  remains  inclosed  as  in  a  case  within  the 
persistent  parts  of  the  vertebral  column  which  are  developed  around 
it.  It  is  permanent,  however,  only  in  a  few  animals:  in  the  majority 
only  traces  of  it  persist  in  the  adult  animal. 

In  many  fish  no  true  vertebrae  are  developed,  and  there  is  every 
graduation  from  the  amphioxus,  in  which  the  notochord  persists 
through  life  and  there  are  no  vertebrae,  through  the  lampreys  in  which 
there  are  a  few  scattered  cartilaginous  vertebrae,  and  the  sharks,  in 
which  many  of  the  vertebrge  are  partly  ossified,  to  the  bony  fishes,  such 
as  the  cod  and  herring,  in  which  the  vertebral  column  consists  of  a 
number  of  distinct  ossified  vertebra,  with  remnants  of  the  notochord 
between  them.  In  amphibia,  reptiles,  birds,  and  mammals,  there  are 
distinct  vertebrae,  which  are  formed  as  follows: — 

The  mesoblastic  somites,  which  have  been  already  mentioned  (p. 
799),  send  processes  downward  and  inward  to  surround  the  notochord, 
and  also  upward  between  the  medullary  canal  and  the  epiblast  covering 
it.  In  the  former  situation,  the  cartilaginous  bodies  of  the  vertebrae 
make  their  appearance,  in  the  latter  their  arches,  which  inclose  the 
neural  canal. 

The  vertebrae  do  not  exactly  correspond  in  their  position  with  the 
protovertebrae :  but  each  permanent  vertebra  is  developed  from  the  con- 
tiguous halves  of  two  protovertebras.  The  original  segmentation  of  the 
protovertebrae  disappears  and  a  fresh  subdivision  occurs  in  such  a  way 
that  a  permanent  invertebral  disc  is  developed  opposite  the  centre  of 
each  protovertebra.  Meanwhile  the  protovertebrae  split  into  a  dorsal 
and  ventral  portion.  The  former  is  termed  the  musculo-cuta neons  plate, 
and  from  it  are  developed  all  the  muscles  of  the  back  together  with  the 
cutis  of  the  dorsal  region  (the  epidermis  being  derived  from  the  epiblast). 
The  ventral  portions  of  the  protovertebrae,  as  we  have  already  seen, 
give  rise  to  the  vertebras  and  heads  of  the  ribs. 

The  chorda  is  now  inclosed  in  a  case,  formed  by  the  bodies  of  the 
vertebrae,  but  it  gradually  wastes  and  disappears.  Before  the  disappear- 
ance of  the  chorda,  the  ossification  of  the  bodies  and  arches  of  the  verte- 
bra begins  at  distinct  points. 

The  ossification  of  the  body  of  a  vertebra  is  first  observed  at  the 
point  where  the   two  primitive  elements  of  the  vertebrae  have  united 


DEVELOPMENT.  759 

inferiorly.  Those  vertebra  which  do  not  bear  ribs,  such  as  the  cer- 
vical vertebrse,  have  generally  an  additional  centre  of  ossification  in 
the  transverse  process,  which  is  to  be  regarded  as  an  abortive  rudi- 
ment of  a  rib.  In  the  foetal  bird,  these  additional  ossified  portions 
exist  in  all  the  cervical  vertebrae,  and  gradually  become  so  much  developed 
in  the  lower  part  of  the  cervical  region  as  to  form  the  upper  false  ribs 
of  this  class  of  animals.  The  same  parts  exist  in  mammalia  and  man; 
those  of  the  last  cervical  vertebrsB  are  the  most  developed,  and  in  chil- 
dren may,  for  a  considerable  period,  be  distinguished  as  a  separate 
part  on  each  side  like  the  root  or  head  of  a  rib. 

The  true  cranium  is  a  prolongation  of  the  vertebral  column,  and  is 
developed  at  a  much  earlier  period  than  the  facial  bones.  Originally, 
it  is  formed  of  but  one  mass,  a  cerebral  capsule,  the  chorda  dorsalis 
being  continued  into  its  base,  and  ending  there  with  a  tapering  point. 
At  an  early  period  the  head  is  bent  downward  and  forward  round  the 
end  of  the  chorda  dorsalis  in  such  a  way  that  the  middle  cerebral  vesicle, 
and  not  the  anterior,  comes  to  occupy  the  highest  position  in  the  head. 

Pituitary  Body. — In  connection  with  this  must  be  mentioned  the 
development  of  the  pituitary  body.  It  is  formed  by  the  meeting  of  two 
outgrowths,  one  from  the  foetal  brain,  which  grows  downward,  and  the 
other  from  the  epiblast  of  the  buccal  cavity,  which  grows  up  toward  it. 
The  surrounding  mesoblast  also  takes  part  in  its  formation.  The  con- 
nection of  the  first  process  with  the  brain  becomes  narrowed,  and  per- 
sists as  the  infundibulum,  while  that  of  the  other  process  with  the  buccal 
cavity  disappears  completely  at  a  spot  corresponding  with  the  future 
position  of  the    body  of  the  sphenoid. 

Cranium. — The  first  appearance  of  a  solid  support  at  the  base  of  the 
cranium  observed  by  Muller  in  fish,  consists  of  two  elongated  bands  of  car- 
tilage (trabeculfe  cranii),  one  on  the  right  and  the  other  on  the  left  side, 
which  are  connected  with  the  cartilaginous  capsule  of  the  auditory  ap- 
paratus, and  which  diverge  to  "inclose  the  pituitary  body  uniting  in 
front  to  form  the  septum  nasi  beneath  the  anterior  end  of  the  cerebral 
capsule.  Hence,  in  the  cranium,  as  in  the  spinal  column,  there  are  at 
first  developed  at  the  sides  of  the  chorda  dorsalis  two  symmetrical  ele- 
ments, which  subsequently  coalesce,  and  may  wholly  inclose  the  chorda. 

The  brain-case  consists  of  three  segments:  occipital,  parietal,  and 
frontal,  corresponding  in  their  relative  position  to  the  three  primitive 
cerebral  vesicles;  it  may  also  be  noted  that  in  front  of  each  segment  is 
developed  a  sense-organ  (auditory,  ocular,  and  olfactory,  from  behind 
forward).  The  basis  cranii  consists  at  an  early  period  of  an  unsegmented 
cartilaginous  rod,  developed  round  the  notochord,  and  continued  for- 
ward beyond  its  termination  into  the  trabeculm  cranii^  which  bound  the 
pituitary  fossa  on  either  side. 


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HANDBOOK    OF    PHYSIOLOGY, 


In  this  cartilaginous  rod  three  centres  of  ossification  appear:  basi- 
oecipital,  basi-sphenoid,  and  pre-sphenoid,  one  corresponding  to  each 
segment. 

The  bones  forming  the  vault  of  the  skull,  viz.,  the  frontal,  parietal, 
squamous  portion  of  temporal  and  the  squamo-occipital,  are  ossified  in 
membrane. 

The  Visceral  Clefts  And  Arches. 

As  the  embryo  enlarges,  the  heart,  Avhicli  at  first  occupied  a  position 
close  to  the  cranial  flexure,  is  carried  further  and  further  backward  until  a 
considerable  part,  in  which  the  mesoblast  is  undivided,  intervenes  between 


Fig.  486. — A.  MagTiified  view  from  before  of  the  head  and  neck  of  a  human  embryo  of  about 
three  weeks  (from  Ecker.)— 1,  anterior  cerebral  vesicle  or  cerebrum;  2,  middle  ditto;  3,  middle 
or  fronto-nasal  process;  4,  superior  maxillary  process;  5,  eye;  6,  inferior  maxillary  process,  or 
first  visceral  arch,  and  below  it  the  first  cleft ;  7,  8,  9,  second,  third,  and  fourth  arches  and  clefts. 
B.  Anterior  view  of  the  head  of  a  human  foetus  of  about  the  fifth  week  (from  Ecker,  as  before, 
fig.  IV.).  1,  2,  3,  5,  the  same  parts  as  in  a;  4,  the  external  nasal  or  lateral  frontal  process:  6, 
the  superior  maxillary  process;  7,  the  lower  jaw;  X,  the  tongue;  8,  first  branchial  cleft  becom- 
ing the  meatus  auditorius  externus. 

it  and  the  head.  This  becomes  the  neck.  On  section  it  is  seen  that  in 
it  the  whole  three  layers  are  represented  in  order,  and  that  there  is  no 
interval  between  them.  In  the  neck  thus  formed  soon  appear  the  vis- 
ceral or  branchial  clefts  on  either  side,  in  series,  across  the  axis  of 
the  gut  not  quite  at  right  angles.  They  are  four  in  number,  the  most 
anterior  being  first  found.  At  their  edges  the  hypoblast  and  their 
epiblast  are  continuous.  The  anterior  border  of  each  cleft  forms  a  fold 
or  lip,  the  branchial  or  visceral  fold.  The  posterior  border  of  the  last 
cleft  is  also  formed  into  a  fold,  so  that  there  are  four  clefts  and  five  folds, 
but  the  three  most  anterior  are  far  more  prominent  than  the  others,  and 
of  these  the  second  is  the  most  conspicuous.  The  first  fold  nearly  meets  its 
fellow  in  the  middle  line,  the  second  less  nearly,  and  the  others  in  order 
still  less  so.  Thus  in  the  neck  there  is  a  triangular  interval,  into  which 
by  the  splitting  of  the  mesoblast  at  that  part  the  pleuroperitoneal  cavity 
extends.  The  branchial  clefts  and  arches  are  not  all  permanent.  The 
first  arch  gives  off  a  branch  from  its  front  edge,  which  passes  forward  to 
meet  its  fellow,  but  these  offshoots  do  not  quite  meet,  being  separated 


DEVELOPMENT, 


761 


by  a  process  which  grows  downward  from  the  head.  Between  the 
branches  and  the  main  first  fold  is  the  cavity  of  the  mouth.  The  branches 
represent  the  superior  maxilla,  and  the  main  folds  the  mandible  or  lower 
jaw.  The  central  process,  which  grows  down,  is  the  fronto-nasal  pro- 
cess. 

In  this  way  the  so-called  visceral  arches  and  clefts  are  formed,  four 
on  each  side  (fig.  486,  a). 

From  or  in  connection  with  these  arches  the  following  parts  are  devel- 
oped : — 

The  first  arch  (mandibular)  contains  a  cartilaginous  rod  (Meckel's 
■cartilage),  around  the  distal  end  of  which  the  lower  jaw  is  developed, 
while  the  malleus  is  ossified  from  the  proximal  end. 

When  the  maxillary  processes  on  the  two  sides  fail  partially  or  com- 
pletely to  unite  in  the  middle  line,  the  well-knoAvn  condition  termed 
■cleft  palate  results.  When  the  integument  of  the  face  presents  a  similar 
deficiency,  we  have  the  deformity  known  as  hare-lip.     Though  these  two 


^^^y  xpy^ 


Fig.  487.— Embryo  chick  C4th  clay),  viewed  as  a  transparent  object,  lying  on  its  left  side 
(magnified).  C  H,  cei-ebral  hemispheres;  F B,  fore-brain  or  vesicle  of  third  ventricle,  with  P/i, 
pineal  gland  projecting  from  its  summit;  MB,  mid-brain;  C  b,  cerebellum;  IV.  V,  fourth  ven- 
tricle: L,  lens;  c  h  ,s,  choroidal  slit:  Cen.  V,  auditory  vesicle;  s  ni,  superior  maxillary  process: 
IF,  2F,  etc.,  first,  second,  third,  and  fourth  visceral  folds;  F,  fifth  nerve,  sending  one  branch 
(ophthalmic)  to  the  eye,  and  another  to  the  first  visceral  arch;  TV/,  seventh  nerve,  passing  to 
the  second  visceral  arch;  G.  Ph,  glosso-pharyngeal  nerve,  passing  to  the  third  visceral  arch; 
P  (/^  pneumogastric  nerve,  passing  toward  the  fourth  visceral  arch;  i  v,  investing  mass ;  c  h, 
notochord;  its  front  end  cannot  be  seen  in  the  living  embryo,  and  it  does  not  end  as  shown  in 
the  figu^'e,  but  takes  a  sudden  bend  downward,  and  then  terminates  in  a  point;  Ht,  heart  seen 
through  the  walls  of  the  chest;  MP.  muscle-plates;  W,  wing,  showing  commencing  differentia- 
tion of  segnients,  corresponding  to  arm,  forearm,  and  hand;  S  &',  somatic  stalk;  Al,  allantois; 
H  L,  hind-limb,  as  yet  a  shapeless  bud,  showing  no  differentiation.  Beneath  it  is  seen  the 
curved  tail.     (Foster  and  Balfour.) 


deformities  frequently  co-exist,  they  are  by  no  means  always  necessarily 
associated. 

The  upper  part  of  the  face  in  the  middle  line  is  developed  from  the 
so-c&Wed  frontal- nasal  process  (a,  3,  fig.  486.)     From  the  second  arch 


762 


HANDBOOK    OF    PHYSIOLOGY. 


are  developed  the  incus,  stapes,  and  stapedius  muscle,  the  styloid  process 
of  the  temporal  bone,  the  stylo -hyoid  ligament,  and  the  smaller  cornu  of 
the  hyoid  hone.  From  the  ^A/rfZ  visceral  arch,  the  greater  cornu  and  body 
of  the  hyoid  bone.  In  man  and  other  mammalia  the /owr/A  visceral  arch 
is  indistinct.  It  occupies  the  position  where  the  neck  is  afterward 
developed. 

A  distinct  connection  is  traceable  between  these  visceral  arches  and 
certain  cranial  nerves :  the  trigeminal,  the  facial,  the  glosso-pharyngeal, 
and  the  vagus.  The  ophthalmic  division  of  the  trigeminal  supplies  the 
fronto-nasal  process;  the sujDcrior  and  inferior  maxillary  divisions  supply 
the  maxillary  and  mandibular  arches  respectively. 

The  facial  nerve  distributes  one  branch  (chorda  tympani)  to  the 
first  visceral  arch,  and  others  to  the  second  visceral  arch.  Thus  it 
divides,  inclosing  the  first  visceral  cleft. 

Similarly,  the  glosso-pharyngeal  divides  to  inclose  the  second  visceral 
cleft,  its  lingual  branch  being  distributed  to  the  second,  and  its 
pharyngeal  branch  to  the  third  arch. 

The  vagus,  too,  sends  a  branch  (pharyngeal)  along  the  third  arch, 
and  in  fishes  it  gives  off  paired  branches,  which  divide  to  inclose  several 
successive  branchial  clefts. 


The  Extremities. 

The  extremities  are  developed  in  a  uniform  manner  in  all  verte- 
brate animals.     They  appear  in  the  form  of  leaf-like  elevations  from  the 


^.^ 


Fig.  488.— A  human  embryo  of  the  fourth  week,  31^  lines  in  length.—],  the  chorion;  3,  part 
of  the  amnion;  4,  umbilical  vesicle  with  its  long  pedicle  passing  into  the  abdomen;  7,  the 
heart;  8,  the  liver;  9,  the  visceral  arch  destined  to  form  the  lower  jaw,  beneath  which  are  two 
other  visceral  arches  separated  by  the  branchial  clefts;  10,  rudiment  of  the  upper  extremity;  11, 
that  of  the  lower  extremity;  12,  the  umbilical  cord;  15,  the  eye;  16,  the  ear;  17,  cerebral  hemi- 
spheres; 18,  optic  lobes,  corpora  quadrigemina.     (Miiller.  )• 

parieties  of  the  trunk  (see  fig.  488) ,  at  points  where  more  or  less  of  an 
arch  will  be  produced  for  them  within.  The  primitive  form  of  the 
extremity  is  nearly  the  same  in  all  vertebrata,  whether  it  be  destined  for 


DEVELOPMENT.  '  763 

swimming,  crawling,  walking,  or  flying.  In  the  human  foetus  the  fin- 
gers are  at  first  united,  as  if  webbed  for  swimming;  but  this  is  to  be 
regarded  not  so  much  as  an  approximation  to  the  form  of  aquatic 
animals,  as  the  primitive  form  of  the  hand,  the  individual  parts  of  which 
subsequently  become  more  completely  isolated. 

The  fore-limb  always  appears  before  the  hind-limb,  and  for  some 
time  continues  in  a  more  advanced  state  of  development.  In  both 
limbs  alike,  the  distal  segment  (hand  or  foot)  is  separated  by  a  slight 
notch  from  the  proximal  part  of  the  limb,  and  this  part  is  subsequently 
divided  again  by  a  second  notch  (knee  or  elbow-joint). 

The  Vascular  System. — At  an  early  stage  in  the  development  of 
the  embryo-chick,  the  so-called  area  vasculosa  begins  to  make  its  ajDpear- 
ance.  A  number  of  branched  cells  in  the  mesoblast  send  out  processes 
which  unite  so  as  to  form  a  network  of  protoplasm  with  nuclei  at  the 
nodal  points.  A  large  number  of  nuclei  acquire  red  color ;  these  form  the 
red  blood-corpuscles.  The  protoplasmic  processes  become  hollowed 
out  in  the  centre  so  as  to  form  a  closed  system  of  branching  canals,  in 
the  walls  of  which  the  rest  of  the  nuclei  remain  imbedded.  In  the 
blood-vessels  thus  formed,  the  circulation  of  the  embryonic  blood  com- 
mences. 

According  to  Klein,  the  first  blood-vessels  in  the  chick  are  developed 
from  embryonic  cells  of  the  mesoblast,  which  swell  up  and  become  vacuo- 
lated,while  their  nuclei  undergo  segmentation.  These  cells  send  out  proto- 
plasmic processes,  which  unite  with  corresponding  ones  from  other  cells, 
and  become  liollow^ed,give  rise  to  the  cai^illary  wall  composed  of  endothelial 
cells;  the  blood  corpuscles  being  budded  off  from  the  endothelial  wall  by  a 
process  of  gemmation. 

Heart. — About  the  same  early  period  the  heart  makes  its  appearance 
as  a  solid  mass  of  cells  of  the  splanchnopleure  in  the  manner  before  indi- 
cated. 

At  this  period  the  anterior  part  of  the  alimentary  tube  ends  blindly 
beneath  the  notochord.  It  is  beneath  the  posterior  end  of  this  fore-gut 
that  the  heart  begins  to  be  developed.  The  heart  when  first  formed  is 
made  up  of  two  not  quite  complete  tubes  which  coalesce  to  form  one,  and 
so  when  the  cavity  is  hollowed  out  in  the  mass  of  cells,  the  central  cells 
float  freely  in  the  fluid,  which  soon  begins  to  circulate  by  means  of  the 
rhythmic  pulsations  of    the  embryonic   heart. 

These  pulsations  take  place  even  before  the  appearance  of  a  cavity, 
and  immediately  after  the  first  laying  down  of  the  cells  from  which 
the  heart  is  formed,  and  long  before  muscular  fibres  or  ganglia  have  been 
formed  in  the  cardiac  walls.  At  first  they  seldom  exceed  from  fifteen 
to  eighteen  in  the  minute.  The  fluid  within  the  cavity  of  the  heart 
shortly  assumes  the  characters  of  blood.     At  the  same  time,  the  cavity 


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HANDBOOK    OF    PHYSIOLOGY, 


itself  forms  a  communication  with  tlie  great  vessels  in  contact  with  it, 
and  the  cells  of  which  its  walls  are  comprised  are  transformed  into  fibrous 
and  muscular  tissues,  and  into    epithelium.     In    the  developing  chick 


Fig.  489. 


Fig.  491. 


Fig.  489. — Capillary  blood-vessels  of  the  tail  of  a  young  larval  frog,  a,  capillaries  perme- 
able to  blood ;  6,  fat  granules  attached  to  the  walls  of  the  vessels,  and  concealing  the  nuclei ;  c, 
hollow  prolongation  of  a  capillary,  ending  in  a  point;  d,  a  branching  cell  with  nucleus  and  fat- 
granules;  it  communicates  by  three  branches  with  prolongation  of  capillaries  already  formed; 
€,  e,  blood  corpuscles  still  containing  granules  of  fat.     x  350  times.     cKoUiker. ) 

Fig.  490. —Development  of  capillaries  in  the  regenerating  tail  of  a  tadpole,  a  bed,  sprouts 
and  cords  of  protoplasm.     CArnold. ) 

Fig.  491.— The  same  region  after  the  lapse  of  24  hours.  The  "sprouts  and  cords  of  proto- 
plasm" have  become  channelled  out  into  capillaries.     (Arnold.) 

it  can  be  observed    with  the  naked  eye  as  a  minute  red  pulsating  little 
mass  before  the  end  of  the  second  day  of  incubation. 

Blood-vessels. — ^Blood-vessels  appear  to  be  developed  in  two  ways,  ac- 
cording to  their  size.  In  the  formation  of  large  blood-vessels,  masses  of 
embryonic  cells  similar  to  those  from  which  the  heart  and  other  struct- 
ures of  the  embryo  are  developed,  arrange  themselves  in  the  position, 
form,  and  thickness  of  the  developing  vessel.  Shortly  afterward  the  cells 
in  the  interior  of  a  column  of  this  kind  sem  to  be  developed  into  blood- 


DEVELOPMENT. 


763 


corpuscles,  while  the  external  layer  of  cells  is  converted  into  the  walls 
of  the  vessel. 

In  the  development  of  capillaries  another  plan  is  pursued.  This  has 
been  well  illustrated  by  Kolliker,  as  observed  in  the  tails  of  tadpoles. 
The  first  lateral  vessels  of  the  tail  have  the  form  of  simple  arches,  pass- 
ing between  the  main  artery  and  vein,  and  are  produced  by  the  junction 
of  prolongations,  sent  from  both  the  artery  and  vein,  with  certain  elon- 
gated or  star-shaped  cells,  in  the  substance  of  the  tail.  When  these  arches 
are  formed  and  are  permeable  to  blood,  new  prolongations  pass  from  them, 
join  other  radiated  cells,  and  thus  form  secondary  arches.  In  this  manner, 
thecapillary  network  extends  in  proportion  as  the  tail  increases  in  length 
and  breadth,  and  it,  at  the  same  time,  becomes  more  dense  by  the  forma- 
tion, according  to  the  same  plan,  of  fresh  vessels  within  its  meshes.  The 
prolongations  by  which  the  vessels  communicate  with  the  star-shaped  cells, 
consist  at  first  of  narrow  pointed  projections  from  the  side  of  the  vessels, 
which  gradually  elongate  until  they  come  in  contact  with  the  radiated 
processes  of  the  cells.  The  thickness  of  such  a  prolongation  often  does 
not  exceed  that  of  a  fibril  of  fibrous  tissue,  and  at  first  it  is  perfectly 
solid;  but,  by  degrees,  especially  after  its  junction  with  a  cell,  or  with 
another  prolongation,  or  with  a  vessel  already  permeable  to  blood,  it 
enlarges,  and  a  cavity  then  forms  in  its  interior  (see  figs.  491,  492). 
This  tissue  is  well  calculated  to  illustrate  the  various  steps  in  the  devel- 
opment of  blood-vessels  from  elongating  and  branching  cells. 

In  many  cases  a  whole  network  of  capillaries  is  developed  from  a  net- 
work of  branched,  embryonic  connective-tissue  corpuscles  by  the  join- 


Fig.  492. — Capillaries  from  the  vitreous  humor  of  a  foetal  calf.  Two  vessels  are  seen  con- 
nected by  a  "cord"  of  protoplasm,  and  clothed  with  an  adventitia,  containing  numerous  nuclei, 
a,  insertion  of  this  "cord  "  into  the  primary  walls  of  the  vessels.     (Frey.) 

ing  of  their  processes,  the  multiplication  of  their  nuclei,  and  the  vacuo- 
lation  of  the  cell-substance.  The  vacuoles  gradually  coalesce  till  all  the 
partitions  are  broken  down,  and  the  originally  solid  protoplasmic  cell- 
substance  is,  so  to  speak,  tunnelled  out  into  a  number  of  tubes. 

Capillaries  may  also  be  developed  from  cells  which  are  originally 
spheroidal,  vacuoles  form  in  the  interior  of  the  cells  gradually  becoming 


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HANDBOOK    OF    PHYSIOLOGY. 


united  by  fine  protoplasmic  processes:  by  the  extension  of  the  vacuoles 
into  them,  capillary  tubes  are  gradually  formed. 

Morphology.  Heart. — When  it  first  appears,  the  heart  is  approxi- 
mately tubular  in  form,  being  at  first  a  doiible  fvbe  then  a  single  one.  It 
receives  at  its  two  posterior  angles  the  two  omphalo-mesenteric  or  vitel- 
line veins,  and  gives  off  anteriorly  the  primitive  aorta  (fig.  493).  The 
junction  of  the  two  veins  which  pass  into  the  auricle  becomes  removed 
farther  and  farther  away  from  the  heart,  and  the  vessel  thus  formed  is 
called  sinus  venosus  near  to  the  auricle,  and  ductus  venosus  farther 
away, or  if  it  be  called  by  one  name  that  of  meatus  venosvs  may  be  used. 

It  soon,  however,  becomes  curved  somewhat  in  the  shape  of  a  horse- 
shoe, with  the  convexity  toward  the  right,  the  venous  end  being  at  the 
same  time  drawn  up  toward  the  head,  so  that  it  finally  lies  behind  and 
somewhat  to  the  right,  of  the  arterial.  It  also  becomes  partly  divided  by 
constrictions  into  three  cavities. 

Of  these  three  cavities  which  are  developed  in  all  vertebrata,  that  at 
the  venous  end  is  the  simple  auricle,  with  the  sinus  venosus,  that  at  the 
arterial  end  the  bulbus  arteriosus,  and  the  middle  one  is  the  simple  ven- 
tricle. 

These  three  parts  of  the  heart  contract  in  succession.  The  auricle 
and  the  bulbus  arteriosus  at  this  period  lie  at  the  extremities  of  the 


Fig.  493. 


-FcEtal  heart  in  successive  stages  of  development.    1,  venous  extremity ;  2,  arterial  ex- 
tremity; 3,  3,  pulmonary  branches;  4,  ductus  arteriosus.     (Dalton.) 


horse-shoe.  The  bulging  out  of  the  middle  portion  iuferiorly  gives  the 
first  indication  of  the  future  form  of  the  ventricle  (fig.  493).  The  great 
curvature  of  the  horse-shoe  by  the  same  means  becomes  much  more 
developed  than  the  smaller  curvature  between  the  auricle  and  bulbus; 
and  the  two  extremities,  the  auricle  and  bulb,  approach  each  other 
superiorly,  so  as  to  produce  a  greater  resemblance  to  the  later  form  of 
the  heart,  while  the  ventricle  becomes  more    and  more  developed  in- 


DEVELOPMENT.  767 

feriorly.  The  heart  of  fishes  retains  these  cavities,  no  further  division 
by  internal  septa  into  riglit  and  left  chambers  taking  place.  In 
amphibia,  also,  the  heart  throughout  life  consists  of  the  three  muscular 
divisions  which  are  so  early  formed  in  the  embryo  and  the  sinus  venosus; 
but  the  auricle  is  divided  internally  by  a  septum  into  a  pulmonary  and 
systemic  auricle.  In  reptiles,  not  merely  the  auricle  is  thus  divided  into 
two  cavities,  but  a  similar  septum  but  incomplete  is  more  or  less  developed 


Fig.  494.— Heart  of  the  chick  at  the  45th,  65th,   and   85th  hours  of   incubation.    1,  the  venous 
trunks;  2,  the  auricle;  3,  the  ventricle;  4,  the  bulbus  arteriosus.     (Allen  Thomson.) 

in  the  ventricle.  In  birds  and  mammals,  both  auricle  and  ventricle 
undergo  complete  division  by  septa;  while  in  these  animals  as  well  as  in 
reptiles,  the  bulbus  aortte  is  not  permanent,  but  becomes  lost  in  the  ven- 
tricles. The  septum  dividing  the  ventricle  commences  at  the  apex  and 
extends  uj^ward.  The  subdivision  of  the  auricles  is  very  early  fore- 
shadowed by  the  outgrowth  of  the  two  auricular  appendages,  which 
occurs  before  any  septum  is  formed  externally.  The  septum  of  the 
auricles  is  developed  from  a  semilunar  fold,  which  extends  from  above 
downward.  In  man,  the  septum  between  the  ventricles,  according  to 
Meckel,  begins  to  be  formed  about  the  fourth  week,  and  at  the  end  of 
eight  weeks  is  complete.  The  septum  of  the  auricles,  in  man  and  all 
animals  which  possess  it,  remains  imperfect  throughout  foetal  life.  When 
the  partition  of  the  auricles  is  first  commencing,  the  two  vence  cavae  have 
different  relations  to  the  two  cavities.  The  superior  cava  enters,  as  in 
the  adult,  into  the  right  auricle;  but  the  inferior  cava  is  so  placed  that 
it  appears  to  enter  the  left  auricle,  and  the  posterior  part  of  the  septum 
of  the  auricles  is  formed  by  the  Eustachian  valve,  which  extends  from 
the  point  of  entrance  of  the  inferior  cava.  Subsequently,  however,  the 
septum,  growing  from  the  anterior  wall  close  to  the  upper  end  of  the  ven- 
tricular septum,  becomes  directed  more  and  more  to  the  left  of  the  vena 
cava  inferior.  During  the  entire  period  of  foetal  life,  there  remains 
an  opening  in  the  septum,  which  the  valve  of  the  foramen  ovale,  devel- 
oped in  the  third  month,  imperfectly  closes. 

The  bulbus  arteriosus^  which  is  originally  a  single  tube,  becomes 
gradually  divided  into  two  by  the  growth  of  an  internal  septum,  which 
springs  from  the  posterior  wall,  and  extends  forward  toward  the  front 
wall  and  downward  toward  the  ventricles.  This  partition  takes  a  some- 
what spinal  direction,  so  that  the  two  tubes  (aorta  and  pulmonary  artery) 


7G8  HANDBOOK    OF    PHYSIOLOGY. 

wliicli  result  from  its  completion,  do  not  run  side  by  side,  but  are 
twisted  round  each  other. 

As  the  septum  grows  down  toward  the  ventricles,  it  meets  and  coa- 
lesces with  the  upwardly  growing  ventricular  septum,  and  thus  from 
the  right  and  left  ventricles,  which  are  now  completely  separate,  arise 
respectively  the  pulmonary  artery  and  aorta,  which  are  also  quite  dis- 
tinct. The  auriculo-ventricular  and  semi-lunar  valves  are  formed  by  the 
folds  of  the  endocardium. 

At  its  first  appearance,  as  we  have  seen,  the  heart  is  placed  just 
beneath  the  head  of  the  foetus,  and  is  very  large  relatively  to  the  whole 
body ;  but  with  the  growth  of  the  neck  it  becomes  further  and  further 
removed  from  the  head,  and  is  lodged  in  the  cavity  of  the  thorax. 

Up  to  a  certain  period  the  auricular  is  larger  than  the  ventricular  divi- 
sion of  the  heart;  but  this  relation  is  gradually  reversed  as  development 
proceeds.  Moreover,  all  through  fcetal  life,  the  walls  of  the  right  ven- 
tricle are  of  very  much  the  same  thickness  as  those  of  the  left,  which 
may  probably  be  exi^lained  by  the  fact  that  in  the  foetus  the  right  ven- 
tricle has  to  propel  the  blood  from  the  pulmonary  artery  into  the  aorta, 
and  thence  into  the  placenta,  Avhile  in  the  adult  it  only  drives  the  blood 
through  the  lungs. 

Arteries. — The  primitive  aorta  arises  from  the  bulbus  arteriosus  and 
divides  into  two  branches  which  arch  backward,  one  on  each  side  of  the 
foregut  and  unite  again  behind  it,  and  in  front  of  the  notochord  into  a 
single  vessel. 

This  gives  off  the  two  omphalo-mesenteric  arteries,  which  distribute 
branches  all  over  the  yolk-sac;  this  area  vasculosa  in  the  chick  attaining 
a  large  development,  and  being  limited  all  round  by  a  vessel  known  as 
the  sinus  termiualis. 

The  blood  is  collected  by  the  venous  channels,  and  returned  through 
the  omphalo-mesenteric  veins  to  the  heart. 

Behind  this  pair  of  primitive  aortic  arches,  four  more  pairs  make 
their  appearance  sucessively,  so  that  there  are  five  pairs  in  all,  each  one 
running  along  one  of  the  visceral  arches. 

These  five  are  never  all  to  be  seen  at  once  in  the  embryo  of  higher 
animals,  for  the  two  anterior  pairs  gradually  disappear,  while  the  pos- 
terior ones  are  making  their  appearance,  so  that  at  length  only  three 
remain. 

In  fishes,  however,  they  all  persist  throughout  life  as  the  branchial 
arteries  supplying  the  gills,  while  in  amphibia  three  pairs  persist  through- 
out life. 

In  reptiles,  birds,  and  mammals,  further  transformations  occur. 

In  reptiles  the  fourth  pair  remains  throughout  life  as  the  permanent 
right  and  left  aorta;  in  birds  the  right  one  remains  as  the  permanent 


DEVELOPMENT. 


769 


aorta,    curving   over   the   right   bronchus  instead    of    the   left    as    in 
mammals. 

In  mammals  the  left  fourth  aortic  arch  develops  into  the  permanent 
aorta,  the  right  one  remaining  as  the  subclavian  artery  of  that  side. 
Thus  the  subclavian  artery  on  the  right  side  corresponds  to  the  aortic 
arch  on  the  left,  and  this  homology  is  further  confirmed  by  the  fact  that 


Fig.  495.— Diagram  of  the  aortic  arches  in  a  mammal,  sliowing  transformations  which  give  rise 
to  the  permanent  arterial  vessels.  A,  primitive  arterial  stem  or  aortic  bulb,  now  divided  into 
.4,  the  ascending  part  of  the  aortic  arch,  and  p,  the  pulmonary ;  a  a',  right  and  left  aortic  roots ; 
A',  descending  aorta:  1,  2,  3,  4,  5,  the  five  primitive  aortic  or  branchial  arches;  /,  //,  ///,  /f' 
the  four  branchial  clefts  which,  for  the  sake  of  clearness,  have  been  omitted  on  the  right  side! 
The  permanent  sj'stemic  vessels  are  deeply,  the  pulmonary  arteries  lightly,  shaded ;  the  parts 
of  the  primitive  arches  which  are  transitory  are  simply  outlined;  f,  placed  between  the  per- 
manent common  carotid  arteries;  ce,  external  carotid  arteries;  c  /,  internal  carotid  arteries;  s, 
right  subclavian,  rising  from  the  right  aortic  root  beyond  the  fifth  arch;  r,  right  vertebral  froui 
the  same,  opposite  the  fourth  arch ;  v'  s\  left  vertebral  and  subclavian  arteries  rising  together 
from  the  left  or  permanent  aortic  root,  opposite  the  fourth  arch;  ;j.  pulmonary  arteries  rising 
together  from  the  left  fifth  arch ;  d,  outer  or  back  part  of  the  left  fifth  arch,  forming  ductus 
arteriosis;  j}  n,  p  n\  right  and  left  pneumogastric  nerves  descending  in  front  of  aortic  arch, 
with  their  recurrent  branches  represented  diagrammptically  as  passing  behind,  to  illustrate  the 
relations  of  these  nerves  respectively  to  the  right  subclavian  artery  (4)  and  the  arch  of  the  aorta 
and  ductus  arteriosus  id).     (Allen  Thomson,  after  Rathke.) 

the  recurrent  laryngeal  nerve  hooks  under  the  subclavian  on  the  right 
side,  and  the  aortic  arch  on  the  left. 

The  third  aortic  arch  remains  as  the  internal  carotid  artery,  while 
the  fifth  disappears  on  the  right  side,  but  on  the  left  forms  the  pulmo- 
nary artery.  The  distal  end  of  this  arch  originally  opens  into  the  descend- 
ing aorta,  and  this  communication  (which  is  permanent  throughout 
life  in  many  reptiles  on  both  sides  of  the  body)  remains  through- 
out fcetal  life  under  the  name  of  ductus  arteriosus:  the  branches  of  the 
i:)ulmonary  artery,  to  the  right  and  left  lung,  are  very  small,  and  most 
of  the  blood  which  is  forced  into  the  j)ulmonary  artery  passes  through 
the  wide  ductus  arteriosus  into  the  descending  aorta.  All  these  j^oints 
will  become  clear  on  reference  to  the  accompanying  diagram  (fig.  495). 
49 


770 


HANDBOOK    OF    PHYSIOLOGY. 


As  the  umbilical  vesicle  dwindles  in  size,  the  portion  of  the  omphalo- 
mesenteric arteries  outside  the  body  gradually  disappears,  the  part  inside 
the  body  remaining  as  the  mesenteric  arteries. 

Meanwhile  with  the  growth  of  the  allantois  two  new  arteries  {iwibil- 
ical)  appear,  and  rapidly  increase  in  size  till  they  are  the  largest  branches 
of  the  aorta:  they  are  given  off  from  the  internal  iliac  arteries,  and  for 
a  long  time  are  considerably  larger  than  the  external  iliacs  which  supply 
the  comparatively  small  hind-limbs. 

Veins. — The  chief  veins  in  the  early  embryo  may  be  divided  into 
two  groups,   visceral  and  parietal:    the  former  includes  the  omphalo- 


Fig.  496. 


Fig.  497 


Fig.  490. —Diagram  of  young  embryo  and  its  vessels,  showing  course  of  circulation  in  the 
umbilical  vesicle;  and  also  that  of  the  allantois  Cnear  the  caudal  extremity),  vi'hich  is  just  com- 
mencing.    ( Dalton. ) 

Fig,  497.  —Diagram  of  embryo  and  its  vessels  at  a  later  stage,  showing  the  second  circula- 
tion. The  pharynx,  cesophagus,  and  intestinal  canal  have  become  further  developed,  and  themes- 
enteric  arteries  have  enlarged,  while  the  umbilical  vesicle  and  its  vascular  branches  are  very 
much  reduced  in  size.  The  large  umbilical  arteries  are  seen  passing  out  in  the  placenta.  (Dalton.) 

mesenteric  and  umbilical,   the  latter  the  jugular  and  cardinal  veins. 
The  former  may  be  first  considered. 

The  earliest  veins  to  appear  in  the  foetus  are  the  omphalo-mesenteric 
or  vitelline,  which  return  the  blood  from  the  yolk-sac  to  the  developing 
auricle.  As  soon  as  the  placenta  with  its  umbilical  veins  is  developed, 
these  unite  with  the  omphalo-mesenteric,  and  thus  the  blood  which 
reaches  the  auricle  comes  partly  from  the  yolk-sac  and  partly  from  the 
placenta.  The  right  omphalo-mesenteric  and  the  right  umbilical  veins 
soon  disappear,  and  the  united  left  omphalo-mesenteric  and  umbilical 
veins  pass  through  the  developing  liver  on  the  way  to  the  auricle.  Two 
sets  of  vessels  make  their  appearance  in  connection  with  the  liver  (vente 
hepaticre  advehentes,  and  revehentes),  both  opening  into  the  united 
omphalo-mesenteric  and  umbilical  veins,  in  such  a  way  that  a  portion 
of  the  venous  blood  traversing  the  latter  is  diverted  into  the  developing 


DEYELOPMEXT. 


771 


liver,  and,  having  passed  through  its  capillaries,  returns  to  the  umbili- 
cal vein  through  the  vena?  hepaticse  revehentes  at  a  point  nearer  the 
heart  (see  fig.  498) .  The  portion  of  vein  between  the  afferent  and  effe- 
rent veins  of  the  liver  becomes  the  ductus  venosus.     The  ven^e  hepaticae 


Fig.  498. —Diagrams  illustrating  the  development  of  veins  about  the  liver.  B,  d  c,  ducts  of 
Cuvier,  right  and  left;  c  a,  right  and  left  cardinal  veins;  o.  left  omphalo-meseuteric  vein;  o', 
right  ompiialo-mesenteric  vein,  almost  shrivelled  up;  n  tt',  umbilical  veins,  of  which  u',  the  riglit 
one,  has  almost  disappeared.  Between  the  venas  cardinales  is  seen  the  outline  of  the  rudiment- 
ary liver  with  its  venas  hepaticae  adveheutes,  and  revehentes.  Z>,  ductus  venosus;  I',  hepatic 
veins;  c  i,  vena  cava  inferior;  P,  portal  vein;  P'P',  venae  advehentes;  hi,  mesenteric  veins. 
(KoUilier.) 


advehentes  become  the  right  and  left  branches  of  the  jiortal  vein,  the 
venas  hepaticse  revehentes  become  the  hepatic  veins,  which  open  just  at 
the  junction  of  the  ductus  venosus  with  another  large  vein  (vena  cava 
inferior),  which  is  now  being  developed.  The  mesenteric  portion  of 
the  omphalo-mesenteric  vein  returning  blood  from  the  developing  intes- 
tines remains  as  the  mesenteric  vein,  which,  by  its  union  with  the  sijlenic 
vein,  forms  the  jiortal. 

Thus  the  foetal  liver  is  supplied  with  venous  blood  from  two  sources, 
through  the  umbilical  and  portal  vein  respectively.  At  birth  the  circu- 
lation through  the  umbilical  vein  of  course  completely  ceases  and  the 
vessel  begins  at  once  to  dwindle,  so  that  now  the  only  venous  supply  of 
the  liver  is  through  the  portal  vein.  The  earliest  appearance  of  the 
parietal  system  of  veins  is  the  formation  of  two  short  transverse  veins 
(ducts  of  Cuvier)  opening  into  the  auricle  on  either  side,  which  result 
from  the  union  of  an  anterior  cardinal,  afterward  forming  a  jugular, vein, 
collecting  blood  from  the  head  and  neck,  and  a  posterior  cardinal  vein 
which  returns  the  blood  from  the  Wolffian  bodies,  the  vertebral  column, 
and  the  parieties  of  the  trunk.  This  arrangement  persists  throughout 
life  in  fishes,  but  in  mammals  the  following  transformations  occur. 

As  the  kidneys  are  developing  a  new  vein  appears  (vena  cava  infe- 
rior), formed  by  the  junction  of  their  efferent  veins.  It  receives  branches 
from  the  legs  (iliac)  and  increases  rapidly  in  size  as  they  grow;  further 
up  it  receives  the  hepatic  veins,  which  by  now  have  lost  their  original 
opening  into  the  ductus  venosus.     The  heart  gradually  descends  into 


772 


HANDBOOK    OF    PHYSIOLOGY. 


the  thorax,  causing  the  ducts  of  Cuvier  to  become  oblique  instead  of 
transverse.  As  the  fore-limbs  develop,  the  subclavian  veins  are  formed. 
A  transverse  communicating  trunk  now  unites  the  two  ducts  of 
Cuvier,  and  gradually  increases,  while  the  left  duct  of  Cuvier  becomes 
almost  entirely  obliterated  (all  its  blood  jjassing  by  the  communicating 
trunk  to  the  right  side)  (fig.  499,  c.d.).  The  right  duct  of  Cuvier 
remains  as  the  right  innominate  vein,  while  the  communicating  branch 
forms  the  left  innominate.  The  remnant  of  the  left  duct  of  Cuvier 
generally  remains  as  a  fibrous  band,  running  obliquely  down  to  the  coro- 
nary vein,  which  is  really  the  proximal  p)art  of  the  left  duct  of  Cuvier. 
In  front  of  the  root  of  the  left  lung,  another  relic  may  be  found  in  the 


Fig.  499.— Diagrams  iUustrating  the  development  of  the  great  veins,  d  c,  ducts  of  Cuvier ;  j", 
jugular  veins;  h,  hepatic  veins;  c,  cardinal  veins;  .s,  subclavian  vein;  j  i,  internal  jugular  vein; 
je,  external  jugular  vein;  a  2,  azygos  vein;  c  i.  inferior  vena  cava;  r,  renal  veins;  il,  iliac  veins; 
h  ij,  hypogastric  veins.     (Gegenbaur.) 

form  of  the  so-called  vestigial  fold  of  Marshall,  which  is  a  fold  of  peri- 
cardium running  in  the  same  direction. 

In  many  of  tflie  lower  mammals,  such  as  the  rat,  the  left  ductus 
Cuvieri  remains  as  a  left  superior  cava. 

Meanwhile,  a  transverse  branch  carries  across  most  of  the  blood  of 
the  left  posterior  cardinal  vein  into  the  right;  and  by  this  union  the 
great  azygos  vein  is  formed. 

The  upper  portions  of  the  left  posterior  cardinal  vein  remains  as  the 
left  superior  intercostal  and  vena  azygos  minor. 


Circulation  of  Blood  in  the  Fcetus. 

The  circulation  of  blood  in  the  foetus  differs  considerably  from  that 
of  the  adult.     It  will  be  well,  perhaps,  to  begin  its  description  by  trac- 


DEVELOPMENT. 


773 


ing  the  course  of  the  blood,  which,  after  being  carried  out  to  the  pla- 
centa by  the  two  umbilical  arteries,  has  returned,  cleansed  and  replen- 
ished, to  the  foetus  by  the  umbilical  vein. 

It  is  at  first  conveyed  to  the  under  surface  of  the  liver,  and  there  the 
stream  is  divided, — a  part  of  the  blood  passing  straight  on  to  the  in- 


L.  ^itbclaf 


_X'_  '--->rV=i<or?« 


Su.JU710l'  »•%» 


V«7t       -t\    \ 


it      P 

Vr  -  —  ■  Jyinc-Vrnc  Corn 


{}  'fj 


Fig.  500.  —Diagram  of  the  Foetal  Circulation. 

ferior  vena  cava,  through  a  venous  canal  called  the  ductus  venosus,  while 
the  remainder  passes  into  the  portal  vein,  and  reaches  the  inferior  vena 
cava  only  after  circulating  through  the  liver.  AVhether,  however,  by 
the  direct  route  through  the  ductus  venosus  or  by  the  roundabout  way 
through  the  liver, — all  the  blood  which  is  returned  from  the  placenta  by 
the  umbilical  vein  reaches  the  inferior  vena  cava  at  last,  and  is  carried 
by  it  to  the  right  auricle  of  the  heart,  into  which  cavity  is  also  pouring 


774  HANDBOOK    OF    PHYSIOLOGY. 

the  blood  that  has  circulated  in  the  head  and  neck  and  arms,  and  has 
l)oen  brought  to  the  auricle  by  the  superior  vena  cava.  It  might  be 
naturally  expected  that  the  two  streams  of  blood  would  be  mingled  in 
the  right  auricle,  but  such  is  not  the  case,  or  only  to  a  slight  extent. 
The  blood  from  the  superior  vena  cava — the  less  pure  fluid  of  the  two — 
passes  almost  exclusively  into  the  right  ventricle,  through  the  auriculo- 
ventricular  opening,  just  as  it  does  in  the  adult;  while  the  blood  of  the 
inferior  vena  cava  is  directed  by  a  fold  of  the  lining  membrane  of  the 
heart,  called  the  Eiistacliian  valve,  through  the  foramen  ovale  into  the 
left  auricle,  whence  it  passes  into  the  left  ventricle,  and  out  of  this  into 
the  aorta,  and  thence  to  all  the  body,  but  chiefly  to  the  head  and  neck. 
The  blood  of  the  superior  vena  cava,  which,  as  before  said,  passes  into 
the  right  ventricle,  is  sent  out  thence  in  small  amount  though  the  pul- 
monary artery  to  the  lungs,  and  thence  to  the  left  auricle,  as  in  the 
adult.  The  greater  part,  however,  by  far,  does  not  go  to  the  lungs,  but 
instead,  passes  through  a  canal,  the  ductus  arteriosus,  leading  from  the 
pulmonary  artery  into  the  aorta  just  below  the  origin  of  the  three  great 
vessels  which  supply  the  ujiper  parts  of  the  body ;  and  there  meeting 
that  part  of  the  blood  of  the  inferior  vena  cava  which  has  not  gone  into 
these  large  vessels,  it  is  distributed  with  it  to  the  trunk  and  lower  parts, 
— a  portion  passing  out  by  way  of  the  two  umbilical  arteries  to  the 
placenta.  From  the  placenta  it  is  returned  by  the  umbilical  vein  to  the 
under  surface  of  the  liver,  from  which  the  description  started. 

Changes  after  Birth. — After  birth  the  foramen  ovale  closes,  and  so 
do  the  ductus  arteriosus  and  ductus  venosus,  as  well  as  the  umbilical 
vessels;  so  that  the  two  streams  of  blood  which  arrive  at  the  right  auri- 
cle by  the  superior  and  inferior  vena  cava  respectively,  thenceforth 
mingle  in  this  cavity  of  the  heart,  and  passing  into  the  right  ventricle, 
go  by  way  of  the  pulmonary  artery  to  the  lungs,  and  through  these  after 
purification,  to  the  left  auricle  and  ventricle,  to  be  distributed  over  the 
body. 

The  Nervous  System. 

The  Cranial  and  Spinal  Nerves. — The  cranial  nerves  are  derived  from 
a  continuous  band,  called  the  neural  band.  They  are  formed  before  the 
neural  canal  is  complete.  The  neural  band  is  made  up  of  two  lamina? 
going  from  the  dorsal  edges  of  the  neural  groove  to  the  external  epiblast. 
It  becomes  separated  from  the  epiblast,  and  then  forms  a  crest  attached 
to  the  upper  surface  of  the  brain.  The  posterior  roots  of  the  spinal 
nerves  arise  as  outgrowths  of  median  processes  of  cells  from  the  dorsal 
side  of  the  spinal  cord,  which  become  attached  laterally  to  the  spinal 
cord  as  their  original  point  of  attachment  disappears.  The  anterior 
roots  probably  arise  from  the  ventral  part  of  the  cord  as  a  number  of 


DEVELOPMENT.  775 

strands  for  each  nerve.  They  appear  later  than  the  posterior  roots. 
The  rudiment  of  the  posterior  root  is  differentiated  into  a  jjroximal 
round  nerve  connected  to  the  cord,  a  ganglionic  portion  and  a  distal 
portion.     To  the  last  the  anterior  nerve-root  becomes  attached. 

The  Spinal  Cord.— The  spinal  cord  consists  at  first  of  the  undiffer- 
entiated epiblast  of  the  walls  of  the  neural  canal,  the  cavity  of  which  is 
large,  with  almost  j^arallel  sides.  The  walls  are  at  first  composed  of 
elongated  irregular  nucleated  columnar  cells,  arranged  in  a  radiate 
manner.  The  cavity  then  becomes  narrow  in  the  middle  and  of  an 
liour-glass  shape  (fig,  501).     When  the  spinal  nerves  make  their  first 


Fig.  501. — Diagram  of  development  of  spinal  cord,    c  c,  central   canal;  o/,  anterior  fissure ;  pf, 
posterior  fissure ;  g.  gray  matter;  w,  white  matter.     For  further  ejcplanation.,  see  text. 

appearance,  about  the  fourth  day  in  the  chick,  the  epiblustic  w\ills  be- 
come differentiated  into  three  parts :  («)  the  epithelium  lining  the  central 
canal;  {h)  the  gray  matter;  (c)  the  external  white  matter.  The  last  is 
derived  from  the  outermost  part  of  the  epiblastic  walls  by  the  conversion 
of  the  cells  into  longitudinal  nerve-fibres.  The  fibres  being  without  any 
myelin  sheath,  are  for  a  time  gray  in  ajopearance.  The  white  matter 
corresponds  in  position  to  the  anterior  and  posterior  nerve-roots,  and 
are  the  anterior  and  posterior  white  columns.  It  is  at  first  a  very  thin 
layer,  but  increases  in  thickness  until  it  covers  the  wdiole  cord.  The 
gra)^  matter  too  arises  from  the  cells  by  their  being  prolonged  into  fibres. 
The  change  in  the  central  cells  is  sufficiently  obvious.  The  anterior  and 
posterior  cornua  of  gray  matter  and  the  anterior  gray  commissure  then 
appear.  The  anterior  fissure  is  formed  on  the  fifth  day  by  the  growth 
downward  of  the  anterior  cornua  of  gray  matter  toward  the  middle 
line.  The  posterior  fissure  is  form.ed  later.  The  whole  cord  now  be- 
comes circular.     The  posterior  gray  commissure  is  then  formed. 

When  it  first  appears,  the  spinal  cord  occupies  the  whole  length  of 
the  medullary  canal,  but  as  development  proceeds,  the  spinal  column 
grows  more  rapidly  than  the  contained  cord,  so  that  the  latter  apjiears 
as  if  drawn  up  tiH,  at  birth,  it  is  opposite  the  third  lumbar  vertebra, 
and  in  the  adult  opposite  the  first  lumbar.  In  the  same  way  the  in- 
creasing obliquity  of  the  spinal  nerves  in  the  neural  canal,  as  we  approach 
the  lumbar  region,  and  the  cauda  equina  at  the  lower  end  of  the  cord, 
are  accounted  for. 

Brain. — We  have  seen  that  the  front  portion  of  the  medullary  canal 


77G 


HANDBOOK    OF    PHYSIOLOGY. 


is  almost  from  the  first  widened  out  and  divided  into  three  vesicles. 
From  the  anterior  vesicle  (thalamencephalon)  the  two  primary  optic 
vesicles  are  budded  off  laterally :  their  further  history  will  be  traced  in 
the  next  section.  Somewhat  later,  from  the  same  vesicle  the  rudiments 
of  the  hemispheres  appear  in  the  form  of  two  outgrowths  at  a  higher 
level,  which  grow  upward  and  backward.  These  form  the  prosen- 
cephalon. 

In  the  walls  of  the  posterior  (third)  cerebral  vesicle,  a  thickening 
appears  (rudimentary  cerebellum)  which  becomes  separated  from  the 
rest  of  the  vesicle  by  a  deep  inflection. 

At  this  time  there  are  two  chief  curvatures  of  the  brain  (fig.  502). 
(1.)  A  sharp  bend  of  the  whole  cerebral  mass  downward  round  the  end 


Fig.  502.— Early  stages  in  development  of  human  brain  (magnified).  1,  2,  3,  are  from  an 
embryo  about  seven  weeks  old ;  4,  about  three  months  old.  7?i,  middle  cerebral  vesicle  (mesen- 
cephalon);  c,  cerebellum;  mo,  medulla  oblongata;  /,  thalamencephalon;  h,  hemispheres;  i',  in- 
fundibulum;  Fig.  3  shows  the  several  curves  which  occur  in  the  course  of  development;  Fig. 
4  is  a  lateral  view,  showing  the  great  enlargement  of  the  cerebral  hemispheres  which  have 
covered  in  the  thalami,  leaving  the  optic  lobes,  m,  uncovered.     (Kolliker.) 

N.  B. — In  Fig.  2  the  line  i  terminates  in  the  right  hemisphere;  it  ought  to  be  continued  into 
the  thalamencephalon. 


of  the  notochord,  by  which  the  anterior  vesicle,  which  was  the  highest 
of  the  three,  is  bent  downward,  and  the  middle  one  comes  to  occupy 
the  highest  position.  (2.)  A  sharp  bend,  with  the  convexity  forward, 
which  runs  in  from  behind  beneath  the  rudimentary  cerebellum  sepa- 
rating it  from  the  medulla. 

Thus,  five  fundamental  parts  of  the  foetal  brain  may  be  distinguished, 
which,  together  with  the  parts  developed  from  them,  may  be  presented 
in  the  following  tabular  view : — 


DEVELOPMENT. 


777 


Table  of  Parts  de\t:loped  from  Fundamental  Parts  of  Brain. 


II. 


III. 


Anterior 
Primary 
Vesicle, 
or  Fore- 
brain. 


Middle 
Primary 
Vesicle, 
or  Mid- 
brain. 
Posterior 
Primary 
Vesicle, 
or  Hind- 
brain. 


First    Secondary    Vesicle 
of  Prosencephalon. 


Second  Secondary  Vesicle 
or  Tbalamencephalon 
(Diencephalon) . 


Third    Secondary  Vesicle 
or    Mesencephalon. 


f  Anterior    end  of  third   ventricle, 
j       foramen  of  Monro,  lateral   ven- 
J       tricles,     cerebral     hemispheres, 
I       ooi'pora  striata,  corpus  callosum, 
fornix,   lateral  ventricles,  olfac- 
tor}'  bulb. 
Thalami  optici,  pineal  gland,  part 
of  pituitary  body,  third  ventri- 
cle, optic  nerve  and  retina,  in- 
fundibulum. 


j  Corpora  quadrigemina,  crura  cere- 
i       bri,  aqueduct  of  Sylvius. 


Fourth  Secondary  Vesicle  ' 

or  Epencephalon. 
Fifth    Secondary  Vesicle 

or  Metencephalon. 


Fourth  ven- 
tricle. 


Cerebellum, 
medulla 
gata. 


pons, 
oblon- 


{Quain. ) 


The  cerebral  hemispheres  grow  rapidly  upward  and  backward,  while 
from  their  inferior  surface  the  olfactory  bulbs  are  budded  off,  and  the 
prosencephalon,  from  which  they  spring,  remains  to  form  the  third  ven- 
tricle and  optic  thalami.  The  middle  cerebral  vesicle  (mesencephalon) 
for  some  time  is  the  most  prominent  part  of  the  foetal  brain,  and  in 
fishes,  amphibia,  and  re|Ttiles,  it  remains  uncovered  through  life  as  the 
optic  lobes.  But  in  birds  the  growth  of  the  cerebral  hemispheres  thrusts 
the  optic  lobes  down  laterally,  and  in  mammalia  completely  overlaps 
them. 

In  the  lower  mammalia  the  backward  growth  of  the  hemispheres 
ceases  as  it  were,  but  in  the  higher  groups,  such  as  the  monkeys  and 
man,  they  grow  still  further  back,  until  they  completely  cover  in  the 


Fig.  503.— Side  view  of  foetal  braiu  at  six  months,  showing  commencement  of  formation  of 
the  principal  fissures  and  convolutions.  F,  frontal  lobe ;  P,  parietal ;  O,  occipital ;  T,  temporal ; 
a  a  a,  commencing  frontal  convolutions ;  *-,  Sylvian  fissure;  s\  its  anterior  division;  c,  within 
it  the  central  lobe  or  island  of  Reil ;  r,  fissure  of  Rolando;  p.  perpendicular  fissm-e.  (R. 
Wagner.) 

cerebellum,  so  that  on  looking  down  on  the  brain  from  above,  the  cere- 
bellum is  quite  concealed  from  view.  The  surface  of  the  hemispheres 
is  at  first  quite  smooth,  but  as  early  as  the  third  month  the  great  Sylvian 
fissure  begins  to  be  formed  (fig.  503). 


778  HANDBOOK    OF    PHYSIOLOGY. 

The  next  to  appear  is  the  j)arieto-occipital  or  perpendicular  fissure; 
these  two  great  fissures,  unlike  the  rest  of  the  sulci,  are  formed  by  a  curv- 
ing round  of  the  whole  cerebral  mass. 

In  the  sixth  month  the  fissure  of  Rolando  appears:  from  this  time 
till  the  end  of  foetal  life  the  brain  grows  rapidly  in  size,  and  the  convo- 
lutions api:)ear  in  quick  succession;  first  the  great  primary  ones  are 
sketched  out,  then  the  secondary,  and  lastly  the  tertiary  ones  in  the 
sides  of  the  fissures.  The  commissures  of  the  brain  (anterior,  middle, 
and  posterior),  and  the  corpus  callosum,  are  developed  by  the  growth  of 
fibres  across  the  middle  line. 

The  Hippocampus  major  is  formed  by  the  folding  in  of  the  gray 
matter  from  the  exterior  into  the  lateral  ventricles.  The  essential  points 
in  the  structure  and  arrangement  of  the  various  parts  of  the  brain,  are 
diagrammatically  shown  in  the  two  accompanying  figures  (figs.  502,  503). 

The  Special  Sense  0kg a  ks. 

The  Eye. — Soon  after  the  first  three  cerebral  vesicles  have  become 
distinct  from  each  other,  the  anterior  one  sends  out  a  lateral  vesicle  from 
each  side  (primary  optic  vesicle),  which  grows  out  toward  the  free  sur- 
face, its  cavity  of  course  communicating  with  that  of  the  cerebral  vesicle 
through  the  canal  in  its  pedicle.     It  is  soon  met  and  invaginated  by  an 


Fig.  504.  —Longitudinal  section  of  the  primary  optic  vesicle  in  the  chick  magnified  (from 
Remak).— A,  from  an  embryo  of  sixty-five  hours;  B,  a  few  hours  later;  C,  of  the  fourth  daj^;  c, 
the  corneous  layer  or  epidermis,  presenting  in  A  the  open  depression  for  the  lens,  which  is 
closed  in  B  and  C;  ?,  the  lens  follicle  and  lens;  pr,  the  primary  optic  vesicle;  in  A  and  B,  the 
pedicle  is  shown;  in  C,  the  section  being  to  the  side  of  the  pedicle,  the  latter  is  not  shown;  v, 
the  secondary  ocular  vesicle  and  vitreous  humor. 

ingrowing  process  from  the  ej^iblast  (fig.  504) ,  very  much  as  the  grow- 
ing tooth  is  met  by  the  process  of  epithelium  which  produces  the  enamel 
organ.  This  process  of  the  epiblast  is  at  first  a  depression,  which  ulti- 
mately becomes  closed  in  at  the  edges  so  as  to  joroduce  a  hollow  ball, 
which  is  thus  completely  severed  from  the  epithelium  with  which  it  was 
originally  continuous.  From  this  hollow  ball  the  crystalline  lens  is 
developed.  The  way  in  which  this  occurs  has  been  indicated  in  a  pre- 
vious chapter  under  the  head  of  structure  of  the  lens.  By  the  ingrowth 
of  the  lens  the  anterior  wall  of  the  primary  optic  vesicle  is  forced  back 
nearly  into  contact  with  the  posterior,  and  thus  the  primary  optic  vesi- 


UEVELOPMEXT. 


^79 


cle  is  almost  obliterated.  Tlie  cells  iu  the  anterior  wall  are  much  longer 
than  those  of  the  posterior  wall ;  from  the  former  the  retina  proper  is 
developed,  from  the  latter  the  retinal  pigment. 

The  cup-shaped  hollow  in  which  the  lens  is  now  lodged  is  termed 
the  secondary  optic  vesicle:  its  walls  grow  up  all  round,  leaving,  how- 
ever, a  slit  at  the  lower  part. 

Choroidal  Fissure. — Through  this  slit  (fig.  506),  often  termed  the 
choroidal  fissure,    a  process  of  mesoblast  containing  numerous   blood- 


Fig.  505. 


Fig.  506. 


Fig.  505.— Diagrammatic  sketch  of  a  vertical  longitudinal  section  through  the  eyeball  of  a 
human  foetus  of  four  weeks.  The  section  is  a  little  to  the  side,  so  as  to  avoid  passing  through 
the  ocular  cleft;  c.  the  cuticle  where  it  becomes  later  the  corneal  epithelium:  I.  the  lens:  op, 
optic  nerve  formed  by  the  pedicle  of  the  primary  optic  vesicle;  vj).  primary  medullary  cavity  or 
optic  vesicle;  jj.  the  pigment  layer  of  the  retina:  r.  the  inner  wall  forming  the  retina  projjer; 
rs,  secondary  optic  vesicle  containing  the  rudiment  of  the  vitreous  humor,     x  100.     (Kolliker.) 

Fig.  506.— Transverse  vertical  section  of  the  eyeball  of  a  human  embryo  of  four  weeks.  The 
anterior  half  of  the  section  is  represented:  pr,  the  remains  of  the  cavity  of  the  primarj-  optic 
vesicle;  p.  the  inner  part  of  the  outer  layer  forming  the  retinal  pigment';  r.  the  thickened  inner 
part  giving  rise  to  the  columnar  and  other  structures  of  the  retina ;  r.  the  commencing  vitreous 
humor  within  the  secondary  optic  vesicle;  v'.  the  ocular  cleft  through  which  the  loop  of  the 
central  blood-vessel,  a,  projects  from  below;  I,  the  lens  with  a  central  cavitj-.  x  100. 
(Kolliker.) 


vessels  projects,  and  occupies  the  cavity  of  the  secondary  optic  vesicle 
behind  the  lens,  fi.lling  it  with  vitreous  humor  and  furnishing  the  lens 
capsule  and  the  capsulo-pupillary  membrane.  This  process  in  mammals 
projects,  not  only  into  the  secondary  optic  vesicle,  but  also  into  the 
pedicle  of  the  primary  optic  vesicle  invaginating  it  for  some  distance 
from  beneath,  and  thus  carrying  up  the  arteria  cefitralis  retince  into  its 
permanent  position  iu  the  centre  of  the  optic  nerve. 

This  invagination  of  the  optic  nerve  does  not  occur  in  birds,  and. 
consequently  no  arteria  centralis  retinse  exists  in  them.  But  they  pos- 
sess an  important  permanent  relic  of  the  original  jorotrusion  of  the  meso- 
blast through  the  choroidal  fissure,  in  the  jjectoi,  while  a  remnant  of 
the  same  fissure  sometimes  occurs  in  man  under  the  name  coloboma  iri- 
dis.  The  cavity  of  the  primary  optic  vesicle  becomes  completely  obliter- 
ated, and  the  rods  and  cones  growing  up  from  the  external  limiting 
membrane,  get  into  apposition  wath  the  pigment  layer  of  the  retina. 


780  HANDBOOK    OF    PHYSIOLOGY. 

The  inner  segments  of  the  rods  become  the  first  formed,  then  the  outer. 
The  cavity  of  its  pedicle  disappears  and  the  solid  optic  nerve  is  formed. 
Meanwhile  the  cavity  which  existed  in  the  centre  of  the  primitive  lens 
becomes  filled  up  by  the  growth  of  fibres  from  its  posterior  wall.  The 
epithelium  of  the  cornea  is  developed  from  the  epiblast,  while  the  cor- 
neal tissue  proper  is  derived  from  the  mesoblast  which  intervenes  between 
the  epiblast  and  the  primitive  lens  which  was  originally  continuous 
with  it.  The  sclerotic  coat  is  developed  round  the  eyeball  from  the 
general  mesoblast  in  which  it  is  embedded.  The  choroid  is  developed 
from  the  mesoblast  on  the  outside  of  the  optic  cup  and  the  iris  by  the 
growing  forward  of  the  anterior  edge  of  the  optic  cup,  both  layers  of 
which  becoming  pigmented  remain  as  the  uvea.  Externally  the  cho- 
roidal mesoblast  grows  inward  to  form  the  main  structure.  The  ciliary 
processes  arise  from  the  hypertrophy  of  the  edge  of  the  optic  cup  which 
forms  folds  into  which  the  choroidal  mesoblast  grows,  and  in  which 
blood-vessels  and  pigment-cells  develop. 

The  iris  is  formed  rather  late,  as  a  circular  septum  projecting  in- 
ward, from  the  fore  part  of  the  choroid,  between  the  lens  and  the 
cornea.  In  the  eye  of  the  foetus  of  mammalia,  the  pupil  is  closed  by  a 
delicate  membrane,  the  membrana  pupiUaris,  which  forms  the  front  por- 
tion of  a  highly  vascular  membrane  that,  in  the  foetus,  surrounds  the 


Fig.  507.— Blood-vessels  of  the  capsulo-pupillary  membrane  of  a  new-bom  kitten,  magnified. 
The  drawing  is  taken  from  a  preparation  injected  by  Tiersch,  and  shows  in  the  central  part  the 
convergence'  of  the  network  of  vessels  in  the  pupillary  membrane.     (KoUiker.) 

lens,  and  is  named  the  membrana  capsulo-pupillaris  (fig.  507).  It  is 
supplied  with  blood  by  a  branch  of  the  arteria  centralis  retince,  which, 
passing  forward  to  the  back  of  the  lens,  there  subdivides.  The  mem- 
brana capsulo-pnpillaris  withers  and  disappears  in  the  human  subject  a 
short  time  before  birth. 

The  eyelids  of  the  human  subject  and  mammiferous  animals,  like 


DEVELOPMENT.  781 

those  of  birds,  are  first  developed  in  the  form  of  a  ring.  They  then  ex- 
tend over  the  globe  of  the  eye  until  they  meet  and  become  firmly 
agglutinated  to  each  other.  But  before  birth,  or  in  the  carnivora  after 
birth,  they  again  separate. 

The  Ear. — Very  early  in  the  development  of  the  embryo  a  depres- 
sion or  ingrowth  of  the  epiblast  occurs  on  each  side  of  the  head  which 
deepens  and  soon  becomes  a  closed  follicle.  This  ^^^"it^f^'^^y  oiitic  vesicle^ 
which  closely  corresponds  in  its  formation  to  the  lens  follicle  in  the  eye, 
sinks  down  to  some  distance  from  the  free  surface ;  from  it  are  developed 
the  epithelial  lining  of  the  inemhranous  labyrinth  of  the  internal  ear, 
consisting  of  the  vestibule  and  its  semicircular  canals  and  the  scala  media 
of  the  cochlea.  The  surrounding  mesoblast  gives  rise  to  the  various 
fibrous  bony  and  cartilaginous  parts  which  complete  and  inclose  this 
membranous  labyrinth,  the  bony  semicircular  canals,  the  walls  of  the 
cochlea  with  its  scala  vestibuli  and  scala  tympani.  In  the  mesoblast 
between  the  primary  optic  vesicle  and  the  brain,  the  auditory  nerve  is 
gradually  differentiated  and  forms  its  central  and  peripheral  attachments 
to  the  brain  and  internal  ear  respectively.  According  to  some  authori- 
ties, hov,'ever,  it  is  said  to  take  its  origin  from  and  grow  out  of  the  hind 
brain. 

The  Eustachian  tube,  the  cavity  of  the  tympanum,  and  the  external 
auditory  passage,  are  remains  of  the  first  branchial  cleft.  The  mem- 
brana  tympani  divides  the  cavity  of  this  cleft  into  an  internal  space, 
the  tympanum,  and  the  external  meatus.  The  mucous  membrane  of 
the  mouth,  which  is  prolonged  in  the  form  of  a  diverticulum  through 
the  Eustachian  tube  into  the  tympanum,  and  the  external  cutaneous 
system  come  into  relation  with  each  other  at  this  point;  the  two  mem- 
branes being  separated  only  by  the  proper  membrane  of  the  tympanum. 

The  pinna  or  external  ear  is  developed  from  a  process  of  integument 
in  the  neighborhood  of  the  first  and  second  visceral  arches,  and  probably 
corresponds  to  the  gill-cover  (operculum)  in  fishes. 

The  Nose. — The  nose  originates  like  the  eye  and  ear  in  a  depression 
of  the  superficial  epiblast  at  each  side  of  the  frouto-nasal  process  (pri- 
mary olfactory  groove),  which  is  at  first  completely  separated  from  the 
cavity  of  the  mouth,  and  gradually  extends  backward  and  downward  till 
it  opens  into  the  mouth. 

The  outer  angles  of  the  fronto-nasal  process,  uniting  with  the  max- 
illary process  on  each  side,  convert  what  was  at  first  a  groove  into  a 
closed  canal. 

The  Alimentaky  Caxal. 

The  alimentary  canal  in  the  earliest  stages  of  its  development  con- 
sists of  three  distinct  parts — the  fore  and  hind  gut  ending  blindly  at 


782 


HANDBOOK    OF    PHYSIOLOGY. 


each  end  of  the  body,  and  a  middle  segment  which  communicates  freely 
on  its  ventral  surface  with  the  cavity  of  the  yolk-sac  through  the  vitel- 
line or  omphalo-mesenteric  duct. 

From  the  fore-gut  are  formed  the  pharynx,  oesophagus,  and  stomach ; 
from  the  hind-gut,  the  lower  end  of  the  colon  and  the  rectum.  The 
mouth  is  developed  by  an  involution  of  the  epiblast  between  the  maxil- 
lary and  mandibular  processes,  which  becomes  deeper  and  deeper  till  it 
reaches  the  blind  end  of  the  fore-gut,  and  at  length  communicates  freely 
with  the  pharynx  by  the  absorption  of  the  partition  between  the  two. 

At  the  other  end  of  the  alimentary  canal  the  anus  is  formed  in  a  pre- 
cisely similar  way  by  an  involution  from  the  free  surface,  which  at  length 

D 


Fig.  508. — Outlines  of  the  form  and  position  of  the  alimentary  canal  in  successive  stages  of 
its  development.  A,  alimentary  canal,  etc.,  in  an  embryo  of  fourweeks;  B,  at  six  weeks;  C,  at 
eight  weeks ;  D,  at  ten  weeks ;  I,  the  primitive  lungs  connected  with  the  pharynx ;  s,  the  stomach ; 
d.  duodenum;  j,  the  small  intestine;  i',  the  large;  c,  the  caecum  and  vermiform  appendage;  r,  the 
rectum;  cl,  in  A,  the  cloaca;  a,  in  B,  the  anus  distinct  from  s  i,  the  sinus  urogenitalis;  v,  the 
yolk-sac;  vi,  the  vitello-intestinal  duct;  u,  the  urinary  bladder  and  urachus  leading  to  the  al- 
lantois;  g,  genital  ducts.     (Allen  Thomson.) 

ojDens  into  the  hind-gut.  When  the  depression  from  the  free  surface 
does  not  reach  the  intestine,  the  condition  known  as  imperforate  anus 
results.  A  similar  condition  may  exist  at  the  other  end  of  the  alimen- 
tary canal  from  the  failure  of  the  involution  which  forms  the  mouth,  to 
meet  the  fore-gut.  The  middle  portion  of  the  digestive  canal  becomes 
more  more  and  closed  in  till  its  originally  wide  communication  with  the 
yolk-sac  becomes  narrowed  down  to  a  small  duct  (vitelline).  This  duct 
usually  completely  disappears  in  the  adult,  but  occasionally  the  proximal 
])ortion  remains  as  a  diverticulum  from  the  intestine.  Sometimes  a 
fibrous  cord  attaching  some  part  of  the  intestine  to  the  umbilicus,  re- 
mains to  represent  the  vitelline  duct.  Such  a  cord  has  been  known  to 
cause  in  after-life  strangulation  of  the  bowel  and  death. 


DEVELOPMENT. 


783 


The  alimentary  canal  lies  in  the  form  of  a  straight  tube  close  beneath 
the  vertebral  column,  but  it  gradually  becomes  divided  into  its  special 
parts,  stomach,  small  intestine,  and  large  intestine  (fig.  508),  and  at 
the  same  time  comes  to  be  suspended  in  the  abdominal  cavity  by  means 
of  a  lengthening  mesentery  formed  from  tlie  splanclmopleure  which  at- 
taches it  to  the  vertebral  column.  The  stomach  originally  has  the  same 
direction  as  the  rest  of  the  canal ;  its  cardiac  extremity  being  superior, 
its  pylorus  inferior.  The  changes  of  position  which  the  alimentary  canal 
undergoes  may  be  readily  gathered  from  the  accompanying  figures  (fig. 
508). 

Pancreas  and  Salivary  Glands. — The  principal  glands  in  connec- 
tion with  the  intestinal  canal  are  the  salivary,  pancreas,  and  the  liver. 
lu  mammalia,  each  salivary  gland  first  appears  as  a  simple  canal  with  bud- 


Fig.  509.— Lobules  of  the  parotid,  with  the  salivary  ducts,  in  the  embryo  of  the  sheep,  at  a  more 

advanced  stage. 

like  processes  (fig.  509),  lying  in  a  gelatinous  nidus  or  blastema,  and 
communicating  with  the  cavity  of  the  mouth.  As  the  development  of 
the  gland  advances,  the  canal  becomes  more  and  more  ramified,  increas- 
ing at  the  expense  of  the  blastema  in  which  it  is  still  inclosed.  The 
branches  or  salivary  ducts  constitute  an  independent  system  of  closed 
tubes  (fig.  509).  The  pancreas  is  developed  exactly  as  the  salivary 
glands,  but  is  developed  from  the  hypoblast  lining  the  intestine,  while 
the  salivary  glands  are  formed  from  the  epiblast  lining  the  mouth. 

The  Liver. — The  liver  is  developed  by  the  protrusion,  as  it  were, 
of  a  part  of  the  walls  of  the  fore-gut,  in  the  form  of  two  conical  hollow 
branches,  which  embrace  the  common  venous  stem  (figs.  510,  511).     The 


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HANDBOOK    OF    PHYSIOLOGY. 


outer  part  of  these  cones  involves  the  omphalo-mesenteric  vein,  which 
breaks  up  in  its  interior  into  a  plexus  of  capillaries,  ending  in  venous 
trunks  for  the  conveyance  of  the  blood  to  the  heart.  The  inner  portion 
of  the  cones  consists  of  a  number  of  solid  cylindrical  masses  of  cells. 


Fig:.  510. — Diagram  of  part  of  digestive  tract  of  a  chick  (4th  day).  The  black  line  represents 
hypoblast,  the  outer  shading  mesoblast;  Ig,  lung  diverticulum  witli  expanded  end  forming  pri- 
mary lung-vesicle;  St,  stomach;  ?,  two  hej^atic  diverticula,  with  their  terminations  united  by 
solid  rows  of  hypoblast  cells ;  p,  diverticulum  of  the  pancreas  with  the  vesicular  diverticula 
coming  from  it.     (Gotte.) 

derived  probably  from  the  hypoblast,  which  become  gradually  hollowed 
by  the  formation  of  the  hepatic  ducts,  and  among  which  blood-vessels 
are  rapidly  developed.  The  gland  cells  of  the  organ  are  derived  from 
the  hypoblast,  the  connective  tissue  and  vessels  without  doubt  from  the 


Fig.  511.— Rudiments  of  the  liver  on  the  intestine  of  a  chick  at  the  fifth  day  of  incubation. 
1,  heart;  2,  intestine;  3,  diverticulum  of  the  intestine  in  which  the  liver  (4)  is  developed;  5,  part 
of  the  mucous  layer  of  the  germinal  membrane.     (Miiller.) 


mesoblast.  The  gall-bladder  is  developed  as  a  diverticulum  from  the 
hepatic  duct.  The  spleen,  lymphatic,  and  thymus  glands  are  developed 
from  the  mesoblast :  the  thyroid  partly  also  from  the  hypoblast,  which 
grows  into  it  as  a  diverticulum  from  the  fore-gut. 


development.  785 

The  Eespiratory  Apparatus. 

The  Lungs,  at  their  first  development,  appear  as  small  tubercles  or 
diverticula  from  the  abdominal  surface  of  the  oesophagus. 

The  two  diverticula  at  first  open  directly  into  the  oesophagus,  but  as 
they  grow,  a  separate  tube  (the  future  trachea)  is  formed  at  their  point 
of  fusion,  opening  into  the  oesophagus  on  its  anterior  surface.  These 
primary  diverticula  of  the  hypoblast  of  the  alimentary  canal  send  ofE 
secondary  branches  into  the  surrounding  mesoblast,  and  these  again 
give  off  tertiary  branches,  forming  the  air-cells.  Thus  we  have  the 
lungs  formed:  the  epithelium  lining  their  air-cells,  bronchi,  and  trachea 
being  derived  from  the  hypoblast,  and  all  the  rest  of  the  lung-tissue» 


Fig.  512  illustrates  the  development  of  the  respiratory  organs,  a,  is  the  cEsophagusof  a  chick 
on  the  fourth  day  of  incubation,  with  the  rudiments  of  the  trachea  on  the  lung  of  the  left  side, 
viewed  laterally;  1,  the  inferior  wall  of  the  oesophagus;  2,  the  upper  portion  of  the  same  tube; 
3,  the  rudimentary  lung ;  4,  the  stomach ;  b,  is  the  same  object  seen  from  below,  so  that  both 
lungs  are  visible,  c,  shows  the  tongue  and  respiratory  organs  of  the  embryo  of  a  horse;  1,  the 
tongue;  2,  the  larynx;  3,  the  trachea ;  4,  the  lungs  viewed  from  the  upper  side.     (After  Rathke.) 

nerves,  lymphatics,  and  blood-vessels,  cartilaginous  rings,  and  muscular 
fibres  of  the  bronchi  from  the  mesoblast.  The  diaphragm  is  early  de- 
veloped. 

The  GENiTO-URiisrARY  Apparatus. 

The  Wolffian  bodies  are  organs  peculiar  to  the  embryonic  state, 
and  may  be  regarded  as  temporary,  rather  than  rudimental,  kidneys; 
for  although  they  seem  to  discharge  the  functions  of  these  latter  organs, 
they  are  not  developed  into  them. 

The  Wolffian  duct  makes  its  appearance  at  an  early  stage  in  the  his- 
tory of  the  embryo,  as  a  cord  running  longitudinally  on  each  side  in 
the  mass  of  mesoblast,  which  lies  just  externally  to  the  intermediate  cell- 
mass  {ung,  fig.  513).  This  cord,  at  first  solid,  becomes  gradually  hol- 
lowed out  to  form  a  tube  (Wolffian)  which  sinks  down  till  it  projects 
beneath  the  lining  membrane  into  the  pleuro-peritoneal  cavity. 

The  primitive  tube  thus  formed  sends  off  secondary  diverticula  at 

frequent  intervals  which  grow  into  the  surrounding  mesoblast:  tufts  of 

vessels  grow  into  the  blind  ends  of  these  tubes,  invaginating  them  and 

producing  Malpighian  bodies  very  similar  in  appearance  to  those  of  the 

5° 


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HANDBOOK    OF    PHYSIOLOGY. 


permanent  kidney,  which  constitute  the  substance  of  the  Wolffian  body. 
Meanwhile  another  portion  of  mesoblast  between  the  Wolffian  body  and 
the  mesentery  projects  in  the  form  of  a  ridge,  covered  on  its  free  surface 


Fig.  513.— Transverse  section  of  embryo  chick  (third  day),  mr,  rudimentary  spinal  cord;  the 
primitive  central  canal  has  become  constricted  in  the  middle;  ch,  notochord;  uwh,  primordial 
vertebral  mass;  m,  muscle-plate;  dr,  df,  hypoblast  and  visceral  layer  of  mesoblast  lining 
groove,  which  is  not  yet  closed  in  to  form  the  intestines;  a  o,  one  of  the  primitive  aortae;  u  n, 
Woliflan  body;  ung,  Wolffian  duct;  v c,  vena  cardinalis;  h,  epiblast;  hp,  somatopleure  and  its 
reflection  to  form  af,  amniotic  fold;  p,  pleuro-peritoneal  cavity.     (Kolnker.) 

with  epithelium  termed  germ  epithelium.  From  this  projection  is  de- 
veloped the  reproductive  gland  (ovary  or  testis  as  the  case  may  be). 

Simultaneously,  on  the  outer  wall  of  the  Wolffian  body,  between  it 
and  the  body-wall  on  each  side,  an  involution  is  formed  from  the  pleuro- 
peritoneal  cavity  in  the  form  of  a  longitudinal  furrow,  whose  edges  soon 
close  over  to  form  a  duct  (Miiller's  duct). 

All  the  above  points  are  shown  in  the  accompanying  figures,  513,  514. 

The  Wolffian  bodies,  or  temporary  kidneys,  as  they  may  be  termed, 
give  place  at  an  early  period  in  the  human  fcetus  to  their  successors,  the 
permanent  kidneys,  which  are  developed  behind  them.  They  diminish 
rapidly  in  size,  and  by  the  end  of  the  third  month  have  almost  entirely 
disappeared.  In  connection,  however,  with  their  upper  part,  in  the 
male,  there  are  developed  from  a  new  mass  of  blastema,  the  vasa  effe- 
reniia,  coni  vasculosis  and  globus  major  of  the  epididymis ;  and  thus  is 
brought  about  a  direct  connection  between  the  secreting  part  of  the 
testicle  and  its  duct.  The  Wolffian  ducts  persist  in  the  male,  and  are 
developed  to  form  the  body  and  globus  minor  of  the  epididymis,  the  vas 
deferens,  and  ejaculatory  duct  on  each  side,  the  vesiculge  seminales  form- 
ing diverticula  from  their  lower  part.  In  the  female  a  small  relic  of 
the  Wolffian  body  persists  as  the  parovarium-;  in  the  male  a  similar  relic 
is  termed  the  organ  of  Giraldes.  The  lower  end  of  the  Wolffian  duct 
remains  in  the  female  as  the  duct  of  Gaertner  which  descends  toward, 
and  is  lost  upon,  the  anterior  wall  of  the  vagina. 


DEVELOPMENT. 


787 


From  the  lower  end  of  the  Wolffian  duct  a  diverticulum  grows  back 
along  the  body  of  the  embryo  toward  its  anterior  extremity,  and  ulti- 
mately forms  the  ureter.  Secondary  diverticula  are  given  off  from  it 
and  grow  into  the  surrounding  blastema  of  blood-vessels  and  cells. 

Malpighian  bodies  are  formed  just  as  in  the  Wolffian  body,  by  the 
invagination  of  the  blind  knobbed  end  of  these  diverticula  by  a  tuft  of 
vessels.  This  process  is  precisely  similar  to  the  invagination  of  the  pri- 
mary optic  vesicle  by  the  rudimentary  lens.  Thus  the  kidney  is  devel- 
oped, consisting  at  first  of  a  number  of  separate  lobules;  this  condition 
remaining  throughout  life  in  many  of  the  lower  animals,  e.g.,  seals  and 
whales,  and  traces  of  this  lobulation  being  visible  in  the  human  foetus  at 
birth.     In  the  adult  all  the  lobules  are  fused  into  a  compact  solid  organ. 


Fig.  514.— Section  of  intermediate  ceU-mass  on  the  fourth  day.  m,  mesentery;  I,,  somato- 
pleure;  a,  germinal  epithelium,  from  which  2,  the  duct  of  Miiller,  becomes  involuted;  a,  thick- 
ened part  of  germinal  epithelium  in  which  the  primitive  ova  O  and  o,  arelj-ing;  E,  modified 
mesoblast,  which  will  form  the  stroma  of  the  ovary;  WK,  Wolffian  body;  y,  Wolffian  duct;  X 
160.     (Waldeyer.) 


The  supra-renal  capsules  originate  in  a  mass  of  mesoblast  just  above 
the  kidneys;  soon  after  their  first  appearance  they  are  very  much  larger 
than  the  kidneys  (see  fig.  515),  but  by  the  more  rapid  growth  of  the 
latter  this  relation  is  soon  reversed. 

The  first  appearance  of  the  generative  gland  has  been  already  de- 
scribed :  for  some  time  it  is  impossible  to  determine  whether  an  ovary 
or  testis  will  be  developed  from  it ;  gradually  however  the  special  char- 
acters belonging  to  one  of  them  appear,  and  in  either  case  the  organ 


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HANDBOOK    OF    PHYSIOLOGY. 


soon  begins  to  assume  a  relatively  lower  position  in  the  body;  the  ovaries 
being  ultimately  placed  in  the  pelvis;  while  toward  the  end  of  fatal 
existence  the  testicles  descend  into  the  scrotum,  the  testicle  entering^ 
the  internal  inguinal  ring  in  the  seventh  month  of  foetal  life,  and  com- 
pleting its  descent  through  the  inguinal  canal  and  external  ring  inta 
the  scrotum  by  the  end  of  the  eighth  month.  A  pouch  of  peritoneum, 
the  processus  vaginalis,  precedes  it  in  its  descent,  and  ultimately  forms 


Fig.  515.  —Diagram  showing  the  relations  of  the  female  (the  left-hand  figure  ?  )  and  of  the 
male  (the  right-hand  figure  J  )  reproductive  organs  to  the  general  plan  (the  middle  figure  of 
these  organs  in  the  higher  vertebrata  (including  man).  CI,  cloaca:  R,  rectum:  B  I,  urinary- 
bladder  ;  U,  ureter ;  K,  kidney ;  U  h,  urethra ;  G,  genital  gland,  ovary,  or  testis ;  W,  Wolffian 
body;  PT  d,»  Wolffian  duct;  JVf,  Mullerian  duct;  P  s  t,  prostate  gland ;  C  p,  Cowper's  gland;  C  sp, 
corpus  spongiosum ;  C  c,  corpus  cavernosum. 

In  the  female.  — V,  vagina;  U  t,  uterus;  Fp,  Fallopian  tube;  G  t,  Gaertner's  duct;  P  v,  par- 
ovarium; ^4,  anus;  C  c,  C  s  p,  clitoris. 

In  the  male. — C  s p,  C  c,  penis;  U  t,  uterus  masculinis;  Fs,  vesicula  seminalis;  Vd,  vas- 
deferens.     (Huxley.) 


the  tunica  vaginalis  or  serous  covering  of  the  organ;  the  communica- 
tion between  the  tunica  vaginalis  and  the  cavity  of  the  peritoneum  being 
closed  only  a  short  time  before  birth.  In  its  descent,  the  testicle  or 
ovary  of  course  retains  the  blood-vessels,  nerves,  and  lymphatics,  which 
were  supplied  to  it  while  in  the  lumbar  region,  and  which  are  compelled 
to  accompany  it,  so  to  speak,  as  it  assumes  a  lower  position  in  the  body. 
Hence  the  explanation  of  the  otherwise  strange  fact  of  the  origin  of  these 
parts  at  so  considerable  a  distance  from  the  organ  to  which  they  are  dis- 
tributed. 

Descent  of  the  Testicles  into  the  Scrotum. — The  means  by  which  the 


DEVELOPMENT.  789 

"descent  of  the  testicles  into  the  scrotum  is  effected  are  not  fully  and 
exactly  known.  It  was  formerly  believed  that  a  membraneous  and  partly 
muscular  cord,  called  the  guhernaculum  testis,  which  extends  while  the 
testicle  is  yet  high  in  the  abdomen,  from  its  lower  part,  through  the 
abdominal  wall  (in  the  situation  of  the  inguinal  canal)  to  the  front  of 
the  pubes  and  lower  part  of  the  scrotum,  was  the  agent  by  the  contraction 
of  which  the  descent  was  effected.  It  is  now  generally  thought,  how- 
•ever,  that  such  is  not  the  case,  and  that  the  descent  of  the  testicle  and 
ovary  is  rather  the  result  of  a  general  process  of  development  in  these 
and  neighboring  parts,  the  tendency  of  which  is  to  produce  this  change 
in  the  relative  position  of  these  organs.  In  other  words,  the  descent  is 
not  the  result  of  a  mere  mechanical  action,  by  which  the  organ  is  dragged 
down  to  a  lower  position,  but  rather  one  change  out  of  many  which 
attend  the  gradual  development  and  re-arrangement  of  these  organs. 
It  may  be  repeated,  however,  that  the  details  of  the  process  by  which 
the  descent  of  the  testicle  into  the  scrotum  is  affected  are  not  accurately 
known. 

The  homologue,  in  the  female,  of  the  guhernaculum  testis  is  a 
structure  called  the  round  ligament  of  the  uterus,  which  extends  through 
the  inguinal  canal,  from  the  outer  and  upper  part  of  the  uterus  to  the 
subcutaneous  tissue  in  front  of  the  symphysis  pubis. 

At  a  very  early  stage  of  foetal  life,  the  Wolffian  ducts,  ureters,  and 
Miillerian  ducts,  open  into  a  receptacle  formed  by  the  lower  end  of  the 
allantois,  or  rudimentary  bladder;  and  as  this  communicates  with  the 
lower  extremity  of  the  intestine,  there  is  for  the  time,  a  common  recep- 
tacle or  cloaca  for  all  these  parts,  which  opens  to  the  exterior  of  the 
hody  through  a  part  corresponding  with  the  future  anus,  an  arrange- 
ment which  is  permanent  in  reptiles,  birds,  and  some  of  the  lower  mam- 
malia. In  the  human  foetus,  however,  the  intestinal  portion  of  the 
•cloaca  is  cut  off  from  that  which  belongs  to  the  urinary  and  generative 
•organs;  a  separate  passage  or  canal  to  the  exterior  of  the  body,  belong- 
ing to  these  parts,  being  called  the  sinus  uro-geyiitaUs.  Subsequently, 
this  canal  is  divided,  by  a  process  of  division  extending  from  before 
backward  or  from  above  downward,  into  a  'pars  urinaria'  and  a  'pars 
genitalis. '  The  former,  continuous  with  the  urachus,  is  converted  into 
the  urinary  bladder. 

The  Fallopian  tubes,  the  uterus,  and  the  vagina  are  developed  from 
the  Miillerian  ducts  (fig.  516,  m),  whose  first  appearance  has  been  al- 
ready described.  The  two  Miillerian  ducts  are  united  below  into  a  sin- 
gle cord,  called  the  genital  cord,  and  from  this  are  developed  the  vagina, 
as  well  as  the  cervix  and  the  lower  portion  of  the  body  of  the  uterus; 
"while  the  ununited  portion  of  the  duct  on  each  side  forms  the  upper 
part  of  the  uterus,  and  the  Fallopian  tube.     In  certain  cases  of  arrested 


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HANDBOOK    OF    PHYSIOLOGY. 


or  abnormal  development,  these  portions  of  the  Miillerian  ducts  may  not 
become  fused  together  at  their  lower  extremities,  and  there  is  left  a 
cleft  or  horned  condition  of  the  upper  part  of  the  uterus  resembling  a. 
condition  which  is  permanent  in  certain  of  the  lower  animals. 

In  the  male,  the  Miillerian  ducts  have  no  special  function,  and  are' 
but  slightly  developed.  The  hydatid  of  Morgagni  is  the  remnant  of  the^ 
upper  part  of  the  Miillerian  duct.  The  small  prostatic  pouch,  litems 
masculinuSy  or  sinus  pocular is,  forms  the  atrophied  remnant  of  the  dis- 


Fig.  516.— Diagram  of  the  Wolffian  bodies,  Miillerian  ducts  and  adjacent  parts  previous  to> 
sexual  distinction,  as  seen  from  before,  sr,  the  supra-renal  bodies;  ?-,  the  kidneys;  ot^  common 
blastema  of  ovaries  or  testicles ;  W,  Wolffian  bodies ;  u\  W' olfflan  ducts ;  m  m,  Miillerian  ducts  ; 
g  c,  genital  cord;  ug,  sinus  urogenitalis ;  i,  intestine;  cl,  cloaca.     (Allen  Thomson.) 

tal  end  of  the  genital  cord,  and  is,  of  course,  therefore,  the  homologue^ 
in  the  male,  of  the  vagina  and  uterus  in  the  female. 

The  external  parts  of  generation  are  at  first  the  same  in  both  sexes. 

The  opening  of  the  genito-urinary  apparatus  is,  in  both  sexes,  bounded 
by  two  folds  of  skin,  Avhile  in  front  of  it  there  is  formed  a  penis-like- 
body  surmounted  by  a  glans,  and  cleft  or  furrowed  along  its  under  sur- 
face. The  borders  of  the  furrows  diverge  posteriorly,  running  at  the 
sides  of  the  genito-urinary  orifice  internally  to  the  cutaneous  folds  just 
mentioned.  In  the  female,  this  body  becoming  retracted,  forms  the 
clitoris,  and  the  margins  of  the  furrow  on  its  under  surface  are  converted 
into  the  nymphae  or  labia  minora,  the  labia  majora  pudenda  being  con- 
stituted by  the  great  cutaneous  folds.     In  the  male  foetus,  the  margins 


DEVELOPMENT.  791 

of  the  furrow  at  the  under  surface  of  the  penis  unite  at  about  the  four- 
teenth week,  and  form  that  part  of  the  urethra  which  is  included  in  the 
penis.  The  large  cutaneous  folds  form  the  scrotum,  and  later  (in  the 
eighth  month  of  development),  receive  the  testicles,  which  descend  into 
them  from  the  abdominal  cavity.  Sometimes  the  urethra  is  not  closed, 
and  the  deformity  called  hypospadias  then  results.  The  appearance  of 
hermaphroditism  may,  in  these  cases,  be  increased  by  the  retention  of 
the  testes  within  the  abdomen. 


APPENDIX. 


CLASSIFICATION  OF   THE  ANIMAL  KINGDOM. 


A.— VERTEBRATA. 


Mammalia 

Monodelphia 
Primates 
Cheiroptera 
Insectivora 
Carnivora 
Proboscidea 
Hyracoidea 
Ungulata 
Sirenia 
Cetacea 
Rodentia     . 
Edentata 

Didelphia  . 

Ornithodelphia 

AVES 

Carinatae 

Ratitae  . 
Reptilia 

Crocodilia 

Ophidia 

Chelonia 

Lacertilia 
Amphibia 

Anura 

Urodela 
Pisces 


Typical  examples. 

Man,  ape. 

Bat. 

Hedgehog. 

Cat,  dog,  bear. 

Elephant. 

Hyrax. 

Horse,  sheep,  pig. 

Dugong. 

Whale. 

Rabbit,  rat. 

Armadillo. 

Kangaroo. 

Duck-billed  platypus 

Fowl,  duck. 
Ostrich. 

Crocodile. 
Snake. 
Tortoise. 
Lizard. 

Frog. 
Newt. 
Lamprey,  shark,  cod. 


B.  — INVERTEBRATA. 


MOLLUSCA 

Odontophora 
Lamellibranchiata 
Brachiopoda 
Polyzoa 

Arthropod A 

Crustacea 

Arachnida 

Insecta 

Myriapoda 
echinodermata  . 
Vermes 

Annelida    . 

Platyhelminthes    . 

Nemathelminthes 

CCELENTERATA 

Actinozoa 
Hydrozoa 
Protozoa 


Whelk,  snail. 
Mussel,  oyster. 
Terebratula. 
Sea  mat. 


Lobster. 
Scorpion, 
Bee,  fly. 
Centipede. 
Sea  stars. 


spider. 


Earthworm. 

Tapeworm,  fluke. 

Round -worm,  thread -worm. 

Sea  anemone. 

Hydra. 

Amoeba,  Vorticella. 


794  APPENDIX. 


Organic  Chemical  Substances. 

Nearly  all  of  the  most  important  substances  found  in  the  animal 
body  have  been  mentioned  and  described  in  the  preceding  pages.  It 
will  be  only  necessary  here  to  add  some  brief  notes. 

Certain  terms  have  been  used  without  explanation. 

Hydrocarbons. — Compounds  of  carbon  and  hydrogen.  Carbon 
being  a  tetrad  element,  the  simplest  hydrocarbon  is  C'''H'4,  methane  or 
marsh  gas.  It  is  found  in  the  gases  of  the  alimentary  canal  (intestines) 
(p.  361).  It  is  the  first  of  the  series  known  as  paraffins.  The  different 
members  of  the  series  increase  by  CHg,  so  that  the  next  paraffin  is  C2H6 
Ethane;  C3  He  propane,  and  so  on.     The  general  formula  being  CnH2„+2. 

Alcohols. — From  a  hydrocarbon,  by  substituting  OH  (hydroxyl) 
for  H,  we  obtain  the  corresponding  alcohol;  thus  from  CH3H  we  obtain 
CH3  OH,  methyl  alcohol;  from  C2H5H,  C2H5  OH,  ethyl  alcohol;  from 
C3H7H,  C3  H7  OH,  propyl  alcohol  and  the  like.  They  are  hydrates  of 
the  hydrocarbons. 

Ethers. — The  ethers  are  obtained  from  their  corresponding  alcohols 
by  dehydration;  e.g.,  2(C2H5)  OH  -  H2O  =  (C2H5)20,  ethylic  ether. 

Aldehydes. — The  aldehydes  are  obtained  by  oxidation  of  alcohols 
thus:— C2H5  OH  +  0  =  CH3  COH  +  H20  ethyl  aldehyde. 

Acids.^ — The  acids  are  obtained  by  further  oxidation,  one  atom  of  0 
being  substituted  for  H2,  e.g.,  CH3  CO  OH,  acetic  acid. 

The  series  of  acids  obtained  from  the  first  series  of  paraffins  is  known 
as  fatty  acids ;  those  which  are  most  familiar  as  fatty  acids  being 
C4H8O21,  butyric  acid ;  C6H12O2,  caproic  acid;  Qm^zi^^  palmitic,  2M^ 
C18  H36  O2,  stearic,  derived  from  C4  Hio  {hutane),  Ce  Hu  {hexane), 
C16H34  {hecdecane),  and  Cig  H38,  respectively. 

Soaps  and  Fats. — The  fatty  acids  in  combination  with  soda  or 
potash,  or  similar  bases,  form  soaps,  and  Avhen  combined  with  glycerine 
form  fats. 

Other  series  of  liydrocarhons. — The  first  series  of  paraffins  consists  of 
saturated  hydrocarbons;  many  other  series  exist,  however,  in  which  the 
C  is  unsaturated.     Their  general  formulae  are  as  follows :  CnH2n;  CnH2n-2; 

CnH2n-4;    GJi-2xx-%,  'ind  SO  OU. 

From  each  series  of  hydrocarbons,  the  corresponding  alcohols,  acids, 
aldehydes,  and  ethers  are  obtainable.  The  alcohols  derived  from  series 
of  ethene,  C2H4,  are  called  glycols.  But  in  glycols  there  are  two  OH 
united  to  the  radicle  instead  of  one — these  are  therefore  called  diatomic 
alcohols;  and  similarly  acids,  of  two  kinds,  may  be  obtained, by  the  sub- 
stitution of  one  or  of  two  atoms  of  0  for  the  corresponding  H2  or  H4. 
An  example  or  two  may  be  cited: — 

C2  H4,  ethene  ;  C2  H4  OH,  ethene  glycol ;  C2  H4  O3,  glycolic  acid  / 


APPENDIX.  795 

C'i  H2  O4,  oxalic  acid  ;  and  C3  He,  propene  ;  C3  He  OH2,  propene  glycol ; 
C5  Hs  O3,  lactic  acid  ;  Cg  H4  O4,  malonic  acid. 

The  next  series  of  hydrocarbons,  On  H2n-2,  is  represented  by  C2  H2 
acetylene  ;  the  next  CnH2„_4,  terebinthene,  Cio  Hie;  the  next  C„H2„_6,  by 
benzene,  Ce  He. 

From  these  we  obtain  triatomic  alcohols,  e.g.  glycerin,  C3  Hs  OH3, 
tetratomic  alcohols,  e.g.  erythrite,  C4  He  OH4,  and  hexatomic  alcohols,. 
e.g.,  mannite,  Ce  Hs  OHe ;  from  the  last,  the  carbohydrates  are  derived. 

Of  the  hydrocarbons,  only  one  is,  as  we  have  said,  found  in  the  body,, 
viz.,  methane;  of  the  alcohols,  cholesterine,  O26  H43  OH,  a  monatomic,. 
and  glycerine,  C3  H3  OH3,  a  triatomic  alcohol.  Phenol,  Ce  H3  OH,  found 
in  combination  in  the  urine  and  faeces. 

Of  the  aldehydes  and  ketones  (analogous  products  to  aldehyde,  ob- 
tained from  isomeric  alcohols).  Acetone,  or  propyl  ketone,  is  found  in 
blood  and  in  urine,  particularly  in  diabetes.  The  glucoses  are  aldehydes 
of  mannite,  and  the  other  carbohydrates  are  derived  from  that  class. 

Fatty  Acids. — Formic,  acetic,  propionic,  butyric,  caproic  and  caprylic, 
are  all  more  or  less  represented  in  the  secretions  and  tissues  of  the  body. 
Palmitic  and  stearic  in  fats. 

Glycol  Acids. — Lactic  acid,  of  which  there  are  three  isomeric  bodies, 
and  leucic  acid  and  two  other  acids,  oxalic  and  succinic. 

Amido-Acids. — These  may  be  looked  upon  as  either  ammonia,  in 
which  one  or  more  atoms  of  H  are  replaced  by  the  acid  radicles;  or  as 
acids  in  which  one  or  more  of  the  H  atoms  of  the  acid  radicle  are  re- 
placed by  amidogen  NH2. 

Of  these  the  following  are  important: — 

Glycin,  C2  H3  (NHo)  O2,  amido-acetic  acid. 

Leucine,  Cs  Hn  NH2  O2,  amido-caproic  acid. 

Tyrosine,  C9  Hn  NO3,  amido-oxyphenyl-propionic  acid. 

Sarcosine  =  methyl  glyciji,  C3  H:  NO2. 

Creatine  =  sarcosine  -J-  cyanamide,  CN  NHa  =  C4  Hg  N3  O2. 

Creatinine  =  creatin — H2O  =  C4  H7  N3  0. 

Taurine,  C2  H7  NSO3,  is  amido-isethionic  acid. 

Cystine,  C3  H7  X5  O3,  amido-lactic  acid  in  which  one  H  is  replaced 
byHS. 

Of  these  bodies  it  is  only  necessary  to  mention  the  following: — 
Glycin,  Glycocol,  Glycocin,  or   )  ^^  ^^  ^^^      f^^^  (n^'nu  )• 
Amido-aretic  acid.  \  ^  \^V  u±i  / 

This  substance  occurs  in  the  body  in  combination  as  in  the  biliary 

acids,  but  is  never  free.     Glycocholic  acid,  when  treated  with  weak  acids,. 

with  alkalies,  or  with  baryta  water,  splits  up  into  cholic  acid  and  glycin,. 

or   amido-acetic   acid.     Thus:    C2eH43N06  +  H2O  =  C26  H40  O5  +  C2  H5 

NO2.     Glycocholic  acid  +  water  =  cholic  acid  +  glycin,  and  under  sim- 


796  APPENDIX. 

ilar  circumstances  Taurocholic  acid  splits  up  into  cholic  acid  and  taurin : 
C26  H45  O3  NSO2  +  H2O  =  C26  H40  O5  +  C2  H7  NSO3,  or  araido-isethi- 
onic.  Taurocholic  acid  +  water  =  cholic  acid  and  taurin.  Glycin  oc- 
curs also  in  hippuric  acid.  It  can  be  prepared  from  gelatin  by  the  action 
of  acids  or  alkalies,  and  can  also  be  obtained  from  hippuric  acid. 

Sarcosi7i  or  Methyl  )  ^i  xj  Air*    f       nxr    /NH  CHsN       t+  i„  „  ^^^ 
Glycin,  \^'^'  ^^'  i  "  ^^'  \C0   OH  )•      ^^  ^'  ^  ^^°- 

•stituent  of  creatin,  and  also  of  caffeine,  but  has  never  been  found 
free  in  the  human  body.  It  may  be  obtained  from  these  bodies  by 
boiling  with  baryta  water. 

Leucm  or  Amido-  \  CgHigNOa  {=  CH3.CH2CH2CH2.CH(NH2)CO  OH 


caproic  Acid, 

•occurs  normally  in  many  of  the  organs  of  the  body,  and  is  a  product 
of  the  pancreatic  digestion  of  proteids.  It  is  present  in  the  urine  in 
certain  diseases  of  the  liver  in  which  there  is  loss  of  substance,  esj)e- 
cially  in  acute  yellow  atrophy.  It  occurs  in  circular  oily  discs  or  crys- 
tallizes ia  plates,  and  can  be  prepared  either  by  boiling  horn  shavings, 
or  any  of  the  gelatins  with  sulphuric  acid,  or  out  of  the  products  of 
pancreatic  digestion. 

Creatin,  C4  H9  N3  O2,  is  one  of  the  primary  j^roducts  of  muscular  dis- 
integration. It  is  always  found  in  the  juice  of  muscle.  It  is  generally 
•decomposed  in  the  blood  into  urea  and  sarcosin,  and  seldom,  unless 
under  abnormal  circumstances,  apjoears  as  such  in  the  urine.  Treated 
with  either  sulphuric  or  hydrochloric  acid,  it  is  converted  into  creatinin; 
thus — 

C4  H9  N3  O2  =  C4  Ih  N3  0  +  H2  0. 

It  has  been  made  synthetically  by  bringing  together  cyanimide  and 
«arcosine. 

Creatinin,  C4  H7  N3  0,  is  present  in  human  urine,  derived  from  oxi- 
dation of  creatin.     It  does  not  appear  to  be  present  in  muscle. 

Taurin  or  Amido- )^^  H,  NSO3  (   -  C2  H4  (%%r  ^^)  is  a  constit- 
tsethionic  Acid,  )  ^  \iMi2     / 

uent  of  the  bile  acid,  taurocholic  acid,  and  is  found  also  in  traces  in  the 
muscles  and  lungs.  It  has  been  prepared  synthetically  from  isethionic 
acid.     It  is  a  crystalline  substance,  very  stable. 

Benzoyl  Amido-Acids. 

'''ZZ^^  \  C'  H.  NO3  =  (C.  H.  CONH  OH.  00  OH),  a  nor- 

mal  constituent  of  human  urine,  the  quantity  excreted  being  increased 
"by  a  vegetable  diet,  and  therefore  it  is  present  in  greater  amount  in  the 
urine  of  herbivora.  It  may  be  decomposed  by  acids  into  glycin  and 
Ijenzoic  acid.  It  crystallizes  in  semi-transparent  rhombic  prisms,  almost 
insoluble  in  cold  water,  soluble  in  boiling  water. 


APPENDIX.  797 

Tyrosin,  Cg  Hn  NO3,  is  fouud  generally  together  with  leucin,  in  cer- 
tain glands,  e.g.,  pancreas  and  spleen;  and  chiefly  in  the  products  of 
pancreatic  digestion  or  of  the  putrefaction  of  proteids.  It  is  found  in 
the  urine  in  some  diseases  of  the  liver,  especially  acute  yellow  atrophy. 
It  crystallizes  in  fine  needles,  which  collect  into  feathery  masses.  It 
gives  the  j^roteid  test  with  Millon's  reagent,  and  heated  with  strong  sul- 
phuric acid,  on  the  addition  of  ferric  chloride  gives  a  violet  color. 

Lecithin,  C42  ^m  PN  O9,  is  a  complex  nitrogenous  fatty  body,  con- 
taining phosphorus,  which  has  been  found  mixed  with  cerebrin  and  oleo- 
i:)hosphoric  acid  in  the  brain.  It  is  also  found  in  blood,  bile  and  serous 
fluids,  and  in  larger  quantities  in  nerves,  pus,  yelk  of  egg,  semen,  and 
white  blood-corpuscles.  On  boiling  with  acids  it  yields  cholin,  glycero- 
phosphoric  acid,  palmic  and  oleic  acids. 

Cerehi-in,  Cn  H33  NO3,  is  found  in  nerves,  pus  corpuscles,  and  in  the 
brain.  Its  chemical  constitution  is  not  known.  It  is  a  light  amorphous 
powder,  tasteless  and  odorless.  Swells  uja  like  starch  when  boiled  with 
water,  and  is  converted  by  acids  into  a  saccharine  substance  and  other 
bodies.     The  so-called  Protagon  is  a  mixture  of  lecithin  and  cerebrin. 

Uric  Acid,  C5  H4  N4  O3,  occurs  in  the  urine,  sparingly  in  human 
urine,  abundantly  in  that  of  birds  and  reptiles,  where  it  represents  the 
chief  nitrogenous  decomposition  product.  It  occurs  also  in  the  blood, 
spleen,  liver,  and  sometimes  is  the  only  constituent  of  urinary  calculi. 
It  is  probably  converted  in  the  blood  into  urea  and  carbonic  acid.  It 
generally  occurs  in  urine  in  combination  with  bases,  forming  urates,  and 
never  free  unless  under  abnormal  conditions.  A  deposit  of  urates  may 
occur  when  the  urine  is  concentrated  or  extremely  acid,  or  when,  as 
during  febrile  disorders,  the  conversion  of  uric  acid  into  urea  is  incom- 
pletely performed. 

Composition. — Very  uncertain;  has  been  however  recently  produced 
artificially,  but  it  is  not  easily  decomposed;  it  may  be  regarded  as  diu- 
reide  of  tartronic  acid.     The  chief  product  of  its  decomposition  is  urea. 

Xanthin,  C5  H4  ^4  O2,  has  been  obtained  from  the  liver,  spleen, 
thymus,  muscle,  and  the  blood.  It  is  found  in  normal  urine,  and  is  a 
constituent  of  certain  rare  urinary  calculi. 

Hgpoxantliin,  C5  H4  N4  0,  or  sarcin,  is  found  in  juice  of  flesh,  in 
the  spleen,  thymus,  and  thyroid. 

Guanin,  C5  H5  N5  0,  has  been  found  in  the  human  liver,  sjjleen,  and 
faeces,  but  does  not  occur  as  a  constant  product. 

Allantoin,  C4  He  N4  O3,  found  in  the  allantoic  fluid  of  the  foetus,  and 
in  the  urine  of  animals  for  a  short  period  after  their  birth.  It  is  one  of 
the  oxidation  products  of  uric  acid,  which  on  oxidation  gives  urea. 

In  addition  to  the  above  compounds  and  probably  related  to  them, 
are  certain  coloring  and  excrementitious  matters,  which  are  also  most 
likely  distinct  decomposition  compounds. 


798  APPENDIX. 

Pigments,  Etc. 

Biliruhin,  Cg  Hg  NO2,  is  the  best  known  of  the  bile  pigments.  It  is 
hest  made  by  extracting  inspissated  bile  or  gall  stones  with  water  (which 
dissolves  the  salts,  etc.),  then  with  alcohol,  which  takes  out  cholesterin, 
fatty  and  biliary  acids.  Hydrochloric  acid  is  then  added,  which  decom- 
poses the  lime  salt  of  bilirubin  and  removes  the  lime.  After  extracting 
with  alcohol  and  ether,  the  residue  is  dried  and  finally  extracted  with 
■chloroform.  It  crystallizes  of  a  bluish-red  color.  It  is  allied  in  com- 
position to  hfematin,  as  has  been  described. 

Biliverdin,  Cs  Hg  ISTOa,  is  made  by  passing  a  current  of  air  through 
an  alkaline  solution  of  bilirubin,  and  by  preciptation  with  hydrochloric 
acid.     It  is  a  green  pigment. 

BiUfusciJi,  Cg  Hu  NO3,  is  made  by  treating  gall  stones  with  ether, 
then  with  dilute  acid,  and  extracting  with  absolute  alcohol.  It  is  a 
non-crystallizable  brown  pigment. 

Billprasin  is  a  pigment  of  a  green  color,  which  can  be  obtained  from 
gall  stones,  and  from  bile  which  has  been  allowed  to  decompose. 

BiUliumin  (Staedeler)  is  a  dark  brown  earthy-looking  substance,  of 
which  the  formula  is  unknown. 

Urochrome  and  Urobilin  occur  in  bile  and  in  urine;  the  latter  is 
probably  identical  with  stercohilin,  which  is  found  in  the  fasces.  Uro- 
erytlirin  is  one  of  the  coloring  matters  of  the  urine.  It  is  orange  red 
and  contains  iron,  as  is  also  Chohtelin. 

Melmmi  is  a  dark  brown  or  black  material  containing  iron,  occurring 
in  the  lungs,  bronchial  glands,  the  skin,  hair,  and  choroid. 

Hcematin  has  been  fully  treated  of,  p.  149,  et  seq. 

Indican  is  supposed  to  exist  in  the  sweat  and  urine.  It  has  not, 
however,  been  satisfactorily  isolated. 

Indigo,  Cs  H5  Ng  0,  is  formed  from  indican,  and  gives  rise  to  the 
bluish  color  which  is  occasionally  met  with  in  the  sweat  and  urine.  • 

Indol,  Cs  Ha  N,  is  found  in  the  -faeces,  and  is  formed  either  by  de- 
composition of  indigo,  or  of  the  proteid  food  materials.  It  is  supposed 
to  give  the  characteristic  disagreeable  smell  to  faeces. 

Nitrogenous  Bodies  of  Uncertain  Nature. 

Ferments  are  bodies  which  possess  the  property  of  exciting  chemical 
changes  in  matter  with  which  they  come  in  contact.  They  are  at  pres- 
ent divided  into-  two  classes,  called  (1)  organized,  and  (3)  unorganized 
or  soluble. 

(1.)  Of  the  organized,  yeast  may  be  taken  as  an  example.  Its  activ- 
ity depends  upon  the  vitality  of  the  yeast  cell,  and  disappears  as  soon  as 
the  cell  dies,  neither  can  any  substance  be  obtained  from  the  yeast  by 
means  of  precipitation  with  alcohol  or  in  any  other  way  which  has  the 


APPENDIX.  799 

power  of  exciting  the  ordinary  change  i^roduced  by  the  plant  itself. 
The  action  of  micro-organisms  in  the  alimentary  canal  and  elsewhere  is 
•also  an  example  of  the  same  nature. 

(2.)  Unorganized  or  soluble  ferments  are  those  which  are  found  in 
secretions  of  glands,  or  are  produced  by  chemical  changes  in  animal  or 
vegetable  cells  in  general;  when  isolated  they  are  colorless,  tasteless, 
amorphous  solids  soluble  in  water  and  glycerin,  and  precipitated  from 
the  aqueous  solutions  by  alcohol  and  acetate  of  lead.  Chemically  many 
of  these  are  said  to  contain  nitrogen. 

Mode  of  act  ion. — Without  going  into  the  theories  of  how  these  un- 
organized ferments  act,  it  will  suflBee  to  mention  that: 

(L)  Their  activity  beyond  a  certain  point  does  not  depend  upon  the 
actual  amount  of  the  ferment  present.  (2.)  That  the  activity  is  de- 
stroyed by  high  temperature,  and  various  concentrated  chemical  re- 
agents, but  increased  by  moderate  heat,  about  40°  C,  and  by  weak  solu- 
tions of  either  an  acid  or  alkaline  fluid.  (3.)  The  ferments  themselves 
appear  to  undergo  no  change  in  their  own  composition,  and  waste  very 
slightly  during  the  process. 

The  chief  classes  of  unorganized  ferments  are : — 

(1.)  Amylolytic,  which  possess  the  j)roperty  of  converting  starch 
into  glucose.  They  add  a  molecule  of  water,  and  may  be  called  hydro- 
lytic.  The  principal  amylolytic  ferments  are  Ptyalin,  found  in  the 
saliva,  and  a  ferment,  probably  distinct,  in  the  jDancreatic  juice,  called 
Ami/IojJsin.  These  both  act  in  an  alkaline  medium.  Amylolytic  fer- 
ments have  been  found  in  the  blood  and  elsewhere. 

(2.)  Proteolytic  convert  proteids  into  peptones.  The  nature  of  their 
action  is  probably  hydrolytic.  The  proteolytic  ferments  of  the  body 
are  called  Pepsin,  acting  in  an  acid  medium  from  the  gastric  juice. 
Trypsin,  acting  in  an  alkaline  medium  from  the  pancreatic  juice.  The 
Succus  entericus  is  said  to  contain  a  third  such  ferment. 

(3.)  Inversive,  which  convert  cane  sugar  or  saccharose  into  grape 
sugar  or  ghicose.  Such  a  ferment  was  found  by  Claude  Bernard  in  the 
Succus  entericus;  and  probably  exists  also  in  the  stomach  mucus. 

(4.)  Ferments  loliicli  act  upon  fats. — Such  a  body,  called  Steapsin, 
lias  been  found  in  pancreatic  juice. 

(5.)  Milk-curdling  ferment s. — It  has  been  long  known  that  rennet, 
a  decoction  of  the  fourth  stomach  of  a  calf,  in  brine,  possessed  the 
power  of  curdling  milk.  This  power  does  not  depend  upon  the  acidity 
of  the  gastric  juice,  since  the  curdling  will  take  place  in  a  neutral  or 
alkaline  medium;  neither  does  it  depend  upon  the  pepsin,  as  pure  pep- 
sin scarcely  curdles  milk  at  all,  and  the  rennet  which  rapidly  curdles 
milk  has  a  very  feeble  proteolytic  action.  From  this  and  other  evidence 
it  is  believed  that  a  distinct  milk-curdling  ferment  exists  in  the  stom- 


800  APPENDIX. 

ach.  W.  Roberts  has  shown  that  a  similar  but  distinct  ferment  exists 
in  pancreatic  extract,  which  acts  best  in  an  alkaline  medium,  next  best 
in  an  acid  medium,  and  worst  in  a  neutral  medium.  The  ferment  of 
rennet  acts  best  in  an  acid  medium,  and  worst  in  an  alkaline,  the  reaction 
ceasing  if  the  alkalinity  be  more  than  slight.  Also  in  the  Succus  entericus. 

In  addition  to  the  above  ferments,  many  others  most  likely  exist  in 
the  body,  of  which  the  following  are  the  most  important: 

(6.)  Fibrin-forming  ferment  (Schmidt),  (see  p.  125,  et  seq.),  found  in 
the  blood,  lymph  and  chyle. 

(7.)  A  ferment  ivliicli  converts  glycogen  into  glucose  in  the  liver; 
being  therefore  an  amylolytic  ferment. 

(8.)  Myosin  ferment. 

Carbo-hydrates  or  Amyloids. 

The  divisions  of  carbo-hydrates,  and  the  chief  substances  forming 
each  class  with  their  properties,  have  been  already  given  (p.  Ill,  et  seq). 
The  following  additional  information  may  be  useful. 

The  glucoses  may  be  considered  as  the  aldehydes  of  mannite,  thus : 
CHa  OH        )  CHa  OH 


(CH  0H)4     \  Ce  Hu  Oe,  (CH  0H)4      \  Ce  H12  0, 
CH2  OH        J  CO  H 

mannite.  glucose. 

The  Saccharoses  or  sncroses  are  made  up  of  two  volumes  of  glucose 
minus  one  molecule  of  water. 

Ce  H12  Oe  +  Ce  H12  Oe  —  H2  0  =  C12  H22  On. 
The   amyloids    are   anhydrides   of   the   glucoses,    Ce  H12  Oe  —  H2  0  = 
CeHioOs. 

Tests  for  Glucose. — (i.)  Trommer's. — This  test  depends  upon  the 
power  sugar  possesses  of  reducing  copper  salts  to  their  sub-oxide.  It  is 
done  in  the  following  way : — An  excess  of  caustic  potash  and  then  a 
solution  of  copper  sulphate,  drop  by  drop,  are  added  to  the  solution 
containing  the  sugar  in  a  test-tube,  as  long  as  the  blue  precipitate  which 
forms  redissolves  on  shaking  the  tube.  The  upper  portion  of  the  fluid  is 
then  heated,  and  a  yellowish-brown  precipitate  of  copper  suboxide  ap- 
pears. The  test  may  also  be  done  by  taking  only  a  drop  or  two  of  the 
copper  sulphate  solution. 

(ii.)  Moore's. — If  a  solution  of  sugar  in  a  test-tube  is  boiled  with 
caustic  potash,  a  brown  coloration  appears. 

(iii.)  Fermentation. — If  a  solution  of  sugar  be  kept  in  the  warm  plate 
for  a  time  after  the  addition  of  yeast,  the  sugar  is  converted  into  alcohol 
and  carbon  dioxide.     (CeHjoOe  =  2C2H5OH  +  2CO2.) 

(iv.)  BottcJier's  test. — A  little  bismuth  oxide  or  subnitrate  and  an 
excess  of  caustic  potash  are  added  to  the  solution  in  a  test-tube,  and  the 
mixture  is  heated ;  the  solution  becomes  at  first  gray  and  then  black. 


APPENDIX.  801 

(v.)  Picric  acid  test. — To  the  solution  about  a  fourth  of  its  bulk  of 
picric  acid  (saturated  solution)  and  an  equal  quantity  of  caustic  potash 
are  added,  and  the  solution  is  boiled;  the  liquid  becomes  of  a  very  deep 
coflfee-brown. 

(vi.)  Indigo-carmine  test. — Add  a  solution  of  indigo  carmine  to  color 
sugar  solution  distinctly  blue,  and  add  solution  of  sodium  carbonate,  and 
heat.  The  blue  color  changes  to  purple  and  then  to  brown  and  yellow, 
but  is  restored  on  shaking  the  solution. 

(vii.)  Phenyl  liiidrazine  test. — A  solution  of  phenyl  hydrazine  hy- 
drochloride and  sodium  acetate  is  added.  Keep  in  water- bath  at  boiling 
for  some  minutes,  then  cool.     Yellow  crystals  result. 

Quantitative  Estimation  of  Grape  Sugar. 

1.  Feliling's  Metliod. — Solution  required  =  copper  suljihate  and  caus- 
tic soda,  with  some  sodic  potassic  tartrate  of  such  a  strength  that  10  c.c. 
of  solution  contain  the  amount  of  cupric  oxide  which  0.5  grm.  of  sugar 
can  reduce  to  cuprous  oxide.  (This  solution  should  be  freshly  pre- 
pared.) It  is  made  as  follows:  Take  of  sulphate  of  copper,  4:0  grms. ; 
neutral  tartrate  of  potash,  160  grms.;  caustic  soda  (sp.  gr.  1.12),  750 
grms.;  add  distilled  water  to  1154.5  c.c.  Each  10  c.c.^contains  .05  grm. 
of  sugar. 

Method. — Take  10  c.c.  of  the  saccharine  solution  free  from  albumen, 
and  add  90  c.c.  of  distilled  water.  Place  this  in  a  burette.  Put  into  a 
flask  or  dish  10  c.c.  of  the  standard  solution,  and  dilute  with  four  times 
its  bulk  of  water  and  boil.  Eun  into  it,  from  burette,  some  of  the 
diluted  urine,  say  20  c.c,  and  boil.  Allow  precipitate  to  settle,  and  if 
supernatant  fluid  is  still  blue,  add,  say,  5  c.c.  from  burette,  and  boil 
again,  and  so  on,  till  the  fluid  ceases  to  have  a  blue  tinge,  taking  care, 
toward  the  end  of  the  process,  to  add  only  a  few  drops  each  time.  If, 
after  adding  20  c.c.  of  diluted  urine  and  boiling,  the  fluid  has  been 
decolorized,  too  much  of  the  solution  has  been  added,  and  another  esti- 
mation with  a  second  10  c.c.  of  standard  solution  must  be  made,  but 
less  than  20  c.c.  of  the  saccharine  solution  should  be  added  (say  10  c.c.) 
in  first  instance. 

When  the  number  of  c.c.  of  diluted  urine  required  to  decolorize  the 
solution  has  been  determined,  that  volume  contains  the  amount  of  sugar 
necessary  to  reduce  10  c.c.  of  standard  solution,  i.e.,  .05  grm.  But  one- 
tenth  only  of  this  is  the  saccharine  solution,  .*.  one-tenth  of  number  of 
c.c.  used  contains  .05  grm.  of  sugar.  From  this,  the  percentage  can  be 
easily  calculated. 

2.  Pavy's  Modification  of  Fehling's  Method. — By  Fehling's  method  it 

is  difficult  and  tedious  to  judge  of  the  point  of  complete  reduction  of 

the  cupric  oxide.     Dr.  Pavy,  accordingly,  uses  a  strongly  ammoniacal 

solution  of  the  above.     A  certain  amount  is  introduced  into  a  small 

51 


802  APPENDIX. 

flask,  which  is  then  heated  till  the  vapor  of  ammonia  escapes  by  a  nar- 
row tube.  The  sugar  solution  is  then  allowed  to  flow  from  a  burette 
into  the  flask  until  the  blueness  has  disappeared,  the  solution  being 
kept  boiling  all  the  time.  The  blueness  is  apt  to  disappear  suddenly, 
and  care  should  therefore  be  taken  toward  the  end  of  the  process. 
Calculate  as  in  Fehling's  method. 

3.  Estimation  of  sugar  hrj  fermentation. — In  the  case  of  saccharine 
urine,  it  is  allowable  as  a  single  test  to  use  the  following  method: — Take 
specific  gravity  of  urine  before  and  after  fermentation.  Each  degree 
of  specific  gravity  lost  by  the  urine  represents  one  grain  of  sugar  per 
ounce  of  urine. 

4.  Sugar  may  also  be  estimated  by  adding  yeast  to  urine,  and  col- 
lecting the  carbon  dioxide  evolved.  The  carbon  dioxide  is  a  measure 
of  the  amount  of  sugar  present. 

5.  The  estimation  may  also  be  done  by  the  saccharimeter,  an  instru- 
ment for  the  estimation  of  the  degree  of  joolarization  which  a  ray  of 
light  undergoes  in  passing  through  a  solution  of  sugar,  either  to  the  left 
or  to  the  right. 

Urea,  00  (NH2)2.  The  properties  and  relations  of  urea  have  been 
treated  of  at  some  length  in  the  chapter  upon  excretion.  There  re- 
mains to  be  described  the  method  of  its  quantitative  estimation  in  the 
urine.     There  are  two  chief  methods,  viz. : — 

(i.)  Hypobromite  Method. — One  of  the  forms  of  apparatus  employed 
in  this  method  (Russell  and  West's)  consists  of  («)  a  water-bath  sup- 
ported by  three  iron  bands,  arranged  as  a  tripod.  The  bath  is  provided 
with  a  cylindrical  depression,  and  with  a  hole,  into  which  fits  a  perfo- 
rated india-rubber  cork;  (f)  a  bulb  tube  with  a  constricted  neck;  {c)  a 
^lass  rod  provided  with  an  india-rubber  band  at  one  extremity;  ((/)  a 
pipette  of  five  cubic  centimetres  capacity ;  (f)  a  graduated  glass  collect- 
ing tube;  (/)  a  spirit  lamp;  {(j)  a  wash-bottle  with  distilled  water;  (A) 
hypobromous  solution.  The  hypobromous  solution  is  made  in  the  fol- 
lowing way:  three  and  a  half  ounces  (100  grm.)  of  solid  caustic  soda  is 
dissolved  in  nine  ounces  (300  grm.)  of  distilled  water.  When  the  solu- 
tion is  cold,  seven  drachms  (25  c.c.)  of  pure  bromine  are  to  be  added 
carefully  and  gradually.  The  mixture  is  not  to  be  filtered ;  it  keeps 
badly,  and  for  this  reason  it  should  be  made  shortly  before  it  is  required ; 
or  the  solution  of  caustic  soda  in  water  may  be  made  in  large  quantities 
as  it  does  not  undergo  any  change,  the  bromine  in  the  jJi'opei'  propor- 
tion being  added  at  the  time  it  is  required  for  use. 

Method. —  Fill  the  pipette  to  the  mark  on  the  stem  with  the  urine  to 
be  examined;  pour  the  5  c.c.  of  urine  thus  measured  oat  into  the  bulb; 
fill  up  the  bulb  tube  as  far  as  the  constricted  neck  with  distilled  water 
from  the  wash-bottle;  insert  the  glass  rod  (c)  in  such  a  way  that  the 
india-rubber  band  at  the  extremity  fills  up  the  constricted  neck;  the 


APPEN'DIX.  803 

diluted  urine  should  exactly  occupy  the  bulb  and  neck  of  the  tube,  no 
bubble  of  air  being  below  the  elastic  band  on  the  one  hand,  while  on 
the  other  the  fluid  should  not  rise  above  the  band;  in  the  former  case 
a  little  more  water  should  be  added,  in  the  latter  a  fresh  portion  of 
urine  must  be  used,  and  the  experiment  repeated.  After  adjusting  the 
glass  rod,  fill  up  the  rest  of  the  bulb  tube  with  hypobromous  solution; 
it  will  not  mix  with  the  urine  so  long  as  the  rod  is  in  place.  The 
water-bath  having  been  previously  erected,  and  the  india-rubber  cork 
fixed  firmly  into  the  aperture,  the  bulb  tube  is  to  be  thi'ust  from  below 
through  the  perforation  in  the  cork.  The  greater  part  of  the  tube  is 
then  beneath  the  watei'-bath,  the  upper  extremity  alone  being  grasped 
by  the  cork.  Fill  the  water-bath  half  full  of  water,  fill  also  the  grad- 
uated glass  tube  {(/)  with  water,  and  invert  it  iu  the  bath;  in  doing 
this  no  air  must  enter  the  tube,  which  when  inverted  should  be  com- 
pletely filled  with  water.  Now  slide  the  graduated  tube  toward  the 
orifice  of  the  bulb  tube,  at  the  same  time  withdrawing  the  glass  rod 
which  projects  into  the  bath  through  the  cork.  At  the  instant  that  the 
rod  is  withdrawn  the  hypobromous  solution  mixes  with  the  diluted 
urine,  and  a  decomposition  takes  place  represented  thus:  C01Sr2H4  + 
SNaBrO  +  2NaH0  =  3  NaBr  +  3HoO  +  Na^COs  +  N2.  Urea  +  sodium 
hypobromite  -f-  caustic  soda  =  sodium  bromide  -j-  water  +  sodium  carbon- 
ate +  nitrogen.  The  nitrogen  produced  is  given  off  as  gas,  and  dis- 
places the  water  in  the  graduated  tube,  which  is  held  over  it.  The  gas 
is  at  first  evolved  briskly,  but  afterward  more  slowly;  to  facilitate  its 
evolution,  the  bulb  of  the  tube  may  be  slightly  warmed  with  a  spirit 
lamp ;  as  a  rule,  however,  this  is  unnecessary.  After  ten  minutes,  the 
amount  of  water  displaced  by  the  gas  should  be  read  off  on  the  tube, 
which  is  divided  into  tenths.  Each  number  on  the  tube  represents  one 
gram  of  urea  in  100  c.c.  of  urine.  Normal  urine  should  yield  roughly 
1.5-2.5  parts  of  nitrogen  by  this  test.  If  5  c.c.  of  urine  gives  off  more 
nitrogen  than  fills  the  tube  to  iii.,  dilute  the  urine  with  an  equal  volume 
of  water,  and  take  5  c.c. ;  read  off  and  multiply  by  two.* 

Several  apparatus  may  be  employed  instead  of  the  one  described,  viz., 
those  of  Duj^re,  Gerard,  and  Squibb.  The  chemical  reactions  in  each 
case  are  the  same. 

(ii.)  Liebig's  Method. — This  method  is  of  greater  accuracy.  The 
soli/tions  required  are  (a)  haryta  mixture  =  2  vols,  of  saturated  solution 
of  barium  nitrate  and  1  vol.  of  saturated  solution  of  barium  hydrate; 
il))  standard  solution  of  mercuric  filtrate,  such  that  1  c.c.  will  precij)itate 
.01  grm.  of  urea,  and  (r)  a  solution  of  carbonate  of  soda. 

Method. — Take  40  c.c.  of  urine,  add  20  c.c.  of  {a),  filter  off  the  pre- 
cipitate of  sulphates  and  phosphates;  keep  the  filtrate.     Fill  a  burette 

*  Several  corrections  have  to  be  made  befoi'e  the  result  can  be  considered  as 
accurate  ;  for  these  the  detailed  accounts  in  practical  handbooks  of  Phj^siology 
should  be  consulted. 


804  APPENDIX. 

with  {b),  and  take  15  c.c.  of  the  filtrate  in  a  dish.  Let  {h)  fall  drop  by 
drop  into  the  15  c.c.  in  the  dish,  stirring  constantly.  Have  ready  a  glass 
plate  with  several  separate  drops  of  {c),  and  from  time  to  time  add  a 
drop  of  the  urine  mixture  by  means  of  a  glass  rod  to  one  of  the  drops. 
When  a  yellow  color  first  appears  in  a  drop  of  the  NaCOs,  the  mercuric 
nitrate  is  just  in  excess.     Eead  the  burette.     Calculate  as  follows: 

1  c.c.  of  mercuric  solution  precipitates  .01  grm.  of  urea  .*.  the  No.  of 
c.c.  used  X  .01  =  amount  of  urea  in  15  c.c.  of  filtrate,  i.e.,  in  10  c.c.  of 
urine.  But  10  c.c.  of  urine  usually  contains  enough  NaCl  to  act  on  2  c.c. 
of  mercury  solution.*  Hence,  when  reckoning  the  number  of  c.c.  of 
standing  mercury  solution  used,  a  deduction  of  2  c.c.  must  always  he 
made. 

Quantitative  Estimation  of  Chlorides. 

LieMg's  Method. —  The  solutions  required  are  a  baryta  mixture  as 
above;  and  {b)  standard  solution  of  mercuric  nitrate,  such  that  1  c.c. 
would  be  capable  of  decomposing  .01  grm.  of  sodium  chloride. 

Method. — Take  40  c.c.  of  urine  free  from  albumen,  and  add  20  c.c.  of 
{a).  Filter.  Take  15  c.c.  of  filtrate  and  place  in  a  flask  or  dish,  adding 
a  drop  or  two  of  nitric  acid.  Fill  a  burette  with  {b),  and  slowly  run 
some  of  this  solution  into  the  filtrate  in  the  dish,  stirring  constantly. 
As  soon  as  a  distinct  cloud  appears  in  the  diluted  urine,  and  does  not 
disappear  on  stirring,  then  all  the  sodium  chloride  in  urine  has  been 
decomposed.       Eead  burette.     Calculate  as  follows : 

1  c.c,  of  mercury  solution  decomposed  .01  grm.  of  NaCl,  .*.  the 
number  of  c.c.  used  X  .01  grm.  =  number  of  grms.  of  NaCl  in  15  c.c.  of 
filtrate,  i,e.,  10  c.c.  of  urine. 

Quantitative  Estimation  of  Phosphates. 

The  solutions  required  are  («)  solution  of  sodium  acetate,  containing 
100  grm.  of  sodium  acetate,  100  c.c.  of  acetic  acid,  and  900  c.c.  of  distilled 
water;  {b)  a  solution  of  uranium  acetate  or  nitrate,  such  that  1  c.c.  will 
precipitate  .005  grm.  of  phosphoric  acid;  and  (c)  a  solution  of  ferro- 
cyanide  of  potassiimi. 

Method. — Take  50  c.c.  of  urine.  Add  some  (a)  solution,  and  heat  on 
water-bath  to  nearly  100°  C.  Fill  burette  with  {b),  and  allow  this  to 
fall  into  the  urine  slowly.  Have  ready  a  glass  plate  with  several  distinct 
drops  of  potassium  ferro-cyanide  solution.  From  time  to  time  add  a 
drop  of  urine  mixture  to  one  of  the  drops;  and  when  there  fiest  ap- 
pears a  reddish-brown  color  in  a  drop  of  potassium  ferro-cyanide,  all  the 
phosphates  are  precipitated.     Read  burette.     Calculate  thus: 

1  c.c.  precipitates  .005  grm.  of  phosphoric  acid,  .-.  the  number  of  c.c. 
used  X  .005  grm.  =  number  of  grms.  of  phosphoric  acid   in  50  c.c.  of 

urine. 

*  This  is  only  a  rough  estimate. 


INDEX. 


Abdominal  muscles,  action  of  in  res- 
piration, 352 
Aberration, 

chromatic,  689 

spherical,  688 
Absorbents.     See  Lymphatics. 
Absorption,  363 

by  blood-vessels,  319 

by  lacteal  vessels,  377 

by  lymphatics,  378 

channels  of,  377 

conditions  for,  364 

by  the  skin,  379 

methods,  363 

process  of  osmosis,  ib. 

rapidity  of,  365 

See  Chyle,  Lymph,  Lymphatics,  Lac- 
teals. 
Accelerator  centre,  570 
Accidental  elements  in  human  body, 

116 
Accommodation  of  eye,  681 

defects  of,  687 
Achroo- dextrin,  297 
Acids,  794 

in  gastric  juice,  316 
Acid -albumin,  107 
Acini  of  secreting  glands,  458 
Actinic  rays,  696 
Adenoid  tissue,  44 
Adipose  tissue,  46.     See  Fat. 

development,  47 

situations  of,  46 

structure  of,  47. 

use,  49 
Adrenals,  484 
After-birth,  755 
Air, 

atmospheric,  composition  of,  259 

breathing,  256 

complemental,  ib. 

reserve,  ib. 

residual,  ib. 

tidal,  ib. 

changes  by  breathing.  259 

quantity  breathed,  256 

transmission  of  sonorous  vibrations 
through,  655 

in   tympanum,    or    hearing,    656   et 
seq. 

undulations    of,    conducted    by   ex- 
ternal ear,  654 


Air-cells,  247 
Air-tubes.     See  Bronchi. 
Albumin,  105 

acid,  107 

action  of  gastric  fluid  on,  317  et  seq. 

alkali.  107 

characters  of,  ib. 

chemical  composition  of,  103 

derived,  106 

egg,  106 

native,  106 

serum,  106 

of  blood,  139 
Albuminoids,  109 
Albuminous  substances,  103 

action  of  gastric  fluid  on,  317 
of  pancreas  on,  337 
Albumoses,  318 
Alkali-albumin,  107 
Allantoin,  400 
AUantois,   749 
Alloxan,  398 
Aluminium,  116 
Ammonia, 

cyanate  of,  isomeric  with  urea,  395 

exhaled  froni  lungs,  262 

urate  of,  397 
Ammonium  sulphate  reaction,  105 
Amnion,  748 

fluid  of,  749 
Amoeba,  4 
Amoeboid  movements,  133 

cells,  4 

colorless  corpuscles,  134 

cornea- cells,  666 

protoplasm,  5 
Tradescantia,  5 
Amphioxus,  758 
Ampulla,  650 
Amyloid  substance,  109 
Amyloids  or  Starches,  111 

action    of    pancreas    and    intestinal 
glands,  338 
of  saliva  on,  297 
Amylopsin,  338,  354 
Amyloses,  111 
Anabolic  nerves,  607 
Anelectrotonus,  449 
Angle,  optical,  680 
Angulus  opticus  seu  visorius,  ib. 
Animal  heat.     See  Heat  and  Tempera- 
ture. 


806 


INDEX. 


Animals,  distinctive  characters,  15 

V.  plants,  15 
Antialbumose,  318 
Antihelix,  646 
Antipeptone,  319 
Antitragus,  674 
Aphasia,  602 
Apnoea,  274 

Appendices  epiploicae,  332 
Appendix  vermiformis,  ib. 
Aquaeductus, 

cochlear,  650 

vestibuli,  ib. 
Aqueous  humor,  676 
Arachnoid,  537 
Arches,  visceral,  760 
Area  germinativa,  739 

opaca,  ib. 

pellucida,  ib. 

vasculosa,  747 
Areolar  tissue,  43 
Arsenic,  116 
Arterial  tension,  192 
Arteries,  167 

circulation  in,  199 

velocity  of,  213 

distribution,  167 

muscular  contraction  of,  233 

effect  of  cold  on,  201 

effect  of  division,  ib. 

elasticity,  199 
purposes  of,  ib. 

muscularit}',  200 
governed  by  nervous  system,  233 
purposes  of,  ib. 

nerves  of,  169 

nervous  system,  influence  of,  233 

office  of,  ib. 

pressure  of  blood  in,  191 

pulse.     See  Pulse. 

rhythmic    contraction,     192,    201    et 
seq. 

structure,  167  et  seq. 

distinctions  in  large  and  small  ar- 
teries, ib. 

systemic,  159 

tone  of,  233 

velocity  of  blood  in,  213 
Articulate  sounds,  classification  of, 

Vowels  and  Consonants,  527 
Arytenoid  cartilages,  516 

effect  of  approximation,  517 

movements  of,  ib. 
Asphyxia,  280 

causes  of  death  in,  282 

experiments  on,  283 

symptoms,  280 
Astigmatism,  688 
Atmospheric  air,  284.     See  Air. 

pressure    in  relation  to  respii'ation, 
ib. 
Auditory  canal,  654  et  seq. 

function,  ib. 
Auditory  centre,  614 


Auditory  nerve,  651,  654 

distribution,  ib. 
Auerbach's  plexus,  327 
Auricles  of  heart.     See  Heart. 
Automatic  action,  439 

cerebrum,   606  et  seq. 

medulla  oblongata,  570  et  seq. 

respiratory,   272 
Axis-cylinder  of  nerve-fibre,  91 

Bacterium  lactis,  467 
Barytone  voice,  524 
Basement- membrane,  454 
Bass  voice,  524 
Battery,  Daniell's,  428 
Benzoic  acid,  114 
Bicuspid  valve,  177 
Bidder's  ganglia,  222 
Bile,  354 

antiseptic  power,  384 

coloring  matter,  346 

composition  of,  345 

digestive  propei'ties,  348 

excrementitious,  349 

fat  made  capable  of  absorption  by, 
348 

functions  in  digestion,  348 

mixture  with  chyme,  349 

mucus  in,  348 

natural  purgative,  349 

process  of  secretion,  ib. 

re -absorption,  350 

salts,  348 

secretion  and  flow,  349 

secretion  in  foetus,  ib. 

tests  for,  346, 

uses,  348 
Bilifulvin,  Biliprasin,  Bilirubin,  Bili- 

verdin,  346 
Bilin,  345 

preparation  of,  ib. 

re- absorption  of,  351 
Binocular  vision,  706 
Bioplasm,  2.     See  Protoplasm. 
Biuret  test,  104 
Bladder,  urinary.    See  Urinary  Blad 

der. 
Blastema.     See  Protoplasm. 
Blastodermic  membrane,  20,  737 
Blind  spot,  691 
Blocking,  224 
Blood,  117 

arterial  and  venous,  152 

buffy  coat,  120 

chemical  composition,  151 

coagulation,  119  et  seq. 

color,  117 

coloring  matter,  144  et  seq. 

coloring  matter,  relation  to  that  of 
bile,  150 

composition,  chemical,  137 
variations  in,  152 

corpuscles     or     cells     of,     129.     See 
Blood  -  corpu  scles. 


INDEX, 


807 


Blood — continued. 

corpuscles,  red,  139 
white,  132 

crystals,  144 

cupped  clot,  121 

development,   154 

extractive  matters,  140 

fattv  matters,  ih. 

fibrin,   121 

separation  of,   122 

gases  of,   142 

haemoglobin,  144 

hepatic,  153 

odor  or  halitus  of,  118 

plasma,    117 

portal,  characters  of,  153 

quantity,   118. 

reaction,   117 

saline  constituents,  141 

serum  of,  139 

specific  gravity,  117 

splenic,    153 

structural  composition,  129 

temperature,   117 

uses,  157 
of  various  constituents,  ih. 

variations    of,   in   different  circum- 
stances,   151 
in  different  parts  of  body,  152 
Blood-corpuscles,  red,  129 

action  of  reagents  on,  130 

chemical  composition,  141 

development,  154 

disintegration  and  removal,  479 

method  of  counting,  135 

rouleaux,   130 

specific  gravity,  129 

stroma,   ih. 

tendency  to  adhere,  130 

varieties,   129 

vertebrate,  various,  131 
Blood -corpuscles,  white,  132 

amoeboid  movements  of,  134 

derivation  of,  157 

formation  of,  in  spleen,  156,  479 

locomotion,    133 

varieties,  ih. 
Blood-crystals,  144 
Blood  pressure,  191  et  seq. 

in  veins.   197 

in  capillaries,  198 
osmotic  character  of,  211  et  seq. 

influence  of  nervous  system  on,  233 
Blood-vessels, 

absorption  by,  397 
Bone,  53 

canaliculi,  55 

cancellous,  54 

chemical  composition,  53 

compact,  54 

development,  58  et  seq. 

functions,  67 

growth,  66 

Haversian  canals,  56 


Bone — continued. 

lacunae,  55 

lamellse,  57 

marrow,  54 

medullary  canal,  ih. 

periosteum,  55 

structure,  53 
Branchial  clefts,  760 
Brain.     See     Cerebellum,     Cerebrum, 
Pons,  etc. 

adult,  596 

amphibia,  597 

apes,  598 

birds,  597 

capillaries  of,  216 

child,  596 

circulation  of  blood  in,  216 

convolutions,  591 

female,  597 

fish,  597 

gorilla,  59§, 

idiots,  597 

lobes,  591 

male,  597 

mammalia,  ih. 

orang,  598 

proportion  of  water  in,  114 

quantity  of  blood  in,  216 

rabbit,  597 

reptiles,  ih. 

weight,  ih. 
relative,  ih. 
Breathing.     See  Respiration. 
Bronchi,    arrangement    and    structure 

of,  242 
Bronchial  arteries  and  veins,  248 
Brunner's  glands,  329 
Buffy  coat,  formation  of,  221 
Bulb.     See  Medulla  oblongata. 
Bulbus  arteriosus,  767 
Burdach's  column,  542 
Butyric  acid,  113. 

Calcification    compared  with  ossifi- 
cation, 66 
Calcium  salts,  145 
Calorimeter,  491 
Calyces  of  the  kidney,  382 
Canal,  alimentary.     See  Stomach,  In- 
testine, etc. 

external  auditory,  646 
function  of.  654 

spiral,  of  cochlea,  651 
Canaliculi  of  bone,  55 
Canal  of  Schlemni,  671 

of  Petit,   676 
Cancellous  texture  of  bone,  54 
Cane  sugar,    112 
Capacity  of  chest,  vital,  256 
Capillaries,   170 

circulation  in,  210 

development,   734  et  seq. 

influence  of  on  circulation,  211 

lymphatic,  369 


808 


INDEX. 


Capillaries — continued. 

network  of,  171 

number,  173 

passage  of  corpuscles  through  walls 
of,  311 

pressure  in,  198 

resistance  to  flow  of  blood  in,  310 

still  layer  in,  ib. 

structure  of,  170 
Capsule  of  Glisson,  340 
Capsules,  Malpighian,  387 
Carbohydrates,  111,  800 
Carbonic  acid  in  atmosphere,  359 

in  blood,   151 

effect  of,  375 

exhaled  from  skin,  419 

increase  of  in  breathed  air,  359 

in  lungs,  265 

in  relation  to  heat  of  body,  492 

Brown  ian  movement,  3 
Carburetted  hydrogen,  114 
Cardiac  orifice  of  stomach,  action  of, 
335 

sphincter  of,  ih. 

relaxation  in  vomiting,  ih. 
Cardiac  revolution,  180 
Cardiograph,  184 
Cardio- inhibitory  centre,  337 
Carotid  gland,  587 
Cartilage,  49 

articular,  51 

cellular,  53 

chondrin  obtained  from,  53 

classification,  49 

development,  53 

elastic,  51 

fibrous,  53.     See  Fibro-cartilage. 

function,  53 

hyaline,  49 

matrix,  49 

nutrition,  51 

ossification,  60 

perichondrium  of,  49 

structure,  49 

temporary,  51 

uses,  53 

varieties,  49 
Cartilage  of  external  ear,  used  in  hear- 
ing, 655 
Cartilages  of  larynx,  515 
Casein.     See  Milk. 
Caseinogen,  107 
Cauda  equina,  537 
Cavity  of  reserve,  78 
Cause  of  fluidity  of  living  blood,  138 
Cell  globulin,  136 
Cells,  3 

amoeboid,  4 

blood.     -See  Blood-corpuscles. 

cartilage,  50 

chemical  transformation,  36 

ciliated,   33 

classification,  24 

connective  tissue,  38 


Cells — continued. 
decay  and  death,  36 
definition  of,  3 

epithelium,  36.     See  Epithelium, 
fission,  13 
formative,  739 
functions,  3  et  seq. 
gemmation,  9 
modes  of  connection,  35 
nutrition,  7 
olfactoi-y,  641 
organized,  20 
pigment,  37 
reproduction,  9 
segmentation,  20 
structure,  9  et  seq. 
transformation,  26 
varieties,  24 
vegetable,  16 
distinctions  from  animal  cells,  15 
et  seq. 
Cellular  cartilage.     See  Cartilage. 
Cellulose,  19 

Cement  of  teeth.     See  Teeth. 
Centres,     nervous,    etc.      See    Nerve- 
centres, 
of  ossification,  59 
Centrifugal  machine,  138 
Centrifugal  nerve-fibres,  531 
Centripetal  nerve-fibres,  ib. 
Cerebellum,  615 
co-ordinating  function  of,  618 
cross-action  of,  ib. 
effects  of  injury  of  crura,  ib. 

of  removal  of,  ib. 
functions  of,  ib. 
in  relation  to  sensation,  617 
to  motion,  ib. 
to  muscular  sense,  619 
structure  of,  615 
Cerebral  hemispheres.     See  Cerebrum. 
Cerebral  nerves,  571 
third,  572 
effects  of  irritation  and  injury  of, 

ib. 
relation  of  to  iris,  573 
fourth,  573 
fifth,  574 
distribution  of,  ib. 
effect  of  division  of,  575 
inflvience  of, 
on  muscles  of  mastication,  575 
on  organs  of  special  sense,  578 
relation  of,  to  nutrition,  578 
resemblance  to  spinal  nerves,  574_ 
sensory  function  of  gi'eater  division 

of  fifth,  576 
sixth,  579 

communication    of,    with  sympa- 
thetic, ib. 
seventh,  579 
eighth,  581 
ninth,  583 
tenth,  583 


INDEX. 


809 


Cerebral  nerves — continued. 

eleventh,  586 

twelfth,   587 
Cerebration,  unconscious,  610 
Cerebrin.  596 

Cerebro-cerebellar  fibres,  604 
Cerebro- spinal    fluid,  relation  to   cir- 
culation, 318 
Cerebro- spinal  nervous  system,  532  et 

seq.     See  Brain,  Spinal  Cord,  etc. 
Cerebrum,  its  structure,  591 

chemical  composition,  596 

convolutions  of,  591  et  seq. 

crura  of,  588 

development,  776 

distinctive  character  in  man,  598 

effects  of  injury,  607 

removal,  607 

electrical  stimulation,  600 

functions  of,  606 

gray  matter,  594 

in  relation  to  speech,  603 

other  parts,  556  et  seq. 

localization  of  functions,  600 

structure,  594  et  seq. 

unilateral  action  of,  609 

weight,   597 

white  matter,  594 
Chambers  of  the  eye,  676 
Characteristics  of  organic  compounds, 

103 
Chemical  composition  of  the  human 

body,  103 
Chest,  340 

Cheyne- Stokes'  breathing,  280 
Chlorides  in  urine,  estimation  of,  803 
Chlorine,  115 
Chlorophyll,  17 
Cholesterin,  347 
Choletelin,  347 
Chondrin,  53,  110 
Chorda  dorsalis,  743 
Chorda  t>-mpani,  299  et  seq. 
Chordae  tendinete.     See  Heart. 
Chorion,  750 
Choroid  coat  of  eye,  667 

blood-vessels,  668 
Choroidal  fissure,  685 
Chromatic  aberration,  689 
Chromophanes,  696 
Chyle,  376  et  seq. 

coagulation  of,  ib. 
Chvle-corpuscles,  376 
Chvme,  371 
CiHa,  33 
Ciliary  epithelium,  32 

function  of,  34 
Ciliary  motion,  34 

nature  of,  ib. 
Ciliary  muscles,  668 

action  of  in  adaptation  to  distances, 
684 
Ciliarj'  processes,  668 
Circulation  of  blood,  158 


Circulation  of  blood — continued. 

action  of  heart,  159 

brain,  316 

capillaries,  310 

course  of,  158  et  seq. 

discovery,  237 

erectile  structures,  218 

forces  regulating,  219 

influence  of  respiration  on,  275 

peculiarities  of,  in   different   parts, 
215 

proofs,  237 

pulmonary,  248 

systemic,  159 
in  veins,  212 

velocity  of,  215 
Circumvallate  papillae,  304 
Claustrum,  590 
Clefts,  visceral,  760 
Clitoris,  718 

development  of,  790 
Cloaca,  789 

Clot  or  coagulum  of  blood.     See  Coag- 
ulation. 
Coagulation  of  blood,  119 

absent  or  retarded,  126 

conditions  affecting,  ib. 

theories  of,  125 

of  chyle,  376 

of  lymph,  ib. 
Coagulated  proteids,  109 
Coccygeal  gland,  487 
Cochlea  of  the  ear,  650 

office  of,  659 
Cohnheim's  fields,  83 
Cold-blooded  animals,  489 
Colloids,  367 
Colostrum,  465 
Color-blindness,  704 
Colors,  optical   phenomena   of,  703  et 

seq. 
Color  sensations,  702 

theories  of,  ib. 
Columnar  epithelium,  31 
Complemental  air,  256 

colors,  704 
Conducting  paths  in  cord,  543 
Conjunctiva,  664 
Connective  tissues,  38 

classification,  41 

corpuscles  of,  41 

fibrous,  ib. 

gelatinous,  44 

general  structure  of,  38 

retiform,  45 

varieties,  41 
Contraction  of  pupil,  685 
Control  centres,  571 
Convolutions,  cerebral,  591  et  seq. 
Co-ordination  of  movements,  611 
Cooking,  effect  of,  289 
Copper,  an  accidental  element  in  the 

body,  116 
Corona  radiata,  589 


810 


INDEX. 


Cord,  spinal.     See  Spinal  Cord. 
Corium,  412 
Cornea,  665 

coi"puscles,  666 

nerves,  ib. 

structure,  665 
Corneo-scleral  junction,  670 
Corpora  Arantii,  167 

geniculata,  591,  620 

quadrigemina,  ib. 
their  function,  ib. 

striata,  590 

their  function,  615 
Corpus  callosum,  558 

dentatuni 

of  cerebellum,  591 
of  olivary  body,  565 

luteum.  738 
of  human  female,  729 
of  mammalian  animals,  tb. 
of    menstruation    and    pregnancy 
compared,  730 
Cori3uscles  of  blood,  129.    See  Blood-cor- 
puscles. 
Corti's  rods,  653  et  seq. 

office  of,  650 
Cowper's  glands,  731 
Cranial  nerves.     See  Cerebral  nerves. 
Cranium,  development  of,  757 
Crassamentum,  119 
Crescents  of  Gianuzzi,  294.     See  Semi- 

lunes  of  Heidenhain. 
Crico-arytenoid  muscles,  517 
Cricoid  cartilage,  515 
Crossed  pyramidal  ti-act,  543 
Crura  cerebelli,  616 

effect  of  dividing,  619  et  seq. 
of  irritating,  ib. 

cerebri,  588 

their  office,  588 
Crusta,  588 
Crusta  petrosa,  74 

phlogistica,  120 
Crystallin,   108 
Crystalline  lens,  669 

in  relation  to  vision  at  different  dis- 
tances, 682 
Crystalloids,  365 

Cupped  appearance  of  blood-clot,  121 
Curdling  ferments,  466 
Currents  of  action,  438 

ascending,  447 

continuous,  428 

descending,  447 

induced,  430 

muscle,    426 

natural,  ib. 

negative  variation,  438 

nerve,  448 

polarizing,  ib. 

rest,  426 
Cuticle.     See  Epidermis,  Epithelium. 
Cutis  vera,  412 
Cystic  duct,  340 


Cystin  in  urine,  402 

Daltonism,  704 

Dan i ell's  battery,  428 

Decidua, 

menstrualis,  728 

reflexa,   753 

serotina,  ib. 

vera,  ib. 
Decomposition,  tendency     of     animal 

compounds  to,   103 
Decomposition-products,  104 
Decussation  of  fibres  in  medulla  ob- 
longata, 564 

in  spinal  cord,  549 

of  optic  nerves,  612 
Defecation,  mechanism  of.  554 

influence  of  spinal  cord  on,  554 
Degeneration  method,  542 
Deglutition.     See  Swallowing. 
Dentine,  71 
Depressor  nerve,  234 
Derived  albuinins,  106 
Derma,  412 

Descemet's  membrane,  666 
Deutero-albumose,  319 
Development,  734 
of  organs,  756 

alimentary  canal,   781 

arteries,  768 

blood-vessels,  ib. 

brain,  775 

capillaries,  768 

cranium,  758 

ear,  781 

extremities,  762 

eye,  778 

face  and  visceral  arches,  760 

fibrous  tissue,  45 

heart,  763 

liver,  783 

lungs,  785 

medulla  oblongata,  776 

muscle,  89 

nerves,    774 

nervous  system,  774 

nose,  781 

organs  of  sense,  778 

pancreas,   783 

pituitarj'  body,  759 

respii-atory  apparatus,  785 

salivary  glands,  783 

spinal  cord,  775 

teeth,  74 

vascular  system,  763 

veins,  770 

vertebral  column  and  cranium,  752 

visceral  arches  and  clefts,  760 

of  Wolffian  bodies,  urinary  appara- 
tus and  sexual  organs,  786 
Dextrin,   112 
Dextrose,  ib. 
Diabetes,  471 
Diapedesis  of  blood -corpuscles,  212 


I]S"DEX. 


811 


Diaphragm.     See  Inspiration,  etc. 
Diastase  of  liver,  469 
Diet,  506  e^seg. 
Digestion,  285 

in  the  intestines,  353,  355.    See  Gas- 
tric fluid.  Food,  Stomach. 
Dilatation  of  pupil,  685 
Diplopia.  706 
Direct  cerebellar  tract,  543 

.  pyramidal  tract,  543 
Dorsal  laminae,  743 
Double  hearing,  663 

vision,  706 
Dreams,  611 

Drowning,  cause  of  death  in,  280 
Ductless  glands,  758 
Ducts  of  Cuvier,  772 
Ductus  arteriosus,  774 

venosus,  773 

closure  of,  774 
Duverney's  glands,  718 
Dj^spnoea,  380 

Ear,  646 

bones  or  ossicles  of,  647 

function  of,  657 
development  of,  781 
external,  646 

function  of,  654 
internal,  649 

function  of,  659 
middle,  647 
function  of,  655 
Egg-albumin,  106 
Elastic  cartilage,  51 
fibres,  40 
tissue,  42 
Elastin,  41,  110 
Electricity, 
in  muscle,  425 
nerve,  446 
retina,  696 
Electrotonus,  448 

Elementary  svibstances   in  the  human 
body,  103 
accidental,  116 
Embryo,  734  et  seq.  See  Development. 
Embryological  method,  542 
Embryonic  shield,  740 
Emmetropic  eye,  687 
Emotions,  connection  of,  with  cerebral 

hemispheres,  608 
Emulsification,  338 
Enamel  of  teeth,  73 
Enamel  organ,   74  , 

Enchj'lema,   9 
End-bulbs,  98 
End -plates,  motorial,  88 
Endocardiac  pressure,  186 
Endocardium,  165 
Endolymph,  653 
Endosmometer,  364 
Endothelium,  37 
distinctive  characters,  ib. 


Endothelium — continued. 

germinating,  39 
Energy, 

daily  amount  expended  in  body,  510 
Epencephalon,  777 
Epiblast,  20,   739 
Epidermis,  410 
Epididymis,  719 
Epiglottis,  341 

structure,  341 
Epithelial  tissues,  26 
Epithelium,  ib. 

ciliated,  33 

cogged,  36 

columnar,  31 

cylindrical,  ib. 

glandular,  ib. 

goblet-shaped,  31 

simple,  27 

spheroidal,  31 

squamous  or  tessellated,  27 

stratified,  35 

ti'ansitional,  ib. 
Erect  position  of  objects,    perception 

of,  696 
Erectile  structures,  circulation  in,  218 
Erection,  ib. 

cause  of,  ib. 

influence  of  muscular  tissue  in,  ib. 

a  reflex  act,  555 
Erythro-granulose,  297 
Ery thro- dextrin,  ib. 
Ethers,  794 
Eustachian  tube,  647 

function  of,  658 
Excretion,  381 
Exercise, 

effects  of,  on  production  of  carbonic 
acid,  261 

on  temperature  of  body,  489 
Expenditure  of  body,  509  et  seq. 
Expiration,  253 

influence  of,  on  circulation,  278 

mechanism  of,  353 

muscles  concerned  in,  ib. 

relative  duration  of,  355 
Expired  air,  properties  of,  359  et  seq. 
Extremities,  development  of,  763 
Eye,  664 

adaptation  of  vision  at  difi'erent  dis- 
tances, 681  et  seq. 

blood-vessels,  676 

development  of,   778 

optical  apparatus  of,  677 

refracting  media  of,  678 

resemblance  to  camera,  ib. 
Eyelids,  663 

development  of,  780 
Eyes,  simultaneous  action  of,  in  vision, 

705 

Face,  development  of,  761 
Facial  nerve,  579 
effects  of  paralysis  of,  580 


812 


INDEX. 


Facial  nerve — continued. 

relation  of,  to  expression,  581 
Faeces,  composition  of,  359 

quantity  of,  ib. 
Fallopian  tubes,  716 
Fasting, 

influence  on  secretion  of  bile,  503 
Fat,  See  Adipose  tissue. 

action  of  bile  on,  348 

of  pancreatic  secretion,  338 
of  small  intestine  on,  354 

absorbed  by  lacteals,  377 

formation  of,  501 

situations,  where  found,  46 

uses  of,  49 
Fatty  acids,  113,  795 
Fechner's  law,  693 
Fehling's  method  for  sugar  in  urine, 

801 
Female  generative  organs,  713 
Fenestra  ovalis,  649 

rotunda,  650 
Ferments,  356 
Fibres  of  Muller,  676 
Fibrils  or  filaments,  13 
Fibrin,   109,  141 

in  chyle,  377 

ferment,  125 

formation  of,  123 

sources  and  properties  of,  109 
Fibrinogen,  122  et  seq.,  108 
Fibrinoplastin,  ib. 
Fibi-o-cartilage,  53 

classification,  ib. 

development,  53 

white,  52 

yellow,  51 
Fibrous  tissue,  41 

white,  ib. 

yellow,  43 

development,  45 
Fick's  kymograph,  195 
Field  of  vision,  actual  and  ideal  size 

of,  698 
Fifth  nerve.     See  Cerebral  Nerves. 
Fillet,  605 
Filtration,  403 
Flesh,  of  animals,  285 
Fluids,  passage  of,  through  membranes, 

363 
Fluoride  of  calcium,  115 
Focal  distance,  681 
Foetus, 

circulation  in,  772 

communication  with  mother,  754 

membranes,  747  et  seq. 
Folds,  head  and  tail,  744 
Follicles,  Graafian.    See  Graafian  Ves- 
icles. 
Food,  385 

classification  of,  ib. 

digestibility  of  articles  of,  386 

value  dependent  on,  ib. 

improper,  504 


Food — continued. 
of  man,  506 
too  little,  501 
too  much,  505 
vegetable,  contains  nitrogenous  prin- 
ciples, 288 

Foot-pound,  191 

Foot- ton,  ib. 

Forced  movements,  620 

Form  of  bodies,  how  estimated,  700 

Formation  of  fat,  503  et  seq. 
urinary  solids,  475 

Formic  acid,  113 

Fornix,  558 

Fourth    cranial    nerve.     See    Cerebral 
nerves. 

Fovea  centralis,  675 

Fundus  of  eye,  693 

Fundus  of  uterus,  717 

Funiculus  of  Rolando,  563 

Furfur  aldehyde,  346 

Fuscin,  696 

Galactophorous  ducts,  463 
Galactose,  113 
Gall-bladder,  344 

structure,  ib. 
Galvanometers,  424 
Ganglia.     See  Nerve-centres. 
Ganglion,  Gasserian,  623 
Gases,  114 

in  bile,  348 

in  blood,  143 

extraction  from  blood,  ib. 

in  stomach  and  intestines,  360 

in  urine,  391 
Gastric  glands,  313 
Gastric  juice,  315 

acids  in,  316 

acid,  test  for,  ib. 

action  of,  on  nitrogenous  food,  319 
on  non- nitrogenous  food,  ib. 
on  saccharine  and  amyloid  prin- 
ciples, ib. 

characters  of,  315 

composition  of,  316 

digestive  power  of,  317 

experiments  with,  317 

pepsin  of,  316 

quantity  of,  316 

secretion  of,  333 
how  excited,  ib. 

influence  of,  nervous  system  on,  323 
Gelatin,  109 

as  food,  505 

action  of  gastric  juice  on,  319 

action  of  pancreatic  juice  on,  338 
Gelatinous  substances,  109 
Generation  and  development,  712 
Generative  organs  of  the  female,  713 

of  the  male,  718 
Gerlach's  network,  540 
Germinal  area,  737 

epithelium,  713 


INDEX. 


813 


Germinal  membrane, 

spot,  3,  715 

vesicle,  ib. 
Giant  cells,  54 

Gland.     See  names  of  different. 
Gland,  prostate,  724 
Glisson's  capsule,  342 
Globulin,  108 

distinctions  from  albumin,  ib. 
Globus,   major  and  minor,  720 

development,  786 
Glosso-pliaryngeal  nerve,  272,  582 

communications  of,  583 

motor  filaments,  583 

a  nerve  of  common  sensation  and  of 
taste,  ib. 
Glottis,    action  of    laryngeal    muscles 
on,  517 

forms  assumed  by,  522 

narrowing  of,  proportioned  to  height 
of  note,  523 

respiratory  movements  of,  523 
Glucose,  111,  112,  800 

in  liver,  468 

test  for,  113 
Gluten  in  vegetables,  288 
Glycerine.  Ill,  338 
Glycin,  345,  795 
Glycocholic  acid,  345 
Glycogen,  19,  112 

characters,  113 

destination,  469 

preparation,  ib. 

quantity  formed,  ib. 

variation  with  diet,  ib. 
Glycosuria,  470 

artificial  production  of,  ib. 
Gmelin's  test,  347 
Golgi,  101 
Goll's  column,  542 
Graafian  vesicles,  718 

formation  and  development  of,  718  et 
seq. 

i-elation  of  ovum  to,  ib. 

rupture  of,  changes  following,  728  et 
seq. 
Granular  layers  of  retina,  673 
Grape-sugar.     See  Glucose. 
Gray  matter  of  cerebellum,  562 

of  cerebrum,  ib. 

of  crura  cerebri,  ib. 

of  medulla  oblongata,  ib. 

of  pons  Varolii,  ib 

of  spinal  cord,  540 
Groove,  primitive,  740 
Growth,  7 

coincident  with  development,  8 

of  bone,  66 

not  peculiar  to  living  beings,  8 

Habitual  movements,  609 
Haematin,   149 

hydrochlorate  of,  150 
Haemadvnamometer,  194 


Haematoidin,  150 
Hjematoporphyrin,  149 
Haemin,   150 
Ha?mochromogen,  ib. 
Ha^mocytometer,  136  et  seq. 
Haemoglobin,  144  et  seq. 
action  of  gases  on,  146 
derivatives  of,  149 
distribution,  144 
estimation  of,  147 
spectrum,  146 
Hair-follicles,  415 

their  secretion,  471 
Hairs,  415 

structure  of,  ib. 
Hamulus,  653 

Hassall.  concentric  corpuscles  of,  481 
Haversian  canals.  56 
Head -folds,  744 

Hearing,  anatomy  of  organ  of,  646 
double,  662 
impaired  by  lesion  of  facial  nerve, 

580 
influence  of  external  ear  on,  654 
of  labyrinth,  659 
of  middle  ear,  665 
physiology  of,  654 
See  Sound,   Vibrations,  etc. 
Heart,  159  et  seq. 
action  of,  176 
accelerated,    226 
force  of,  189 
frequency  of,  ib. 
inhibited,  225 
after  removal,  221 
rhj'thmic,  220  et  seq. 
work  of,  191 
auricles  of,  161,  168 

See  Auricles, 
capacity,  164 
chambers,  161 
chordae  tendineae  of.  166 
columnae  carnae  of,  ib. 
course  of  blood  in,  159 
development,  766 
electrical  phenomena,  231 
endocardium,  165 
force,  189 
frog's,  331 
ganglia  of,  ib. 
impulse  of,  183 

tracing  by  cardiograph,  184  et  seq, 
influence  of    pneumogastric    nerve 
335 
of  sympathetic  nerve,  326 
investing  sac,  159 
metabolism,  331 
muscular  fibres  of,  86,  164 
musculi  papillaries,  66 
nervous  connections  with  other  or- 
gans, 337 
rhythm,  330 
nervous  system,  influence  on,  32£ 
revolution  of,  180 


814 


INDEX. 


Heart — contimied. 

rhythmical  contractility,  320 

situation,  159 

sounds  of,  181 
causes,  181 

structure  of,  164 

valves,  165 
arterial  or  semilunar,  166 
function  of,  179 

auriculo-ventricular,  164 
function  of,   177 

ventricles,  their  action,  163 

work  of,  191 
Heat,  animal.     See  Temperature. 

influence  of  nervous  system,  495 
of  various  circumstances  on,  494  et 
seq. 

losses  by  radiation,  etc.,  493 

sources  and  modes  of  production,  490 
Heat  centres,  497 
Heat-producing  tissues,  491 
Heat  or  rut, 

analogous  to  menstruation,  ib. 
Height,    relation    to    respiratory     ca- 
pacity, 257 
Helicotrema,  652 
Helix  of  ear,  646 

Hemispheres,  Cerebral.  See  Cerebrum. 
Herbivorous  animals, 

perception  of  odors  by,  644 
Hering's  theory,  702 
Hetero-albumose,  318 
Hiccough,  mechanism  of,  267 
Hippuric  acid,  475 
Horse's  blood,  peculiar  coagulation  of, 

120 
Hunger,  sensation  of,  628 
Hyaloplasm,  9 

Hybernation,  state  of  thymus  in,  482 
Hydrobilirubin.  347 
Hydrocarbons,  794 
Hydrocele  fluid,  122 
Hydrogen,  114 
Hydrolytic  ferments,  799 
Hymen,  718 
Hypermetropia,  688 
Hyperpnoea,  280 
Hyperpyrexia,  489 
Hypoblast,   20 
Hypoglossal  nerve,  587 
Hypoxanthin,  400  ^ 

Ideas,  connection  of,  with  cerebrum, 

606 
Ileo-csecal  valve,  334 
Illusions,  629 

Image,  formation  of,  on  retina,  680 
Impulse  of  heart,  183 
Income  and  output  of  energy,  509 
Incus,  648 

function  of,  656 
Indican,  399 
Indigo,  ib. 
Indol,  337 


Induction 

coil,  429 

current,  ib. 
Infundibulum,  247 
Inhibitory   influence  of  pneumogastric 

nerve,  225 
Inhibitory  heat-centre,  498 
Inogen,  451 

Inorganic  matter,  distinction  from  or- 
ganized, 102 

principles,  114 
Inosite,  113 
Insalivation,   291 
Inspiration,   249 

elastic  resistance  overcome  by,  ib. 

extraordinary^  251 

force  employed  in,  257 

influence  of,  on  circulation,  275 

mechanism  of,  249 
Intercellular  substance,  39 

passage,  247 
Intercostal  muscles,  action  in  inspira- 
tion,  251  et  seq. 

in  expiration,  252 
Internal  capsule,  589 
Intestinal  juice,  352,  355 
Intestines,  digestion  in, 

gases,  360 

large,  digestion  in,  355 

movements,  357 

small,  changes  of  food  in,  353 
Inversive  ferments,  ib. 
Involuntary  muscles, 

actions  of,  446 

structure  of,  79 
Iris,  668 

action  of,  ib.  et  seq. 

in  adaptation  to  distances,  686 

development  of,  780 
Iron,  116 
Irradiation,  690 

Jacobson's  nerve,  583 

Jaw,  interarticular  cartilage,  291 

Judgment,  637 

Juice,  gastric,  315 

pancreatic,  336 
Jumping,  446 

Kaeyokinesis,  13 

Karyomitosis,   ib. 

Katabolic  nerves,  627 

Katelectrotonus,  448 

Keratin,  111 

Key,  428 

Kidneys,  their  structure,  381 

blood-vessels  of,  how  distributed,  386 

capillaries,  of,  ib 

development  of,  785 

function  of.     See  Urine. 

Malpighian  corpuscles  of,  383 

nerves,  389 

tubules  of,  382  et  seq. 
Kreatin,  423,  796 


INDEX. 


815 


Kreatinin,  423,  400,  796 
Kymograph,  194 

tracings,  195 

spring-,  196 

Labia,  externa  and  interna,  718 
Labyrinth  of  the  ear.     See  Ear. 
Lachrymal  apparatus,  664 

gland,  ib. 
Lacteals,  331 
Lactic  acid,  114 

in  gastric  fluid,  316 
Lactose,  112 
LaBvulose,   ib. 
Laminae  dorsales,  742 

■viscerales  or  ventrales,  746 
Lardacein,  109 

Large  intestine.     See  Intestine. 
Larynogscope,  519 
Larynx,  construction  of,  240,  515 

muscles  of,  517 

nerves  of,  519 

variations  in  according  to  sex  and 
age,  524 

vocal  cords  of,  515 
Lateral  plate,  743 
Lateral  ventricles,  558 
Laughing,  269 
Law  of  contraction,  449 
Lead  an  accidental  element,  116 
Leaping,  446 
Lecithin,  347 
Lens,  crj'.stalline,  669 
Lenticular  ganglion,  relation  of  third 
nerve  to,  573 

nucleus,  590 
Leucin,  337 
Leucocytes.     See  Blood  corpuscles 

(white) . 
Lieberkuhn's  glands,  328 
Lingual  branch  of  fifth  nei've,  578 
Lips,  influence  of  fifth  nerve  on  move- 
ments of,  575 
Liquor  amnii,  749 
Liquor  sanguinis,  or  plasma,  117 
Liver,  340 

action    of,    on  albuminous  matters, 
472 

on  saccharine   matters,  468 

blood-vessels  of,  342 

capillaries  of,  ib. 

cells  of,  341 

circulation  in,  342 

development  of.  783 

functions  of,  153,  467  et  seq. 

gh'cogenic  function  of,  468 

secretion  of.     See  Bile. 

structure  of,  341 

sugar  formed  by,  468  et  seq. 
Loop  of  Henle,  384 
Ludwig's  air-pump,  142 
Lungs,  244 

blood -supply,  248 

capillaries  of,  ib. 


Lungs — continued. 

cells  of,  246 

changes  of  air  in,  259 

changes  of  blood  in,  264 

circulation  in,  248 

contraction  of,  253 

coverings  of,  245 

development  of,  785 

lobes  of,  246 

lobules  of,  ib. 

lymphatics,  249 

muscular  tissue  of,  245 

nerves,  249 

nutrition  of,  248 

position  of,  244 

structure  of,  246 
Luxus  consumption,  504 
Lymph,  376 

compared  with  chyle,  377 
with  blood,  ib. 

current  of,  371 

quantity  formed,  377 
Lymph-corpuscles,  ib. 
Lymph-hearts,     structure    and    action 
of,  372 

relation  of  to  spinal  cord,  ib. 
Lymphatic  glands,  372 
Lymphatic  vessels,  367 

absorption  by,  378 

arteries  and  veins  of,  175 

communication  with  serous  cavities, 
370 

communication  with   blood-vessels, 
368 

course  of  fluid  in,  371 

distribution  of,  367 

origin  of,  369 

structure  of,  371  et  seq. 

valves  of,  371 
Lymphoid  or  retiform  tissue,  44.  See 
Adenoid  Tissue. 

Macula  germinativa,  715 
Male  sexual  functions,  731 
Malleus,  648 

function  of,  655 
Malpighian    bodies   or    corpuscles    of 
kidney,  383.     See  Kidney, 

corpuscles  of  spleen,  478  et  seq. 
Maltose,  112,  297 
Mammary  glands,  462 

evolution,  463 

involution,  464 

lactation,  ib. 

structure,  462 
Mandibular  arch,  761 
Manganese,  116 
Mastication,  291 

centre,  291 

fifth  nerve  supplies  muscles  of,  291 

muscles  of,  ib. 
Mastoid  cells,  647 
Meatus  of  ear,  646 
Medulla  oblongata,  562  et  seq. 


816 


INDEX. 


Medulla  oblongata— cow^wMed. 
columns  of,  ib. 

conduction  of  impressions,  568 
decussation  of  fibres,  5(54 
effects  of  injury  and  disease  of,  569 
fibres  of,  how  distributed,  563 
functions  of,  568  et  seq. 
important  to  life,  569 
nerve-centres  in,  ib. 
pyramids  of,  anterior,  563 
posterior,  ib. 
structure  of,  ib. 
Medullary  folds, 
groove,  ib. 
plate,  ib. 
Meissner's  plexus,  337 
Melanin,  696 
Membrana  decidua,  753 
granulosa,  714 
development  of   into  corpus  luteum, 

729 
limitans  externa,  674 
interna,   672 
Membrana  propria  or  basement  mem- 
brane.    See  Basement  Membrane, 
tympani,  648 
office  of,  656 
Membrane,  blastodermic,  737 
of  the  brain  and  spinal  cord,  537 
vitelline,  714 
Membranes  of  brain,  537 
Membranes,  mucous.  See  Mucous  mem- 
branes. 
Membranes,  passage  of  fluids  through. 

See  Osmosis. 
Membranes,  serous.     See  Serous  mem- 
branes. 
Membranous  labyrinth.     See  Ear. 
Memory    relation    to    cerebral   hemi- 
spheres, 606  et  seq. 
Menstrual  discharge,    composition  of, 

727 
Menstruation,   725 

coincident  with    discharge  of   ova, 

ib. 
corpus  luteum  of,  730 
time  of  appearance  and    cessation, 
728 
Mercurial  manometer,  193 
Mesencephalon,  777 
Mesoblast,  20,  739 
Mesocephalon,  777 
Metencephalon,  ib. 
Methaemoglobin,  147 
Micro-organisms  in  intestines,  356 
Micturition,  409 
Milk,  as  food,  287 
chemical  composition,  466 
properties  of,  ib. 
secretion,  of  464 
Milk-curdling  ferments,  466,  799 
Milk-globules,  465 
Milk-teeth,  67  et  seq. 
Millon's  reagent  and  test,  105 


Mind,  cerebral  hemisphere  the  organs 

of,  606 
Modiolus,   650 
Molars.     See  Teeth. 
Molecular  base  of  Chyle.     See  Chyle. 
Molecular  layers,  673,  674 
Morphological  development,.  20 
Motor  areas,  599 

Motor    impulses,    transmission    of    in 
cord,  549 

nerve- fibres,  531 

laws  of  action  of,  ib. 
Moutli,  changes  of  food  in,  290  et  seq. 
Movements, 

of  eyes,  685 

of  intestines,  357 

protoplasm,  4 
Mucigen,  302 
Mucin,   110 
Mucous  membrane,  456 

basement  membrane  of,  457 

epithelium-cells  of,  ib.     See  Epithe- 
lium. 

digestive  tract,  456 

gastro- pulmonary  tract,  ib. 

genitourinary  tract,  457 

gland -cells  of,  457 

of  intestines,  458 

of  stomach,  ib. 

of  uterus,  changes  of  in  pregnancy, 
752 

respiratory  tract,  456 
Mucus,  457 
Muller's  fibres,  672 
Murexide,  398 
Muscle,  79 

activity,  426 

casket,  83 

chemical  constitution,  421 

clot,  422 

contractility,  426 

contraction,  mode  of,  433 

corpuscles,  83 

curves,  434 

development,  89 

disc  of  Hensen,  83 

elasticity,  423 

electric  currents  in,  424 

fatigue,  436 
curves,  ib. 

growth,   89 

heart,  86 

heat  developed  in  contraction  of,  436 

involuntary,  446 
actions  of,  447 

metabolism,  421 

natural  currents,  424 

nerves  of,  87 

non-striated,   79 

physiology  of,  421 

plain,  79 

plasma,   421 

reaction,  422 

response  to  stimuli,  427  et  seq 


INDEX. 


817 


Muscle — continued. 

rest  of,  423 

reticulum,  84 

rigor,  440 

sarcolemnia,  82 

serum,  421 

shape,  changes  in,  437 

skeletal,  80 

sound,  developed  in  contraction  of,  436 

source  of  action  of,  451 

stimuli,  427 

striated.  80 

structure,  ib.  et  seq. 

tetanus,  434 

twitch,  433 

unstriped,  79 

voluntary,  80 
actions  of,  441 

work  of,  435 
Muscular  action,  426 

conditions  of,  438 

force,  435 
Muscular  irritability,  427 

duration  of,  after  death,  441 
Muscvilar  motion,  426  et  seq. 

sense,  636 
Muscularis    mucosas,  331 
Musical  sounds,  661 
Myo-albumin,  422 
Myograph,  431 

pendulum,  432 
Myo-haematin,  423 
Myopia,  or  short-sight,  687 
Myosin,   108,  422 

ferment,  422 
Myosinogen,  422 

Nails,  416 

growth  of,  417 

sti-ucture  of,  ib. 
Nasal  cavities  in  relation  to  smell,  641 

et  seq. 
Native    albumins,  106 
Near  point,   684 

Nerve-centre,    533.      See    Cerebellum, 
Cerebrum,  etc. 

ano- spinal,  554 

automatic  action,  570 

cardio-inhibitory,  ib. 

cilio-spinal,  570 

deglutition,  569 

diabetic,   571 

erection,  555 

gen  i  to -urinary,  ib. 

mastication,  569 

micturition,  554 

muscular  co-ordination,  611 

reflection  in,  533 

laws  and  conditions  of,  534 

respiratory,   270 

secretion  of  saliva,  299 

sweat,  571 

vaso-motor,   233 

vesico-spinal,  554 

52 


Nerve-corpuscles,  96  et  seq. 

caudate  or  stellate,  ib. 

polar,  ib. 
Nerves,   530 

action  of  stimuli  on,  447 
currents  of,  446 

afferent,  531 

axis-cylinder  of,  91 

cells,  96 

centrifugal,   531 

centripetal,  ib. 

cerebrospinal,   532 

classification,  89 

conduction  by,  530  et  seq. 
rate  of,  532 

cranial.     See  Cerebral  Nerves. 

efferent,  531 

electrical  currents  of,  446 

functions  of,  530 

funiculi  of,  94 

gray,  89,   92 

impressions     on,     referred     to     pe- 
riphery 531 

inhibitory.     See  Inhibitory  Action. 

intercentral,  531 

laws  of  conduction,  531  et  seq. 

medullary  sheath,  90 

medullated,   89 

neurilemma,   90 

nodes  of  Ranvier,  92 

non- medullated,  92 

nuclei,  90 

plexuses  of,  95 

primitive  nerve  sheath,  90 

size  of,  92 

spinal.     See  Spinal  Nerves. 

stimuli,  447 

structure,  89 

sympathetic.        See       Sympathetic 
nerve. 

terminations  of,  95 
central,  ib. 
in  cells,  ib. 

in  corpuscles  of  Golgi,  100 
in  corpuscles  of  Grandry,  101 
in  corpuscles  of  Herbst,  98 
in  end- bulbs,  ib. 
in  motorial  end-plates,  88 
in  networks  or  plexuses,  ib. 
in  Pacinian  corjiuscles,  97 
in  touch-corpuscles,  99 

trophic,  626 

varieties  of,  89,  531 

velocity  of  nerve  force,  532 
Nervous  force,  velocity  of,  ib. 
Nervous  system,  530 

cerebro-spinal,    532 

development,  774 

sympathetic,  621 
Neural  canal,  742 
Neurenteric  canal,  746 
Neurilemma,  90 
Neurin,  347 
Neuroglia,  538 


818 


INDEX. 


Nitrogen,   114 

in  relation  to  food,  285  et  seq. 
Nitrogenous  compounds,  285 

non- nitrogenous  compounds,  288 
Nitrogenous  equilibrium,  503 
Nitrogenous  food,  effects  of,  502 
Nodal  point,  678 
Nodes  of  Ranvier,  29 
Nose.     See  Smell. 

development  of,  781 
Notochord,  742 
Nuclein,   HI 
Nucleoli,  2 
Nucleus,  2,  11  et  seq. 

division,  13 

position,  11 

staining  of,  ib. 

structure,  12 
Nutrition,  499 
Nymphse,  718 

Odontoblasts,  76 
Odors,  644 

causes  of,  641  et  seq. 

different  kinds  of,  644 

perception  of,  ib. 

varies  in  different  classes,  ib. 

relation  to  taste,  639 
Oleaginous  principles,  digestion  of.  111 
Oleic  acid.  111 
Olfactory  cells,  642 

centre,  614 

nerve,  ib. 
subjective  sensations  of,  645 
Olivary  body,  565 

fasciculus,  ib. 
Omphalo-mesenteric 

arteries,  768 

duct,  746 

veins,  770 
Oncograph,  404 
Oncometer,  ib. 
Ophthalmoscope,  693 
Optic 

centres,  612 

lobes,  corpora  quadrigemina,  homo- 
logues  of,  620 
functions  of,  ib. 

nerve,  decussation  of,  612 

thalamus,  function  of,  591,  615 

vesicle,  primary,  776 
secondary,  ib. 
Optical  angle,  680 

apparatus  of  eye,  677 
Optogram,   695 
Ora  serrata  of  retina,  671 
Organ  of  Corti,  653 
Organic  compounds  in  body,  103 

instability  of,  ib. 
Organs  of  sense,  development  of,  778 
Os  uteri,   718 
Osseous  labyrinth,  649 
Ossicles  of  the  ear,  647 
Ossification,  59  et  seq. 


Osteoblasts,  59  v 

Osteoclasts,  63 
Otoconia,  or  Otoliths,  651 
Ovaries,  712 

Graafian  vesicles  in,  713 
Ovisacs,  ib. 
Ovum,  ib. 

action  of  seminal  fluid  on,  735  et  seq. 

changes  of,  in  ovary,  734 
previous  to  formation  of  embryo, 
ib. 

subsequent  to  cleavage,  736  et  seq. 

in  uterus,  734  et  seq. 

leaving  of  yolk,  736 

connection  of  with  uterus,  734 

discharge  of  from  ovary,  ib. 

formation  of,  715 

germinal  vesicle    and    spot  of,    714 
et  seq. 

impregnation  of,  735 

structure  of,  714 

un impregnated,   734 
Oviduct,  or  Fallopian  tube,  716 
Oxaluric  acid,  400 
Oxygen,  102 

Pacinian  bodies  or  corpuscles,  97,  336 
Pain,  635 
Pancreas,  334 

development  of,  783 

functions  of,  337  et  seq. 

structure,   334 
Pancreatic  fluid,  336 
Papillae, 

of  the  kidney,  382 

of  skin,  distribution  of,  412 

of  tongue,  304 
Paraglobulin,  108,  123 
Par  vagum.    See  Pneumogastric  nerve. 
Paraplasma,  9 
Paraglobulin,  108 
Partial  pressui'e,  143 
Parotid  gland,  saliva  from,  298 

nerves  influencing  secretion  by,  301 
Pars  ciliaris  retinae,  676 
Patellar  reflex,  51 
Pavy's  method,  801 
Pelvis  of  the  kidney,  382 
Penis,  722 

structure,  ib. 
Pepsin,  316 
Pepsinogen,  314 
Peptic  cells,  313 
Peptones,  109 
Perceptions,  630 
Perfusion  canula,  229 
Pericardium,  159 
Perilj'mph,    or   fluid  of   labyrinth   of 

ear,  649 
Peripheral  resistance,  192,  232 
Peristaltic    movements   of   intestines, 
357 

of  stomach,  320 
Permanent  teeth.    See  Teeth. 


INDEX. 


819 


Perspiration,  cutaneous,  417 

insensible  and  sensible,  ib. 

ordinary  constituents  of,  ib. 
Pettenkofer's  test,  346 
Peyer's  glands,  329 

patches,   ib. 

structure  of,  330 
Pflliger's  law,  449 
Phagocj^tosis,    134 
Phakoscope,  683 
Pharj;nx,  306 

action  of  in  swallowing,  ib. 

influence  of  glosso-pharyngeal  nerve 
on,  ib. 

of  pneumogastric  nerve  on,  ib. 
Phenol,   114,   337 
Phenomena  of  life,  1 
Phosphates,   115 
Phosphates,    estimation    of   in    urine, 

804 
Phosphorus  in  the  human  body,  ib. 
Phrenograph,  254 
Pigment  cells  of  retina,  675 
Pineal  gland,  486 
Piotrowski's  reaction,  104 
Pituitary  body,  486 

development,  759 
Placenta,  752 

foetal  and  maternal,  ib. 
Plasma  of  blood,  137 

salts  of,  139 
Plasm  ine,  122 

composition,  ib. 

nature  of,  ib. 
Plethysmograph,  232 
Pleura,  245 

Pleuro- peritoneal  cavity,  743 
Plexus, 

terminal,   101 
Pneumogastric  nerve,   583 

distribution  of,   ib. 

influence  on 
action  of  heart,   225 
deglutition,   584 
gastric  digestion,  ib. 
larynx,  ib. 
lungs,  ib. 
oesophagus,  ib. 
pharynx,  584 
respiration,  271 

mixed  function  of,  584 

origin  from  medulla  oblongata,  583 
Pneumograph.  24 
Polar  ceil,  734 
Pons  Varolii,  its  structure,  587 

functions,  ib. 
Portal  blood.    See  Liver. 
Potassium,  116 

sulphocyanate,  296 
Pregnancy,    absence   of  menstruation 
during,  726  et  seq. 

corpus  luteum  of,  729 
Presbyopia,  690 
Pressor  nerves,  234 


Primitive  groove,  740 

streak,  ib. 
Primitive  nerve-sheath,  or  Schwann's 

sheath,  90 
Pro-nucleus,  female,  735 

male,  ib. 
Propionic  acid,   113 
Prosencephalon,  776 
Prostate  gland,  724 
Proteids,  103 

chemical  properties,  103  et  seq. 

physical  properties,  ib. 

tests  for,  ib. 

varieties  of,  ib. 
Proteoses,  109,  318 
Proto-albumose,  318 
Protoplasm,  1 

chemical  characters,  3 

movement,  4 

physical  characters,  3  et  seq. 

physiological  characters,  ib. 

repi'oduction,  8 

structure  of  cells,  9 
Proloplasma,  ib. 
Proto- vertebrae,  744 
Pseudoscope,  711 
Pseud  o-stomata,  30 
Ptyalin,  296 

action  of,  ib. 
Puberty, 

changes  at  period  of,  728 

indicated  by  menstruation,  ib. 
Pulmonary  artery,  valves  of  heart,  166 
Pulse,  arterial,  192  et  seq. 
Pui-kinje's  figures,  691 
Pyramidal  tracts,  543  et  seq. 
Pyramids  of  medulla  oblongata,  563 

Quantity  of  air  breathed,  256 
blood,  118  et  seq. 
saliva,  296 

Eami  viscerales,  623 

efl'erentes,  ib. 

communicantes,   ib. 
Recurrent  sensibility,  546 
Reflex  actions,  533 

augmentation,  535 

conditions  necessary  to,  534 

cutaneous,  551 

inhibition  of,  535 

irregular  in  disease,  553 

laws  of,  534 

morbid,  553 

muscle,   551 

of  medulla  oblongata,  568  et  seq. 

of  spinal  cord,  550 

purposive  in  health,  533 
Refracting  media  of  eye.  678 
Refraction,   laws  of,    ib. 
Regions  of  body.     See  Frontispiece. 
Relations  of   different  parts  of  brain, 

556 
Remak,  2 


820 


INDEX. 


Remak's  ganglia,  222 
Rennin,   319,  338,  799 
Requisites  of  diet,  506 
Reserve  air,  256 
Residual  air,  ib. 
Respiration,  239 
abdominal  type,  253 
changes  of  air,  259 
of  blood,  264 
of  the  tissues,  265 
costal  type,  252 

foi'ce,  257 
frequency,   257 

influence  of  nervous  system,  269 
mechanism,  249  et  seq. 
movements,  249 
methods  of  recording,  253 
nitrogen  in  relation  thei-eto,  262 
■organic  matter  excreted,  263 
quantity  of  air  changed,  256 
relation  to  the  pulse,  257 
suspension  and  arrest,  291  et  seq. 
types  of,  252 
Hespiratory  acts,  special,  266 
apparatus,  239 
capacity  of  chest,  257 
cells,  246 
movements,  249 
axes  of  rotation,  250  et  seq. 
of  glottis,  '255 
influence  on  amount  of   carbonic 

acid,  260 
on  arterial  tension,  275  et  seq. 
rate,  257 

relation  to  pulse  rate,  ib. 
size  of  animal,  ib. 
relation  to  will,  269  et  seq 
various  mechanism,  266 
muscles,  249  et  seq. 
daily  work,  258 
power  of,  ib. 
nerve-centre,  269 
rhythm,   255 
sounds,  ib. 
Restiform  bodies,  565  et  seq. 
Retiform  or  adenoid,  or  lymphoid  tis- 
sue, 44 
Heticulum,  9 
Retina,  671 

blind  spot.  691 

blood-vessels,  676 

duration  of  impression  on,  692 

of  after-sensations,  ib. 
excitation  of,  691 
focal  distance  of,  681 
fovea  centralis,  671 
functions  of,  691 

image  on,    how   formed    distinctly, 
680 
inversion  of,  how  corrected,  696 
insensible  at  entrance  of  optic  nerve, 

691 
layers,    671 
in  quadrupeds,  708 


Retina — continued. 
reciprocal  action  of  parts  of,  704 
in  relation   to  direction  of  visioi', 
691 
to  motion  of  bodies,  699 
to  single  vision,  705 
to  size  of  field  of  vision,  697 
structure  of,  671 
visual  purple,  695 

Rheoscopic  frog,  446 

Rhinencephalon,  776 

Rigor  mortis,  440 
affects  all  classes  of  muscles,  440 
phenomena  and  causes  of,  ib. 

Ritter's  tetanus,  450 

Rods  and  cones,  674 

Rolandic  area,  604 

Rotatory  movements,  620 

Running,  mechanism  of,  446 

Rut  or  heat,  725 

Saccharine  principles  of  food,  diges- 
tion of,  288 
Saccharoses,  112 
Sacculus,  651 
Saliva,  295 

composition,  ib. 

process  of  secretion,  301 

quantity,  296 

rate  of  secretion,  ib. 

uses,  ib. 
Salivary  glands,  292 

develoimient  of,  783 

influence  of  nervous  system,  298 

mixed,  294 

nerves,  ib. 

secretion,  295 

structure,  292 

true,  293 

varieties,  ib. 
Sanson's  images,  683 
Saponification,  338 
Sarcode,  2.     See  Protoplasm. 
Sarcosin,  473,  796 
Scheiner's  experiment,  684 
Schematic  eye,  680 
Schiff's  test,  398 
Schneiderian  membrane,   641 
Sclerotic,  664 
Sebaceous  glands,  414 

their  secretion,  417 
Secreting  glands,  453,  458 

aggregated,  ib. 

convoluted  tubular,  ib. 

tubular  or  simple,  ib. 
Secreting    membranes.       See    Mucous 

and  Serous  membranes. 
Secretion,  453 

apparatus  necessary  for,  458  et  seq. 

changes  in  gland-cells  during,  460 

circumstances  influencing,  461 

discharge  of,  ib. 

influence  of  nervous  system,  461 

of  urine,  406 


INDEX. 


831 


Secretion — con  tin  ned. 

process   of   physical   and  chemical, 
460 
Segmentation  of  cells,  736 

in  chick,  737 

ovum,  ib. 
Semen,  731 

composition  of,  733 

filaments  or  spermatozoa,  731 

tubes.  720 
Semicircular  canals  of  ear,  650 

development  of,  781  et  seq. 

use  of,  659 
Semilunar  valves.     See  Heart  valves. 
Semilunes  of  Heidenhain,  294. 
Sensation,  628 

color,  702 

common,  628 

conditions  necessaiy  to,  ib. 

excited  b}'  mind,  ib. 
by  internal  causes,  ib. 

of  motion,  636 

nerves  of,  546 

of  pain,  635 

of  pressure,  631 

special,  629 
nerves  of,  571 

stimuli  of,  531 
of  special,  ib. 

subjective,    632.     See    also    Special 
Senses. 

tactile,  631 

temperature,  634 

tickling,  628 

touch,  631 

of  weight,  636 
Senses,  special,  628 

organs  of,  development  of,  778 
Sensorium,  629 

Sensory  centres  in  cerebral  cortex,  612 
Sensorj'    impressions,    conduction    of, 
548 

b}'  spinal  cord,  ib. 

in  brain,  606 

nerves,  548 
Serine,  139 
Serous  membranes,  454 

arrangement  of,  ib. 

communication  of  lymphatics  with, 
454 

fluid  secreted  by,  ib. 

functions,  ib. 

lining  joints,  etc. ,  454  et  seq. 
visceral  cavities,  ib. 

structure  of,  454 
Serum, 

of  blood,  139 

albumin,   106 

separation  of,  139 
Seventh  cerebral  nerve.     See  Cerebral 

nerves. 
Sexual    organs  and    functions   in  the 
female,  712 

in  the  male,  718 


Sighing,  mechanism  of,  267 

Sight,  663.     See  Vision. 

Silica,  parts  in  which  found,  116 

Silicon,  ib. 

Sinuses  of  dura  mater,  217  et  seq. 

of  Valsalva,  167 
Sixth  cerebral  nerve,  579 
Size  of  field  of  vision,  698 
Skatol,  337 

Skeleton.     See  Frontispiece. 
Skin,  410 

absorption  by,  379 

of  metallic  substances,  ib. 
of  water,  ib. , 

cutis  vera  of,  412 

epidermis  of,  410 

evaporation  from,  493 

excretion  by,  417 

exhalation  of  carbonic  acid    from, 
419 
of  watery  vapor  from,  ib. 
functions  of,  417 

papilla?  of,  412 

perspiration  of,  417 

rete  mucosum  of,  410 

sebaceous  glands  of,  414 

structure  of,  ib. 

sudoriferous  glands  of,  413 
Sleep,  610 

Small  intestine,  326 
Smell,  sense  of,  641 

conditions  of,  ib. 

different  kinds  of  odors,  644 

impaired  by  lesion  of  facial  nerve, 
581 

impaired  by  lesion  of  fifth  nerve,  578 

internal  excitants  of,  645 

limited  to  olfactory  i-egion,  641 

structure  of  organ  of.  ib. 

subjective  sensations,  644 

varies  in  difl'erent  animals,  ib. 
Sneezing,  centre,  570 

mechanism  of,  268 
Sniffing,  mechanism,   of,  268 

smell  aided  by,  642 
Soaps,  794 
Sobbing,  269 
Sodium,  115 

Solitary  glands.     See  Pej^er's. 
Soluble  ferments,  355 
Somatopleure,   743 
Somnambulism,  611 
Sonorous    vibrations,   how    communi- 
cated in  ear,  654  et  seq. 

in  air  and  in  water,  ib.     See  Sound. 
Sound, 

binaural  sensations,  662 

conduction  of  by  ear,  654 

heart,  181 

movements  and  sensations  produced 
by,  663 

perception, 
of  direction  of,  661 
of  distance  of,  662 


822 


INDEX. 


Sound — continued. 

permanence  of  sensation  of,  ib. 

production  of,  661 

subjective,  663 
Source  of  water,  114 
Spaces  of  Fontana,  670 
Spasms,  reflex  acts,  534 

centre,   571 
Speaking,  268 

mechanism  of,  527 
Special  senses,  631 
Speech,  527 
Spermatozoa,  development  of,  731 

form  and  structure  of,  ib. 

function  of,  735 

motion  of,  731 
Spherical  aberration,  688 

correction  of,  ib. 
Sphincter  ani.     See  Defsecation. 

vesicae,  390 
Sphygmograph,  202 

tracings,  203  et  seq. 
Sphygmometer,  204 
Spinal  accessory  nerve,  586 
Sijinal  cord,  537 

automatism,  535 

canal  of,  537 

centres  in,  553 

a  collection  of  nervous  centres,  ib. 

columns  of,   538 

commissures  of,  ib. 

conduction  of    impressions    by,  546 
et  seq. 

course  of  fibres  in,  543 

development  of,   775 

fissures  and  fui'rows  of,  537 

functions  of;  546 
of  columns,  543 

influence  on  lymph-hearts,  555 
on  sphincter  ani,  554 
on  tone,  555 

morbid  irritability  of,  553 

nerves  of,  544 

reflex  action  of,  550 
inhibition  of,  552 

special  centres  in,  553 

structure  of,  537  et  seq. 

tracts,  543 

weight,  598 
relative,  ib. 

white  matter,  537 
gray  matter,  540 
Spinal  nerves,  544 

origin  of,  544  et  seq. 

physiology  of,  546 
Spindle,   15 
Spirem,  14 
Spirometer,  256 
Splanchnopleure,  743 
Spleen,  477 

functions,  479 

hilus  of,  477 

influence  of  nervous  system,  480 

Malpighian  corpuscles  of,  478 


Spleen — continued. 

pulp,  477  et  seq. 

stroma  of,  ib. 
structure  of,  ib. 

trabecular  of,  477  et  seq. 
Spongioplasm,  9 
Spontaneous  movement,  4 
Spot,  germinal,  715 
Stannius'  experiments,  233 
Stapes,  648 
Starch,  17 

digestion  of,  in  mouth,  290 
Starvation,  501  et  seq. 
Steapsin,  339 
Stearic  acid.  111 
Stearin,  ib. 
Stercorin,  551 

allied  to  cholesterin,  ib. 
Stereoscope,  700 
Stethograph,  254 
Stethometer,  ib. 
Stimuli,  protoplasmic,  6 
St.  Martin,  Alexis,  case  of,  315 
Stomach,  310 

blood-vessels,  314 

development,  782  et  seq. 

digestion  in,  317 
circumstances  favoring,  319 
products  of,  318 

digestion  after  death,  323 

glands.  312 

lymphatics,  314 

movements,  320 

influence  of  nervous  system,  322 

mucous  membrane,  311 

muscular  coat,  311 

nerves,  314 

secretion  of.     See  Gastric  fluid. 

structure,  310 

temperature,  319 
Stomata,  29 

Stratum  intermedium  (Hannover),  77 
Striated  muscle.     See  Muscle. 
Stroma-fibrin,   121 
Stromuhr,  214 
Structure  of  cells,  9 
Submaxillary  gland,  294  et  seq. 
Substantia  nigra,  389 
Succus  entericus,  352 

functions  of,  352 
Sucking,  mechanism  of,  269 

centre,  570 
Sudoriferous  glands.     -See  Skin. 
Sugar.     See  Glucose. 

estimation  of,  801  et  seq. 
Sulphates,  116 

in  tissues,  ib. 

in  urine,  400 
Sulphuretted  hydrogen,  357 
Superior  laryngeal  nerve,  271 
Suprarenal  capsules,  484 

development  of,  787 

disease  of,  relation   to  discoloration 
of  skin,  486 


IXDEX. 


823 


Suprarenal  capsules — continued. 

structure,  484 
Swallowing,  809 
centre,  310 
nerves  engaged,  ih. 
Sweat,  417 

Sympathetic  nervous  system,  621 
distribution,  ih. 
divisions  of,  ib. 

fibres,  differences   of   from  cerebro- 
spinal fibres,  624 
functions,  624  et  seq. 
ganglia  of,  623 
action  of,  624  et  seq. 
structure,  623 
in  substance  of  organs,  621 
heart,  226 
structure  of,  626 
Synovial  fluid,  secretion  of,  455 

membranes,  454 
Svstemic  circulation.     See  Circulation. 

vessels,  ib. 
Systole  of  heart,  176 

Table  of  diet,  507 
Taste,  638 

after- tastes,  640 

centre,  614 

conditions  for  perception  of,  638 

connection  with  smell,  639 

impaired  by  injury 
of  facial  nerve,  580 
of  fifth  nerve,  583 

nerves  of,  ib. 

seat  of,  638 

subjective  sensations,  640 

varieties.  639 
Taste -goblets,  306 
Tauriu.  345 
Taurocholic  acid,  ib. 
Teeth,  67 

development,  74 

eruption,  times  of,  68 

structure  of,  70  et  seq. 

temporary  and  permanent,  68  et  seq. 
Tegmentum,  588 
Temperature,  488 

average  of  body,  ib. 

changes  of,  effects  of,  488  et  seq. 

circumstances  modifying,  492 

of  cold-blooded    and  warm-blooded 
animals,  489 

in  disease,  ib. 

loss  of,  492 

maintenance  of,  490 

of  Mammalia,  Birds,  etc.,  489 

regulation  of,  492 

sensation  of  variation  of.  634.      See 
Heat. 
Temporo-maxillary  fibro-cartilage,  291 
Tendon-reflex,  551 
Tension,  arterial,  191 

of  gases  in  lungs,  264 
Tensor  choroideaj,  683 


Tensor  tympaui  muscle,  648 

office  of,  ib. 
Testicle,  719 

development,  788 

descent  of,  ib. 

structure  of,  719  et  seq. 
Tetanus,  434 
Thalamencephalon,  776 
Thalami  optici,  function  of,  615 
Thermogenesis,  491  et  seq. 
Thermogenic  nerves  and  nerve-centres, 

496 
Thirst,  628 
Thoracic  duct,  368 
Thymus  gland,  480 

function  of,  482 

structure,  481 
Thvro-arytenoid  muscles,  518 
Thyroid-gland,  483 

function  of,  484 

structure,  483 
Timbre  of  voice,  524 
Tone  of  blood-vessels,  233 

of  muscles,  555 

of  voice,  524 
Tongue,  303 

action  of  in  deglutition,  309 

epithelium  of,  305 

papilla?  of,  304 

parts  most  sensitive  to  taste,  639 

structure  of,  303 
Tonic  centres,  571 
Tonometer.  230 
Tonsils,  307 
Touch,  631 

after  sensation,  634 

conditions  for  perfection  of,  631 

connection  of  with  muscular  sense, 
636 

co-operation  of  mind  with,  637 

hand  an  organ  of,  632 

illusions,  633 

modifications  of,  631 

special  organs,  632 

subjective  sensations,  634 

the  tongue  an  organ  of,  638 

various  degrees  of  in  different  parts, 
632 
Touch -corpuscles,  632 
Trachea,  242 

Tracts  in  the  spinal  cord,  543 
Traube-Hering's  curves,  280 
Tricuspid  valve,  165 
Trigeminal  or  fifth  nerve,  574 
Trommer's  test,  297 
Trophic  nerves,  578 
Trypsin.  336 

Tubes,  Fallopian.     See  Fallopian  tubes. 
Tubuli  seminiferi,   720 

uniferi,  382  et  seq. 
Tunica  albuginea  of  testicle,   716 
Tympanum  or  middle  ear,  647 

development  of,   781 

functions  of,  656 


824 


INDEX. 


Tympanum  or  middle  ear — continued. 

membrane  of,  647 

structure  of,  ib. 

use  of  air  in,  655 
Types  of  respiration,  249 
Tyrosin,  337 

Ulceration  of  parts  attending  inju- 
ries of  nerves,  578 
Umbilical  arteries,  773 

cord,  ib. 

vesicle,  746 
Unicellular  organisms,  1 
Unorganized  ferments,  317 
Unstriped  muscular  fibre,  79 

development,  89 

distribution,  79 

structure,  ib. 
Urate  of  ammonium,  397 

of  sodium,  ib. 
Urea,  393 

apparatus  for   estimating  quantity, 
802 

chemical  composition  of,  393 

identical   with    cyanate    of    ammo- 
nium, lb.,  395 

properties,  394 

quantity,  392 

in    relation    to    muscular    exertion, 
473 

sources,  471 
Ureter,  389 
Uric  acid,  396 

condition    in    which    it    exists    in 
urine,  397 

forms  in  which  it  is  deposited,  396 

proportionate  quantity  of,  397 

source  of,  397 

tests,  397 

variations  in  quantity,  397 
Urina  sanguinis,  potus,  et  cibi,  393 
Urinary  bladder,  390 

development,  789 

nerves,  390 

structure,  390 
Urinary  ferments,  391 
Urine,  390 

abnormal,  393 

analysis  of,  391 

chemical  composition,  ib. 

coloring  matter  of,  398 

cyst  in  in,  402 

decomposition  by  mucus,  400 

effect  of  blood -pressure  on,  408 

expulsion,  409 

extractives,  400 

flow  of  into  bladder,  409 

gases.  403 

hippuric  acid  in,  398 

mucus  in,  400 

oxalic  acid  in,  402 

physical  characters,  390 

pigments,  398 

quantity  of  chief  constituents,  392 


Urine — con  tinned. 
reaction  of,  391 

in  different  animals,  ib. 
made  alkaline  by  diet,  391 
saline  matter,  400 
secretion,  403 
rate  of,  ib. 
solids,  392 

variations  of,  ib. 
specific  gravity  of,  392 

variations  of,  ib. 
urates,  397 
urea,  393 
uric  acid  in,  396 

variations  of  specific  gravity,  392 
of  water,  392 
Urobilin,  398 
Urochrome,  ib. 
Uroerythrin,  399 
Uromelanin,  ib. 
Uterus,   717 
change    of    mucous    membrane    of, 

752  et  seq. 
development  of  in  pregnancy,  ib. 
follicular  glands  of,   752 
structure,  717 

Vagina,  structure  of,  718 

Vagus  nerve.     See  Pneumogastric. 

Valves  of  heart,  165.  See  Heart  valves. 

Valvulse  conniventes,  327 

Vas  deferens,  719 

Vasa  effereutia  of  testicle,  720,  788 

recta  of  testicle,  ib. 
Vascular  area,  763 
Vascular  glands,  476 

in  relation  to  blood,  487 

several  offices,  of,  ib. 
Vascular  system,  development  of,  763 
Vaso-constrictor  nerves,  236 
Vaso-dilator  nerves,  ib. 
Vaso-motor  nerves,  233 

effect  of  section,  233  ef  seq. 

influence  upon  blood-pressure,  236 
Vasomotor  nerve-centres,  ib.,  283 

reflection,  285 
Vegetables  and    animals,  distinctions 

between,  15 
Veins,  173 

circulation  in,  215  et  seq. 

rate  of,  215 

cardinal,  770 

collateral  circulation  in,  175 

development,  770 

distribution,  178 

influence  of  gravitation  in,  212 

parietal  system  of,  771  et  seq. 

pressure  in,  197 

rhythmical  action  in,  218 

structure  of,  178 

umbilical,  772 

valves  of,  174 

velocity  of  blood  in,  215 

visceral  system  of,  771  et  seq. 


IXDEX. 


825 


Velocih'  of  blood  in  arteries,  213 
in  capillaries,  215 
in  veins,  ib. 
of  circulation,  213 
of  nervous  force,  533 
conditions  modifying,  ib. 
Venae  hepaticae  advehentes,  771 

i-evehentes,  ib. 
Ventricles  of  heart.     See  Heart. 
Vertebra?,   development  of,    757 
Vertebral  plate,   743 
Vesicle,  germinal,  715 
Vesicula  germinativa,  ib. 
Vesicular  semiuales,  721 

structure,  ib. 
A^'ibrations,  conveyance  of  to  auditory 

nerve,  655  et  seq. 
Villi  in  chorion,   751 
in  placenta,  755 
of  intestines,  330 
Visceral  arches,  development  of,  760 
connection  with  cranial  nerves,  762 
laminje  or  plates,  746 
Visceral  plates,  ib. 
Viscero- inhibitory  nerves,  625 

motor,  ib. 
Vision,  663 
angle  of,  680 
at  different  distances,  adaptation  of 

eye  to,  681  et  seq. 
centre,  612 
corpora  quadrigemina,  tlie  principal 

nerve-centres  of,  620 
correction  of  aberration,  688  et  seq. 

of  inversion  of  image,  696 
defects  of,  686  et  seq. 
distinctness  of,  how  secured,  681  et 

seq. 
duration  of  sensation  in,  692 
estimation  of  the  form  of  objects, 
700 
of  their  dii'ection,  ib. 
of  their  motion,  701 
of  their  size,  699 
field  of.  size  of,  698 
focal  distance  of,  681 
impaired  by   lesion  of  fifth  nerve, 

578 
influence  of  attention  on,  701 
purple,  695 

single,  with  two  eyes,  705  et  seq. 
Visual  directioD,  700 
Vitellin,  109 
Vitelline  duct,  783 


Vitelline  membrane,  714 

spheres,  ib. 
Vitreous  humor,  676 
Vocal  cords,  515  et  seq. 

action  of  in  respiratory  actions,  522 

approximation  of,  effect  on  height 
of  note,  523 

vibrations  of,  cause  voice,  515 
Voice,  514  et  seq. 
Vomiting,  325 

action  of  stomach  in,  325 

centre,  326 

nerve-actions  in,  326,  570 

voluntary  and  acquired,  ib. 
V'owels  and  consonants,  527 
Vulvo- vaginal  or  Duverney's   glands, 
718 

Walking,  443 

Wallerian  method,  542 

Water,  114 
forms  large  part  of  human  body.  114 

Wave  of  blood  causing  the  pulse,  202 
velocity  of,  ib. 

Wharton's  jelly,  44 

White  corpuscles.      See  Blood-corpus- 
cles, white  ;  and  Lymph-corpuscles. 

White  fibro-cartilage.     See  Fibro-car- 
tilage.  white, 
fibrous  tissue,  41 

Willis,  circle  of,  217 

Wolffian  bodies,  786  et  seq. 

Wooldridge,  126 

Work  of  heart,  191 

Xanthin,  475 
Xantho-proteic  reaction,  104 

Yawning,  269 

Yellow  elastic  fibre,  40 

fibro-cartilage,  51 

spot  of  Sommering,  671 
Yolk,  or  vitellus,  715 

changes  of,  in  Fallopian  tube,  736 

cleaving  of,  ib. 

constriction  of,  by  ventral  laminas, 
746 
Yolk-sac,  746  et  seq. 
Young-Helmholtz  theory.  702 

ZiMMERMANN,  corpuscles  of,  483 
Zona  pellncida,  714 
Zonule  of  Zinn.  676 
Zymogen,  336 


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